JP5191870B2 - Image processing apparatus, image processing method, program, and display apparatus - Google Patents

Description

  The present invention relates to an image processing device, an image processing method, a program, and a display device.

  In recent years, as an alternative to a CRT display (Cathode Ray Tube display), an organic EL display (Organic Light Emitting Diode display) or FED (Field Emission Display) is used. Various display devices such as LCD (Liquid Crystal Display), PDP (Plasma Display Panel), and projectors have been developed.

  Further, for example, an image signal transmitted from a broadcasting station or the like can generally represent 256 gradations with 8 bits, but some display devices as described above have gradation performances such as 10 bits and 12 bits. A display panel having a display has appeared.

  Under such circumstances, a technique for correcting the number of gradations of an input image signal has been developed in order to bring out the gradation performance of the display panel. As a technique for detecting a region where gradation changes gently based on an image signal and smoothing the detected region to expand the number of gradations, for example, Patent Document 1 is cited. As a technique for reducing noise enhancement and false contour generation related to tone correction by setting a weighting factor based on the sum value of high-frequency components based on image signals, for example, Patent Document 2 can be cited. .

JP 2006-245752 A JP 2004-173065 A

  The region where the gradation changes gradually can be further divided into a region with a small number of unevenness (hereinafter referred to as “gradation region”) and a region with a large number of unevenness (hereinafter referred to as “texture region”). it can. However, the conventional technique for smoothing the detected area and extending the number of gradations merely detects an area where the gradation changes gently based on the image signal, and smoothes the detected area. Therefore, it is impossible to distinguish between the gradation area and the texture area. Therefore, in an image processing apparatus using a conventional technique that smoothes the detected area and expands the number of gradations, fine irregularities are lost due to the correction of the image signal. For example, textures such as walls and distant mountains are damaged. , The image quality is degraded.

  Also, the conventional technique for reducing noise enhancement and false contour generation related to tone correction simply performs tone correction by setting a weighting factor based on the sum value of high-frequency components based on image signals. Not too much. Therefore, the conventional technique for reducing noise enhancement and the generation of false contours related to gradation correction is similar to the conventional technique for smoothing the detected area and extending the number of gradations. Can not be distinguished. Therefore, even if a conventional technique for reducing noise enhancement and generation of false contours related to tone correction is used, there is a risk that the texture of, for example, a wall or a distant mountain will be damaged by the correction of the image signal.

  Therefore, even if the conventional technique for correcting the number of gradations of the input image signal is used, fine irregularities may be lost due to the correction of the image signal.

  The present invention has been made in view of the above problems, and an object of the present invention is to determine a gradation area based on an input image signal and selectively smooth the input image signal. It is an object of the present invention to provide a new and improved image processing device, image processing method, program, and display device that can be converted into an image signal having a larger number of gradations than the image signal.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided an image signal processing apparatus to which a plurality of N-bit (N is a positive integer) input image signals are input, For each signal, a frequency component detector that detects a signal in a predetermined frequency band based on the corresponding input image signal for each pixel, and a plurality of the input image signals based on the detection signal detected by the frequency component detector A maximum value selection unit that selects a detection signal having the maximum detection signal in each corresponding pixel, and a detection value that smoothes each detection signal corresponding to each pixel based on the detection signal selected by the maximum value selection unit Based on the detection signal smoothed by the smoothing unit, the detection value smoothing unit, a control signal generation unit that generates a control signal for defining a gradation area for each pixel, and the N-bit input image signal N + k bits (k is a positive number) in which the number of gradations of the input image signal is expanded by a predetermined number for each of the plurality of input image signals input based on a control signal generated for each pixel. The first output image signal of the integer), or the gradation number expansion unit that outputs the second output image signal of N + k bits in which the input image signal is smoothed and the number of gradations is expanded by a predetermined number for each pixel. An image processing apparatus is provided.

  With this configuration, it is possible to determine a gradation region based on an input image signal, selectively smooth the image signal, and convert the image signal to an image signal having a larger number of gradations than the input image signal.

  In addition, a selection signal generation unit that generates a selection signal for setting the predetermined frequency band for each of the input image signals based on each of the input image signals, and the frequency component detection unit includes the input image signal Based on the selection signal corresponding to each, the signal of the predetermined frequency band may be detected for each pixel.

  With this configuration, it is possible to determine a gradation region corresponding to the sampling frequency of the input image signal.

  The frequency component detection unit includes a plurality of detection units corresponding to the input image signals, and each of the plurality of detection units detects a first frequency band signal for each pixel. And a second frequency component detector that detects a signal in a higher frequency than the first frequency band for each pixel, and a first output from the first frequency component detector based on the corresponding selection signal. You may provide the selection part which outputs any one of a detection value or the 2nd detection value output from the said 2nd frequency component detection part as a signal of the said predetermined | prescribed frequency band.

  With this configuration, it is possible to determine a gradation region corresponding to the sampling frequency of the input image signal.

  Further, the number of gradations of the first output image signal or the second output image signal corresponding to each of the plurality of input image signals output from the gradation number expansion unit is set to N bits using a pseudo intermediate gradation. A first pseudo gradation processing unit that converts the image signal into the image signal may be further provided.

  With such a configuration, the gradation performance of the gradation area can be improved.

  Also, a first non-linear tone conversion that non-linearly corrects the first output image signal or the second output image signal corresponding to each of the plurality of input image signals output from the tone number expansion unit according to the signal level. And the number of gradations of the corrected first output image signal or second output image signal output from the nonlinear gradation converter are converted into an N-bit image signal using a pseudo intermediate gradation. A second pseudo gradation processing unit may be further provided.

  With this configuration, the gradation area can be smoothed and the gradation performance can be improved.

  The image processing apparatus further includes a second nonlinear gradation conversion unit that nonlinearly corrects each of the N-bit input image signals in accordance with a signal level, and the gradation number expansion unit includes the second nonlinear gradation conversion unit. The corrected input image signal output from the unit may be input.

  With this configuration, the gradation area can be smoothed without erroneous detection.

  In order to achieve the above object, according to the second aspect of the present invention, a predetermined number based on a corresponding input image signal is provided for each of a plurality of input N bit (N is a positive integer) input image signals. And detecting a signal having the maximum detection signal at each pixel corresponding to each of the plurality of input image signals based on the detection signal detected in the detection step and the detection signal detected in the detection step. Smoothing each detection signal corresponding to each pixel based on the detection signal selected in the selecting step, and gradation region based on the detection signal smoothed in the smoothing step And generating a control signal for each pixel, based on the control signal generated in the generating step. A first output image signal of N + k bits (k is a positive integer) obtained by extending the number of gradations of the input image signal by a predetermined number for each of the input image signals of N bits, or the input image signal is smoothed. And outputting a second output image signal of N + k bits whose number of gradations has been expanded by a predetermined number for each pixel.

  By using such a method, it is possible to determine a gradation region based on an input image signal, selectively smooth the image signal, and convert the image signal to an image signal having a larger number of gradations than the input image signal. .

  In order to achieve the above object, according to a third aspect of the present invention, a predetermined number based on a corresponding input image signal is provided for each of a plurality of N-bit input image signals (N is a positive integer). Detecting a signal in the frequency band of each pixel, and selecting a detection signal having the maximum detection signal in each pixel corresponding to each of the plurality of input image signals based on the detection signal detected in the detection step Smoothing each detection signal corresponding to each pixel based on the detection signal selected in the selecting step, and defining the gradation region based on the detection signal smoothed in the smoothing step A step of generating a control signal for each pixel, based on the control signal generated in the step of generating A first output image signal of N + k bits (k is a positive integer) in which the number of gradations of the input image signal is expanded by a predetermined number for each bit of the input image signal, or the input image signal is smoothed and gradation There is provided a program for causing a computer to execute a step of outputting a second output image signal of N + k bits expanded in number by a predetermined number for each pixel.

  By using such a program, it is possible to determine a gradation region based on an input image signal, selectively smooth the image signal, and convert the image signal to an image signal having a larger number of gradations than the input image signal. .

  In order to achieve the above object, according to the fourth aspect of the present invention, a plurality of N-bit (N is a positive integer) input image signals are input, and the input image signals are corrected. An image signal correction unit; and an image display unit capable of displaying an image indicated by an image signal of N + k bits (N and k are positive integers) based on the image signal corrected by the image signal correction unit. The signal correction unit includes, for each of the plurality of input image signals, a frequency component detection unit that detects a signal in a predetermined frequency band based on the corresponding input image signal for each pixel, and a detection signal detected by the frequency component detection unit A maximum value selection unit that selects a detection signal having the maximum detection signal in each pixel corresponding to each of the plurality of input image signals, and each pixel based on the detection signal selected by the maximum value selection unit You A detection value smoothing unit for smoothing each detection signal; a control signal generation unit for generating a control signal for defining a gradation region for each pixel based on the detection signal smoothed by the detection value smoothing unit; N + k in which a plurality of input image signals are input and the number of gradations of the input image signal is expanded by a predetermined number for each of the input image signals input based on a control signal generated for each pixel. A gradation for outputting a first output image signal of bits (k is a positive integer) or an N + k-bit second output image signal obtained by smoothing the input image signal and expanding the number of gradations for each pixel. A display device comprising a number expansion unit is provided.

  With this configuration, an image with improved gradation performance in the gradation area can be displayed.

  According to the present invention, it is possible to determine a gradation region based on an input image signal, selectively smooth the image signal, and convert the image signal to an image signal having a larger number of gradations than the input image signal.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

(Outline of processing of display device according to embodiment of present invention)
Before describing the display device according to the embodiment of the present invention, first, an outline of processing of the display device according to the embodiment of the present invention will be described. In the following description, it is assumed that an image signal is input to the display device according to the embodiment of the present invention. However, the image signal input to the display device may indicate a still image, or It may be a moving image (so-called video).

  In the following description, it is assumed that the image signal input to the display device according to the embodiment of the present invention is a digital signal. However, the present invention is not limited to the above. For example, an analog signal used in analog broadcasting is an A / D converter. It can also be converted into a digital signal by (Analog to Digital converter). In addition, the image signal input to the display device according to the embodiment of the present invention can be transmitted from a broadcast station and received by the display device, for example, but is not limited thereto. For example, the image signal input to the display device according to the embodiment of the present invention may be transmitted from an external device via a network such as a LAN (Local Area Network) and received by the display device, or The display device may read a video file or an image file held in a storage unit included in the display device.

  The processing in the display device according to the embodiment of the present invention is divided into [1] an image processing phase for correcting the input image signal and [2] a display phase for displaying the corrected image signal.

[1] Image Processing Phase In the image processing phase, the display device according to the embodiment of the present invention performs the following processes [1-1] and [1-2], for example, and inputs N bits (N is a positive value). Image signal (hereinafter referred to as “input image signal”) is converted into an image signal (hereinafter referred to as “output image signal”) of N + k (k is a positive integer). Here, the value of k can be a value corresponding to the gradation performance of the display unit on which the display device according to the embodiment of the present invention displays an image. In addition, when the display device according to the embodiment of the present invention has N-bit gradation performance of the display unit that displays an image, the display device according to the embodiment of the present invention outputs N + k bits. The image signal can be further corrected to N bits.

[1-1] Judgment of gradation area The display device according to the embodiment of the present invention uses an “edge area” indicating an edge and an “gradation” indicating an area having a small number of irregularities other than the edge area. The “region” and the “texture region” indicating a region having a large number of irregularities other than the edge region are roughly classified, and the gradation region is determined based on the input image signal. Here, the display device according to the embodiment of the present invention determines the gradation region for each pixel corresponding to the input image signal, for example.

[1-2] Image signal correction The display device according to the embodiment of the present invention is configured to display an image signal as shown in (A) and (B) below for each pixel based on the determination result in [1-1]. Perform the correction.

(A) When it is determined that the area is not a gradation area When the display apparatus according to the embodiment of the present invention determines that the area is not a gradation area (that is, an edge area or a texture area), for example, The image signal is shifted to the left by k bits, and a first output image signal with a fixed value of k bits added to the lower order of the input image signal is output.

(B) When judged as a gradation region When the display device according to the embodiment of the present invention is judged as a gradation region, the input image signal is smoothed and the second output expanded to N + k bits. Output image signal.

  The display device according to the embodiment of the present invention performs the correction (A) or (B) on the input image signal corresponding to each pixel, thereby converting the N-bit input image signal into the N + k-bit output image signal. Can be corrected.

  In addition, the display device according to the embodiment of the present invention determines a gradation area based on the input image signal, and smoothes the input image signal for the gradation area based on the determination result, thereby obtaining an edge area or a texture area. In contrast, the input image signal is not smoothed. Therefore, in the display device according to the embodiment of the present invention, fine irregularities are not lost by the correction of the input image signal, and for example, the texture of walls and distant mountains is not impaired, so that high image quality can be achieved. it can.

[2] Display Phase The display device according to the embodiment of the present invention displays an image based on the image signal (output image signal) corrected in the image processing phase of [1].

  The display device according to the embodiment of the present invention determines the gradation area based on the input image signal by the above-described processing, smoothes the input image signal, and converts it to an output image signal having a larger number of gradations than the input image signal. And an image can be displayed.

  Therefore, the display device according to the embodiment of the present invention can bring out the display performance of the display unit even when the gradation performance of the display unit is higher than that of the input image signal, and can correct the input image signal. As a result, fine irregularities are not lost, so that high image quality can be achieved.

  The configuration of the display device according to the embodiment of the present invention will be specifically described below. In the following, the display device according to the embodiment of the present invention includes a configuration including the [1] “image processing unit” responsible for the image processing phase and the [2] “display unit” responsible for the display phase. . The embodiment of the present invention is not limited to the above configuration, and for example, the following image processing unit can be realized as an independent device (image processing device).

(First embodiment)
FIG. 1 is a block diagram showing a display device 1000 according to the first embodiment of the present invention. FIG. 1 shows a configuration in which the image processing unit 100 performs a monochrome image process or a process for one channel among a plurality of channels of a color image as the display device 1000.

[Configuration of Display Device 1000]
Referring to FIG. 1, the display device 1000 includes an image processing unit 100 and a display unit 190.

  The display device 1000 includes, for example, a control unit (not shown) configured by an MPU (Micro Processing Unit) or the like that can control the entire display device 1000, a program used by the control unit, an operation parameter, and the like. ROM (Read Only Memory) (not shown) in which control data is recorded, RAM (Random Access Memory (not shown)) that primarily stores programs executed by the control unit, image signals transmitted from broadcast stations, etc. A receiving unit (not shown) for receiving video, a storage unit (not shown) capable of storing video files and image files, an operation unit (not shown) operable by the user, and an external device (not shown) You may provide the communication part (not shown) etc. for performing communication. The display device 1000 connects the above-described constituent elements by, for example, a bus as a data transmission path.

  Here, as the storage unit (not shown), for example, a magnetic recording medium such as a hard disk, an EEPROM (Electronically Erasable and Programmable Read Only Memory), a flash memory, a MRAM (Magnetoresistive Random Access) Non-volatile memory such as Memory (RAM), FeRAM (Ferroelectric Random Access Memory), PRAM (Phase change Random Access Memory), and the like, but is not limited thereto. Further, examples of the operation unit (not shown) include operation input devices such as a keyboard and a mouse, buttons, direction keys, and combinations thereof, but are not limited thereto.

  The display device 1000 and an external device (not shown) include, for example, a USB (Universal Serial Bus) terminal, an IEEE 1394 standard terminal, a DVI (Digital Visual Interface) terminal, or an HDMI (High-Definition Multimedia Interface) terminal. It may be physically connected via a wireless LAN, or may be connected wirelessly using WUSB (Wireless Universal Serial Bus), IEEE 802.11, or the like. Furthermore, the display device 1000 and an external device (not shown) can be connected via a network, for example. Examples of the network include a wired network such as a LAN or a WAN (Wide Area Network), a wireless network such as a WLAN (Wireless Local Area Network) using MIMO (Multiple-Input Multiple-Output), or TCP / IP (Transmission Control). Examples include, but are not limited to, the Internet using a communication protocol such as Protocol / Internet Protocol. Therefore, the communication unit (not shown) has an interface corresponding to the connection form with the external device (not shown).

  The image processing unit 100 converts the input N-bit (N is a positive integer) input image signal Di into an N + k (k is a positive integer) -bit output image signal Do. More specifically, the image processing unit 100 determines the gradation area for each pixel of the image indicated by the input image signal Di, and for each pixel based on the control signal Dc output from the control unit 102. A gradation number expansion unit 104 that expands the number of gradations or corrects the input image signal Di and expands the number of gradations. Details of the image processing unit 100 will be described later.

  The display unit 190 has N + k bit gradation performance and displays an image indicated by the N + k bit output image signal Do output from the image processing unit 100.

[Configuration Example of Display Unit 190]
The display unit 190 includes, for example, an image display unit (not shown), a row driving unit (not shown), a column driving unit (not shown), a power supply unit (not shown), and a display control unit. (Not shown).

  The image display unit includes, for example, a plurality of pixels arranged in a matrix (matrix). For example, an image display unit that displays an SD (Standard Definition) resolution image has at least 640 × 480 = 307200 pixels (data lines × scanning lines), and the pixels are red for color display. In the case of being composed of green and blue sub-pixels, it has sub-pixels of 640 × 480 × 3 = 921600 (data lines × scanning lines × number of sub-pixels). Similarly, for example, a display unit that displays an HD (High Definition) resolution image has 1920 × 1080 pixels, and has 1920 × 1080 × 3 sub-pixels for color display.

  Further, the image display unit may include, for example, a pixel circuit for controlling the amount of voltage / current applied to each pixel. The pixel circuit includes, for example, a switch element and a drive element for controlling the amount of current by an applied scanning signal and a voltage signal, and a capacitor for holding a voltage signal. The switch element and the drive element are composed of, for example, a thin film transistor.

  For example, the row driving unit and the column driving unit apply voltage signals to a plurality of pixels included in the image display unit to cause each pixel to emit light. Here, one of the row driving unit and the column driving unit applies a voltage signal (scanning signal) that determines ON / OFF of a pixel, and the other applies a voltage signal (image signal) corresponding to an image to be displayed. Can be fulfilled. In addition, as a driving method of the row driving unit and the column driving unit, for example, a dot sequential driving scanning method in which light is emitted for each pixel arranged in the matrix, and a line in which the pixels arranged in the matrix are emitted for each column. Examples include a sequential driving scanning method, and a surface sequential driving scanning method in which all the pixels arranged in the matrix form emit light.

  The power supply unit supplies power to the row driving unit and the column driving unit, and a voltage is applied to the row driving unit and the column driving unit. The magnitude of the voltage applied by the power supply unit to the row driving unit and the column driving unit varies according to the output image signal Do output from the image processing unit 100.

  The display control unit is configured by, for example, an MPU, and in accordance with an output image signal Do output from the image processing unit 100, a voltage for determining ON / OFF of the pixel is applied to one of the row driving unit and the column driving unit A control signal to be applied to is input, and an image signal is input to the other. The display control unit can also control the supply of power to the row driving unit and the column driving unit by the power supply unit according to the output image signal Do output from the image processing unit 100.

  The display unit 190 displays an image according to the output image signal Do with the above configuration. Here, examples of the display unit 190 include an organic EL display, a self-luminous display device such as an FED and a PDP, and a backlight display device such as an LCD, but are not limited thereto.

  The display apparatus 1000 according to the first embodiment of the present invention has a configuration as shown in FIG. 1 and determines a gradation area for each corresponding pixel based on an input image signal, and the input image signal according to the determination result. The number of gradations of Di is expanded, or the input image signal Di is corrected (for example, smoothed) and the number of gradations is expanded. The display apparatus 1000 can display an image based on an image signal with an expanded number of gradations, that is, an output image signal Do. Next, the image processing unit 100 according to the first embodiment of the present invention will be described in more detail. In the following, for simplification of description, description will be made by taking an example of processing in the horizontal direction.

[Image Processing Unit 100 According to First Embodiment]
FIG. 2 is a block diagram showing the image processing unit 100 according to the first embodiment of the present invention. Referring to FIG. 2, the image processing unit 100 includes a control unit 102 and a gradation number expanding unit 104. The control unit 102 includes a frequency component detection unit 106, a detection value smoothing unit 108, and a control signal generation unit 110.

  The frequency component detection unit 106 detects a predetermined frequency component for each pixel from the input image signal Di, and outputs the detection result as a frequency component detection value Df.

  FIG. 3 is a block diagram illustrating a configuration example of the frequency component detection unit 106 according to the first embodiment of the present invention. Referring to FIG. 3, the frequency component detection unit 106 includes a band-pass filter 112 (Band-Pass Filter; hereinafter sometimes referred to as “BPF”) and an absolute value conversion unit 114.

  The band pass filter 112 passes only the image signal of a specific frequency band and attenuates the image signal of the other band, thereby outputting the BPF output Dbpf for each pixel. FIG. 4 is an explanatory diagram showing an example of the frequency characteristics of the bandpass filter 112 according to the first embodiment of the present invention. Referring to FIG. 4, the bandpass filter 112 has a pass band having a peak at the frequency f. Here, the frequency f can be determined so that, for example, many components near the frequency f are included in the texture region according to the frequency characteristics of the texture region. The frequency f can be set according to the screen size and the number of pixels of the display unit 190 and the assumed viewing distance.

  The absolute value converter 114 calculates the absolute value of the BPF output Dbpf and outputs it as a frequency component detection value Df.

  The components of the image processing unit 100 will be described with reference to FIG. 2 again. The detection value smoothing unit 108 smoothes the frequency component detection value Df for each pixel based on the frequency component detection value Df corresponding to each pixel output from the frequency component detection unit 106, and smoothed average detection. Outputs the value Dave. Here, the average detection value Dave is used for determination of a gradation area in the control signal generation unit 110 described later.

  The detection value smoothing unit 108 sets a predetermined smoothing region including a target pixel corresponding to a pixel to be smoothed for each pixel, and calculates an average value of the frequency component detection values Df corresponding to the pixels included in the smoothing region. By calculating, the average detection value Dave is output for each pixel. FIG. 5 is an explanatory diagram for explaining an example of the smoothing process in the detection value smoothing unit 108 according to the first embodiment of the present invention, and an area having a size of 8 pixels in the horizontal direction as a smooth area. A set example is shown. Here, the smoothing region set by the detection value smoothing unit 108 is not limited to the region of the size of 8 pixels in the horizontal direction shown in FIG. 5, but is a region of any size in the horizontal direction and / or the vertical direction. be able to. In addition, the smooth region is not limited to being set to the same size for all the target pixels, and for example, the size may be changed according to the position on the screen.

  The average value calculated by the detection value smoothing unit 108 can be obtained by, for example, an arithmetic average, but is not limited to such a calculation method, and may be, for example, a geometric average or a weighted average with a predetermined weight. You can also

  The components of the image processing unit 100 will be described with reference to FIG. 2 again. Based on the average detection value Dave output from the detection value smoothing unit 108, the control signal generation unit 110 performs gradation region determination for each pixel by threshold processing.

[Significance of performing determination based on average detection value Dave]
Here, the significance of the image processing unit 100 determining the gradation area based on the average detection value Dave will be described.

  The frequency component detection value Df increases in the edge region, while the frequency component detection value Df decreases in both the gradation region and the texture region. Therefore, when attention is paid only to the magnitude of the frequency component detection value Df, the gradation area and the texture area cannot be distinguished.

  Here, focusing on the frequency of detection of the frequency component detection value Df in the smooth area, the frequency of detection of the frequency component detection value Df is low in the gradation area, but the detection frequency is relatively high in the texture area. Further, the frequency component detection value Df included in the smooth region has the same size in both the gradation region and the texture region. That is, focusing on the average frequency component detection value Df in the smooth region, that is, the average detection value Dave, the average detection value Dave in the texture region is larger than the average detection value Dave in the gradation region.

  Therefore, if threshold processing based on the average detection value Dave and an appropriate threshold TH for distinguishing the gradation area and the texture area is performed, if the average detection value Dave is smaller than the threshold TH, the gradation area or the average detection When the value Dave is larger than the threshold value TH, it can be distinguished as a texture region or an edge region. Here, the value of the threshold value TH can be determined using, for example, an image signal indicating an image having an area clearly showing gradation and an image signal showing an image having an area clearly showing texture.

  FIG. 6 is an explanatory diagram for explaining threshold processing in the control signal generation unit 110 according to the first embodiment of the present invention. As shown in FIG. 6, when the average detection value Dave is smaller than the threshold value TH, the control signal generator 110 outputs “1” indicating the gradation region as the control signal Dc, and when the average detection value Dave is equal to or larger than the threshold value TH, the texture is generated. “0” indicating an area or edge area, that is, other than the gradation area, is output as the control signal Dc.

  Here, the information on the threshold TH used by the control signal generation unit 110 to determine the gradation area is stored in, for example, a storage unit included in the image processing unit 100 and is input from the storage unit. Here, examples of the storage means included in the image processing unit 100 include a nonvolatile memory such as an EEPROM or a flash memory, but are not limited thereto. The information on the threshold TH can be held by the control signal generation unit 110 with a storage unit, for example, and is stored in a storage unit (not shown) of the display device 1000. The control signal generation unit 110 Needless to say, the data may be appropriately read from the storage unit (not shown).

  The control unit 102 includes the frequency component detection unit 106, the detection value smoothing unit 108, and the control signal generation unit 110 as described above, so that the gradation region can be determined for each pixel based on the input image signal.

  Next, the gradation number expansion unit 104 will be described. FIG. 7 is a block diagram showing the gradation number expanding unit 104 according to the first embodiment of the present invention.

  Referring to FIG. 7, the tone number expansion unit 104 includes an image smoothing unit 116 and a selection unit 118.

  The image smoothing unit 116 smoothes the N-bit input image signal Di and outputs an N + k-bit smoothed image signal Ds. For example, the image smoothing unit 116 performs smoothing in the same manner as the low-pass filter (not shown) that attenuates an image signal having a frequency higher than the cutoff frequency and the detection value smoothing unit 108 included in the control unit 102. The detection value smoothing unit (not shown) that outputs a smoothed image signal Ds with N + k-bit accuracy can be used. Here, the smoothed image signal Ds corresponds to the above-described second output image signal. Note that the smoothing region set for smoothing by the image smoothing unit 116 can be the same region as the detection value smoothing unit 108 included in the control unit 102, but may be a different region.

  Further, the image smoothing unit 116 is not limited to a configuration including a low-pass filter, and may include, for example, an ε filter (ε-Filter) or a bilateral filter. It is known that the filter has a characteristic that only a minute image change is smoothed and a large image change is not smoothed. By using these, even if the determination result of the region is wrong, the deterioration of the edge region can be suppressed to the minimum.

  Based on the control signal Dc output from the control signal generation unit 110, the selection unit 118 selectively selects the N + k-bit output image signal Do for each corresponding pixel, as shown in (i) or (ii) below. Output to.

(I) When the control signal Dc is “0” indicating an area other than the gradation area When the control signal Dc is “0” indicating an area other than the gradation area, the selection unit 118 receives the input image signal Di. Shift to the left by k bits, and output a first output image signal of N + k bits in which a fixed value of k bits is added to the lower order of the input image signal Di.

(Ii) When the control signal Dc is “1” indicating a gradation region When the control signal Dc is “1” indicating a gradation region, the selection unit 118 outputs N + k bits output from the image smoothing unit 116. The second output image signal (smoothed image signal Ds) is output as the output image signal Do.

  The gradation number expanding unit 104 selectively outputs the first output image signal or the second output image signal as the output image signal Do according to the control signal Dc output from the control unit 102 with the configuration shown in FIG. be able to.

[Each signal in the image processing unit 100]
The image processing unit 100 according to the first embodiment determines the gradation area based on the input image signal Di by the above-described configuration, and the N + k-bit first output image signal or the smoothed N + k-bit second image signal. The output image signal can be selectively output as the output image signal Do. Here, each signal described above in the image processing unit 100 is shown for each of the gradation region, the texture region, and the edge region.

  FIG. 8 is an explanatory diagram illustrating an example of each signal in the image processing unit 100 according to the first embodiment of the present invention. Here, FIG. 8A shows the input image signal Di, and FIG. 8B shows the BPF output Dbpf. Similarly, FIGS. 8C to 8G show the frequency component detection value Df, the average detection value Dave, the control signal Dc, the smoothed image signal Ds, and the output image signal Do, respectively.

[A] Gradation area (Fig. 8 (1))
(A-1) FIG. 8 (a)
As an example of the input image signal Di, a gradation region that changes stepwise by one gradation is given as an example.

(A-2) FIG. 8B
The amplitude of the BPF output Dbpf output from the bandpass filter 112 is small and the frequency of detection is low.

(A-3) FIG. 8 (c)
The BPF output Dbpf is converted into an absolute value by the absolute value converter 114, and the frequency component detection value Df is output. The frequency component detection value Df is small and the frequency of detection is low.

(A-4) FIG. 8 (d)
In the detection value smoothing unit 108, the average value of the frequency component detection values Df in the smooth region is calculated for each corresponding pixel, and the average detection value Dave is output. The average detection value Dave is a value smaller than the threshold value TH.

(A-5) FIG. 8 (e)
By performing threshold processing in the control signal generation unit 110, the control signal Dc is output. Since the average detection value Dave shown in FIG. 8D is smaller than the threshold value TH, the control signal Dc indicates “1” representing the gradation region.

(A-6) FIG. 8 (f)
Since the smoothed image signal Ds output from the image smoothing unit 116 has an accuracy of N + k bits, the image changes more smoothly than the N-bit input image signal Di.

(A-7) FIG. 8 (g)
Since the control signal Dc shown in FIG. 8E is “1” indicating the gradation region, the selection unit 118 selects the smoothed image signal Ds (second output image signal) output from the image smoothing unit 116. Output as an output image signal Do.

  As shown in FIG. 8, since the smoothed image signal Ds (second output image signal) is output as the output image signal Do in the gradation area, the change in the gradation area becomes smoother.

[B] Texture area ((2) in FIG. 8)
(B-1) FIG. 8 (a)
As an example of the input image signal Di, a texture region in which irregularities are formed while changing one gradation at a time.

(B-2) FIG. 8B
Compared to the gradation region in FIG. 8A, the BPF output Dbpf output from the bandpass filter 112 has the same amplitude, but is detected more frequently.

(B-3) FIG. 8C
The BPF output Dbpf is converted into an absolute value by the absolute value converter 114, and the frequency component detection value Df is output. Compared with the gradation region in FIG. 8A, the frequency component detection value Df is similar, but the frequency of detection is high.

(B-4) FIG. 8 (d)
In the detection value smoothing unit 108, the average value of the frequency component detection values Df in the smooth region is calculated for each corresponding pixel, and the average detection value Dave is output. In addition, the average detection value Dave is a relatively larger value than the threshold value TH.

(B-5) FIG. 8 (e)
By performing threshold processing in the control signal generation unit 110, the control signal Dc is output. Since the average detection value Dave shown in FIG. 8D is larger than the threshold value TH, the control signal Dc indicates “0” representing an area other than the gradation area.

(B-6) FIG. 8 (f)
Since the smoothed image signal Ds output from the image smoothing unit 116 has N + k-bit accuracy, the image changes more smoothly than the N-bit input image signal Di, but the unevenness changes less.

(B-7) FIG. 8 (g)
Since the control signal Dc shown in FIG. 8E is “0” indicating an area other than the gradation area, the selection unit 118 adds a k-bit fixed value to the lower order of the input image signal Di and converts it to N + k bits. The first output image signal thus output is output as an output image signal Do.

  As shown in FIG. 8, in the texture region, the first output image signal converted to N + k bits by adding a fixed value of k bits to the lower order of the input image signal Di as the output image signal Do is output. No change is lost. Therefore, blurring of the image can be prevented.

[C] Edge region ((3) in FIG. 8)
(C-1) FIG. 8 (a)
As an example of the input image signal Di, an edge region that changes sharply is given.

(C-2) FIG. 8B
The BPF output Dbpf output from the bandpass filter 112 has a range in amplitude.

(C-3) FIG. 8 (c)
The BPF output Dbpf is converted into an absolute value by the absolute value converter 114, and the frequency component detection value Df is output. Compared with the gradation region in FIG. 8A and the texture region in FIG. 8B, the frequency component detection value Df is very large.

(C-4) FIG. 8 (d)
In the detection value smoothing unit 108, the average value of the frequency component detection values Df in the smooth region is calculated for each corresponding pixel, and the average detection value Dave is output. The average detection value Dave is sufficiently larger than the threshold value TH in the vicinity of the edge.

(C-5) FIG. 8 (e)
By performing threshold processing in the control signal generation unit 110, the control signal Dc is output. Since the average detection value Dave shown in FIG. 8D is larger than the threshold value TH in the area near the edge, the control signal Dc indicates “0” representing an area other than the gradation area. In the region far from the vicinity of the edge, the average detection value Dave shown in FIG. 8D is smaller than the threshold value TH, so the control signal Dc indicates “1” representing the gradation region.

(C-6) FIG. 8 (f)
Since the smoothed image signal Ds output from the image smoothing unit 116 has an accuracy of N + k bits, the image changes more smoothly than the N-bit input image signal Di, but the sharpness of the edge is dull.

(C-7) FIG. 8 (g)
In the area near the edge, since the control signal Dc shown in FIG. 8E is “0” indicating an area other than the gradation area, the selection unit 118 adds a fixed value of k bits to the lower order of the input image signal Di. Then, the first output image signal converted into N + k bits is output as the output image signal Do. Further, in the region far from the vicinity of the edge, the control signal Dc shown in FIG. 8E is “1” indicating the gradation region, and therefore the selection unit 118 outputs the smoothed image signal Ds (first) output from the image smoothing unit 116. 2 output image signal) is selected and output as an output image signal Do.

  As shown in FIG. 8, in the edge region, the image is not smoothed in the vicinity of the edge, and the image is smoothed and smoothed in a region with a small change other than in the vicinity of the edge.

  Based on the input input image signal Di, the image processing unit 100 generates an output image signal Do suitable for preventing degradation in image quality for each of the gradation area, texture area, and edge area, as shown in FIG. Can be output.

[Signal when the image processing unit does not include a detection value smoothing unit]
Next, as a comparative example of FIG. 8, when the image processing unit does not include the detection value smoothing unit, that is, when the threshold value processing is performed on the frequency component detection value Df, [I] when the threshold value TH is large , [II] Each case where the threshold value is small is shown.

[I] When Threshold TH is Large FIG. 9 is an explanatory diagram illustrating a first example of a signal when the image processing unit does not include a detection value smoothing unit. Here, FIG. 9A shows the frequency component detection value Df, and FIG. 9B shows the control signal Dc.

  Referring to FIG. 9A, as described above, the frequency component detection value Df is a small value of the same degree in both the gradation area and the texture area. Here, as shown in FIG. 9A, when the threshold value TH is set to be slightly larger so that the frequency component detection value Df in the gradation area falls below the threshold value TH, the frequency component detection value Df also falls below the threshold value TH in the texture area. Probability is high. At this time, as shown in FIG. 9B, the control signal Dc indicates “1” indicating the gradation region in both the gradation region and the texture region.

  Therefore, the selection unit 118 selects the smoothed image signal Ds (second output image signal) output from the image smoothing unit 116 for both the gradation region and the texture region, and outputs it as the output image signal Do. . In the above case, since the smoothed image signal Ds (second output image signal) is output also to the texture region, there is a problem that the unevenness of the texture region is impaired, that is, the image is blurred.

  In the edge region, the frequency component detection value Df is sufficiently larger than the threshold value TH near the edge. Therefore, since the control signal Dc is “0” indicating an area other than the gradation area only in the vicinity of the edge, it is not smoothed in the vicinity of the edge, and the gradation area other than the edge is smoothly converted. That is, no particular problem occurs in the edge region.

[II] When Threshold TH is Small FIG. 10 is an explanatory diagram illustrating a second example of a signal when the image processing unit does not include a detection value smoothing unit. Here, FIG. 10A shows the frequency component detection value Df, and FIG. 10B shows the control signal Dc.

  As shown in FIG. 10A, when the threshold value TH is set to be slightly smaller so that the frequency component detection value Df in the gradation area exceeds the threshold value TH, there are places where the frequency component detection value Df exceeds the threshold value TH even in the gradation area. Come. Here, the place where the frequency component detection value Df exceeds the threshold value TH means a place where the input image signal Di changes, but as shown in FIG. 10B, the control signal Dc is other than the gradation area. It becomes “0” indicating an area. Accordingly, there is a problem in that the portion where the input image signal Di changes is not smoothed, and the stepwise change in the gradation region as shown in FIG. 8A cannot be smoothed.

  Further, in the edge area, the control signal Dc is “0” indicating the area other than the gradation area even in the gradation area other than the vicinity of the edge.

  As shown in FIGS. 9 and 10, when the image processing unit does not include the detection value smoothing unit, a problem occurs in each of the gradation region, the texture region, and the edge region.

  On the other hand, the image processing unit 100 according to the first embodiment of the present invention includes the detection value smoothing unit 108 and performs the detection value smoothing process, whereby a gradation region and a region other than the gradation region (texture region) And edge regions). In particular, since the image processing unit 100 can accurately discriminate between the texture area and the gradation area, it is possible to prevent image quality deterioration such as a reduction in sharpness due to erroneous smoothing of the texture area.

  As described above, the display apparatus 1000 according to the first embodiment of the present invention includes the image processing unit 100 that corrects the N-bit input image signal Di to the N + k-bit output image signal Do, and the N + k-bit gradation performance. And a display unit 190 having. The image processing unit 100 includes a control unit 102 and a gradation number expanding unit 104. The control unit 102 determines a gradation area for each pixel based on the input image signal Di, outputs a control signal Dc, and outputs a control signal Dc. The gradation number expansion unit 104 adds a k-bit fixed value to the lower order of the input image signal Di and converts it to N + k bits, or N + k bits obtained by smoothing the input image signal Di. The second output image signal is selectively output as an output image signal Do. Therefore, the display apparatus 1000 determines a gradation region based on the input image signal, selectively smoothes the image signal, converts the image signal into an image signal having a larger number of gradations than the input image signal, and displays the image signal. be able to.

  In addition, since the display apparatus 1000 determines the gradation area and selectively corrects the gradation area more smoothly, the gradation performance of the gradation area can be improved. In addition, since the display device 1000 does not correct the input image in the edge region or the texture region, the image indicated by the output image signal Do does not lose sharpness.

  In general, when the gradation performance is insufficient, the image quality deterioration such as a false contour is generated visually in the gradation area, and the image quality deterioration is observed in the edge area and the texture area. Inconspicuous. Since the display device 1000 selectively improves the gradation performance of the gradation area, it is possible to visually obtain the same effect as the gradation performance is improved on the entire image.

  Further, the display apparatus 1000 detects a signal (BPF output Dbpf) in a predetermined frequency band, and performs threshold processing based on the result of smoothing the detection value in a predetermined smooth region. Accordingly, the display device 1000 can accurately discriminate between the texture area and the gradation area, and can prevent image quality deterioration such as a reduction in sharpness due to erroneous smoothing of the texture area.

[Modification of Display Device 1000]
[First Modification]
In the above, as the display apparatus 1000 according to the first embodiment, the configuration in which the frequency component detection unit 106 includes the single bandpass filter 112 and outputs the frequency component detection value Df as illustrated in FIG. . However, the frequency component detection unit according to the first embodiment of the present invention is not limited to the configuration of FIG. 3, and may be configured to include a plurality of bandpass filters.

  FIG. 11 is a block diagram showing a frequency component detection unit according to a first modification of the first embodiment of the present invention. FIG. 11 shows an example of a configuration including two bandpass filters, but a modification of the frequency component detection unit according to the first embodiment of the present invention includes two bandpass filters. Needless to say, the configuration is not limited.

  Referring to FIG. 11, the frequency component detection unit according to the first modification includes a first bandpass filter 112a, a first coefficient multiplication unit 120a, a first absolute value conversion unit 114a, A band-pass filter 112b, a second coefficient multiplier 120b, a second absolute value converter 114b, and a maximum value selector 122 are provided.

  The input image signal Di is input to the first bandpass filter 112a, and a BPF output Dbpf1 is output based on the frequency characteristics having the peak at the frequency f1.

  The first coefficient multiplier 120a multiplies the BPF output Dbpf1 by a predetermined coefficient K1, and outputs a weighted BPF output Dk1. Here, the information on the coefficient K1 used for multiplication by the first coefficient multiplication unit 120a is stored in, for example, a storage unit included in the image processing unit 100, and is input from the storage unit, but is not limited thereto. For example, the information on the coefficient K1 can be held by the first coefficient multiplication unit 120a with a storage unit, and is stored in a storage unit (not shown) of the display device, and the first coefficient multiplication unit 120a. Can be appropriately read from the storage unit (not shown).

  The first absolute value converter 114a calculates the absolute value of the weighted BPF output Dk1 and outputs the first frequency component detection value Df1.

  The second band pass filter 112b receives the input image signal Di and outputs a BPF output Dbpf2 based on the frequency characteristic having the peak at the frequency f2. The second coefficient multiplier 120b multiplies the BPF output Dbpf2 by a predetermined coefficient K2 and outputs a weighted BPF output Dk2, and the second absolute value converter 114b outputs the weighted BPF output Dk2. The absolute value is calculated and the second frequency component detection value Df2 is output. Here, the information on the coefficient K2 used for multiplication by the second coefficient multiplier 112b is stored in, for example, a storage unit included in the image processing unit 100, similarly to the coefficient K1 used for multiplication by the first coefficient multiplier 112a. However, it is not limited to the above.

  The maximum value selection unit 122 selects the larger one of the frequency component detection values Df1 and Df2 for each corresponding pixel and outputs the selected value as the frequency component detection value Df.

  Here, the significance of the frequency component detection unit according to the first modification taking the configuration of FIG. 11 will be described. FIG. 12 is an explanatory diagram for explaining a frequency component detection unit according to a first modification of the first embodiment of the present invention. FIG. 12 shows an example in which the coefficient K1 = 1 and the coefficient K2 = 0.5 are set, but the values of the coefficients K1 and K2 are not limited to the above.

  FB shown in FIG. 12 is a band of main frequency components included in a large amount in the texture region, and the first bandpass filter 112a is set so that the main frequency component in the texture region becomes the frequency f1. Here, the first band-pass filter 112a has a characteristic that peaks at the frequency f1, but the first band-pass filter 112a alone cannot cover the entire range of the frequency band FB. For example, when the texture region includes many components near the frequency f2, the BPF output Dbpf1 takes a value almost close to 0 (zero), and the frequency component detection value Df is almost 0 (zero). There is a risk of erroneous detection as a gradation area.

  Dk1 shown in FIG. 12 indicates a characteristic obtained by multiplying the BPF output Dbpf1 by a coefficient K1 = 1, and Dk2 indicates a characteristic obtained by multiplying the BPF output Dbpf2 by a coefficient K2 = 0.5. By selecting the maximum value of the first frequency component detection value Df1 and the second frequency component detection value Df2 obtained by converting Dk1 and Dk2 into absolute values, the first frequency component detection value Df1 is selected near the frequency f1, and the frequency f2 In the vicinity, the second frequency component detection value Df2 is selected.

  Therefore, the entire band FB can be covered by using a plurality of bandpass filters having different frequency characteristics as shown in FIG.

  The display device according to the first modification of the first embodiment of the present invention is different from the frequency component detection unit 106 shown in FIG. 3 in the configuration of the frequency component detection unit, but the frequency component based on the input image signal Di. The detection value Df can be output. Further, the other configuration of the display device according to the first modification is the same as that of the display device 1000 according to the first embodiment. Therefore, the display device according to the first modification can achieve the same effects as the display device 1000 according to the first embodiment described above.

[Second Modification]
Moreover, the frequency component detection part which concerns on the 1st Embodiment of this invention is not restricted to the structure shown in FIG. 3, FIG. FIG. 13 is a block diagram illustrating a frequency component detection unit according to a second modification of the first embodiment of the present invention.

  Referring to FIG. 13, the frequency component detection unit according to the second modification has basically the same configuration as the frequency component detection unit according to the first modification shown in FIG. The selection unit 122 is replaced with an addition unit 124.

  The adder 124 adds the first frequency component detection value Df1 and the second frequency component detection value Df2 for each corresponding pixel, and outputs a frequency component detection value Df (= Df1 + Df2). At this time, the ratio of the first frequency component detection value Df1 to the frequency component detection value Df is high near the frequency f1, and the ratio of the second frequency component detection value Df2 to the frequency component detection value Df is high near the frequency f2. Therefore, even in the above case, the frequency component detection value Df can be output satisfactorily over the entire band FB shown in FIG.

  The display device according to the second modification of the first embodiment of the present invention differs from the frequency component detection unit 106 shown in FIG. 3 in the configuration of the frequency component detection unit, but the first modification shown in FIG. Similarly to the frequency component detection unit according to the above, the frequency component detection value Df can be output based on the input image signal Di. In addition, the other configuration of the display device according to the second modification is the same as that of the display device 1000 according to the first embodiment. Therefore, the display device according to the second modification can achieve the same effect as the display device 1000 according to the first embodiment described above.

[Third Modification]
In the above, as a display device according to the first embodiment, the first modified example, and the second modified example, the image processing unit uses a single threshold TH and the binary control signal Dc as shown in FIG. Is generated, and the first output image signal or the second output image signal is selectively output as the output image signal Do. However, the display device according to the first embodiment of the present invention is not limited to the above configuration. Therefore, next, as a display device according to the third modification of the first embodiment of the present invention, the image processing unit controls the control signal Dc that defines the mixing ratio of the first output image signal and the second output image signal. Will be described, and an output image signal Do corresponding to the mixing ratio indicated by the control signal Dc will be output. Note that the image processing unit of the display device according to the third modification has the same configuration as that of FIG.

  FIG. 14 is an explanatory diagram for explaining threshold processing in the control signal generation unit according to the third modification of the first embodiment of the present invention. The control signal generation unit according to the third modification outputs the control signal Dc by threshold processing using the thresholds TH1 and TH2 and the average detection value Dave output from the detection value smoothing unit.

  Specifically, when the average detection value Dave is smaller than the threshold value TH1, the control signal generation unit according to the third modification example generates a control signal “1” representing a gradation region, and the average detection value Dave is less than the threshold value TH2. When it is larger, a control signal “0” indicating an area other than the gradation area is generated. Further, when the average detection value Dave is between the threshold value TH1 and the threshold value TH2, the control signal generation unit according to the third modification example, for example, a straight line connecting Dc = 1 and Dc = 0 (that is, Based on the threshold values TH1 and TH2, the control signal Dc having an intermediate value is generated. The control signal Dc generated as described above indicates the mixing ratio of the second output image signal (smoothed image signal Ds).

  Here, the information on the thresholds TH1 and TH2 used by the control signal generation unit according to the third modification to determine the gradation area is stored in, for example, a storage unit included in the image processing unit, and is input from the storage unit. However, it is not limited to the above. For example, the information of the thresholds TH1 and TH2 can be held by the control signal generation unit with a storage unit, and is stored in a storage unit (not shown) of the display device, and the control signal generation unit is stored in the storage unit. It is also possible to read appropriately from (not shown).

  FIG. 15 is a block diagram illustrating a gradation number expanding unit according to a third modification of the first embodiment of the present invention. The gradation number expanding unit according to the third modification includes an image smoothing unit 116 and a mixing unit 126.

  The image smoothing unit 116 has the same configuration as the image smoothing unit 116 shown in FIG. 7, smoothes an N-bit input image signal, and outputs an N + k-bit smoothed image signal Ds.

  The mixing unit 126 adds a smoothed image signal Ds (second output image signal) and a fixed value of k bits to the lower order of the input image signal Di for each corresponding pixel according to the mixing ratio indicated by the control signal Dc. The N + k-bit first output image signal is mixed at a ratio of Dc: (1−Dc) and output as an output image signal Do.

  Here, the significance that the gradation number expanding unit according to the third modification mixes and outputs the smoothed image signal Ds (second output image signal) and the first output image signal will be described. When minute noise is mixed in the input image signal Di, the average detection value Dave corresponding to the same display position of a similar image changes with time, and may exceed or fall below the threshold value TH. At this time, in the simple threshold processing, the control signal Dc alternates between “1” indicating the gradation region and “0” indicating the region other than the gradation region, and thus the first output image signal and the smoothed image signal Ds. (Second output image signal) may be alternately selected and may flicker and be visually recognized by the user.

  On the other hand, in the mixing process, since the control signal Dc indicating the mixing ratio can take an intermediate value between “1” and “0”, the first output image signal and the smoothed image signal Ds (second output image signal) The ratio never changes drastically. Therefore, the display device according to the third modification can suppress flickering more than the display device 1000 according to the first embodiment.

  In the display device according to the third modification of the first embodiment of the present invention, the configuration of the control signal Dc generating unit and the gradation number extending unit in the control signal generating unit is the same as that of the first embodiment described above. Although different from the display device 1000, the output image signal Do can be output and displayed based on the control signal Dc, as with the display device 1000. Therefore, the display device according to the third modification can achieve the same effects as the display device 1000 according to the first embodiment described above.

[Fourth Modification]
In the above description, the processing in the horizontal direction has been described as an example of the display device according to the first embodiment and the first to third modifications, but the image of the display device according to the first embodiment of the present invention is described. The processing performed by the processing unit is not limited to horizontal processing. Accordingly, a configuration in which the image processing unit sequentially performs processing in the horizontal direction and the vertical direction will be described as a display device according to a fourth modification of the first embodiment of the present invention.

  FIG. 16 is a block diagram showing a display device 1500 according to a fourth modification of the first embodiment of the present invention. Referring to FIG. 16, the display device 1500 includes an image processing unit 150 and a display unit 190. Here, the display unit 190 has the same configuration as the display unit 190 illustrated in FIG. 1 and has N + k-bit gradation performance.

  The image processing unit 150 includes a horizontal control unit 102h, a horizontal gradation number extending unit 104h, a vertical control unit 102v, and a vertical gradation number expanding unit 104v.

  The horizontal control unit 102h outputs, for each pixel, a horizontal control signal Dhc indicating whether or not it is a gradation region in the horizontal direction, based on the input image signal Di input. Here, the horizontal control unit 102h can output the horizontal control signal Dhc, for example, by adopting the same configuration as the control unit 102 shown in FIG.

  Based on the horizontal control signal Dhc, the horizontal gradation number expanding unit 104h selectively smoothes the image in the horizontal direction for each corresponding pixel and outputs an N + k-bit image signal Dho. Here, the gradation performance of the image signal Dho is improved in the horizontal direction, but the gradation performance is not improved in the vertical direction, and is equivalent to the input image signal Di. Further, the horizontal gradation number expanding unit 104h can output the image signal Dho by adopting the same configuration as the gradation number expanding unit 104 shown in FIG. 2, for example.

  Based on the input image signal Dho, the vertical control unit 102v outputs, for each pixel, a vertical control signal Dvc indicating whether or not it is a vertical gradation region. Here, the vertical control unit 102v can output the vertical control signal Dvc, for example, by adopting the same configuration as the control unit 102 shown in FIG.

  Based on the vertical control signal Dvc, the vertical tone number expanding unit 104v selectively smoothes the image in the vertical direction for each corresponding pixel and outputs an output image signal Do of N + k bits. Here, the output image signal Do has improved gradation performance in the vertical direction in addition to the horizontal direction. Further, the vertical gradation number expanding unit 104v can output the output image signal Do by adopting the same configuration as the gradation number expanding unit 104 shown in FIG. 2, for example.

  As shown in FIG. 16, by sequentially executing horizontal processing and vertical processing, the display device 1500 according to the fourth modification causes the texture region and the edge region in both the horizontal direction and the vertical direction. The gradation performance of the gradation area can be improved without impairing the sharpness of the image.

  In addition, the display device 1500 according to the fourth modification can perform the horizontal processing and the vertical processing in the same manner as the display device 1000 according to the first embodiment, and thus the first implementation described above. The same effect as the display device 1000 according to the embodiment can be obtained.

  In the above description, the display device 1500 according to the fourth modification example is configured such that the image processing unit 150 sequentially executes horizontal processing and vertical processing, but the first embodiment of the present invention. The display device according to is not limited to the above. For example, the display device according to the first embodiment can also execute the horizontal direction and the vertical direction in a batch by two-dimensional processing. Even with such a configuration, as in the display device according to the fourth modification, the gradation performance of the gradation area is improved without deteriorating the sharpness of the texture area and the edge area in both the horizontal direction and the vertical direction. Can be made.

(Image processing apparatus according to the first embodiment)
In the above, the display device according to the first embodiment has been described. However, the image processing unit included in the display device according to the first embodiment described above (including modifications) is independent of the display unit. It can also be realized as an apparatus, that is, an image processing apparatus.

(Program according to the first embodiment)
[Programs related to display devices]
A program for causing a computer to function as the display device according to the first embodiment of the present invention determines a gradation area based on an input image signal, selectively smoothes the image signal, and inputs an image It can be converted into an image signal having a larger number of gradations than the signal.

[Program for image processing apparatus]
A program for causing a computer to function as the image processing apparatus according to the first embodiment of the present invention determines a gradation area based on an input image signal, selectively smoothes the image signal, and inputs the image signal. It can be converted into an image signal having a larger number of gradations than the image signal.

(Image processing method according to the first embodiment)
Next, an image processing method according to the first embodiment of the present invention will be described. FIG. 17 is a flowchart showing an example of an image processing method according to the first embodiment of the present invention. In the following description, the image processing method illustrated in FIG. 17 is described as being performed by the display apparatus 1000, but it is needless to say that the image processing method can be applied to the image processing apparatus according to the first embodiment of the present invention.

  The display apparatus 1000 detects a predetermined frequency component for each pixel from the N-bit input image signal Di (S100). The detection in step S100 can be performed using, for example, one or a plurality of bandpass filters.

  The display apparatus 1000 smoothes the detection value (frequency component detection value Df) detected in step S100 (S102), and generates the control signal Dc based on the smoothed detection value (average detection value Dave) (S104). ).

  Based on the input image signal Di and the control signal Dc generated in step S104, the display apparatus 1000 adds the k-bit fixed value to the lower order of the input image signal Di and converts the first output image signal to N + k bits. Alternatively, the N + k-bit second output image signal obtained by smoothing the input image signal Di is selectively output (S106).

  By using the image processing method shown in FIG. 17, the display apparatus 1000 determines a gradation area based on the input image signal, selectively smoothes the image signal, and has a gradation number higher than that of the input image signal. Can be converted into an image signal having a large amount of image data.

(Second Embodiment)
In the above description, the display device according to the first embodiment is configured to perform monochrome image processing or processing for one channel among a plurality of channels of a color image. However, the display device according to the embodiment of the present invention is not limited to the above configuration. Accordingly, a configuration for processing a plurality of channels of a color image will be described next as a display device according to the second embodiment. In the following, red (hereinafter referred to as “R”), green (hereinafter referred to as “G”), and blue (hereinafter referred to as “B”) image signals are input as a plurality of channels of a color image. An example is shown.

  FIG. 18 is a block diagram showing a display device 2000 according to the second embodiment of the present invention. Referring to FIG. 18, the display device 2000 includes an image processing unit 200 and a display unit 190, and the image processing unit 200 includes a control unit 202 and a gradation number expansion unit 204.

  The image processing unit 200 receives N-bit R / G / B input image signals Ri, Gi, Bi, respectively, and converts them into N + k-bit output image signals Ro, Go, Bo for output. The display unit 190 has N + k-bit gradation performance like the display unit 190 according to the first embodiment shown in FIG. 1, and displays an image based on the N + k-bit output image signals Ro, Go, and Bo. indicate. Hereinafter, the configuration of the image processing unit 200 will be specifically described.

[Configuration Example of Image Processing Unit 200]
FIG. 19 is a block diagram showing an image processing unit 200 according to the second embodiment of the present invention.

  Referring to FIG. 19, the control unit 202 includes a first frequency component detection unit 106a, a second frequency component detection unit 106b, a third frequency component detection unit 106c, a maximum value selection unit 206, and a detection value. A smoothing unit 108 and a control signal generation unit 110 are provided. In addition, the gradation number expansion unit 204 includes a first gradation number expansion unit 204a, a second gradation number expansion unit 204b, and a third gradation number expansion unit 204c.

[Control unit 202]
The input image signal Ri is input to the first frequency component detector 106a, the input image signal Gi is input to the second frequency component detector 106b, and the input image signal Bi is input to the third frequency component detector 106c. Is done. Here, each of the first frequency component detection unit 106a to the third frequency component detection unit 106c can have the same configuration as the frequency component detection unit 106 according to the first embodiment shown in FIG. Therefore, the first frequency component detection unit 106a detects a predetermined frequency component from the input image signal Ri and outputs a frequency component detection value Rf. Similarly, the second frequency component detection unit 106b has a frequency component detection value. Gf, the third frequency component detection unit 106c can output the frequency component detection value Bf.

  The maximum value selection unit 206 selects the maximum value for each corresponding pixel from the frequency component detection values Rf, Gf, and Bf, and outputs the maximum detection value Dmax.

  Similar to the detection value smoothing unit 108 according to the first embodiment shown in FIG. 2, the detection value smoothing unit 108 calculates the average value of the maximum detection values Dmax in the smooth region and outputs the average detection value Dave.

  Similar to the control signal generation unit 110 according to the first embodiment illustrated in FIG. 2, the control signal generation unit 110 determines the gradation region by threshold processing using the average detection value Dave and the threshold TH, and controls the determination result. Output as signal Dc.

[Gradation number expansion unit 204]
Each of the first gradation number expanding section 204a, the second gradation number expanding section 204b, and the third gradation number expanding section 204c is a gradation number expanding section 104 according to the first embodiment shown in FIG. It has the same configuration as. Therefore, the first gradation number expansion unit 204a adds a k-bit fixed value to the lower order of the N-bit input image signal Ri and converts it to N + k bits based on the control signal Dc, Alternatively, the N + k-bit second output image signal obtained by smoothing the input image signal Ri can be selectively output as the output image signal Ro. Similarly, the second gradation number expanding unit 204b and the third gradation number expanding unit 204c can output the output image signals Go and Bo, respectively.

  As described above, the image processing unit 200 can output the output image signals Ro, Go, and Bo with the configuration of FIG.

  Next, the significance of using the maximum value of the R / G / B frequency component detection result by the image processing unit 200 will be described. FIG. 20 is an explanatory diagram illustrating an example of each signal in the image processing unit 200 according to the second embodiment of the present invention. Here, FIG. 20 shows an example of each signal in the texture region. In a texture area in a color image, the R / G / B image signals of the three colors do not always change at the same frequency, but rather, the frequency of change is generally different between R / G / B. is there.

  20A to 20C show the input image signals Ri, Gi and Bi, respectively. 20D to 20F show the frequency component detection values Rf, Gf, and Bf, respectively. Here, since the input image signal Ri in FIG. 20A is relatively uneven, the frequency component detection value Rf in FIG. 20D is detected at a relatively high frequency. Also, since the input image signals Gi and Bi in FIGS. 20B and 20C have little change, the detection of the frequency component detection value Gf in FIG. 20E and the frequency component detection value Bf in FIG. The frequency is low.

  FIG. 20G shows the maximum detection value Dmax. Here, since the image processing unit 200 selects the maximum value of the frequency component detection values Rf, Gf, and Bf for each pixel, the maximum detection value Dmax is higher than that of the frequency component detection values Rf, Gf, and Bf alone. The frequency of detection increases.

  FIG. 20 (h) shows the average detection value Dave, and FIG. 20 (i) shows the control signal Dc. Here, since the detection frequency of the maximum detection value Dmax is high, the average detection value Dave takes a value larger than the threshold value TH, and the control signal Dc is “0” indicating an area other than the gradation area.

  Here, if the region is determined for each color without selecting the maximum value for the frequency component detection values Rf, Gf, and Bf, the gradation region for G and B with little change in the input image signal And the image may be smoothed. Even in the case of an image signal with little change such as the input image signals Gi and Bi shown in FIG. 20, since the width of the change in the image signal is small in the texture region, the contribution to the sharpness cannot be ignored. That is, in the texture region, the sharpness is lost by smoothing the input image signal with little change. The image processing unit 200 can prevent the occurrence of the above problem by using the maximum value of the R / G / B frequency component detection result.

  The image processing unit 200 performs smoothing of the detection value and threshold processing on the maximum value (maximum detection value Dmax) of the frequency component detection values Rf, Gf, and Bf, thereby detecting the gradation region without making a mistake with the texture region. can do. Therefore, it is possible to suppress image quality deterioration such as a reduction in sharpness caused by smoothing the texture region.

  As described above, the display device 2000 according to the second embodiment of the present invention receives a plurality of channels of input image signals Ri, Gi, and Bi (each N-bit input image signal) indicating a color image by N + k bits. An image processing unit 200 that corrects output image signals Ro, Go, and Bo and a display unit 190 having N + k-bit gradation performance are provided. The image processing unit 200 includes a control unit 202 and a gradation number expansion unit 204. The control unit 202 determines a gradation area for each pixel based on the input image signals Ri, Gi, Bi, and outputs a control signal Dc. Based on the control signal Dc, the first output image signal or the input image signal smoothed by the number-of-tones expansion unit 204 is converted to N + k bits by adding a fixed value of k bits to the lower order of the input image signal. The second output image signal of N + k bits is selectively output as output image signals Ro, Go, Bo. Therefore, the display device 2000 determines the gradation area based on the input image signal, selectively smoothes the image signal, similarly to the display device 1000 according to the first embodiment, and based on the input image signal. Can be converted into an image signal having a large number of gradations and displayed.

  Further, as with the display device 1000 according to the first embodiment, the display device 2000 can determine the gradation region and selectively correct the gradation region more smoothly, so that the gradation performance of the gradation region can be improved. Can be improved. In addition, since the display device 2000 does not correct the input image in the edge region or the texture region, the image indicated by the output image signals Ro, Go, Bo does not lose sharpness.

  Further, since the display device 2000 selectively improves the gradation performance of the gradation area in the same manner as the display device 1000 according to the first embodiment, the gradation performance is visually improved over the entire image. Similar effects can be obtained.

  Furthermore, the display device 2000 smoothes the detection value and performs threshold processing on the maximum value (maximum detection value Dmax) of the frequency component detection values Rf, Gf, and Bf, so that the gradation region is not mistaken for the texture region. Can be detected. Therefore, it is possible to suppress image quality deterioration such as a reduction in sharpness caused by smoothing the texture region.

[Modification of Display Device 2000]
The display device according to the second embodiment can take a modification similar to the modification of the display device according to the first embodiment described above.

(Image processing apparatus according to the second embodiment)
In the above, the display device according to the second embodiment has been described. However, the image processing unit included in the display device according to the second embodiment described above (including modifications) is independent of the display unit. It can also be realized as an apparatus, that is, an image processing apparatus.

(Program according to the second embodiment)
[Programs related to display devices]
A program for causing a computer to function as a display device according to the second embodiment of the present invention determines a gradation region based on an input image signal, selectively smoothes the image signal, and inputs an image It can be converted into an image signal having a larger number of gradations than the signal.

[Program for image processing apparatus]
A program for causing a computer to function as an image processing apparatus according to the second embodiment of the present invention determines a gradation region based on an input image signal, selectively smoothes the image signal, and inputs the image signal. It can be converted into an image signal having a larger number of gradations than the image signal.

(Image processing method according to the second embodiment)
Next, an image processing method according to the second embodiment of the present invention will be described. FIG. 21 is a flowchart showing an example of an image processing method according to the second embodiment of the present invention. In the following description, the image processing method shown in FIG. 21 is described as being performed by the display device 2000. However, the image processing method can also be applied to the image processing device according to the second embodiment of the present invention.

  The display device 2000 detects a predetermined frequency component for each pixel from each of the N-bit input image signals Ri, Gi, Bi (S200).

  The display device 2000 selects the maximum value for each pixel based on the detection values (frequency component detection values Rf, Gf, Bf) detected in step S200 (S202).

  The display device 2000 smoothes the maximum value (maximum detection value Dmax) selected in step S202 (S204), and generates a control signal Dc based on the smoothed detection value (average detection value Dave) (S206). .

  The display device 2000 adds a fixed value of k bits to the lower order of the input image signal based on the input image signals Ri, Gi, Bi for each channel and the control signal Dc generated in step S206, and N + k bits. The first output image signal converted into, or the N + k-bit second output image signal obtained by smoothing the input image signal is selectively output for each channel (S208).

  By using the image processing method shown in FIG. 21, the display device 2000 determines a gradation region based on the input image signal, selectively smoothes the image signal, and has a gradation number higher than that of the input image signal. Can be converted into an image signal having a large amount of image data.

(Third embodiment)
In the above description, the configuration in which the display unit has the gradation performance of N + k bits has been described as the display device according to the first and second embodiments. However, the display unit included in the display device according to the embodiment of the present invention is not limited to the N + k-bit gradation performance, and may have N-bit gradation performance. Thus, next, a configuration in which the display unit has N-bit gradation performance as a display device according to the third embodiment of the present invention will be described.

  FIG. 22 is a block diagram showing a display device 3000 according to the third embodiment of the present invention. Referring to FIG. 22, the display device 3000 includes an image processing unit 300 and a display unit 390.

  The image processing unit 300 includes a control unit 102, a gradation number expansion unit 104, and a pseudo gradation processing unit 302. The control unit 102 and the gradation number expanding unit 104 have the same configurations as the control unit 102 and the gradation number expanding unit 104 included in the image processing unit 100 according to the first embodiment shown in FIG. That is, the control unit 102 generates the control signal Dc based on the input image signal Di, and the gradation number expanding unit 104 adds a k-bit fixed value to the lower order of the input image signal Di based on the control signal Dc. The first output image signal converted to N + k bits or the N + k bit second output image signal obtained by smoothing the input image signal Di is selectively output as the image signal De.

  The pseudo gradation processing unit 302 converts the N + k-bit image signal De into an N-bit output image signal Do using a pseudo intermediate gradation.

  Here, the pseudo gradation processing in the pseudo gradation processing unit 302 will be described. FIG. 23 is an explanatory diagram for explaining an example of the pseudo gradation processing in the pseudo gradation processing unit 302 according to the third embodiment of the present invention, and an example in which dither processing is used as the pseudo gradation processing. Show. FIG. 23A shows a 2 × 2 pixel area where dither processing is performed, and FIG. 23B shows an example of a dither pattern.

  In the dither processing, after adding a value corresponding to each pixel position of the dither pattern in FIG. 23B to the pixels a to d in the N + k-bit image signal De in FIG. This is a process of outputting the upper N bits as an output image signal by rounding. Here, the dither processing is a kind of pseudo gradation processing, and it is known that gradation with a larger number of bits can be displayed in a pseudo manner with a smaller number of bits.

  The pseudo gradation processing unit 302 converts the N + k-bit image signal De by using dither processing as the pseudo gradation processing, and outputs an N-bit output image signal Do that improves the gradation performance of the gradation area. be able to.

[Another example of pseudo gradation processing]
Note that the pseudo gradation processing in the pseudo gradation processing unit 302 is not limited to the dither processing. For example, the pseudo gradation processing unit 302 can use error diffusion processing as the pseudo gradation processing. Here, the error diffusion processing is performed by adding or subtracting a value of lower k bits (referred to as “error data”) obtained by rounding an N + k-bit image signal to N bits to the surrounding pixel signal, and converting the error data. This is a method of obtaining pseudo halftones by diffusing. Even if the pseudo gradation processing unit 302 performs the pseudo gradation processing using the error diffusion processing, the same effect as in the case of using the dither processing can be obtained.

  With reference to FIG. 22 again, the components of the display device 3000 will be described. The display unit 390 has N-bit gradation performance and displays an image indicated by the N-bit output image signal Do output from the image processing unit 300.

  As described above, in the display device 3000, after the image processing unit 300 temporarily converts the N-bit input image signal Di into the N + k-bit image signal De by expanding the number of gradations, the pseudo-gradation such as dither processing is performed. By converting the output image signal Do into N bits using processing, the gradation performance of the gradation area can be improved. Therefore, the display device 3000 can display an image in which the gradation performance of the gradation area is improved even if the gradation performance of the display unit 390 is N bits.

  In FIG. 22, the input image signal is described as an example of a monochrome image input image signal (or an image signal corresponding to one of a plurality of channels of a color image) Di. Like the display device 2000 according to the embodiment, for example, the same effect can be obtained for an image signal of a color image composed of R / G / B.

  As described above, the display device 3000 according to the third embodiment of the present invention converts the N-bit input image signal Di into the N + k-bit image signal De and then converts the N-bit input image signal Di into the N-bit Do using the pseudo gradation processing. An image processing unit 300 for conversion and a display unit 390 having N-bit gradation performance are provided. The image processing unit 300 includes a control unit 102 and a gradation number expanding unit 104 having the same configuration as the control unit 102 and the gradation number expanding unit 104 according to the first embodiment, and is input based on the control signal Dc. The first output image signal converted to N + k bits by adding a k-bit fixed value to the lower order of the image signal Di, or the second output image signal of N + k bits obtained by smoothing the input image signal Di is selectively imaged. Output as signal De. Accordingly, the display device 3000 determines the gradation area based on the input image signal, selectively smoothes the image signal, and performs smoothing of the image signal based on the input image signal, similarly to the display device 1000 according to the first embodiment. Can also be converted into an image signal having a large number of gradations.

  In the display device 3000, the image processing unit 300 includes a pseudo gradation processing unit 302, and converts the N + k-bit image signal De into an N-bit output image signal Do using pseudo gradation processing such as dither processing. Thus, the gradation performance of the gradation area is improved. Therefore, the display device 3000 can display an image in which the gradation performance of the gradation area is improved even if the gradation performance of the display unit 390 is N bits.

[Modification of Display Device 3000]
The display device according to the third embodiment can take a modification similar to the modification of the display device according to the first embodiment described above.

(Image processing apparatus according to the third embodiment)
In the above, the display device according to the third embodiment has been described. However, the image processing unit included in the display device (including the modification example) according to the third embodiment described above is independent of the display unit. It can also be realized as an apparatus, that is, an image processing apparatus.

(Program according to the third embodiment)
[Programs related to display devices]
A program for causing a computer to function as a display device according to the third embodiment of the present invention determines a gradation region based on an input image signal, selectively smoothes the image signal, and inputs an image The gradation performance can be improved by performing pseudo gradation processing after converting the image signal to have more gradations than the signal.

[Program for image processing apparatus]
A program for causing a computer to function as an image processing apparatus according to the third embodiment of the present invention determines a gradation region based on an input image signal, selectively smoothes the image signal, and inputs The gradation performance can be improved by performing the pseudo gradation process after converting the image signal to an image signal having a larger number of gradations than the image signal.

(Image processing method according to the third embodiment)
Next, an image processing method according to the third embodiment of the present invention will be described. FIG. 24 is a flowchart showing an example of an image processing method according to the third embodiment of the present invention. In the following description, the image processing method shown in FIG. 24 is described as being performed by the display device 3000, but the image processing method can also be applied to the image processing device according to the third embodiment of the present invention.

  The display device 3000 detects a predetermined frequency component for each pixel from the N-bit input image signal Di as in step S100 shown in FIG. 17 (S300).

  The display device 3000 smoothes the detection value (frequency component detection value Df) detected in step S300, similarly to steps S102 and S104 shown in FIG. 17 (S302), and smoothes the detection value (average detection value Dave). ) To generate a control signal Dc (S304).

  The display device 3000 adds a k-bit fixed value to the lower order of the input image signal Di based on the input image signal Di and the control signal Dc generated in step S304, as in step S106 shown in FIG. The first output image signal converted to N + k bits or the N + k bit second output image signal obtained by smoothing the input image signal Di is selectively output (S306).

  The display device 3000 performs pseudo gradation processing on the image signal (first output image signal or second output image signal) output in step S306, and converts it into an N-bit image signal (output image signal Do). (S308). Here, the display device 3000 can perform the pseudo gradation processing in step S308 by using, for example, dither processing or error diffusion processing.

  By using the image processing method shown in FIG. 24, the display device 3000 determines a gradation area based on the input image signal, selectively smoothes the image signal, and has a gradation number higher than that of the input image signal. The gradation performance can be improved by performing pseudo gradation processing after converting the image signal into a large amount of image signal.

(Fourth embodiment)
Next, a display device according to a fourth embodiment, which is another embodiment of the display device according to the embodiment of the present invention, will be described. FIG. 25 is a block diagram showing a display device 4000 according to the fourth embodiment of the present invention.

  Referring to FIG. 25, the display device 4000 includes an image processing unit 400 and a display unit 390. The image processing unit 400 basically has the same configuration as that of the image processing unit 300 according to the third embodiment illustrated in FIG. 22, but further includes a nonlinear gradation conversion unit 402. In addition, the display unit 390 has N-bit gradation performance similarly to the display unit 390 according to the third embodiment shown in FIG.

  The control unit 102 generates a control signal Dc based on the input image signal Di, and the gradation number expanding unit 104 adds a k-bit fixed value to the lower order of the input image signal Di based on the control signal Dc, and N + k The first output image signal converted into bits or the N + k-bit second output image signal obtained by smoothing the input image signal Di is selectively output as the image signal De.

  The non-linear tone conversion unit 402 receives the image signal De output from the tone number expansion unit 104, and performs non-linear tone conversion such as contrast enhancement processing and gamma processing to output the image signal Dg. Here, a case where contrast enhancement processing is performed as nonlinear gradation conversion processing in the nonlinear gradation conversion unit 402 will be described.

  FIG. 26 is an explanatory diagram for explaining the nonlinear gradation conversion processing in the nonlinear gradation conversion unit 402 according to the fourth embodiment of the present invention, and shows an example of input / output conversion characteristics for performing contrast enhancement. ing.

  Referring to FIG. 26, the gradation difference is compressed in the dark portion L1 and the bright portion L3, and the gradation difference is widened in the intermediate gradation L2. For example, the nonlinear gradation conversion unit 402 can output the image signal Dg in which the contrast of the image is enhanced by correcting the image signal De as shown in FIG.

  The pseudo gradation processing unit 302 converts the N + k-bit image signal Dg by using dither processing or error diffusion processing as the pseudo gradation processing, thereby improving the gradation performance of the gradation region. Do can be output.

  Here, an example of each signal in the image processing unit 400 is shown. FIG. 27 is an explanatory diagram showing an example of each signal in the image processing unit 400 according to the fourth embodiment of the present invention, and shows a gradation area as in FIG. FIG. 27A shows the input image signal Di, and FIG. 27B shows the frequency component detection value Df. Similarly, FIG. 27C to FIG. 27F show the average detection value Dave, the control signal Dc, the image signal De whose number of gradations is expanded, and the image signal Dg after the nonlinear gradation conversion processing, respectively. Yes.

  As the input image signal Di, as in FIG. 8A, a gradation region that changes stepwise by one gradation is taken as an example (FIG. 27A). Similarly to FIG. 8C, the frequency component detection value Df is small and the frequency of detection is low (FIG. 27B). Similarly to FIG. 8D, the average detection value Dave is The value is smaller than the threshold value TH (FIG. 27 (c)). Further, since the average detection value Dave shown in FIG. 27C is smaller than the threshold value TH, the control signal Dc indicates “1” representing the gradation area (FIG. 27D). Since the control signal Dc shown in FIG. 27D is “1” indicating the gradation region, the gradation number expanding unit 104 performs the smoothed second output signal (smoothed image signal Ds) having an accuracy of N + k bits. ) Is selected and output as an output image signal De (FIG. 27E).

  Since the image signal De shown in FIG. 27E output from the gradation number expansion unit 104 is input to the nonlinear gradation conversion unit 402, the gradation region can be smoothed without erroneous detection ( FIG. 27 (f)).

[Modification of Image Processing Unit According to Fourth Embodiment]
In the image processing unit 400 according to the fourth embodiment shown in FIG. 25, the configuration in which the nonlinear gradation conversion process is performed after the number of gradations is expanded is shown. However, after the nonlinear gradation conversion process is performed, the number of gradations is changed. It is also possible to expand. FIG. 28 is a block diagram showing an image processing unit 450 according to a modification of the fourth embodiment of the present invention.

  Referring to FIG. 28, the image processing unit 450 basically has the same configuration as the image processing unit 400 shown in FIG. 25, but the input image signal Di is input to the nonlinear gradation conversion unit 402, and nonlinear gradation conversion is performed. The image processing unit 400 is different from the image processing unit 400 in that the number of gradations is expanded based on the image signal Dg after nonlinear gradation conversion output from the unit 402.

  Here, an example of each signal in the image processing unit 450 is shown. FIG. 29 is an explanatory diagram showing an example of each signal in the image processing unit 450 according to the modification of the fourth embodiment of the present invention, and shows a gradation area as in FIG. FIG. 28A shows the input image signal Di, and FIG. 28B shows the image signal Dg after the nonlinear gradation conversion processing. Similarly, FIGS. 28C to 28F show the frequency component detection value Df, the average detection value Dave, the control signal Dc, and the image signal De in which the number of gradations is expanded.

  As an example of the input image signal Di, a gradation region that changes in a step-by-step manner is given as in FIG. 27A (FIG. 28A). The input image signal Di shown in FIG. 28A is input to the nonlinear gradation conversion unit 402, and nonlinear gradation conversion processing is performed on the input image signal Di. The part where the difference in tone spreads appears (FIG. 28B).

  Since the control unit 102 determines the gradation area based on the image signal Dg after the nonlinear gradation conversion processing shown in FIG. 28B, the part other than the gradation area is used at a part where the difference in gradation partially spreads. It may be determined as a region (FIG. 28 (c) to FIG. 28 (e)).

  The gradation number expanding unit 104 performs image signal Dg (first output image signal) after nonlinear gradation conversion processing or image signal Dg after nonlinear gradation conversion processing in accordance with the control signal Dc shown in FIG. The N + k-bit second output image signal obtained by smoothing is selectively output as the image signal De. Therefore, the gradation number expanding unit 104 does not perform smoothing at the portion where the difference in gradations is widened (the first output image signal is output), and thus the gradation area may not be converted smoothly. (FIG. 28 (f)).

  As shown with reference to FIGS. 28 and 29, the image processing unit according to the fourth embodiment can take a modified example in which the number of gradations is expanded after the nonlinear gradation conversion process. However, the processing order may affect the processing result.

  As described above, the display device 4000 according to the fourth embodiment of the present invention converts the N-bit input image signal Di into the N + k-bit image signal De, performs the non-linear gradation conversion process, and further performs pseudo gradation. An image processing unit 400 that converts the data into N-bit Do using processing, and a display unit 390 having N-bit gradation performance are provided. The image processing unit 400 includes a control unit 102 having the same configuration as the control unit 102 and the gradation number expansion unit 104 according to the first embodiment, and a gradation number expansion unit 104, and is based on the control signal Dc. A first output image signal converted to N + k bits by adding a k-bit fixed value to the lower order of the input image signal Di or an N + k bit second output image signal obtained by smoothing the input image signal Di is selectively Output as an image signal De. Accordingly, the display device 4000 determines the gradation area based on the input image signal, selectively smoothes the image signal, and performs smoothing of the image signal based on the input image signal, similarly to the display device 1000 according to the first embodiment. Can also be converted into an image signal having a large number of gradations.

  Further, the display device 4000 includes a non-linear gradation conversion unit 402 that performs non-linear gradation conversion such as contrast enhancement processing and gamma processing on the N + k-bit image signal De output from the gradation number expansion unit 104. The gradation area can be smoothed while performing non-linear gradation conversion without erroneous detection.

  Further, in the display device 4000, similarly to the display device 3000 according to the third embodiment, the image processing unit 400 includes a pseudo gradation processing unit 302, and a non-linear gradation using pseudo gradation processing such as dither processing. By converting the N + k-bit image signal Dg output from the conversion unit 402 into an N-bit output image signal Do, the gradation performance of the gradation area is improved. Therefore, as with the display device 3000 according to the third embodiment, the display device 4000 displays an image with improved gradation performance in the gradation area even if the gradation performance of the display unit 390 is N bits. can do.

[Modification of display device 4000]
FIG. 25 shows a configuration in which the display unit 390 has N-bit gradation performance and the image processing unit 400 includes the pseudo gradation processing unit 302, but the display device according to the fourth embodiment is shown in FIG. It is not restricted to the structure of. For example, the display device according to the modification of the fourth embodiment may include a display unit having N + k bit gradation performance, and the image processing unit may not include the pseudo gradation processing unit. Even with such a configuration, the display device according to the modification of the fourth embodiment can smooth the gradation area without erroneous detection.

  Further, the display device according to the fourth embodiment can take a modification similar to the modification of the display device according to the first embodiment described above.

(Image processing apparatus according to the fourth embodiment)
Although the display device according to the fourth embodiment has been described above, the image processing unit included in the display device (including the modification example) according to the above-described fourth embodiment is independent of the display unit. It can also be realized as an apparatus, that is, an image processing apparatus.

(Program according to the fourth embodiment)
[Programs related to display devices]
A program for causing a computer to function as a display device according to the fourth embodiment of the present invention determines a gradation area based on an input image signal, selectively smoothes the image signal, and inputs an image The gradation area can be smoothed and the gradation performance can be improved by performing the nonlinear gradation conversion process and the pseudo gradation process after the conversion to an image signal having a larger number of gradations than the signal.

[Program for image processing apparatus]
A program for causing a computer to function as an image processing apparatus according to the fourth embodiment of the present invention determines a gradation region based on an input image signal, selectively smoothes the image signal, and inputs the image signal. By converting the image signal into an image signal having a larger number of gradations than the image signal, and further performing nonlinear gradation conversion processing and pseudo gradation processing, the gradation region can be smoothed and the gradation performance can be improved.

(Image processing method according to the fourth embodiment)
Next, an image processing method according to the fourth embodiment of the present invention will be described. FIG. 30 is a flowchart showing an example of an image processing method according to the fourth embodiment of the present invention. In the following description, the image processing method shown in FIG. 30 is described as being performed by the display device 4000, but the image processing method can also be applied to the image processing device according to the fourth embodiment of the present invention.

  The display device 4000 detects a predetermined frequency component for each pixel from the N-bit input image signal Di as in Step S100 shown in FIG. 17 (S400).

  The display device 4000 smoothes the detection value (frequency component detection value Df) detected in step S400 (S402), similarly to steps S102 and S104 shown in FIG. 17, and smoothes the detection value (average detection value Dave). ) To generate a control signal Dc (S404).

  The display device 4000 adds a k-bit fixed value to the lower order of the input image signal Di based on the input image signal Di and the control signal Dc generated in step S404, as in step S106 shown in FIG. The first output image signal converted into N + k bits or the N + k bit second output image signal obtained by smoothing the input image signal Di is selectively output (S406).

  The display device 4000 performs nonlinear gradation conversion processing on the N + k-bit image signal (image signal De) output in step S406 (S408). Here, examples of the nonlinear gradation conversion processing in step S408 include, but are not limited to, contrast enhancement processing and gamma processing.

  The display device 4000 performs pseudo gradation processing on the image signal (image signal Dg) on which the nonlinear gradation conversion processing has been performed in step S408 in the same manner as in step S308 shown in FIG. The output image signal Do) is converted (S410).

  By using the image processing method illustrated in FIG. 30, the display device 4000 determines a gradation region based on the input image signal, selectively smoothes the image signal, and has a gradation number higher than that of the input image signal. By converting the image signal into a large amount of image signal and further performing nonlinear gradation conversion processing and pseudo gradation processing, the gradation area can be smoothed and the gradation performance can be improved.

[Modification of Image Processing Method According to Fourth Embodiment]
FIG. 30 shows an image processing method for converting an N + k-bit image signal into an N-bit image signal by pseudo gradation processing in step S410, but the image processing method according to the fourth embodiment is shown in FIG. It is not limited to the method shown. For example, the display device according to the fourth embodiment can display an N + k-bit image signal on the N + k-bit display unit without performing the process of step S410 shown in FIG. Even when the image processing method according to the above modification is used, the display device according to the fourth embodiment can obtain the same effects as when the image processing method shown in FIG. 30 is used.

(Fifth embodiment)
In the above, as a modification of the image processing unit according to the fourth embodiment, a configuration in which nonlinear gradation conversion processing is performed on the input image signal Di as shown in FIG. 28 is shown, and the order of processing is as shown in FIG. It was shown that the processing result might be affected. However, the display device according to the embodiment of the present invention can smoothly correct the gradation area even when the nonlinear gradation conversion process is performed on the input image signal Di. Therefore, next, a display device according to a fifth embodiment of the present invention will be described.

  FIG. 31 is a block diagram showing a display device 5000 according to the fifth embodiment of the present invention. Referring to FIG. 31, the display device 5000 includes an image processing unit 500 and a display unit 390. The image processing unit 500 basically has the same configuration as the image processing unit 450 according to the modification of the fourth embodiment shown in FIG. 28, but the input image signal Di is input to the control unit 102, and the input image signal The point which determines a gradation area | region based on Di differs from the image process part 450 which concerns on the modification of 4th Embodiment. In addition, the display unit 390 has N-bit gradation performance similarly to the display unit 390 according to the third embodiment shown in FIG.

  Here, an example of each signal in the image processing unit 500 is shown. FIG. 32 is an explanatory diagram showing an example of each signal in the image processing unit 500 according to the modification of the fifth embodiment of the present invention, and shows a gradation area as in FIG. FIG. 32A shows the input image signal Di, and FIG. 32B shows the image signal Dg after nonlinear gradation conversion processing. Similarly, FIG. 32C to FIG. 32F show the frequency component detection value Df, the average detection value Dave, the control signal Dc, and the image signal De whose number of gradations is expanded, respectively.

  As the input image signal Di, as in FIG. 27A, a gradation region that changes stepwise by one gradation is taken as an example (FIG. 32A). The input image signal Di shown in FIG. 32A is input to the nonlinear gradation conversion unit 402, and nonlinear gradation conversion processing is performed on the input image signal Di. The part where the difference in tone spreads appears (FIG. 32 (b)).

  The input image signal Di is input to the control unit 102, and a gradation area is determined based on the input image signal Di. Accordingly, the frequency component detection value Df is small and the frequency of detection is low (FIG. 32 (c)) as in FIG. 27 (b), and the average detection value Dave is the same as in FIG. 27 (c). Becomes a value smaller than the threshold value TH (FIG. 32D). Further, since the average detection value Dave shown in FIG. 32D is smaller than the threshold value TH, the control signal Dc indicates “1” representing the gradation area (FIG. 32E).

  Since the control signal Dc shown in FIG. 32 (e) is “1” indicating the gradation region, the gradation number expanding unit 104 has an accuracy of N + k bits obtained by smoothing the image signal Dg after the nonlinear gradation conversion processing. The second output signal (smoothed image signal Ds) is selected and output as the output image signal De (FIG. 32 (f)).

  Therefore, the image processing unit 500 can smooth the gradation area without erroneous detection, as shown in FIG.

  As described above, the display device 5000 according to the fifth embodiment of the present invention includes the image processing unit 500 and the display unit 390 having N-bit gradation performance. The image processing unit 500 performs nonlinear gradation conversion processing on the N-bit input image signal Di, and after the nonlinear gradation conversion processing according to the control signal Dc generated based on the N-bit input image signal Di. The image signal Dg is converted into an N + k-bit image signal De. Further, the image processing unit 500 converts the N + k-bit image signal De into N-bit Do by using pseudo gradation processing. Here, the image processing unit 500 includes a nonlinear gradation conversion unit 402 according to the fourth embodiment, and a control unit 102 having the same configuration as the control unit 102 and the gradation number expansion unit 104 according to the first embodiment. And the gradation number expanding unit 104, and an image signal Dg (first output image signal) after nonlinear gradation conversion processing or an image after nonlinear gradation conversion processing according to a control signal Dc based on the input image signal Di The N + k-bit second output image signal obtained by smoothing the signal Dg is selectively output as the image signal De. Therefore, the display device 5000 determines the gradation area based on the input image signal, and smoothly converts the gradation area without erroneous detection and converts the gradation area into an image signal having a larger number of gradations than the input image signal. can do.

  Further, in the display device 5000, similarly to the display device 3000 according to the third embodiment, the image processing unit 500 includes the pseudo gradation processing unit 302, and the number of gradations is determined using pseudo gradation processing such as dither processing. By converting the N + k-bit image signal De output from the extension unit 104 into an N-bit output image signal Do, the gradation performance of the gradation area is improved. Therefore, as with the display device 3000 according to the third embodiment, the display device 5000 displays an image with improved gradation performance in the gradation area even if the gradation performance of the display unit 390 is N bits. can do.

[Modification of Display Device 5000]
The display device according to the fifth embodiment includes a display unit having a gradation performance of N + k bits, as in the modification of the display device according to the fourth embodiment described above, and the image processing unit performs pseudo gradation processing. It can also be set as the structure which is not provided with a part. Even with this configuration, the display device according to the modification of the fifth embodiment can achieve the same effects as the display device 5000 shown in FIG.

  Further, the display device according to the fifth embodiment can take a modification similar to the modification of the display device according to the first embodiment described above.

(Image processing apparatus according to the fifth embodiment)
In the above, the display device according to the fifth embodiment has been described. However, the image processing unit included in the display device according to the fifth embodiment (including the modification example) is independent of the display unit. It can also be realized as an apparatus, that is, an image processing apparatus.

(Program according to the fifth embodiment)
[Programs related to display devices]
A program for causing a computer to function as a display device according to the fifth embodiment of the present invention determines a gradation area based on an input image signal and smoothly corrects the gradation area without erroneous detection. The gradation performance can be improved by converting the input image signal into an image signal having a larger number of gradations than that of the input image signal and performing pseudo gradation processing.

[Program for image processing apparatus]
A program for causing a computer to function as an image processing apparatus according to the fifth embodiment of the present invention determines a gradation area based on an input image signal and smoothly corrects the gradation area without erroneous detection. By converting the image signal into an image signal having a larger number of gradations than the input image signal and performing pseudo gradation processing, the gradation performance can be improved.

(Image processing method according to the fifth embodiment)
Next, an image processing method according to the fifth embodiment of the present invention will be described. FIG. 33 is a flowchart showing an example of an image processing method according to the fifth embodiment of the present invention. In the following description, it is assumed that the image processing method shown in FIG. 33 is performed by the display device 5000, but the image processing method can also be applied to the image processing device according to the fifth embodiment of the present invention.

  The display device 5000 detects a predetermined frequency component for each pixel from the N-bit input image signal Di as in step S100 shown in FIG. 17 (S500).

  The display device 5000 smoothes the detection value (frequency component detection value Df) detected in step S500 (S502), similarly to steps S102 and S104 shown in FIG. 17, and smoothes the detection value (average detection value Dave). ) To generate a control signal Dc (S504).

  The display device 5000 performs nonlinear gradation conversion processing on the N-bit input image signal Di in the same manner as in step S408 shown in FIG. 30 (S506). FIG. 33 shows an example in which step S506 is performed after step S504, but the present invention is not limited to this method, and the process of step S506 can be performed before the process of step S500.

  The display device 5000 uses the nonlinear gradation conversion process based on the image signal (image signal Dg) after the nonlinear gradation conversion process performed in Step 506 and the control signal Dc generated in Step S504. An N + k-bit second output image signal obtained by smoothing the image signal after the conversion process (image signal Dg, first output image signal) or the image signal after the non-linear gradation conversion process (image signal Dg) is selectively used. It outputs (S508).

  The display device 5000 performs pseudo gradation processing on the image signal (image signal De) output in step S508 in the same manner as in step S308 shown in FIG. 24, and converts it into an N-bit image signal (output image signal Do). Conversion is performed (S510).

  By using the image processing method shown in FIG. 33, the display device 5000 determines the gradation area based on the input image signal, and smoothly corrects the gradation area while performing nonlinear gradation conversion without erroneous detection. The gradation performance can be improved by converting the input image signal into an image signal having a larger number of gradations than that of the input image signal and performing pseudo gradation processing.

[Modification of Image Processing Method According to Fifth Embodiment]
FIG. 33 shows an image processing method for converting an N + k-bit image signal into an N-bit image signal by pseudo gradation processing in step S510, but the image processing method according to the fifth embodiment is shown in FIG. It is not limited to the method shown. For example, the display device according to the fifth embodiment can display an N + k-bit image signal on the N + k-bit display unit without performing the process of step S510 illustrated in FIG. Even when the image processing method according to the above modification is used, the display device according to the fifth embodiment can obtain the same effects as when the image processing method shown in FIG. 33 is used.

(Sixth embodiment)
In the above, the display apparatus which selectively smoothes based on the input image signal inputted as the display apparatus according to the first to fifth embodiments has been described. Here, the display device according to the embodiment of the present invention is, for example, an input image signal based on the NTSC (National Television System Committee) standard or a high definition television broadcast (hereinafter referred to as “HDTV”). In some cases, input image signals having different sampling frequencies of the input image signal are input, such as an input image signal corresponding to). When the same processing is performed on input image signals having different sampling frequencies as described above, fine unevenness determination (texture region determination) cannot be performed correctly based on the input image signal. There is a risk that the image quality will deteriorate due to the loss of the texture of distant mountains. Further, for example, when input image signals of a plurality of channels expressed in the YCbCr color space are input to the display device according to the embodiment of the present invention, the sampling frequency of each channel is different, and thus the same problem as described above. May occur. Therefore, next, as a display device according to the sixth embodiment of the present invention, the processing to be performed based on the input image signal that has been input is switched (more precisely, the detection criterion of the frequency component detected from the input image signal is A configuration that can prevent deterioration in image quality by switching) will be described.

  FIG. 34 is a block diagram showing a display device 6000 according to the sixth embodiment of the present invention. Here, FIG. 34 shows an example in which input image signals of three channels of input image signals Di1, Di2, and Di3 are input to the display device 6000. The input image signal input to the display device according to the sixth embodiment of the present invention is not limited to the above. For example, the display device according to the sixth embodiment of the present invention has two channels including an input image signal of one channel indicating a monochrome image and a signal in which a Y signal, a Pb signal, and a Pr signal are superimposed. An input image signal may be input.

  Referring to FIG. 34, the display device 6000 includes an image processing unit 600 and a display unit 190. The image processing unit 600 includes a selection signal generation unit 602, a control unit 604, and a gradation number expansion unit 606, and each of the input N-bit input image signals Di1, Di2, and Di3 is an N + k-bit output image signal. Convert to Do1, Do2, Do3 and output.

  The selection signal generation unit 602 selects selection signals (Sel1 to Sel3 shown in FIG. 34) for switching detection criteria of signals in a predetermined frequency band detected from the input image signal based on the input image signals Di1, Di2, and Di3. Is generated. For example, the selection signal generation unit 602 calculates the sum of high-frequency components (frequency components greater than or equal to a predetermined threshold) for each of the input image signals Di1, Di2, and Di3, and determines whether the sum is greater than or equal to a predetermined threshold. By doing so, a selection signal corresponding to the determination result can be generated, but is not limited to the above. In the following, the selection signal generation unit 602 generates, for example, two types of selection signals of a high level (when the threshold is equal to or greater than the threshold) and a low level (when the threshold is smaller than the threshold) by threshold processing related to the sum of the high frequency component thresholds. It will be explained as a thing.

  34, the selection signal generation unit 602 generates a plurality of selection signals Sel1 to Sel3 based on the input image signals Di1, Di2, and Di3, and transmits the generated selection signals Sel1 to Sel3 to the control unit 604. However, the present invention is not limited to the above. For example, the selection signal generation unit according to the sixth embodiment of the present invention selects any one of the selection signals Sel1 to Sel3 illustrated in FIG. 34 (for example, a selection signal obtained by ORing the selection signals Sel1 to Sel3). ) Can also be transmitted to the control unit 604.

  The control unit 604 receives input image signals Di1, Di2, and Di3 and selection signals Sel1, Sel2, and Sel3, respectively, and determines a gradation area for each pixel. Further, the gradation number expansion unit 606 expands the gradation number of the input image signals Di1 to Di3 for each pixel based on the control signal Dc output from the control unit 604, or corrects and corrects the input image signals Di1 to Di3. The number of gradations is expanded.

  The display unit 190 has gradation performance of N + k bits similarly to the display unit 190 according to the first embodiment shown in FIG. 1, and displays an image based on output image signals Do1, Do2, and Do3 of N + k bits. . Hereinafter, the configuration of the image processing unit 600 will be specifically described.

[Configuration Example of Image Processing Unit 600]
FIG. 35 is a block diagram showing an image processing unit 600 according to the sixth embodiment of the present invention. Here, in FIG. 35, the selection signal generation unit 602 is omitted.

  Referring to FIG. 35, the control unit 604 includes a first frequency component detection unit 610a (detection unit), a second frequency component detection unit 610b (detection unit), and a third frequency component detection unit 610c (detection unit). ), A maximum value selection unit 206, a detection value smoothing unit 108, and a control signal generation unit 110. In addition, the gradation number expansion unit 606 includes a first gradation number expansion unit 606a, a second gradation number expansion unit 606b, and a third gradation number expansion unit 606c.

[Control unit 604]
The input image signal Di1 and the selection signal Sel1 are input to the first frequency component detection unit 610a, and the input image signal Di2 and the selection signal Sel2 are input to the second frequency component detection unit 610b. Then, the input image signal Di3 and the selection signal Sel3 are input to the third frequency component detection unit 610c.

<Configuration Example of Frequency Component Detection Unit 610>
Here, a configuration example of the frequency component detection unit 610 according to the sixth embodiment of the present invention will be described. The first frequency component detection unit 610a to the third frequency component detection unit 610c can have the same configuration. Therefore, hereinafter, the first frequency component detection unit 610a will be described as an example, and description of the second frequency component detection unit 610b and the third frequency component detection unit 610c will be omitted.

  FIG. 36 is a block diagram illustrating a configuration example of the frequency component detection unit 610 according to the sixth embodiment of the present invention. Here, FIG. 36 illustrates an example of the configuration of the first frequency component detection unit 610a.

  The first frequency component detection unit 610a includes a first frequency component detection unit 612, a second frequency component detection unit 614, and a selection unit 616. The first frequency component detection unit 612 and the second frequency component detection unit 614 can each have the same configuration as the frequency component detection unit 106 according to the first embodiment shown in FIG. The pass band of Di1 is different. More specifically, the first frequency component detection unit 610a includes, for example, the peak frequency f1 of the first frequency component detection unit 612 (see FIG. 4 for the peak frequency) and the second frequency component detection unit 614. The first frequency component detection unit 612 and the second frequency component detection unit 614 are provided so that the relationship with the peak frequency f2 is “f1 <f2”. With the above-described configuration, the detection signal Df1_2 (second detection value) detected from the second frequency component detection unit 614 is the detection signal Df1_1 (first detection value) detected from the first frequency component detection unit 612. ) Is greater than the frequency component. In other words, the second frequency component detection unit 614 serves to detect a higher frequency signal than the first frequency component detection unit 612. Here, the values of the peak frequencies f1 and f2 and the pass bands of the first frequency component detection unit 612 and the second frequency component detection unit 614 are, for example, an input image signal based on the NTSC standard or an input corresponding to HDTV. Although it can be determined according to the frequency characteristics such as the sampling frequency of the image signal or the signal in the YCbCr color space, it is not limited to the above. Moreover, the frequency component detection part with which the 1st frequency component detection part which concerns on the 6th Embodiment of this invention is provided is not restricted to two of the 1st frequency component detection part 612 and the 2nd frequency component detection part 614. For example, the first frequency component detection unit according to the sixth embodiment of the present invention may include three or more frequency component detection units having different signal pass bands.

  Based on the selection signal Sel1 transmitted from the selection signal generation unit 602, the selection unit 616 selectively outputs either the detection signal Df1_1 or the detection signal Df1_2 as the frequency component detection value Df1. Here, FIG. 36 illustrates a configuration in which the selection unit 616 includes the switch SW1 that switches according to the signal level of the selection signal Sel1, but the configuration of the selection unit 616 according to the embodiment of the present invention is described above. Not limited to. For example, the selection unit 616 may include two thin film transistors having different conductivity types. Even with the above configuration, the selection unit 616 can selectively output either the detection signal Df1_1 or the detection signal Df1_2 as the frequency component detection value Df1 according to the signal level of the selection signal Sel1.

  For example, with the configuration shown in FIG. 36, the first frequency component detection unit 610a selectively outputs either the detection signal Df1_1 or the detection signal Df1_2 as the frequency component detection value Df1 according to the signal level of the selection signal Sel1. . Similarly to the first frequency component detection unit 610a, the second frequency component detection unit 610b selectively selects one of the detection signal Df2_1 and the detection signal Df2_2 according to the signal level of the selection signal Sel2. Output as detection value Df2. Then, the third frequency component detection unit 610c selectively outputs either the detection signal Df3_1 or the detection signal Df3_2 as the frequency component detection value Df3 according to the signal level of the selection signal Sel3.

  Therefore, the frequency component detection unit 610 performs, for each of the plurality of input image signals, a signal in a predetermined frequency band based on the corresponding input image signal (a predetermined frequency band obtained as a result of switching the detection reference according to the input image signal). Can be detected for each pixel. Needless to say, the configuration of the frequency component detection section according to the sixth embodiment of the present invention is not limited to the configuration shown in FIG.

  The maximum value selection unit 206 selects the maximum value for each corresponding pixel from the frequency component detection values Df1, Df2, and Df3, similarly to the maximum value selection unit 206 according to the second embodiment shown in FIG. The maximum detection value Dmax is output.

  Similar to the detection value smoothing unit 108 according to the first embodiment shown in FIG. 2, the detection value smoothing unit 108 calculates the average value of the maximum detection values Dmax in the smooth region and outputs the average detection value Dave.

  Similar to the control signal generation unit 110 according to the first embodiment illustrated in FIG. 2, the control signal generation unit 110 determines the gradation region by threshold processing using the average detection value Dave and the threshold TH, and controls the determination result. Output as signal Dc.

[Grayscale number expansion unit 606]
Each of the first gradation number expanding unit 606a, the second gradation number expanding unit 606b, and the third gradation number expanding unit 606c is a gradation number expanding unit 104 according to the first embodiment shown in FIG. It has the same configuration as. Therefore, the first gradation number expanding unit 606a adds a k-bit fixed value to the lower order of the N-bit input image signal Di1 and converts it to N + k bits based on the control signal Dc, Alternatively, the N + k-bit second output image signal obtained by smoothing the input image signal Di1 is selectively output as the output image signal Do1. Similarly, the second gradation number expanding unit 606b and the third gradation number expanding unit 606c output output image signals Do2 and Do3 based on the control signal Dc, respectively.

  As described above, the image processing unit 600 can output the output image signals Do1, Do2, and Do3, for example, with the configuration of FIG.

  The image processing unit 600 generates selection signals Sel1 to Sel3 based on the input image signals Di1 to Di3, respectively, and a detection standard for a signal in a predetermined frequency band detected from the input image signal based on the generated selection signals Sel1 to Sel3. Switch. Therefore, the image processing unit 600 can receive an input image signal having a different sampling frequency, such as an input image signal based on the NTSC standard or an input image signal corresponding to HDTV, for example. A corresponding control signal Dc can be derived.

  Similarly to the image processing unit 200 according to the second embodiment, the image processing unit 600 selectively smoothes the input image signals Di1 to Di3 for each channel based on the control signal Dc. Therefore, the image processing unit 600 determines a gradation area based on the input image signal and selectively smoothes the image signal. Therefore, in the conventional technique for performing correction that extends the number of gradations of the input image signal. It is possible to prevent the image quality from being deteriorated due to the loss of fine irregularities due to the correction of the image signal that may occur.

  As described above, the display device 6000 according to the sixth embodiment of the present invention receives the input image signals Di1, Di2, and Di3 (each N-bit input image signal) of a plurality of channels and the N + k-bit output image signal Do1. , Do2 and Do3, and an image processing unit 600 and a display unit 190 having N + k-bit gradation performance. The image processing unit 600 includes a selection signal generation unit 602, a control unit 604, and a gradation number expansion unit 606. The selection signal generation unit 602 generates selection signals Sel1 to Sel3 corresponding to the input image signals Di1 to Di3 based on the input image signals Di1 to Di3, respectively. The control unit 604 determines a gradation area for each pixel based on the input image signals Di1, Di2, Di3 and the selection signals Sel1 to Sel3, and outputs a control signal Dc. Therefore, the image processing unit 600 can receive an input image signal having a different sampling frequency, such as an input image signal based on the NTSC standard or an input image signal corresponding to HDTV, for example. A corresponding control signal Dc can be derived. Then, based on the control signal Dc, the gradation number expanding unit 606 smoothes the first output image signal or the input image signal converted to N + k bits by adding a fixed value of k bits to the lower order of the input image signal. The N + k-bit second output image signal is selectively output as output image signals Do1, Do2, Do3. Accordingly, the display device 6000, like the display device 1000 according to the first embodiment, determines a gradation region based on the input image signal, selectively smoothes the image signal, and uses the input image signal. Can be converted into an image signal having a large number of gradations and displayed.

  Further, the display device 6000 can determine the gradation area and selectively correct the gradation area more smoothly similarly to the display apparatus 1000 according to the first embodiment, so that the gradation performance of the gradation area can be improved. Can be improved. Further, the display device 6000 does not correct the input image in the edge region or the texture region, so that the images indicated by the output image signals Do1, Do2, and Do3 do not lose sharpness.

  In addition, the display device 6000 selectively improves the gradation performance of the gradation area in the same manner as the display device 1000 according to the first embodiment, so that the gradation performance is visually improved over the entire image. Similar effects can be obtained.

  Further, similarly to the display device 2000 according to the second embodiment, the display device 6000 smoothes detection values and performs threshold processing on the maximum values (maximum detection values Dmax) of the frequency component detection values Df1, Df2, and Df3. By performing the above, it is possible to detect the gradation area without making a mistake with the texture area. Therefore, it is possible to suppress image quality deterioration such as a reduction in sharpness caused by smoothing the texture region.

[Modification of Display Device 6000]
34 shows a configuration in which the image processing unit 600 of the display device 6000 includes the selection signal generation unit 602, the configuration of the display device according to the sixth embodiment of the present invention is not limited to the above. For example, the display device according to the sixth embodiment of the present invention has a predetermined frequency band detected from an input image signal based on selection signals Sel1 to Sel3 input from an external device serving as the selection signal generation unit 602. It is also possible to switch the detection standard of the signal.

  Also, in FIG. 36, the first frequency component detection unit 610a (the same applies to the second frequency component detection unit 610b and the third frequency component detection unit 610c) constituting the control unit 604 of the image processing unit 600 also selects the selection signal. Although the configuration in which either the detection signal Df1_1 or the detection signal Df1_2 is selectively output as the frequency component detection value Df1 according to the signal level of Sel1 has been described, the configuration is not limited thereto. For example, the frequency component detection unit according to the sixth embodiment can also derive a frequency component detection value using a plurality of detection signals for each input image signal of each channel (for example, in FIGS. 11 and 13). Configuration as shown).

  Further, the display device according to the sixth embodiment can take a modification similar to the modification of the display device according to the first embodiment described above.

  Furthermore, the display device according to the sixth embodiment includes a pseudo gradation processing unit 302 according to the third embodiment, a non-linear gradation conversion unit 402 according to the fourth embodiment, and a non-linearity according to the fifth embodiment. A gradation conversion unit 402 and the like can be further provided. With the above configuration, the display device according to the sixth embodiment can further achieve the same effects as the display devices according to the third to fifth embodiments.

(Image processing apparatus according to the sixth embodiment)
In the above, the display device according to the sixth embodiment has been described. However, the image processing unit included in the display device according to the sixth embodiment (including the modification example) is independent of the display unit. It can also be realized as an apparatus, that is, an image processing apparatus.

(Program according to the sixth embodiment)
[Programs related to display devices]
A program for causing a computer to function as a display device according to the sixth embodiment of the present invention determines a gradation region based on an input image signal, selectively smoothes the image signal, and inputs an image It can be converted into an image signal having a larger number of gradations than the signal.

[Program for image processing apparatus]
A program for causing a computer to function as an image processing apparatus according to the sixth embodiment of the present invention determines a gradation region based on an input image signal, selectively smoothes the image signal, and inputs It can be converted into an image signal having a larger number of gradations than the image signal.

(Image Processing Method According to Sixth Embodiment)
Next, an image processing method according to the sixth embodiment of the present invention will be described. FIG. 37 is a flowchart showing an example of an image processing method according to the sixth embodiment of the present invention. In the following, the image processing method shown in FIG. 37 is described as being performed by the display device 6000, but the image processing method can also be applied to the image processing device according to the sixth embodiment of the present invention. In the following, a case where the display device 6000 processes input image signals Di1 to Di3 of three channels will be described as an example, but the present invention is not limited to the above.

  The display device 6000 generates selection signals Sel1 to Sel3 corresponding to the input image signals Di1 to Di3 based on the N-bit input image signals Di1, Di2, and Di3, respectively (S600). Here, for example, the display device 6000 calculates the sum of high-frequency components (frequency components equal to or higher than a predetermined threshold) for each of the input image signals Di1, Di2, and Di3, and determines whether the total is equal to or higher than a predetermined threshold. Although the selection signals Sel1 to Sel3 corresponding to the determination result can be generated by the determination, the selection signals are not limited to the above.

  The display device 6000 detects a plurality of frequency components for each pixel from each of the N-bit input image signals Di1, Di2, and Di3 (S602). Here, the display device 6000 can perform the process of step S602 by using, for example, a plurality of bandpass filters having different passbands, but is not limited thereto.

  For each input image signal Di1 to Di3, display device 6000 selects one detection value for each pixel from the plurality of detection values detected in step S602 based on selection signals Sel1 to Sel3 corresponding to the input image signal. Select (S604). Here, the display device 6000 can perform the process of step S604 by including a switching element that performs switching based on the selection signals Sel1 to Sel3, but is not limited thereto.

  The display device 6000 selects the maximum value for each pixel based on the detection values (frequency component detection values Df1, Df2, and Df3) selected in step S604 (S606).

  The display device 6000 smoothes the maximum value (maximum detection value Dmax) selected in step S606 (S608), similarly to steps S204 and S206 shown in FIG. 21, and the smoothed detection value (average detection value Dave). The control signal Dc is generated based on (S610).

  The display device 6000 adds a fixed value of k bits to the lower order of the input image signal based on the input image signals Di1, Di2, and Di3 for each channel and the control signal Dc generated in step S610, and adds N + k bits. The first output image signal converted into, or the N + k-bit second output image signal obtained by smoothing the input image signal is selectively output for each channel (S612).

  By using the image processing method shown in FIG. 34, the display device 6000 determines a gradation area based on the input image signal, selectively smoothes the image signal, and has a gradation number higher than that of the input image signal. Can be converted into an image signal having a large amount of image data.

  As mentioned above, although the display apparatus was mentioned and demonstrated as 1st-6th embodiment, embodiment of this invention is not restricted to this form. For example, the embodiment of the present invention is applied to an organic EL display, a self-luminous display device such as an FED and a PDP, a backlight display device such as an LCD, and a receiving device that receives a television broadcast. can do. The embodiments of the present invention can be applied to various devices such as computers such as PCs (Personal Computers) and servers (Servers), and portable communication devices such as mobile phones.

  The image processing apparatus according to the first to sixth embodiments is applied to various devices such as a display device such as an organic EL display and an LCD, a computer such as a PC, and a portable communication device such as a mobile phone. Can do.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  For example, in the display device according to the sixth embodiment, a configuration in which processing for three channels is performed is shown, but the embodiment of the present invention is not limited to this configuration. For example, the display device according to the embodiment of the present invention can process an input image signal of one channel, and can also process input image signals of a plurality of channels of two channels or four or more channels.

  The configuration described above shows an example of the embodiment of the present invention, and naturally belongs to the technical scope of the present invention.

1 is a block diagram illustrating a display device according to a first embodiment of the present invention. It is a block diagram which shows the image process part which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structural example of the frequency component detection part which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows an example of the frequency characteristic of the band pass filter which concerns on the 1st Embodiment of this invention. It is explanatory drawing for demonstrating an example of the smoothing in the detection value smoothing part which concerns on the 1st Embodiment of this invention. It is explanatory drawing for demonstrating the threshold value process in the control-signal production | generation part which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the gradation number expansion part which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows an example of each signal in the image processing part which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows the 1st example of a signal in case an image process part is not provided with a detection value smoothing part. It is explanatory drawing which shows the 2nd example of a signal in case an image process part is not provided with a detection value smoothing part. It is a block diagram which shows the frequency component detection part which concerns on the 1st modification of the 1st Embodiment of this invention. It is explanatory drawing for demonstrating the frequency component detection part which concerns on the 1st modification of the 1st Embodiment of this invention. It is a block diagram which shows the frequency component detection part which concerns on the 2nd modification of the 1st Embodiment of this invention. It is explanatory drawing for demonstrating the threshold value process in the control signal generation part which concerns on the 3rd modification of the 1st Embodiment of this invention. It is a block diagram which shows the gradation number expansion part which concerns on the 3rd modification of the 1st Embodiment of this invention. It is a block diagram which shows the display apparatus which concerns on the 4th modification of the 1st Embodiment of this invention. 3 is a flowchart illustrating an example of an image processing method according to the first embodiment of the present invention. It is a block diagram which shows the display apparatus which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the image process part which concerns on the 2nd Embodiment of this invention. It is explanatory drawing which shows an example of each signal in the image process part which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows an example of the image processing method which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the display apparatus which concerns on the 3rd Embodiment of this invention. It is explanatory drawing for demonstrating an example of the pseudo gradation process in the pseudo gradation process part which concerns on the 3rd Embodiment of this invention. It is a flowchart which shows an example of the image processing method which concerns on the 3rd Embodiment of this invention. It is a block diagram which shows the display apparatus which concerns on the 4th Embodiment of this invention. It is explanatory drawing for demonstrating the nonlinear gradation conversion process in the nonlinear gradation conversion part which concerns on the 4th Embodiment of this invention. It is explanatory drawing which shows an example of each signal in the image processing part which concerns on the 4th Embodiment of this invention. It is a block diagram which shows the image process part which concerns on the modification of the 4th Embodiment of this invention. It is explanatory drawing which shows an example of each signal in the image processing part which concerns on the modification of the 4th Embodiment of this invention. It is a flowchart which shows an example of the image processing method which concerns on the 4th Embodiment of this invention. It is a block diagram which shows the display apparatus which concerns on the 5th Embodiment of this invention. It is explanatory drawing which shows an example of each signal in the image process part which concerns on the modification of the 5th Embodiment of this invention. It is a flowchart which shows an example of the image processing method which concerns on the 5th Embodiment of this invention. It is a block diagram which shows the display apparatus which concerns on the 6th Embodiment of this invention. It is a block diagram which shows the image process part which concerns on the 6th Embodiment of this invention. It is a block diagram which shows the structural example of the frequency component detection part which concerns on the 6th Embodiment of this invention. It is a flowchart which shows an example of the image processing method which concerns on the 6th Embodiment of this invention.

Explanation of symbols

100, 150, 200, 300, 400, 450, 500, 600 Image processing unit 102, 202, 604 Control unit 104, 204, 606 Tone number expansion unit 106, 610 Frequency component detection unit 108 Detection value smoothing unit 110 Control signal Generation unit 116 Image smoothing unit 118, 616 Selection unit 122, 206 Maximum value selection unit 124 Addition unit 126 Mixing unit 190, 390 Display unit 302 Pseudo gradation processing unit 402 Non-linear gradation conversion unit 602 Selection signal generation unit 1000, 1500, 2000, 3000, 4000, 5000, 6000 Display device

Claims (9)

An image signal processing apparatus to which a plurality of N-bit (N is a positive integer) input image signals are input,
For each of the plurality of input image signals, a frequency component detection unit that detects a signal in a predetermined frequency band based on the corresponding input image signal for each pixel;
Based on the detection signal detected by the frequency component detection unit, a maximum value selection unit that selects a detection signal having the maximum detection signal in each pixel corresponding to each of the plurality of input image signals;
A detection value smoothing unit that smoothes each detection signal corresponding to each pixel based on the detection signal selected by the maximum value selection unit;
Based on the detection signal smoothed by the detection value smoothing unit, a control signal generating unit that generates a control signal for defining a gradation region for each pixel;
A plurality of N-bit input image signals are input, and the number of gradations of the input image signal is expanded by a predetermined number for each of the plurality of input image signals input based on a control signal generated for each pixel Output N + k bit first output image signal (k is a positive integer), or N + k bit second output image signal in which the input image signal is smoothed and the number of gradations is expanded by a predetermined number, for each pixel. The number of gradations to be expanded,
Equipped with a,
The control signal generation unit generates a control signal indicating a gradation region when the detection signal smoothed by the detection value smoothing unit is smaller than a predetermined threshold,
The gradation number expansion unit
When the control signal indicates an area other than the gradation area, the first output image signal is output,
The image processing apparatus , wherein the second output image signal is output when the control signal indicates a gradation area . A selection signal generating unit that generates a selection signal for setting the predetermined frequency band for each of the input image signals based on each of the input image signals;
The image processing apparatus according to claim 1, wherein the frequency component detection unit detects a signal in the predetermined frequency band for each pixel based on a selection signal corresponding to each of the input image signals. The frequency component detection unit includes a plurality of detection units corresponding to the input image signals,
Each of the plurality of detection units is
A first frequency component detector that detects a signal in the first frequency band for each pixel;
A second frequency component detector that detects a signal in a higher frequency than the first frequency band for each pixel;
Based on the corresponding selection signal, either the first detection value output from the first frequency component detection unit or the second detection value output from the second frequency component detection unit is set to the predetermined value. A selection unit that outputs a signal in a frequency band;
The image processing apparatus according to claim 2, further comprising:   The number of gradations of the first output image signal or the second output image signal corresponding to each of the plurality of input image signals output from the gradation number expanding unit is an N-bit image using pseudo intermediate gradations. The image processing apparatus according to claim 1, further comprising a first pseudo gradation processing unit that converts the signal into a signal. A first non-linear tone conversion unit that non-linearly corrects a first output image signal or a second output image signal corresponding to each of the plurality of input image signals output from the tone number extension unit according to a signal level; ,
The number of gradations of the corrected first output image signal or second output image signal output from the first nonlinear gradation conversion unit is converted into an N-bit image signal using a pseudo intermediate gradation. A second pseudo gradation processing unit;
The image processing apparatus according to claim 1, further comprising: A second non-linear gradation conversion unit that non-linearly corrects each of the N-bit input image signals in accordance with the signal level;
The image processing apparatus according to claim 1, wherein a corrected input image signal output from the second nonlinear gradation conversion unit is input to the gradation number expansion unit. Detecting for each pixel a signal of a predetermined frequency band based on the corresponding input image signal for each of a plurality of input N-bit input image signals (N is a positive integer);
Selecting a detection signal having the maximum detection signal in each pixel corresponding to each of the plurality of input image signals based on the detection signal detected in the detecting step;
Smoothing each detection signal corresponding to each pixel based on the detection signal selected in the selecting step;
Generating a control signal for defining a gradation region for each pixel based on the detection signal smoothed in the smoothing step;
Based on the control signal generated in the generating step, N + k bits (k is a positive integer) obtained by extending the number of gradations of the input image signal by a predetermined number for each input N-bit input image signal. Outputting a first output image signal or an N + k-bit second output image signal obtained by smoothing the input image signal and expanding the number of gradations by a predetermined number for each pixel;
I have a,
In the generating step, when the detection signal smoothed in the smoothing step is smaller than a predetermined threshold, a control signal indicating a gradation region is generated,
In the outputting step,
When the control signal indicates an area other than the gradation area, the first output image signal is output;
The image processing method , wherein the second output image signal is output when the control signal indicates a gradation area . Detecting for each pixel a signal of a predetermined frequency band based on the corresponding input image signal, for each of a plurality of input N-bit input image signals (N is a positive integer);
A step of selecting a detection signal having a maximum detection signal in each pixel corresponding to each of the plurality of input image signals based on the detection signal detected in the detecting step;
Smoothing each detection signal corresponding to each pixel based on the detection signal selected in the selecting step;
Generating a control signal for defining a gradation region for each pixel based on the detection signal smoothed in the smoothing step;
Based on the control signal generated in the generating step, N + k bits (k is a positive integer) obtained by extending the number of gradations of the input image signal by a predetermined number for each input N-bit input image signal. Outputting a first output image signal or an N + k-bit second output image signal obtained by smoothing the input image signal and expanding the number of gradations by a predetermined number for each pixel;
To the computer ,
In the generating step, when the detection signal smoothed in the smoothing step is smaller than a predetermined threshold, a control signal indicating a gradation region is generated,
In the outputting step,
When the control signal indicates an area other than the gradation area, the first output image signal is output;
A program in which the second output image signal is output when the control signal indicates a gradation area . A plurality of N-bit (N is a positive integer) input image signals are input and an image signal correction unit that corrects each of the input image signals;
An image display unit capable of displaying an image represented by an image signal of N + k bits (N and k are positive integers) based on the image signal corrected by the image signal correction unit;
With
The image signal correction unit
For each of the plurality of input image signals, a frequency component detector that detects a signal of a predetermined frequency band based on the corresponding input image signal for each pixel;
Based on the detection signal detected by the frequency component detection unit, a maximum value selection unit that selects a detection signal having the maximum detection signal in each pixel corresponding to each of the plurality of input image signals;
A detection value smoothing unit that smoothes each detection signal corresponding to each pixel based on the detection signal selected by the maximum value selection unit;
Based on the detection signal smoothed by the detection value smoothing unit, a control signal generating unit that generates a control signal for defining a gradation region for each pixel;
A plurality of N-bit input image signals are input, and the number of gradations of the input image signal is expanded by a predetermined number for each of the plurality of input image signals input based on a control signal generated for each pixel Output N + k bit first output image signal (k is a positive integer), or N + k bit second output image signal in which the input image signal is smoothed and the number of gradations is expanded by a predetermined number, for each pixel. A gradation number expansion unit to be
Equipped with a,
The control signal generation unit generates a control signal indicating a gradation region when the detection signal smoothed by the detection value smoothing unit is smaller than a predetermined threshold,
The gradation number expansion unit
When the control signal indicates an area other than the gradation area, the first output image signal is output,
The display device , wherein the second output image signal is output when the control signal indicates a gradation region .

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