JP2011133683A - Image processing apparatus, image processing method, program, and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus capable of determining a gradation region based on an image signal to be input to selectively smooth an image signal, and converting the smoothed image signal into an image signal with larger number of gradations than that of the image signal to be input, and to provide an image processing method, a program, and a display device. <P>SOLUTION: The image processing apparatus includes: a frequency component detection unit which detects signals of a predetermined frequency band from N bits (N is a positive integer) of input image signals for every pixel; a detected value smoothing unit which spatially smoothes detection signals corresponding to the respective pixels detected by the frequency component detection unit, respectively; a control signal generation unit which generates, for every pixel, control signals for regulating the gradation region based on the smoothed detection signals; and a gradation number extension which outputs N+k bits (k is a positive integer) of first output image signals, in which the number of gradations of the input image signal is extended by the predetermined number based on the control signals, or N+k bits of second output image signals, in which the input image signal is smoothed temporally and the number of gradations is extended by the predetermined number, for every pixel. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  In recent years, organic EL displays (also referred to as organic light emitting diode displays) or FEDs (Field Emission Displays) as display devices that replace CRT displays (Cathode Ray Tube displays). 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. For example, Patent Document 1 discloses a technique for determining a gradation region based on an input image signal, selectively smoothing the image signal, and converting the image signal into an image signal having a larger number of gradations than the input image signal. Can be mentioned.

  In addition, techniques for removing noise such as block distortion and mosquito noise have been developed. As a technique for performing temporal smoothing processing while preventing edge smoothing, for example, Patent Document 2 can be cited.

JP 2009-124451 A JP-A-10-229546

  A conventional technique for performing correction that expands the number of gradations of an input image signal in order to bring out the gradation performance of the display panel (hereinafter sometimes referred to as “conventional technique 1”) is an input image. Based on the signal, a region showing gradation (a region where the difference value between adjacent pixels is equal to or less than a predetermined value and having a small number of irregularities; hereinafter referred to as “gradation region”) is detected and detected. Smooth the gradation area spatially. That is, when the conventional technique 1 is used, an area indicating an edge (hereinafter referred to as an “edge area”) or an area indicating a texture (an area where a difference value between adjacent pixels is a predetermined value or less) In the region having a large number of irregularities (hereinafter referred to as “texture region”), the image signal is not corrected, and in the gradation region, the image signal is corrected so that the gradation region becomes smoother. Therefore, higher image quality can be achieved by using the conventional technique 1.

  However, when the conventional technique 1 is used, since the spatially detected gradation area is spatially smoothed, the larger the gradation area that can be detected (the gentler the gradation), the spatial A filter with a wide reference range is required. For this reason, when the conventional technique 1 is used, the larger the gradation area that can be detected, the larger the filter size of the filter, because a larger tap filter must be provided. When the filter is realized by software, the larger the detected gradation area, the larger the number of steps, which may lead to an increase in processing time.

  In addition, a conventional technique for removing noise (hereinafter sometimes referred to as “conventional technique 2”) is a pixel at the same position in a smoothed image one frame before and an image indicated by an input image signal. When the difference values are small, that is, when the temporal change is small, temporal smoothing is performed. Further, in the case of the conventional technique 2, when the difference value is large, that is, when the temporal change is large, it is determined that the edge of the display screen is moving and smoothing is not performed. Therefore, when the conventional technique 2 is used, the edge region whose position changes in the display screen can be protected, and therefore there is a possibility that the deterioration of the image quality can be prevented to some extent.

  However, since the conventional technique 2 selectively performs smoothing according to the difference value, smoothing is performed without distinguishing between a gradation area and a texture area that are areas other than the edge area. In addition, since the conventional technique is a technique for removing noise, no consideration is given to more smoothly correcting the gradation area (gradation improvement). Therefore, when the conventional technique 2 is used, fine unevenness is lost by smoothing, and thus, for example, the texture of a wall or a distant mountain is damaged, and the image quality is deteriorated.

  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.

  To achieve the above object, according to the first aspect of the present invention, a frequency component for detecting a signal in a predetermined frequency band for each pixel from an input N-bit input image signal (N is a positive integer). A detection value smoothing unit that spatially smoothes a detection signal corresponding to each pixel based on the detection signal detected by the frequency component detection unit, and a detection signal smoothed by the detection value smoothing unit. And a control signal generation unit that generates a control signal for defining a gradation region for each pixel, and the N-bit input image signal is input, and the input image signal is generated based on the control signal generated for each pixel. The first output image signal of N + k bits (k is a positive integer) with the number of gradations expanded by a predetermined number, or N + k bits with the number of gradations expanded by a predetermined number by smoothing the input image signal temporally Second of A gradation number expansion unit that outputs a force image signal for each pixel, and the gradation number expansion unit performs temporal smoothing of the input image signal according to a temporal change amount of the input image signal. An image processing apparatus that performs selectively is provided.

  In such a configuration, the gradation area is spatially detected, and temporal smoothing of the input image signal is selectively performed based on the detection result. Therefore, with this configuration, it is possible to achieve high image quality without increasing the circuit scale and processing time of the filter for smoothing.

  The gradation number expanding unit stores the first output image signal or the second output image signal, and outputs a delayed image signal one frame before the input image signal, and the input image signal. And a temporal smoothing calculation unit that selectively performs temporal smoothing of the input image signal for each pixel according to a temporal change amount of the input image signal based on the delay image signal and the delayed image signal; When the control signal indicates a gradation region based on the control signal generated in step (b), the input image signal selectively smoothed in the temporal smoothing calculation unit is output as the second output image signal, When the control signal indicates a region other than the gradation region, a selection unit that shifts the input image signal by k bits and outputs it as the first output image signal may be provided.

  Further, the control signal generation unit uses the detection signal smoothed by the detection value smoothing unit and a plurality of threshold values to mix the first output image signal and the second output image signal in each corresponding pixel. A control signal defining the ratio is output, and the gradation number expanding unit stores the first output image signal or the second output image signal, and outputs a delayed image signal one frame before the input image signal. Temporal smoothing of the input image signal selectively for each pixel in accordance with a temporal change amount of the input image signal based on the frame memory, the input image signal, and the delayed image signal. Based on the control signal in which the smoothing calculation unit, the input image signal, and the input image signal selectively smoothed in the temporal smoothing calculation unit are input, and the mixing ratio is defined for each pixel, Corresponding The first output image obtained by shifting the input image signal by k bits so that the ratio of the first output image signal and the second output image signal in each pixel is the same as the mixing ratio defined by the control signal. A mixing unit may be provided that mixes the signal and the second output image signal, which is the input image signal selectively smoothed by the temporal smoothing calculation unit, for each pixel.

  The temporal smoothing unit subtracts the input image signal whose number of gradations is extended to N + k bits from the delayed image signal, and calculates a difference value for each pixel, and the difference value for each pixel. And a predetermined threshold for determining a temporal change amount of the input image signal, and a non-linear conversion unit that converts the difference value for each pixel into a value according to a comparison result, and the non-linear conversion unit An addition unit that adds the difference value for each pixel output from the pixel and the input image signal in which the number of gradations is expanded to N + k bits, and the input image signal in which the number of gradations is expanded to N + k bits And a weighted average calculation unit that outputs the second output image signal by performing a weighted average calculation for each pixel based on the image signal output from the addition unit.

  In order to achieve the above object, according to a second 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, A frequency component detection unit that detects a signal of a predetermined frequency band from each signal for each pixel, and a detection signal in each pixel corresponding to each of the plurality of input image signals based on the detection signal detected by the frequency component detection unit. A maximum value selection unit that selects the maximum detection signal, a detection value smoothing unit that spatially smoothes each detection signal corresponding to each pixel based on the detection signal selected by the maximum value selection unit, and the detection value Based on the detection signal smoothed by the smoothing unit, a control signal generating unit that generates a control signal for defining a gradation area for each pixel, and a plurality of N-bit input image signals are input, A first output 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 of the plurality of input image signals input based on the control signal generated in A gradation number expansion unit that outputs, for each pixel, an image signal or an N + k-bit second output image signal in which the input image signal is smoothed in time and the number of gradations is expanded by a predetermined number. The logarithmic expansion unit is provided with an image processing device that selectively performs temporal smoothing of each of the plurality of input image signals according to a temporal change amount of each of the plurality of input image signals.

  In such a configuration, the gradation region is spatially detected, and temporal smoothing is performed on each of the plurality of input image signals selectively based on the detection result. Therefore, with this configuration, it is possible to achieve high image quality without increasing the circuit scale and processing time of the filter for smoothing.

  In order to achieve the above object, according to the third aspect of the present invention, a signal in a predetermined frequency band is detected for each pixel from the input N-bit (N is a positive integer) input image signal. Step, spatially smoothing the detection signal corresponding to each pixel based on the detection signal detected in the detecting step, and based on the detection signal smoothed in the smoothing step, A step of generating a control signal for defining a gradation area for each pixel, and N + k bits (N + k bits) in which the number of gradations of the N-bit input image signal is expanded by a predetermined number based on the control signal generated in the generating step. K is a positive integer) first output image signal or N + k bits in which the N-bit input image signal is smoothed in time and the number of gradations is expanded by a predetermined number And outputting a second output image signal for each pixel. In the outputting step, temporal smoothing of the input image signal is selectively performed according to a temporal change amount of the input image signal. An image processing method to be performed is provided.

  In such a method, the gradation area is spatially detected, and temporal smoothing is selectively performed on the input image signal based on the detection result. Therefore, by using such a method, it is possible to achieve high image quality without increasing the circuit scale and processing time of the filter related to smoothing.

  In order to achieve the above object, according to the fourth aspect of the present invention, a signal in a predetermined frequency band is detected for each pixel from an input N-bit input image signal (N is a positive integer). A step of spatially smoothing the detection signal corresponding to each pixel based on the detection signal detected in the detecting step, and a gradation region based on the detection signal smoothed in the smoothing step N + k bits (k is a positive value) obtained by expanding the number of gradations of the N-bit input image signal by a predetermined number based on the control signal generated in the generating step. The first output image signal of N) or the N-bit input image signal is temporally smoothed and the number of gradations is expanded by a predetermined number to obtain an N + k-bit second The step of outputting the force image signal for each pixel is executed by the computer, and in the step of outputting, the temporal smoothing of the input image signal is selectively performed according to the temporal change amount of the input image signal. Program is provided.

  In a computer that executes such a program, the gradation area is spatially detected, and the input image signal is temporally smoothed selectively based on the detection result. Therefore, by using such a program, it is possible to achieve high image quality without increasing the circuit scale and processing time of the filter for smoothing.

  In order to achieve the above object, according to a fifth aspect of the present invention, an image signal correcting unit that corrects an input image signal, and an image signal corrected by the image signal correcting unit, N + k An image display unit capable of displaying an image indicated by an image signal of bits (N and k are positive integers), and the image signal correction unit receives a signal in a predetermined frequency band from the input N-bit input image signal For each pixel, a detection value smoothing unit for spatially smoothing the detection signal corresponding to each pixel based on the detection signal detected by the frequency component detection unit, and the detection value smoothing A control signal generating unit that generates a control signal for defining a gradation area for each pixel based on the detection signal smoothed by the unit, and a control signal generated for each of the pixels by inputting the N-bit input image signal Based on this, the first output image signal of N + k bits in which the number of gradations of the input image signal is expanded by a predetermined number, or N + k bits in which the number of gradations is expanded by a predetermined number of times by smoothing the input image signal. A gradation number expansion unit that outputs the second output image signal for each pixel, and the gradation number expansion unit is configured to change the time of the input image signal according to a temporal change amount of the input image signal. A display device that selectively performs smoothing is provided.

  In such a configuration, the gradation area is spatially detected, and temporal smoothing of the input image signal is selectively performed based on the detection result. Therefore, with this configuration, it is possible to achieve high image quality without increasing the circuit scale and processing time of the filter for smoothing.

  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.

It is explanatory drawing which shows an example of correction | amendment of the gradation area | region by the temporal smoothing filter in the display apparatus which concerns on embodiment of this 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 an example of a structure 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 process in the detected 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 explanatory drawing which shows an example of the control signal Dc which the control part which concerns on the 1st Embodiment of this invention produces | generates. It is a block diagram which shows an example of a structure of the gradation number expansion part which concerns on the 1st Embodiment of this invention. It is a block diagram which shows an example of a structure of the temporal smoothing calculating part which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows the 1st example of the process of the nonlinear transformation part which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows the 2nd example of the process of the nonlinear transformation part which concerns on the 1st Embodiment of this invention. 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. 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 block diagram which shows the image process part 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 an example of the pseudo gradation process in the pseudo gradation process part which concerns on the 4th Embodiment of this invention.

  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, but the image signal input to the display device is a moving image (so-called video). Needless to say, when an image signal indicating a still image is input to the display device according to the embodiment of the present invention, the display device according to the embodiment of the present invention can display the still image.

  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. The image signal according to the embodiment of the present invention may be, for example, an analog signal used in analog broadcasting or the like converted into a digital signal by an A / D converter (Analog to Digital converter). Examples of the image signal input to the display device according to the embodiment of the present invention include an image signal transmitted from a broadcasting station and received by the display device. The image signal input to the display device according to the embodiment of the present invention may be a signal transmitted from an external device and received by the display device via a network such as a LAN (Local Area Network). Further, 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 is a value according 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 the case where the display device according to the embodiment of the present invention has N bits that have the same gradation performance as that of the input image signal, the display device that displays an image, the display device according to the embodiment of the present invention has, for example, N + k bits. Are 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 spatially detects the gradation area based on the input image signal, thereby determining the gradation area for each pixel corresponding to the input image signal.

[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 an image signal (hereinafter sometimes referred to as “first output image signal”) in which a fixed value of k bits is added to the lower order of the input image signal is output.

(B) When judged to be a gradation region When the display device according to the embodiment of the present invention is judged to be a gradation region by spatial detection, the input image signal is temporally smoothed to N + k bits. An extended image signal (hereinafter sometimes referred to as “second output image signal”) is output.

  As described above, when the detected gradation area is spatially smoothed, the larger the gradation area that can be detected, the greater the problem that a larger tap filter must be provided. There is a fear. Therefore, the display device according to the embodiment of the present invention smoothes the detected gradation area by using a temporal filter (hereinafter referred to as “temporal smoothing filter”). In addition, the display device according to the embodiment of the present invention provides an input image corresponding to a temporal change amount of the input image signal (a change amount for each pixel in the image signal of the current frame and the output image signal of the previous frame). Selectively smoothes the signal temporally.

[Correction of gradation area by temporal smoothing filter]
FIG. 1 is an explanatory diagram showing an example of correction of a gradation area by a temporal smoothing filter in a display device according to an embodiment of the present invention.

  In a region such as a gradation region where an image changes gradually, a gradation step is generated by quantization. Then, the gradation step is visually recognized as a pseudo contour (Contouring) (FIG. 1A).

  In particular, when the image signal indicates a video image compressed at a high compression rate, a phenomenon that the position of the pseudo contour fluctuates greatly with time is observed. Here, for example, in a compression method in block units such as MPEG-2 (ISO / IEC13818), the high frequency component of the image signal is omitted in block units. Therefore, when the image signal is an image signal according to a block-unit compression method, the high frequency component tends to be omitted particularly in the gradation region, and the contribution of the remaining DC (Direct Current) component is dominant. Become. Therefore, in the above case, a gradation step is likely to occur at the block boundary, and further, the value of the DC component of the block fluctuates with time due to the mixing of random noise. It varies with time in units. As a result, the position of the pseudo contour generated in the gradation area appears to fluctuate greatly in time (FIG. 1B).

  In the gradation area as described above, by smoothing the image signal temporally, not only temporal variations can be suppressed, but also a spatially smooth gradation can be displayed on the display screen (FIG. 1 ( c).

  Further, since the temporal smoothing filter uses image signals (image data) that are spatially corresponding positions and temporally different, even if the gradation step varies widely in time, Time smoothing can be performed without expanding the general reference range. When a temporal smoothing filter is used, even if the detected gradation area is a large area (even if the gradation is gentle), the circuit scale of the filter is the same as when spatially smoothing is performed. There is no risk of increasing processing time.

  A display device according to an embodiment of the present invention smoothes a spatially detected gradation area using a temporal smoothing filter, thereby preventing the gradation area from being increased without increasing the filter circuit scale or processing time. It can be selectively smoothed.

  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. To correct.

  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 and temporally smoothes the input image signal by the above-described processing, and outputs an output image having a larger number of gradations than the input image signal. Convert to signal and display image.

  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 display device according to the embodiment of the present invention spatially detects a gradation region based on an input image signal, and selectively performs temporal smoothing on the input image signal based on the detection result. Therefore, the display device according to the embodiment of the present invention can achieve high image quality without increasing the circuit scale and processing time of the filter.

  The configuration of the display device according to the embodiment of the present invention will be specifically described below. In addition, in the following, as the display device according to the embodiment of the present invention, a configuration including the [1] “image processing unit” responsible for the image processing phase and the [2] “display unit” responsible for the display phase is shown. . In the embodiment of the present invention, for example, the following image processing unit may be realized as an independent device (image processing device).

(First embodiment)
FIG. 2 is a block diagram showing the display device 1000 according to the first embodiment of the present invention. Note that FIG. 2 illustrates 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. 2, 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 (Electrically Erasable and Programmable Read Only Memory), a flash memory, a MRAM (Magnetoresistive Random Access) Non-volatile memory such as Memory, FeRAM (Ferroelectric Random Access Memory) and PRAM (Phase change Random Access Memory). 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.

  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) may 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). 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 an input image signal Di of N bits (N is a positive integer) into an output image signal Do (first output image signal or second output image) of N + k (k is a positive integer). Signal, the same shall apply hereinafter). 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 the pixel, and the other applies a voltage signal (image signal) corresponding to an image to be displayed. Fulfill. 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 controls the supply of power to the row driving unit and the column driving unit by the power supply unit in accordance with 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.

  The display apparatus 1000 according to the first embodiment of the present invention has a configuration as shown in FIG. 2 and determines a gradation area for each corresponding pixel based on the input image signal, and the input image signal according to the determination result. Di correction (expansion of gradation number or correction of input image signal Di and expansion of gradation number) is performed. The display device 1000 displays an image based on the corrected image signal, that is, the 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. 3 is a block diagram showing the image processing unit 100 according to the first embodiment of the present invention. Referring to FIG. 3, 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. 4 is a block diagram showing an example of the configuration of the frequency component detection unit 106 according to the first embodiment of the present invention. Referring to FIG. 4, 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. 5 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. 5, the band pass filter 112 has a pass band having a peak at the frequency f. Here, the frequency f is determined so that many components near the frequency f are included in the texture region, for example, according to the frequency characteristics of the texture region. The frequency f is set according to, for example, 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. 3 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.

  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. 6 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. Note that the smoothing region set by the detection value smoothing unit 108 may be a region of any size in the horizontal direction and / or the vertical direction, for example. In addition, the size of the smooth region may be changed according to the position on the screen, for example.

  The detection value smoothing unit 108 calculates an average value by, for example, an arithmetic average, a geometric average, or a weighted average with a predetermined weight.

  The components of the image processing unit 100 will be described with reference to FIG. 3 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 TH is 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. 7 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. 7, 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. Examples of the storage means included in the image processing unit 100 include a nonvolatile memory such as an EEPROM or a flash memory. Note that the threshold TH information may be held by the control signal generation unit 110 with a storage unit, for example, or stored in a storage unit (not shown) of the display device 1000. Needless to say, the data may be appropriately read from the storage unit (not shown).

  FIG. 8 is an explanatory diagram illustrating an example of the control signal Dc generated by the control unit 102 according to the 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 8E show the frequency component detection value Df, the average detection value Dave, and the control signal Dc, respectively. Hereinafter, with reference to FIG. 8, what kind of control unit 102 does in the gradation area ((1) in FIG. 8), the texture area (FIG. 8 (2)), and the edge area ((3) in FIG. 8)? Whether to generate the control signal Dc will be described.

[A] gradation area ((1) in FIG. 8)
(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.

[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.

[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.

  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, thereby determining the gradation area for each pixel based on the input image signal.

  Next, the gradation number expansion unit 104 will be described. FIG. 9 is a block diagram showing an example of the configuration of the gradation number expanding unit 104 according to the first embodiment of the present invention. The gradation number expansion unit 104 includes a frame memory 130, a temporal smoothing calculation unit 116, and a selection unit 118.

  The frame memory 130 stores the output image signal Do (first output image signal or second output image signal), and outputs the output image signal Do stored at a timing delayed by one frame as the delayed image signal Dm. The output control of the delayed image signal Dm from the frame memory 130 may be performed by other components such as a control unit (not shown), for example.

  The temporal smoothing calculation unit 116 receives the input image signal Di and the delayed image signal Dm, and the temporal smoothing calculation unit 116 determines the time of the input image signal Di according to the temporal change amount of the input image signal Di. Smoothing is selectively performed. More specifically, the temporal smoothing calculation unit 116 temporally smoothes a portion having a large temporal change amount (for example, a portion having motion) in the image indicated by the input image signal Di. Further, temporal smoothing is performed on a portion (for example, a stationary portion) where the temporal variation is small.

  FIG. 10 is a block diagram showing an example of the configuration of the temporal smoothing calculation unit 116 according to the first embodiment of the present invention. The temporal smoothing calculation unit 116 includes a shift unit 132, a subtraction unit 134, a non-linear conversion unit 136, an addition unit 138, and a weighted average calculation unit 140.

  The shift unit 132 shifts the input image signal Di to the left by k bits, and outputs an N + k-bit input image signal Di ′ in which a fixed value of k bits is added to the lower order of the input image signal Di.

  Note that the gradation number expanding unit 104 according to the embodiment of the present invention may be configured to include the shift unit 132 in front of the temporal smoothing calculation unit 116 and the selection unit 118 instead of the temporal smoothing calculation unit 116. Good. In the case of adopting the above configuration, the selection unit 118 described later selectively outputs an input image signal Di ′ output from the shift unit 132 as a first output image signal.

  The subtracting unit 134 subtracts the input image signal Di ′ from the delayed image signal Dm to calculate a difference value DIF for each pixel, as shown in Equation 1 below. Then, the subtraction unit 134 outputs the difference value DIF for each pixel to the nonlinear conversion unit 136.

DIF = Dm−Di ′
... (Formula 1)

  The nonlinear conversion unit 136 compares the difference value DIF for each pixel with a predetermined threshold value for determining the temporal change amount of the input image signal Di, and calculates the difference value DIF for each pixel according to the comparison result. Convert to value DIF '.

  FIG. 11 is an explanatory diagram illustrating a first example of processing of the nonlinear conversion unit 136 according to the first embodiment of the present invention. In FIG. 11, the horizontal axis indicates the difference value DIF that is the input of the nonlinear conversion unit 136, and the vertical axis indicates the difference value DIF ′ that is the output of the nonlinear conversion unit 136.

  As illustrated in FIG. 11, the nonlinear conversion unit 136 converts the difference value DIF into a difference value DIF ′ limited by the threshold Lim. More specifically, the nonlinear conversion unit 136 outputs DIF ′ = DIF when | DIF | ≦ Lim, and outputs DIF ′ = 0 when | DIF |> Lim.

  Here, when | DIF | ≦ Lim, the nonlinear conversion unit 136 regards that the amount of temporal change of the input image signal Di is small, that is, a stationary portion. When | DIF |> Lim, it is considered that the amount of temporal change of the input image signal Di is large, that is, a moving part. Examples of the case where | DIF |> Lim include a case where an object in the image or the entire image moves, or a case where there is a scene change.

  The non-linear conversion unit 136 can convert the difference value DIF for each pixel non-linearly according to the temporal change amount of the input image signal Di, for example, by performing the processing shown in FIG.

  FIG. 12 is an explanatory diagram illustrating a second example of the process of the nonlinear conversion unit 136 according to the first embodiment of the present invention. In FIG. 12, as in FIG. 11, the horizontal axis indicates the difference value DIF that is the input of the nonlinear conversion unit 136, and the vertical axis indicates the difference value DIF ′ that is the output of the nonlinear conversion unit 136.

  As shown in FIG. 12, the nonlinear conversion unit 136 continuously changes the difference value DIF ′ between the threshold value Lim and 0 in the range of Lim <| DIF | ≦ 2Lim. Therefore, the nonlinear conversion unit 136 performs the processing shown in FIG. 12 to prevent the video flickering caused by, for example, the discontinuity of the conversion characteristics, and the difference value DIF for each pixel as the input image signal. Non-linear conversion can be performed according to the amount of change in Di over time.

  The nonlinear conversion unit 136 converts the difference value DIF for each pixel into a nonlinear manner according to the temporal change amount of the input image signal Di, for example, by performing the processing shown in FIGS.

  The addition unit 138 adds the input image signal Di ′ and the difference value DIF ′ for each pixel output from the nonlinear conversion unit 136 as shown in Equation 2 below, and adds the added image signal Dm ′. The result is output to the weighted average calculation unit 140. Here, when the delayed image signal Dm is within the range of ± Lim with respect to the input image signal Di ′, the adder 138 outputs the delayed image signal Dm as the image signal Dm ′, and the delayed image signal Dm When the input image signal Di ′ is outside the range of ± Lim, the input image signal Di ′ is output as the image signal Dm ′.

Dm ′ = Di ′ + DIF ′
... (Formula 2)

  For example, as shown in the following Equation 3, the weighted average calculation unit 140 uses a ratio of α: 1−α for each pixel based on the input image signal Di ′ and the image signal Dm ′ output from the addition unit 138. To perform a weighted average calculation (where α is 0 ≦ α ≦ 1). Then, the weighted average calculation unit 140 outputs the result of the weighted average calculation as a temporally smoothed image signal Ds. The temporally smoothed image signal Ds output from the weighted average calculating unit 140 corresponds to the above-described second output image signal.

Ds = (1-α) XDi ′ + αXDm ′
... (Formula 3)

  Here, since the contribution of the image signal Dm ′ increases as α increases, the temporal smoothing strength for the temporally smoothed image signal Ds output from the weighted average calculation unit 140 increases. Conversely, the smaller α is, the smaller the temporal smoothing intensity for the temporally smoothed image signal Ds output from the weighted average calculation unit 140 is. For example, when α = 0, Ds = Di ′ and the input image signal Di ′ is output as it is, so that temporal smoothing is not performed.

  For example, the weighted average calculation unit 140 performs processing according to a value of α defined in advance. Note that the weighted average calculation unit 140 may perform processing by appropriately setting the value of α in accordance with, for example, an operation signal corresponding to a user operation transmitted from an operation unit (not shown).

  The temporal smoothing calculation unit 116 selectively performs temporal smoothing of the input image signal Di according to the temporal change amount of the input image signal Di, for example, with the configuration shown in FIG. Here, the temporal smoothing calculation unit 116 converts the input image signal to Dm ′ = Di ′ when the difference value between the delayed image signal Dm and the input image signal Di ′ exceeds a predetermined threshold (± Lim). The temporally smoothed image signal Ds, which is the weighted average calculation result of Di ′ and the image signal Dm ′, remains as the input image signal Di ′. Therefore, the temporal smoothing calculation unit 116 does not perform temporal smoothing on a portion having a large amount of temporal change (for example, a portion having motion) in the image indicated by the input image signal Di. Further, temporal smoothing can be performed on a portion with a small amount of temporal change (for example, a stationary portion).

  With reference to FIG. 9 again, an example of the configuration of the gradation number expanding unit 104 will be described. 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. The first output image signal of N + k bits obtained by shifting to the left by k bits and adding a fixed value of k bits to the lower order of the input image signal Di is output as the output image signal Do. As described above, when the gradation number expanding unit 104 includes the shift unit 132 before the selection unit 118, the selection unit 118 receives the input image signal Di ′ output from the shift unit 132. , And output as an output image signal Do (first output image signal).

(Ii) When the control signal Dc is “1” indicating the gradation area When the control signal Dc is “1” indicating the gradation area, the selection unit 118 outputs N + k output from the temporal smoothing calculation unit 116. A bit second output image signal (temporal smoothed image signal Ds) is output as an output image signal Do.

  For example, with the configuration illustrated in FIG. 9, 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 in accordance with the control signal Dc output from the control unit 102. To do.

  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 spatially detects the gradation area based on the input image signal Di, thereby determining the gradation area for each pixel and outputting the control signal Dc. Further, the gradation number expansion unit 104 adds the k-bit fixed value to the lower order of the input image signal Di based on the control signal Dc, and converts the first output image signal Di or the input image signal Di into N + k bits. The time-smoothed N + k-bit second output image signal is selectively output as the output image signal Do. Therefore, the display apparatus 1000 determines a gradation region based on the input image signal, selectively smoothes the image signal temporally, and converts the image signal into an image signal having a larger number of gradations than the input image signal. Can be displayed.

  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 degradation such as a false contour is generated visually in the gradation area, and the image quality degradation is observed in the edge area and 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.

  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.

  Further, the image processing unit 100 of the display apparatus 1000 smoothes the spatially detected gradation area using a temporal smoothing filter. Therefore, the display apparatus 1000 can selectively smooth the gradation area without increasing the filter circuit scale and processing time as in the case of spatial smoothing.

[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 may be configured to include a plurality of bandpass filters.

  FIG. 13 is a block diagram illustrating a frequency component detection unit according to a first modification of the first embodiment of the present invention. FIG. 13 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. 13, 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 the first bandpass filter 112a outputs the BPF output Dbpf1 based on the frequency characteristic having the peak at the frequency f1.

  The first coefficient multiplier 112a 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 112a is stored in, for example, a storage unit included in the image processing unit 100, and is input from the storage unit. Note that the information on the coefficient K1 can be held, for example, by the first coefficient multiplication unit 112a including a storage unit, and is also stored in a storage unit (not shown) of the display device and is stored in the first coefficient multiplication unit. The unit 112a may 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.

  Further, the input image signal Di is input to the second bandpass filter 112b, and the second bandpass filter 112b outputs the 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. The second absolute value converter 114b calculates the absolute value of the weighted BPF output Dk2, and outputs the second frequency component detection value Df2. 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 by the first coefficient multiplier 112a for multiplication. From the storage means.

  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. 13 will be described. FIG. 14 is an explanatory diagram for explaining a frequency component detection unit according to a first modification of the first embodiment of the present invention. For example, FIG. 14 shows a case where the coefficient K1 = 1 and the coefficient K2 = 0.5 are set.

  FB shown in FIG. 14 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.

  14 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 in frequency component detection unit from the frequency component detection unit 106 shown in FIG. 4, but the frequency component is 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]
FIG. 15 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. 15, the frequency component detection unit according to the second modification basically has 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. 4 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]
As a display device according to a third modification of the first embodiment of the present invention, the image processing unit generates a control signal Dc that defines a mixing ratio of the first output image signal and the second output image signal, and performs control. A configuration for outputting the output image signal Do corresponding to the mixing ratio indicated by the signal Dc will be described. Note that the image processing unit of the display device according to the third modification has the same configuration as that of FIG.

  FIG. 16 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. The Note that the information on the thresholds TH1 and TH2 may be stored in the storage unit provided by the control signal generation unit, for example, or stored in the storage unit (not shown) of the display device. The signal generation unit may appropriately read from the storage unit (not shown).

  FIG. 17 is a block diagram showing the gradation number expanding unit according to the third modification of the first embodiment of the present invention. The gradation number expansion unit according to the third modification includes a frame memory 130, a temporal smoothing calculation unit 116, and a mixing unit 126.

  The frame memory 130 and the temporal smoothing calculation unit 116 have the same functions and configurations as the frame memory 130 and the temporal smoothing calculation unit 116 shown in FIG.

  The mixing unit 126 adds a temporally 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 temporally smoothed image signal Ds (second output image signal) and the first output image signal will be described. When a 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, since the control signal Dc alternates between “1” indicating the gradation area and “0” indicating the area other than the gradation area, the first output image signal and the temporally smoothed image signal Ds (second output image signal) is 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 temporally smoothed image signal Ds (second output image signal) The ratio does not change 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]
As a display device according to a fourth modification of the first embodiment of the present invention, a configuration in which an image processing unit performs processing in each of the horizontal direction and the vertical direction will be described.

  FIG. 18 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. 18, 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 vertical control unit 102v, and a gradation number expanding unit 142.

  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 outputs the horizontal control signal Dhc, for example, by taking the same configuration as the control unit 102 shown in FIG.

  The vertical control unit 102v outputs, for each pixel, a vertical control signal Dvc indicating whether the gradation region is in the vertical direction based on the input image signal Di input. Here, the vertical control unit 102v outputs the vertical control signal Dvc by taking the same configuration as the control unit 102 shown in FIG. 3, for example.

  The gradation number expanding unit 142 uses the first output image signal or the temporally smoothed second output image signal as the output image signal Do based on the horizontal control signal Dhc and the vertical control signal Dvc for each pixel. Selectively output. More specifically, the gradation number expanding unit 142 outputs the second output image signal as the output image signal Do when both the horizontal control signal Dhc and the vertical control signal Dvc indicate a gradation region. Here, the gradation number expansion unit 142 has basically the same configuration as the gradation number expansion unit 104 shown in FIG. 9, and the selection unit of the gradation number expansion unit 142 has the horizontal control signal Dhc and the vertical control signal Dvc. Is different from the gradation number expanding unit 104 shown in FIG.

  By having the configuration shown in FIG. 18, the image processing unit 150 can prevent the sharpness of the texture area and the edge area from being impaired in both the horizontal direction and the vertical direction.

(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 may be an apparatus, that is, an image processing apparatus.

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

[Program for image processing apparatus]
A program for causing the image processing apparatus according to the first embodiment of the present invention to function as a computer 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.

(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. In the following description, the image processing method according to the first embodiment is described as being performed by the display device 1000, but it is needless to say that the image processing method can be applied to the image processing device 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 is performed using, for example, one or a plurality of bandpass filters.

  Display apparatus 1000 spatially smoothes the detection value (frequency component detection value Df) detected in step S100 (S102), and generates 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, an N + k-bit second output image signal obtained by smoothing the input image signal Di in terms of time is selectively output (S106). In step S106, the display apparatus 1000 selectively performs temporal smoothing of the input image signal Di according to the temporal change amount of the input image signal Di.

  The display apparatus 1000 determines the gradation area based on the input image signal and selectively smoothes the image signal temporally by performing the processing of steps S100 to S106, and the display device 1000 performs the smoothing over the input image signal. It can be converted into an image signal having a large number of gradations.

(Second Embodiment)
Next, as a display device according to the second embodiment, a configuration for processing a plurality of channels of a color image will be described. 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. 19 is a block diagram showing a display device 2000 according to the second embodiment of the present invention. Referring to FIG. 19, 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 expanding unit 204.

  N-bit R / G / B input image signals Ri, Gi, Bi are respectively input to the image processing unit 200, and the image processing unit 200 converts the input image signals Ri, Gi, Bi into an N + k-bit output image signal Ro. , Go, and Bo and 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. 20 is a block diagram showing an image processing unit 200 according to the second embodiment of the present invention. Referring to FIG. 20, 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 outputs a 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. 3, 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 detection value smoothing unit 108 according to the first embodiment illustrated in FIG. 3, 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 unit 204a, the second gradation number expanding unit 204b, and the third gradation number expanding unit 204c is a gradation number expanding unit 204 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, an N + k-bit second output image signal obtained by temporally smoothing the input image signal Ri is selectively output as the output image signal Ro. Similarly, the second gradation number expanding section 204b and the third gradation number expanding section 204c output output image signals Go and Bo, respectively.

  The image processing unit 200 outputs output image signals Ro, Go, and Bo, for example, 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. 21 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.

  FIGS. 21A to 21C show the input image signals Ri, Gi, and Bi, respectively. FIGS. 21D to 21F show the frequency component detection values Rf, Gf, and Bf, respectively. Here, since the input image signal Ri in FIG. 21A is relatively uneven, the frequency component detection value Rf in FIG. 21D is detected with a relatively high frequency. Further, since the input image signals Gi and Bi in FIGS. 21B and 21C have little change, the frequency component detection value Gf in FIG. 21E and the frequency component detection value Bf in FIG. The frequency of detection is low.

  FIG. 21G 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. 21 (h) shows the average detection value Dave, and FIG. 21 (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. 21, 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 can detect the gradation area without making a mistake with the texture area by performing smoothing of the detection value and threshold processing on the maximum value Dmax of the frequency component detection values Rf, Gf, and Bf. 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 spatially detects the gradation area based on the input image signals Ri, Gi, Bi, thereby determining the gradation area for each pixel and outputting the control signal Dc. Further, the gradation number expanding unit 204 adds the k-bit fixed value to the lower order of the input image signal based on the control signal Dc, and converts the first output image signal or the input image signal into N + k bits in terms of time. The smoothed N + k-bit second output image signal is selectively output as output image signals Ro, Go, Bo. Accordingly, in the same way as the display device 1000 according to the first embodiment, the display device 2000 determines a gradation region based on the input image signal, selectively smoothes the image signal in terms of time, and inputs the image signal. It can be converted into an image signal having more gradations than the image signal and displayed.

  Further, as with the display device 1000 according to the first embodiment, the display device 2000 determines the gradation region and selectively corrects the gradation region more smoothly, thereby improving the gradation performance of the gradation region. Can do. 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.

  Further, the display device 2000 can detect the gradation area without making a mistake with the texture area by performing smoothing of the detection value and threshold processing on the maximum value Dmax of the frequency component detection values Rf, Gf, and Bf. . Therefore, it is possible to suppress image quality deterioration such as a reduction in sharpness caused by smoothing the texture region.

  Furthermore, the image processing unit 200 of the display device 2000 smoothes the spatially detected gradation area using a temporal smoothing filter, as with the image processing unit 100 of the display device 1000 according to the first embodiment. . Therefore, like the display device 1000 according to the first embodiment, the display device 2000 selectively selects a gradation area without increasing the filter circuit scale or processing time as in the case of spatial smoothing. Can be smoothed.

[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 may be an apparatus, that is, an image processing apparatus.

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

[Program for image processing apparatus]
A program for causing an image processing apparatus according to the second embodiment of the present invention to function as a computer 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.

(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. In the following, the image processing method according to the second embodiment of the present invention will be described as being performed by the display device 2000, but it can also be applied to the image processing apparatus 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 spatially smoothes the maximum 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 temporally smoothing the input image signal is selectively output for each channel (S208).

  The display device 2000 determines the gradation area based on the input image signal and selectively smoothes the image signal temporally by performing the processing of steps S200 to S208, and the display device 2000 is more than the input image signal. It can be converted into an image signal having a large number of gradations.

(Third embodiment)
Next, another configuration for processing a plurality of channels of a color image will be described as a display device according to the third embodiment. Hereinafter, as a plurality of channels of a color image, a luminance signal (hereinafter referred to as “Y”), a signal indicating a difference between the luminance signal and the blue component (hereinafter referred to as “U”), and a difference between the luminance signal and the red component. A signal (hereinafter, referred to as “V”) indicating “” is input as an image signal.

  A display device (not shown) according to the third embodiment includes an image processing unit 250 and a display unit 190. N-bit Y / U / V input image signals Yi, Ui, and Vi are input to the image processing unit 250, and the image processing unit 250 converts the input image signals Yi, Ui, and Vi into N + k-bit output image signals Yo. , Uo, and Vo 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 Yo, Uo, and Vo. indicate. Hereinafter, the configuration of the image processing unit 250 will be specifically described.

[Configuration Example of Image Processing Unit 250]
FIG. 22 is a block diagram showing an image processing unit 250 according to the third embodiment of the present invention. Referring to FIG. 22, the image processing unit 250 includes a control unit 252 and a gradation number expanding unit 254.

[Control unit 202]
The control unit 252 has the same configuration as the control unit 102 according to the first embodiment shown in FIG. The input image signal Yi is input to the control unit 252. The control unit 252 spatially detects the gradation region based on the input image signal Yi, thereby determining the gradation region for each pixel and outputting the control signal Dc. To do. Here, the reason why the image processing unit 250 according to the third embodiment determines the gradation area for each pixel based on the input image signal Yi and outputs the control signal Dc is that the input image signals Ui and Vi relating to the colors are This is because the signal may be a band-compressed signal.

  Note that the image processing unit according to the embodiment of the present invention spatially detects the gradation area based on the input image signals Yi, Ui, and Vi, thereby determining the gradation area for each pixel and outputting the control signal Dc. May be. In the above case, the control unit of the image processing unit according to the embodiment of the present invention has the same configuration as the control unit 202 according to the second embodiment shown in FIG. Further, the above configuration is particularly effective when, for example, the band of the input image signals Ui and Vi relating to color is high.

[Gradation number expansion unit 254]
The gradation number expansion unit 254 includes a first gradation number expansion unit 254a, a second gradation number expansion unit 254b, and a third gradation number expansion unit 254c. Each of the first gradation number expanding section 254a, the second gradation number expanding section 254b, and the third gradation number expanding section 254c is a gradation number expanding section 204 according to the first embodiment shown in FIG. It has the same configuration as. Therefore, the first gradation number expanding unit 254a adds a k-bit fixed value to the lower order of the N-bit input image signal Yi based on the control signal Dc, and converts the first output image signal into N + k bits, Alternatively, an N + k-bit second output image signal obtained by temporally smoothing the input image signal Yi is selectively output as the output image signal Ro. Similarly, the second gradation number expanding unit 254b and the third gradation number expanding unit 254c output output image signals Uo and Vo, respectively.

  The image processing unit 250 outputs the output image signals Yo, Uo, Vo with the configuration of FIG. 22, for example.

  As described above, the display device according to the third embodiment of the present invention outputs a plurality of channels of input image signals Yi, Ui, and Vi (each N-bit input image signal) indicating a color image and outputs N + k bits. An image processing unit 250 that corrects the image signals Yo, Uo, and Vo, and a display unit 190 that has N + k-bit gradation performance are provided. The image processing unit 250 includes a control unit 252 and a gradation number expanding unit 254. The control unit 252 spatially detects the gradation area based on the input image signal Yi, thereby determining the gradation area for each pixel and outputting the control signal Dc. Further, the gradation number expanding unit 254 adds the k-bit fixed value to the lower order of the input image signal based on the control signal Dc, and converts the first output image signal or the input image signal into N + k bits in terms of time. The smoothed N + k-bit second output image signal is selectively output as output image signals Yo, Uo, Vo. Therefore, similarly to the display device 1000 according to the first embodiment, the display device according to the third embodiment determines the gradation area based on the input image signal and selectively outputs the image signal temporally. It can be smoothed, converted into an image signal having a larger number of gradations than the input image signal, and displayed.

  Further, the display device according to the third embodiment determines the gradation area and selectively corrects the gradation area more smoothly similarly to the display apparatus 1000 according to the first embodiment. Toning performance can be improved. Further, since the display device according to the third embodiment does not correct the input image in the edge region or the texture region, the image indicated by the output image signals Yo, Uo, Vo does not impair sharpness.

  In addition, the display device according to the third embodiment selectively improves the gradation performance of the gradation area in the same manner as the display device 1000 according to the first embodiment. The same effect as the performance can be improved.

  Further, the image processing unit 250 of the display device according to the third embodiment, like the image processing unit 100 of the display device 1000 according to the first embodiment, applies a temporally smoothed gradation region to spatially detected gradation regions. Use to smooth. Therefore, like the display device 1000 according to the first embodiment, the display device according to the third embodiment does not increase the circuit scale and processing time of the filter as in the case of spatial smoothing. The gradation area can be selectively smoothed.

[Modification of Display Device According to Third Embodiment]
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 may be an apparatus, that is, an image processing apparatus.

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

[Program for image processing apparatus]
A program for causing an image processing apparatus according to the third embodiment of the present invention to function as a computer 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.

(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. Hereinafter, the image processing method according to the third embodiment of the present invention will be described as being performed by the display device according to the third embodiment. However, the image processing method is applied to the image processing device according to the third embodiment of the present invention. You can also.

  The display device according to the third embodiment detects a predetermined frequency component from the N-bit input image signal Yi for each pixel (S300).

  The display device according to the third embodiment spatially smoothes the detection value (frequency component detection value Df) detected in step S300 (S302), and based on the smoothed detection value (average detection value Dave). The control signal Dc is generated (S304).

  The display device according to the third embodiment has a fixed value of k bits below the input image signal based on the input image signals Yi, Ui, Vi for each channel and the control signal Dc generated in step S304. The first output image signal converted to N + k bits by adding or the second output image signal of N + k bits obtained by temporally smoothing the input image signal is selectively output for each channel (S306).

  The display device according to the third embodiment determines the gradation area based on the input image signal and selectively smoothes the image signal temporally by performing the processes of steps S300 to S306. It can be converted into an image signal having a larger number of gradations than the image signal to be processed.

(Fourth embodiment)
Next, as a display device according to the fourth embodiment of the present invention, a configuration when the display unit has N-bit gradation performance will be described.

  FIG. 23 is a block diagram showing a display device 3000 according to the fourth embodiment of the present invention. Referring to FIG. 23, 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 into N + k bits or the N + k bit second output image signal obtained by temporally 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. 24 is an explanatory diagram for explaining an example of the pseudo gradation processing in the pseudo gradation processing unit 302 according to the fourth embodiment of the present invention, and an example in which dither processing is used as the pseudo gradation processing. Show. FIG. 24A shows a 2 × 2 pixel area where dither processing is performed, and FIG. 24B 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. 24B 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. .

[Another example of pseudo gradation processing]
Note that the pseudo gradation processing unit 302 may use error diffusion processing as the pseudo gradation processing, for example. 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. 23 again, 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, pseudo-gradation processing such as dither processing is performed. Is converted into an N-bit output image signal Do, thereby improving the gradation performance of the gradation region. 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. 23, 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. As in the display device 2000 according to the embodiment and the display device according to the third embodiment, for example, the same effect can be obtained for an image signal of a color image composed of R / G / B or Y / U / V. be able to.

  As described above, the display device 3000 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 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. That is, the image processing unit 300 spatially detects the gradation area based on the input image signal Di, thereby determining the gradation area for each pixel and generating the control signal Dc. Then, the image processing unit 300 adds the k-bit fixed value to the lower order of the input image signal Di based on the control signal Dc, and converts the first output image signal Di or the input image signal Di into N + k bits in terms of time. The smoothed N + k-bit second output image signal is selectively output as the image signal De. Accordingly, the display device 3000 determines the gradation area based on the input image signal, selectively smoothes the image signal temporally, and inputs the same as in the display device 1000 according to the first embodiment. It can be converted into an image signal having a larger number of gradations than the image signal.

  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 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 may be an apparatus, that is, an image processing apparatus.

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

[Program for image processing apparatus]
A program for causing an image processing apparatus according to the fourth embodiment of the present invention to function as a computer 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.

(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. In the following description, the image processing method according to the fourth embodiment of the present invention is described as being performed by the display device 3000. However, the image processing method according to the fourth embodiment of the present invention can also be applied.

  The display device 3000 detects a predetermined frequency component for each pixel from the N-bit input image signal Di as in step S100 according to the first embodiment described above (S400).

  The display device 3000 spatially smoothes the detection value (frequency component detection value Df) detected in step S400, similarly to steps S102 and S104 according to the first embodiment described above (S402), and is smoothed. A control signal Dc is generated based on the detected value (average detected value Dave) (S404).

  The display device 3000 fixes k bits below 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 according to the first embodiment described above. A first output image signal that is converted to N + k bits by adding a value, or a second output image signal of N + k bits obtained by temporally smoothing the input image signal Di is selectively output (S406).

  The display device 3000 performs pseudo gradation processing on the image signal (first output image signal or second output image signal) output in step S406 and converts the image signal into an N-bit image signal (output image signal Do). (S408). Here, the display device 3000 performs the pseudo gradation processing in step S408 by using, for example, dither processing or error diffusion processing.

  The display device 3000 performs the processes of steps S400 to S408 to determine a gradation region based on the input image signal, and selectively smooth the image signal temporally. The gradation performance can be improved by converting the image signal into an image signal having a large number of gradations and further performing pseudo gradation processing.

  As described above, the display device has been described as the first to fourth embodiments. However, the first to fourth embodiments of the present invention described above are, for example, organic EL displays, self-luminous types such as FEDs and PDPs. The present invention can be applied to a display device, a backlight-type display device such as an LCD, and a receiving device that receives a television broadcast. The display devices according to the first to fourth embodiments of the present invention described above are applied to various devices such as computers such as PCs (Personal Computers) and servers (Servers), and portable communication devices such as mobile phones. be able to.

  The image processing apparatuses according to the first to fourth embodiments are applied to various devices such as display devices such as organic EL displays and LCDs, computers such as PCs, and portable communication devices such as mobile phones. 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 fourth embodiment, a configuration has been described in which processing of a monochrome image or processing of one channel among a plurality of channels of a color image is performed as an input image signal. For example, the display device according to the embodiment can process a plurality of channels of a color image by combining the second embodiment or the third embodiment with each of the fourth embodiments.

  In the above description, it has been shown that a program (computer program) for causing a computer to function as the information processing apparatus according to the embodiment of the present invention is provided. However, the embodiment of the present invention further includes the above program. Can also be provided.

  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.

100, 150, 200, 250, 300 Image processing unit 102, 202, 252 Control unit 104, 142, 204, 254 Tone number expansion unit 106 Frequency component detection unit 108 Detection value smoothing unit 110 Control signal generation unit 116 Temporal smoothing Calculation unit 118 Selection unit 122, 206 Maximum value selection unit 124, 138 Addition unit 126 Mixing unit 130 Frame memory 132 Shift unit 134 Subtraction unit 136 Non-linear conversion unit 140 Weighted average calculation unit 190, 390 Display unit 302 Pseudo gradation processing unit 1000 1500, 2000, 3000 display device

Claims (8)

A frequency component detection unit that detects a signal of a predetermined frequency band for each pixel from the input N-bit (N is a positive integer) input image signal;
A detection value smoothing unit that spatially smoothes the detection signal corresponding to each pixel based on the detection signal detected by the frequency component detection 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;
First, N + k bits (k is a positive integer) obtained by inputting the N-bit input image signal and expanding the number of gradations of the input image signal by a predetermined number based on a control signal generated for each pixel. An output image signal, or a gradation number expansion unit that outputs, for each pixel, an N + k-bit second output image signal in which the input image signal is time-smoothed and the number of gradations is expanded by a predetermined number;
With
The image processing apparatus according to claim 1, wherein the gradation number extending unit selectively performs temporal smoothing of the input image signal in accordance with a temporal change amount of the input image signal. The gradation number expansion unit
A frame memory for storing the first output image signal or the second output image signal and outputting a delayed image signal one frame before the input image signal;
A temporal smoothing operation unit that selectively performs temporal smoothing of the input image signal for each pixel in accordance with a temporal change amount of the input image signal based on the input image signal and the delayed image signal; ,
Based on the control signal generated for each pixel, when the control signal indicates a gradation region, the input image signal selectively smoothed by the temporal smoothing calculation unit is output as the second output image signal. When the control signal indicates a region other than the gradation region, a selection unit that shifts the input image signal by k bits and outputs it as the first output image signal;
The image processing apparatus according to claim 1, further comprising: The control signal generation unit uses the detection signal smoothed by the detection value smoothing unit and a plurality of threshold values to determine a mixing ratio of the first output image signal and the second output image signal in each corresponding pixel. Output the control signal to be specified,
The gradation number expansion unit
A frame memory for storing the first output image signal or the second output image signal and outputting a delayed image signal one frame before the input image signal;
A temporal smoothing operation unit that selectively performs temporal smoothing of the input image signal for each pixel in accordance with a temporal change amount of the input image signal based on the input image signal and the delayed image signal; ,
Based on the control signal in which the input image signal and the input image signal selectively smoothed in the temporal smoothing calculation unit are input and the mixing ratio is defined for each pixel, The first output image signal obtained by shifting the input image signal by k bits so that the ratio of the first output image signal and the second output image signal is the same as the mixing ratio defined by the control signal; A mixing unit that mixes and outputs the second output image signal, which is the input image signal selectively smoothed in the temporal smoothing calculation unit, for each pixel;
The image processing apparatus according to claim 1, further comprising: The temporal smoothing calculation unit is
A subtraction unit that subtracts an input image signal in which the number of gradations is expanded to N + k bits from the delayed image signal, and calculates a difference value for each pixel;
A non-linear conversion unit that compares the difference value for each pixel with a predetermined threshold for determining a temporal change amount of the input image signal, and converts the difference value for each pixel into a value according to the comparison result. When,
An addition unit that adds, for each pixel, a difference value for each pixel output from the nonlinear conversion unit and an input image signal in which the number of gradations is expanded to N + k bits;
A weighted average that outputs the second output image signal by performing a weighted average operation for each pixel based on the input image signal in which the number of gradations is expanded to N + k bits and the image signal output from the adder. An arithmetic unit;
The image processing apparatus according to claim 2, further comprising: An image signal processing apparatus to which a plurality of N-bit (N is a positive integer) input image signals are input,
A frequency component detector that detects a signal of a predetermined frequency band for each pixel from each of the input image signals;
Based on the detection signal detected by the frequency component detection unit, a maximum value selection unit that selects a detection signal with the maximum detection signal in each pixel corresponding to each of the plurality of input image signals;
A detection value smoothing unit that spatially 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 The N + k-bit first output image signal (k is a positive integer) or the N + k-bit second output image signal in which the input image signal is time-smoothed and the number of gradations is expanded by a predetermined number of pixels. The number of gradations to be output every time,
With
The gradation number expanding unit selectively performs temporal smoothing of each of the plurality of input image signals according to a temporal change amount of each of the plurality of input image signals. Processing equipment. Detecting a signal of a predetermined frequency band for each pixel from an input N-bit (N is a positive integer) input image signal;
Spatially smoothing the detection signal corresponding to each pixel based on the detection signal detected in the detecting step;
Generating a control signal for defining a gradation region for each pixel based on the detection signal smoothed in the smoothing step;
A first output image signal of N + k bits (k is a positive integer) obtained by expanding the number of gradations of the N-bit input image signal by a predetermined number based on the control signal generated in the generating step, or N bits Outputting a second output image signal of N + k bits in which the input image signal is smoothed in time and the number of gradations is expanded by a predetermined number for each pixel;
Have
In the outputting step, the temporal smoothing of the input image signal is selectively performed according to the temporal change amount of the input image signal. Detecting a signal of a predetermined frequency band for each pixel from the input N-bit (N is a positive integer) input image signal;
Spatially smoothing the detection signal corresponding to each pixel based on the detection signal detected in the detecting step;
Generating a control signal for defining a gradation region for each pixel based on the detection signal smoothed in the smoothing step;
A first output image signal of N + k bits (k is a positive integer) obtained by expanding the number of gradations of the N-bit input image signal by a predetermined number based on the control signal generated in the generating step, or N bits Outputting a second output image signal of N + k bits in which the input image signal is smoothed in time and the number of gradations is expanded by a predetermined number for each pixel,
To the computer,
In the output step, temporal smoothing of the input image signal is selectively performed according to a temporal change amount of the input image signal. An image signal correction unit for correcting the input image signal;
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
A frequency component detection unit that detects a signal in a predetermined frequency band from the input N-bit input image signal for each pixel;
A detection value smoothing unit that spatially smoothes the detection signal corresponding to each pixel based on the detection signal detected by the frequency component detection 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;
The input image signal of N bits is input, and the first output image signal of N + k bits in which the number of gradations of the input image signal is expanded by a predetermined number based on the control signal generated for each pixel, or the input A gradation number expanding unit that outputs, for each pixel, an N + k-bit second output image signal in which the image signal is temporally smoothed and the number of gradations is expanded by a predetermined number;
With
The display device according to claim 1, wherein the gradation number extending unit selectively performs temporal smoothing of the input image signal in accordance with a temporal change amount of the input image signal.

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