JP7257768B2 - Image processing device, its control method, and program - Google Patents

Description

The present invention relates to an image processing apparatus, its control method, and a program.

In recent years, as the display brightness of displays has increased, HDR (high dynamic range) camera systems have become available that can reproduce images with gradations that are closer to the human eye, instead of the previously compressed gradations on the high-brightness side. Proposed. An HDR camera system uses an OETF (Opto-electronic transfer function) that is used as a transfer function when outputting an image. The OETF curve is a curve that shows the reverse characteristics of the EOTF (Electro-optical transfer function) characteristics described in ST2084 or the like of the HDR standard handled by HDR monitors. In an HDR camera system, by subjecting a captured image to conversion processing using an OETF curve (hereinafter also referred to as gamma processing), it is possible to display gradations on the high-luminance side on an HDR monitor.

In an HDR camera system, it is desirable to perform gradation correction that utilizes the high luminance output of an HDR monitor. Output in tonality. Therefore, it is not appropriate to perform gradation correction according to the scene after performing gamma processing. On the other hand, when gradation correction is performed before gamma processing, the characteristics of gradation correction are determined by considering both the exposure of the input camera and the OETF curve corresponding to the output D (dynamic) range. Since it is necessary to create it, there was a problem that the processing was complicated.

In order to solve such a problem, Patent Document 1 discloses that a plurality of gamma curves are prepared in advance, and a curve generated by interpolating from the plurality of gamma curves according to the brightness difference of the subject area of the shooting scene is applied to the gamma processing. Techniques are disclosed.

JP 2014-121019 A

However, in the technique disclosed in Japanese Patent Application Laid-Open No. 2002-200010, since the gamma curve including the gradation correction is dynamically changed according to the brightness of the subject area (simply referred to as the scene), development such as color processing and edge enhancement processing is required. Processing also had to be adjusted according to the gamma curve. In addition, there is a limit to generating optimal characteristics for gradation correction by interpolating based on multiple gamma curves prepared in advance. There is a need to.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to implement gamma processing and gradation correction processing using a gamma curve in a simpler manner without increasing the amount of data to be prepared in advance or items to be adjusted. be.

In order to solve this problem, for example, the image processing apparatus of the present invention has the following configuration. That is, a first determining means for determining a normalization characteristic for normalizing a signal of an input image, a second determining means for determining a gradation correction characteristic for correcting the gradation of the image, and the determined normalization characteristic. correction processing means for performing gradation correction processing on the input image using the gradation correction characteristics; and gamma processing means for applying predetermined gamma characteristics to the image subjected to the gradation correction processing. wherein the predetermined gamma characteristic is configured to output a signal within a predetermined dynamic range, and the predetermined gamma characteristic is obtained for a signal having a luminance higher than that of the reference signal. and outputting a signal with a wider dynamic range than the output of the characteristic, wherein the first determining means determines the normalized characteristic based on the predetermined gamma characteristic corresponding to the dynamic range of the signal of the input image. and the gamma processing means uses the same predetermined gamma characteristic even when the dynamic ranges of the input images are different.

According to the present invention, gamma processing and gradation correction processing using a gamma curve can be realized by a simpler method without increasing the amount of data to be prepared in advance or items to be adjusted.

2 is a block diagram showing an example of the functional configuration of the digital camera according to the first embodiment; FIG. 3 is a block diagram showing an example of the functional configuration of an image processing unit according to the first embodiment; FIG. 4 is a flowchart showing a series of operations by an image processing unit according to the first embodiment; FIG. 4 is a diagram for explaining normalization characteristics in the first embodiment; FIG. 4 is a diagram for explaining gradation correction characteristics obtained by inputting a signal after normalization processing according to the first embodiment; FIG. 4 is a diagram for explaining gamma characteristics according to the first embodiment; FIG. 11 is a block diagram showing an example of the functional configuration of an image processing unit according to the second embodiment; 8 is a flowchart showing a series of operations by an image processing unit according to the second embodiment; FIG. 11 is a diagram for explaining tone correction characteristics using a signal after normalization processing in the second embodiment as an input; Diagram for explaining an example of gradation correction characteristics Diagram explaining the relationship between the D range of the input image and the EOTF curve corresponding to the HDR monitor

Exemplary embodiments of the invention will now be described in detail with reference to the drawings. As an example of an image processing apparatus, a digital camera capable of tone-converting a captured image signal will be described below. However, the following embodiments are applicable not only to digital cameras but also to other electronic devices capable of tone-converting captured images. These electronic devices may include, for example, mobile phones including smartphones, game machines, tablet terminals, watch-type and eyeglass-type information terminals, medical devices, monitoring systems, and equipment for in-vehicle systems. In addition, the following embodiments are also applicable to electronic devices such as personal computers and display devices that do not have means for capturing an image and that can acquire an image captured externally and apply gradation conversion. It is possible.

(Outline of gradation correction)
First, the outline of tone correction described below will be described with reference to FIG. 10A to 10D show the gradation correction characteristics, the horizontal axis represents the brightness of the input image expressed in terms of absolute luminance, and the vertical axis represents the brightness when the output image is displayed. is expressed in terms of absolute luminance. Curves 1003 to 1006 indicated by thick lines represent gradation correction characteristics for generating an output image from an input image.

For example, in conventional gradation correction processing, as shown in FIG. There was an area to However, when high-luminance gradation expression becomes possible with HDR monitors, by extending the brightness of the output (increasing the number of gradations on the high-luminance side) as shown by the curve 1004 in FIG. Gradation correction processing with reduced gradation compression becomes possible. The same applies to the general reverse S-shaped characteristic used in highlight/shadow correction as shown in FIG. 10(c). For a region such as the intermediate luminance region 1002 where the contrast has been reduced due to the gradation compression, the gradation in which the gradation compression is reduced by extending the brightness of the output like the gradation correction characteristic shown in FIG. Correction processing becomes possible. In this way, the gradation correction characteristic is generated in consideration of extending the brightness of the output (increasing the number of gradations), and the gradation correction processing is performed so as not to cause the gradation compression as much as possible.

In order to perform such processing, it is necessary to apply an EOTF curve that extends the brightness of the output (that is, a gamma characteristic with an increased number of brightness gradations) in the gamma processing. However, in addition to changing the EOTF curve that matches the D range of the input image as shown in FIG. is desirable. However, in order to do so, it is necessary to perform processing for generating gradation correction characteristics by calculating back the created EOTF curve for each scene, which complicates control. Therefore, in the following embodiments, the process of extending the brightness of the output is realized only by controlling the gradation correction process without changing the EOTF curve according to the scene or the D range of the input image.

(Embodiment 1)
A specific example according to the first embodiment will be described. In the first embodiment, the EOTF curve used in gamma processing is fixed to a curve extended to the upper limit value that can be output, normalization characteristics corresponding to the D range of the input image and the gamma processing, and gradation correction characteristics according to the scene. are determined respectively, and gradation correction processing is performed before gamma processing.

(Configuration of digital camera)
Next, a functional configuration example of the digital camera 100 of this embodiment will be described with reference to FIG. In FIG. 1 , the imaging lens 103 constitutes a lens group including a zoom lens, a focus lens, and a shift lens, and forms a subject image on the imaging surface of the imaging unit 22 . A diaphragm 101 is a diaphragm used for adjusting the amount of light. An ND (Neutral Density) filter 104 has a filter used for dimming. The image pickup unit 22 has an image pickup element configured by a CCD, a CMOS element, or the like that converts an optical image into an electric signal. The image pickup unit 22 also has functions such as control of charge accumulation in the image pickup device by an electronic shutter, change of analog gain, and change of readout speed. to output The A/D converter 23 converts the analog signal output from the imaging section 22 into a digital signal. The barrier 102 covers the imaging system including the imaging lens 103 of the digital camera 100 to prevent the imaging system including the imaging lens 103, the diaphragm 101, and the imaging unit 22 from being soiled or damaged.

The image processing unit 24 processes a digital image signal (simply referred to as image data) containing three components of R, G, and B for each pixel, which is output from the A/D converter 23. Image processing is performed to output image data after gradation conversion including three components of R, G, and B. Further, it performs predetermined arithmetic processing based on the captured image data, and transmits the arithmetic result to the control unit 50 . The control unit 50 performs, for example, exposure control, ranging control, white balance control, etc., based on the transmitted calculation result. As a result, TTL (through-the-lens) AF (autofocus) processing, AE (automatic exposure) processing, AWB (automatic white balance) processing, and the like are performed.

The gyro 40 detects movements and posture changes of the digital camera 100 due to camera shake and the like. Based on the movement detected by the gyro 40, the control unit 50 operates the shift lens of the imaging lens 103 or shifts the image by the image processing unit 24, thereby correcting the image blur.

The memory control unit 15 controls writing of data to the memory 32 and reading of data from the memory 32 . For example, the memory control unit 15 writes output data from the A/D converter 23 directly or via the image processing unit 24 to the memory 32 .

The memory 32 stores image data captured by the imaging unit 22 and converted into digital data by the A/D converter 23 and image data to be displayed on the display unit 28 . The memory 32 has a storage capacity sufficient to store a predetermined amount of time of video and audio. The memory 32 also serves as an image display memory (video memory).

The D/A converter 13 converts image display data stored in the memory 32 into an analog signal and supplies the analog signal to the display unit 28 . The image data for display written in the memory 32 in this manner is displayed on the display section 28 via the D/A converter 13 . The display unit 28 includes a display configured by an LCD or the like, and displays on the display according to the analog signal from the D/A converter 13 . By sequentially displaying the image signals output from the imaging unit 22 on the display unit 28 via the A/D converter 23 and the memory control unit 15, an electronic viewfinder is realized and through image display can be performed. Note that the display unit 28 does not necessarily have to be included in the digital camera 100 . Even if the display unit 28 is not included in the digital camera 100, the digital camera 100 may have display control means (for example, the control unit 50) for controlling an image or display content to be displayed on the display unit. Just do it.

The non-volatile memory 56 is an electrically erasable/recordable memory, such as an EEPROM. The nonvolatile memory 56 stores constants, programs, etc. for the operation of the control unit 50 .

The control unit 50 includes a CPU or MPU, and controls the overall operation of the digital camera 100 by loading and executing programs in the system memory 52 . In the system memory 52, constants and variables for operation of the control unit 50, programs read from the nonvolatile memory 56, and the like are developed. The control unit 50 also performs display control by controlling the memory 32, the D/A converter 13, the display unit 28, and the like. The control unit 50 may also have the function of the image processing unit 24 and perform calculations related to various image processing instead of the image processing unit 24 . The system timer 53 is a time measuring unit that measures the time used for various controls in the digital camera 100 and the time of the built-in clock.

A mode changeover switch 60 , a recording switch 61 , and an operation section 70 are operation means for inputting various operation instructions to the control section 50 . The mode changeover switch 60 receives an operation instruction from the user for switching the operation mode of the control unit 50 to any one of a moving image recording mode, a still image recording mode, a reproduction mode, and the like. Modes included in the moving image recording mode and the still image recording mode include an auto shooting mode, an automatic scene determination mode, a manual mode, various scene modes that provide shooting settings for each shooting scene, a program AE mode, a custom mode, and the like. By operating the mode changeover switch 60, it is possible to directly switch to any one of these modes included in the moving image shooting mode. Alternatively, after once switching to the moving image shooting mode with the mode switching switch 60, it may be switched to any of these modes included in the moving image shooting mode using another operation member. The recording switch 61 receives an operation instruction for switching between a shooting standby state and a shooting state. When the recording switch 61 is turned on, the control section 50 starts a series of operations from reading signals from the imaging section 22 to writing moving image data to the recording medium 200 .

Each operation member of the operation unit 70 is appropriately assigned a function for each scene by selecting and operating various function icons displayed on the display unit 28, and operates as various function buttons. The function buttons include, for example, an end button, a return button, an image forward button, a jump button, a narrowing down button, an attribute change button, and the like. For example, when the menu button is pressed, a menu screen on which various settings can be made is displayed on the display unit 28 . The user can intuitively perform various settings by using the menu screen displayed on the display unit 28, four-way four-direction cross keys, and the SET button. Moreover, the operation unit 70 may include a touch panel.

The power supply control unit 80 includes a battery detection circuit, a DC-DC converter, a switch circuit for switching blocks to be energized, and the like, and detects whether or not a battery is installed, the type of battery, and the remaining amount of the battery. Also, the power supply control unit 80 controls the DC-DC converter based on the detection results and instructions from the control unit 50, and supplies necessary voltage to each unit including the recording medium 200 for a necessary period. The power supply unit 30 includes, for example, a primary battery such as an alkaline battery or a lithium battery, a secondary battery such as a NiCd battery, a NiMH battery, or a Li ion battery, an AC adapter, or the like.

The I/F 18 is an interface with a recording medium 200 such as a memory card or hard disk and an external display device 300, and functions as output means for outputting predetermined data from the digital camera 100 to the external display device 300 or the like. . A recording medium 200 is a recording medium such as a memory card for recording captured images, and is composed of a semiconductor memory, a magnetic disk, or the like. Note that the recording medium 200 may be configured to be detachable.

The external display device 300 includes, for example, an HDR monitor capable of high-luminance gradation expression, receives image data processed by the image processing unit 24 after being imaged through the imaging system from the I / F 18, and outputs the image data. indicate.

(Configuration of image processing unit and a series of operations related to gradation conversion processing)
Next, with reference to FIGS. 2 and 3, the configuration of the image processing unit 24 according to the present embodiment and a series of operations related to gradation conversion processing will be described. As described above, the image processing unit 24 receives image data (input image) composed of three components of R, G, and B, performs image processing, and outputs image data (output image). The image processing unit 24 includes a normalization characteristic determination unit 201, a normalization processing unit 202, a gradation correction characteristic determination unit 203, a gradation correction processing unit 204, and a gamma processing unit 205, as shown in FIG. Note that FIG. 2 discloses only the main configuration related to the present embodiment included in the image processing unit 24, but other configurations, such as a configuration for executing AF, for exhibiting other functions. configuration. Also, in the following description, the image processing unit 24 will be described as an example in which it is configured by hardware. However, the image processing unit 24 is composed of a programmable processor such as a CPU or GPU, and a program is developed from an internal non-volatile memory (not shown) to an internal volatile memory (not shown) and executed. may implement the function of Description of each configuration shown in FIG. 2 will be made together with description of a series of operations of the image processing unit 24 described below with reference to FIG.

In S301, the normalization characteristic determination unit 201 determines a normalization characteristic for normalizing the signal of the input image according to the EOTF characteristic and the D range of the input image, which are used in later-stage gamma processing, which will be described later. This normalization characteristic has the characteristic of converting the signal value of the input image so that gamma processing can be performed using the fixed EOTF characteristic at the later stage even if the D range of the input image changes. The normalized characteristics according to this embodiment are as shown in FIG. 4, for example. Here, the horizontal axis of FIG. 4 represents the signal value of the input image, and the vertical axis represents the normalized output value. Normalization characteristics 401, 402, and 403 indicate normalization characteristics corresponding to the D range of the input image being 100%, 200%, and 400%, respectively. Note that in the present embodiment, the D range of the input image when the digital camera 100 is used to shoot with proper exposure is set to 100%. The D-range of the input image shot with .

As shown in FIG. 4, the normalization characteristic has a linear characteristic until the output value reaches the reference signal value (reference white) T, and the signal value higher than the reference signal value T gradually becomes a curve. have. The normalization characteristic 401 in the case of the D range of 100% has a straight line characteristic with a slope of 1 that outputs the signal value as it is until the magnitude of the input value reaches the reference signal value T. FIG. On the other hand, the signal value higher than the reference signal value T has the characteristic that it tends toward MAX_100, which indicates the maximum value of the signal value MAXD range 100% where the input value is the maximum value. Also, the normalization characteristic 402 in the case of the D range of 200% has a straight line characteristic with a double slope until the magnitude of the input value reaches the reference signal value T/2. On the other hand, the signal value higher than the reference signal value T/2 has a characteristic of MAX_200 indicating the maximum value of the D range 200% at the signal value MAX where the input value is the maximum value. where MAX_200 is a higher signal value than MAX_100. Similarly, the normalization characteristic 303 when the D range is 400% has a straight line characteristic with a slope of four times the magnitude of the input value up to the reference signal value T/4. On the other hand, the signal value higher than the reference signal value T/4 has a characteristic of MAX_400 indicating the maximum value of the D range 400% at the signal value MAX where the input value is the maximum value. where MAX_400 is a higher signal value than MAX_200. In this embodiment, the D range of 400% is the maximum value of the output image, so the signal value MAX, which is the maximum input value, and MAX_400, which indicates the maximum value of the D range of 400%, are the same value. The normalization characteristic determination unit 201 selects such normalization characteristic according to the D range of the input image. That is, the normalization characteristic is determined based on the predetermined EOTF characteristic corresponding to the D range of the signal of the input image.

In S302, the normalization processing unit 202 performs normalization processing on the input image using the normalization characteristics determined in S301. Normalization processing is table conversion using normalization characteristics. Assuming that the signal of the input image is in and the image signal after normalization is in_norm, the normalization processing using the normalization characteristic y=norm_tbl(x) is calculated according to Equation (1). It should be noted that in the present embodiment, the processing of equation (1) is applied to all of the input image R, G, and B signals.

in_norm = norm_tble(in) … (1)

In S303, the gradation correction characteristic determination unit 203 determines gradation correction characteristics according to the brightness (scene) of the subject area based on the input image signal normalized in S302 and the normalization characteristic. In the present embodiment, first, a gradation correction characteristic as shown in FIG. 5 is created by inputting a signal after normalization processing. As is clear from FIG. 5, the determined gradation correction characteristic is a gradation correction characteristic capable of outputting a signal value exceeding the maximum signal value in the D range of the input image. Then, the final gradation correction characteristic is determined by synthesizing the gradation correction characteristic and the normalization characteristic. The final gradation correction characteristic out=hosei_tbl (in) can be calculated according to Equation (2) below. Here, y = hosei_tbl_norm(x), normalization characteristic y = norm_tbl(x), input image signal in, tone corrected signal out and

out = hosei_tbl(in) = hosei_tbl_norm(norm_tbl(in)) ……(2)

In this embodiment, the processing of equation (2) is applied to all of the input image R, G, and B signals. As for the method of calculating the gradation correction characteristics using the signal after the normalization processing as input, for example, a method using a known histogram, which is described in Japanese Unexamined Patent Application Publication No. 2015-195498, can be used.

In S304, the tone correction processing unit 204 performs tone correction processing on the input image using the tone correction characteristics determined in S303. The luminance signal Y_in obtained according to Equation (3) is used in the gradation correction processing of this embodiment, which will be described later. R_in, G_in, and B_in are input signals of R, G, and B at the same pixel position of the input image.

Y_in = 0.263 × R_in + 0.678 × G_in + 0.059 × B_in … (3)

Next, the luminance signal Y_in generated according to equation (3) is input, and the signal of the input image is multiplied by the gain signal according to equation (4). This is performed by generating a gain signal from the tone-corrected signal converted by Equation (2) and multiplying it by the signal of the input image. In of the equation (4) represents the R, G, and B signals of the input image, and out represents the R, G, and B signals after the gradation correction processing.

As shown in equations (3) and (4), by performing tone correction processing using the luminance signal, tone correction processing can be performed without changing the hue of the input image. However, it is not always necessary to use the luminance signal, and gradation correction processing in which expression (4) is applied using the maximum values of the R, G, and B signals of the input image without using the luminance signal generated according to expression (3). may be performed. Further, the gradation correction process may be performed by directly applying the gradation correction characteristic of equation (2) to the signal of the input image.

In S305, the gamma processing unit 205 performs gamma processing on the image after performing the tone correction processing in S304 using the fixed (that is, predetermined) EOTF characteristics. FIG. 6 shows an example of EOTF characteristics used in this embodiment. T and MAX_100 to MAX_400 in the figure are the reference signal value T, the signal maximum value MAX_100 at D range 100%, the signal maximum value MAX_200 at D range 200%, and the D range 400%, similarly to the normalization characteristics described above in S301. represents the maximum signal value MAX_400 of . As shown in FIG. 6, the fixed EOTF characteristic 601 draws a curve similar to the EOTF characteristic when the D range is 100% up to the reference signal value T. When the input signal value is MAX_100, the maximum value of the EOTF characteristic 602 when the D range is 100% is passed, and when the input signal value is MAX_200, the maximum value of the EOTF characteristic 603 when the D range is 200% is passed. When the input signal value is MAX_400, it passes through the maximum value of the EOTF characteristic 604 when the D range is 400%. That is, the EOTF characteristic 601 is a curve that provides an output equivalent to a narrow D range of 100% on the low luminance side, and a characteristic that provides an output equivalent to a wide D range of 400% on the high luminance side. . That is, the fixed EOTF characteristic is wider than the output of the predetermined EOTF characteristic for a signal having a higher luminance than the reference signal, with respect to the predetermined EOTF characteristic 602 to 604 that output the signal in the predetermined D range. It is configured to output a dynamic range signal. By using such an EOTF characteristic, even when the output value is larger than the maximum value of the D range of the input image as in the gradation correction characteristic of FIG. 5, it can be handled. The image processing unit 24 then outputs the gamma-converted signal output from the gamma processing unit 205, and ends this series of operations.

In the above description, the case where each functional block calculates the values according to the formulas (1) to (4) has been described as an example. However, the above calculations are performed in advance and the results are stored as a table in the non-volatile memory 56 or the like, and in each of the steps described above, the stored table is referenced to obtain the calculation results, thereby determining each of the above characteristics. good too.

As described above, in this embodiment, gamma processing is performed using a fixed gamma curve after tone correction is performed by performing normalization processing according to the D range of the input image. At this time, as the brightness increases, the gamma curve is fixed assuming a wider D range than usual, and then the gradation is dynamically controlled in the gradation correction process before the gamma process. By doing so, the mapping of the gradation correction process is facilitated. In other words, gamma processing and gradation correction processing based on OETF characteristics can be realized in a simpler manner without increasing the amount of data prepared in advance or items to be adjusted in consideration of the output brightness of the gamma curve according to the output D range. can do.

(Embodiment 2)
Next, the configuration of the second embodiment will be described. The second embodiment differs from the first embodiment in that different gradation correction characteristics are used for the output signal of the luminance signal and the output signal of the color difference signal. In other words, in the present embodiment, it is possible to generate an output image that does not have excessively high saturation even if the gradation correction process is performed. Although the second embodiment differs from the first embodiment in the configuration of the image processing unit, the configuration of the digital camera 100 is substantially the same. Therefore, substantially the same configuration and the same processing are denoted by the same reference numerals, redundant explanations are omitted, and different points are mainly explained.

The image processing unit 24 according to the second embodiment will be described below with reference to FIG. The difference from the configuration of the image processing unit of the first embodiment is that the output image is a Y image composed of luminance signals and a UV image composed of color difference signals. Next, the image processing unit 24 includes a brightness gradation correction processing unit 702 and a brightness gamma processing unit 704 for brightness, and a color gradation processing unit 704 for color difference signals to output a Y image and a UV image. The difference is that a tone correction processing unit 703 and a color gamma processing unit 705 are provided. Finally, the difference is that the image processing unit 24 includes a Y signal generation processing unit 706 and a UV signal generation processing unit 707 for generating a Y signal and a UV signal from the RGB signals generated for luminance and color. .

FIG. 8 shows a series of operations related to the image processing unit 24 of the second embodiment. A series of operations related to the gradation conversion process according to the second embodiment will be described below with reference to FIGS. 7 and 8. FIG. First, the image processing unit 24 executes the processing of S301 to S302 in the same manner as in the first embodiment.

In S801, the tone correction characteristic determination unit 701 generates tone correction characteristics for luminance and color. The method of generating the gradation correction characteristics is the same as the processing in step S303 of the first embodiment, but differs in that different characteristics are used for the gradation correction characteristics for luminance and the gradation correction characteristics for colors. Gradation correction characteristics in this embodiment will be described with reference to FIG.

FIG. 9 shows gradation correction characteristics obtained by inputting a signal after normalization processing using gradation correction characteristics 901 for luminance and gradation correction characteristics 902 for colors. The gradation correction characteristic 901 for luminance is similar to the gradation correction characteristic of Embodiment 1. As the value of the input signal increases, the output becomes larger than the value of the input signal indicated by the thin dotted line. . On the other hand, although the gradation correction characteristic 902 for color has the same inflection point as the gradation correction characteristic 901 for luminance, even if the value of the input signal increases, the input signal indicated by the thin dotted line Draw a characteristic that is no greater than the value of the signal. By doing so, it is possible to generate an output image in which the saturation does not become excessively high.

In step S802, the luminance tone correction processing unit 702 and the color tone correction processing unit 703 perform tone correction processing on the input image using luminance tone correction characteristics and color tone correction characteristics, respectively. and an image for color. Note that the tone correction processing method is substantially the same as the processing of S304 in the first embodiment.

In S803, the luminance gamma processing unit 704 and the color gamma processing unit 705 perform gamma processing with fixed EOTF characteristics on the luminance image and the color image generated in S802. The EOTF characteristics are substantially the same as the processing of S305 in the first embodiment. In this embodiment, the same EOTF characteristics are used for luminance and color. You can change the part.

In S804, the Y signal generation processing unit 706 and the UV signal generation processing unit 707 receive the luminance image and the color image subjected to the gamma processing in S803, respectively, and perform processing for generating YUV images. Assuming that image signals for luminance are R_Y, G_Y, and B_Y, and image signals for color are R_C, G_C, and B_C, Y signal Y_out, U signal U_out, and V signal V_out of the output image are generated according to equation (5). .

Y_out = 0.263 × R_Y + 0.678 × G_Y + 0.059 × B_Y
U_out = -0.140 × R_C + 0.360 × G_C + 0.500 × B_C …………(5)
V_out = 0.500 × R_C - 0.460 × G_C - 0.040 × B_C

After outputting the image of the Y and UV signals, the image processing unit 24 ends a series of operations related to the output image gradation conversion process.

As described above, in this embodiment, the gradation correction characteristics are determined for each of the luminance and color difference of an image. In particular, each gradation correction characteristic is determined so that the output of the gradation correction characteristic for luminance is greater than or equal to the output of the gradation correction characteristic for color difference, and the difference increases as the signal value of the input image increases. made it In other words, the gradation correction characteristic for color difference is designed so that even if the input signal value increases, the converted signal value does not become greater than the input signal value. By doing so, it is possible to generate an output image in which saturation does not become excessively high. Further, in the above-described embodiment, the EOTF curve, which is fixed in advance, is not changed according to the scene or the D range of the input image, but the gradation correction process extends the brightness of the output signal on the high-luminance side by controlling the gradation correction process. I tried to realize By doing so, it is possible to improve the operability of mapping in gamma processing and gradation correction processing using the OETF curve without increasing the amount of data to be stored in advance and the number of items to be adjusted.

(Other embodiments)
The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by processing to It can also be implemented by a circuit (for example, ASIC) that implements one or more functions.

201... Normalization characteristic determination unit 202... Normalization processing unit 203... Gradation correction characteristic determination unit 204... Gradation correction processing unit 205... Gamma processing unit

Claims (9)

a first determining means for determining a normalization characteristic for normalizing the signal of the input image;
a second determining means for determining tone correction characteristics for correcting tone of an image;
correction processing means for performing a gradation correction process on the input image using the determined normalization characteristic and the gradation correction characteristic;
gamma processing means for applying a predetermined gamma characteristic to the image that has undergone the gradation correction process;
With respect to a predetermined gamma characteristic configured to output a signal within a predetermined dynamic range, the predetermined gamma characteristic is output for a signal having a luminance higher than that of the reference signal. configured to output a signal with a wider dynamic range than
The first determination means determines the normalization characteristic based on the predetermined gamma characteristic corresponding to the dynamic range of the signal of the input image ;
The image processing apparatus, wherein the gamma processing means uses the same predetermined gamma characteristic even when the dynamic ranges of the input images are different. 2. The image processing apparatus according to claim 1 , wherein said second determining means determines tone correction characteristics capable of outputting a signal value exceeding a maximum signal value in a dynamic range of said input image. . 3. The image processing apparatus according to claim 1 , wherein said second determining means determines gradation correction characteristics for each of luminance and color difference of an image. The second determining means determines that the output of the gradation correction characteristic for luminance is greater than or equal to the output of the gradation correction characteristic for color difference, and the output of the gradation correction characteristic for luminance increases as the signal value of the input image increases. 4. The image processing apparatus according to claim 3 , wherein each gradation correction characteristic is determined so that a difference in output of the gradation correction characteristic with respect to color difference becomes large. 5. The second determination means determines the gradation correction characteristic based on a signal value to which the normalization characteristic is applied to the input image. The image processing device according to . 6. The correction processing unit according to claim 1, wherein the input image signal is multiplied by a gain signal generated based on a luminance signal of the input image signal and the gradation correction characteristic. 1. The image processing apparatus according to claim 1. 7. The image processing apparatus according to any one of claims 1 to 6 , wherein said predetermined gamma characteristic is configured to be capable of outputting each maximum output value determined for each dynamic range. a first determining step in which the first determining means determines a normalization characteristic for normalizing the signal of the input image;
a second determination step in which the second determining means determines a gradation correction characteristic for correcting the gradation of the image;
a correction processing step in which a correction processing means performs a gradation correction process on the input image using the determined normalization characteristic and the gradation correction characteristic;
a gamma processing step in which gamma processing means applies a predetermined gamma characteristic to the tone-corrected image;
With respect to a predetermined gamma characteristic configured to output a signal within a predetermined dynamic range, the predetermined gamma characteristic is output for a signal having a luminance higher than that of the reference signal. configured to output a signal with a wider dynamic range than
In the first determination step, the normalization characteristic is determined based on the predetermined gamma characteristic corresponding to the dynamic range of the signal of the input image ;
A control method for an image processing apparatus, wherein in the gamma processing step, the same predetermined gamma characteristic is used even when the dynamic ranges of the input images are different. A program for causing a computer to function as each means of the image processing apparatus according to any one of claims 1 to 7 .

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