JP2019139647A - Image processing device, imaging device, image processing method and program - Google Patents

Abstract

To provide a technique for reducing occurrence of hue deviation when a gain is applied to an image signal.SOLUTION: An image processing device comprises: determination means for determining whether or not saturation occurs when first signal processing which includes processing for applying a first gain is individually performed on each of N color signals (N is an integer of 2 or larger); first signal processing means for performing the first signal processing on each of the N color signals so as to apply a second gain smaller than the first gain instead of the first gain if it is determined that the saturation occurs; and second signal processing means for collectively converting the N color signals on which the first signal processing has been performed, using N-dimensional LUT configured so as to perform second signal processing which includes processing for compensating at least a part of difference between the first gain and the second gain, if it is determined that the saturation occurs.SELECTED DRAWING: Figure 4

Description

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

  In recent years, the luminance range that can be displayed on a display has been expanded, and thus Rec. ITU-R BT. HDR standards such as 2100 are defined, and devices such as displays and cameras corresponding to this standard are increasing. On the other hand, there are many viewing environments equipped with a display that supports only the conventional SDR standard. Under such circumstances, there are cases where a video producer has to create both a video corresponding to the HDR standard and a video corresponding to the SDR standard. In order to cope with this, there is a video conversion device having a function of converting an input HDR signal into an SDR signal and outputting the SDR signal.

  By the way, the impression of the SDR signal may be better when the SDR signal is generated by adjusting the brightness by applying gain at the time of conversion than when the HDR signal is subjected to a simple conversion to generate the SDR signal. It is known. Therefore, some of the video conversion devices described above have a function of adjusting the gain when converting from an HDR signal to an SDR signal.

  The method disclosed in Patent Document 1 converts a code value of a video signal of a conversion source into a luminance value using a characteristic of EOTF (Electro Optical Transfer Function) corresponding to the conversion source, and the luminance value is related in advance. Convert to another luminance value. Thereafter, this method converts the code value of the video signal of the conversion destination using the characteristics of the EOTF corresponding to the conversion destination.

Japanese Patent No. 5948618

  However, since the method described in Patent Document 1 does not consider the saturation of the signal value at the time of luminance value conversion, depending on the circuit configuration, one of the RGB signals is saturated and a hue shift occurs. there is a possibility. In particular, if conversion is performed in the direction of amplifying the luminance when converting the luminance value, a hue shift may occur significantly.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a technique for suppressing occurrence of a hue shift when applying a gain to an image signal.

  In order to solve the above-described problem, the present invention provides a case where the first signal processing including the processing of applying the first gain is performed individually for each of the N color signals (N is an integer of 2 or more). Determining means for determining whether or not saturation occurs; and when the saturation is determined to occur, the second gain smaller than the first gain is applied instead of the first gain. First signal processing means for individually performing one-signal processing on each of the N color signals, and when it is determined that the saturation occurs, at least a difference between the first gain and the second gain Second signal processing for collectively converting the N color signals subjected to the first signal processing by using an N-dimensional LUT configured to perform second signal processing including processing for partially compensating the signal. And an image processing characterized by comprising: To provide a location.

  According to the present invention, it is possible to suppress occurrence of a hue shift when applying a gain to an image signal.

  Other features and advantages of the present invention will become more apparent from the accompanying drawings and the following description of the preferred embodiments.

2 is a block diagram showing an internal configuration of the digital video camera 100. FIG. The figure explaining the internal structure of the image process part 115 and the image conversion part 124. FIG. The figure which shows the example of a three-dimensional lookup table (3DLUT). 10 is a flowchart of processing for setting conversion characteristics of the image conversion unit 124; The figure which shows the example of a gradation conversion characteristic.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. Throughout the attached drawings, elements given the same reference numerals represent the same or similar elements. The technical scope of the present invention is determined by the claims, and is not limited by the following individual embodiments. In addition, not all combinations of features described in the embodiments are essential to the present invention. Moreover, it is possible to appropriately combine the features described in different embodiments.

[First Embodiment]
As an example, a configuration in which an image processing apparatus is applied to a digital video camera will be described. However, the image processing apparatus of the present embodiment is not limited to a digital video camera, and can be applied to any apparatus.

  FIG. 1 is a block diagram showing an internal configuration of the digital video camera 100. In FIG. 1, a photographing lens 102 is a lens group including a zoom lens and a focus lens, and forms a subject image. An aperture 103 is an aperture used for light amount adjustment. An ND 104 is an ND filter used for dimming. The imaging unit 105 is an imaging device configured by a CCD, a CMOS device, or the like that converts an optical image into an electrical signal. The imaging unit 105 also has functions such as accumulation control using an electronic shutter, change of analog gain, and readout speed. The A / D converter 106 converts an analog signal into a digital signal. The A / D converter 106 is used to convert an analog signal output from the imaging unit 105 into a digital signal. The barrier 101 covers the photographing lens 102 of the digital video camera 100 to prevent the imaging system including the photographing lens 102, the diaphragm 103, the ND 104, and the imaging unit 105 from being soiled or damaged.

  The image processing unit 115 performs processing such as color conversion processing, gamma correction, and addition of digital gain on the data from the A / D converter 106 or the data from the memory control unit 116. The image processing unit 115 performs predetermined calculation processing using the captured image data, and transmits the calculation result to the system control unit 114. Based on the transmitted calculation result, the system control unit 114 performs exposure control, distance measurement control, white balance control, and the like. As a result, TTL (through-the-lens) AF (autofocus) processing, AE (automatic exposure) processing, AWB (auto white balance) processing, and the like are performed. The image conversion unit 124 performs signal processing on image data (image signal). Details of the image processing unit 115 and the image conversion unit 124 will be described later.

  Output data from the A / D converter 106 is written to the memory 119 via the image processing unit 115 and the memory control unit 116 or via the memory control unit 116. The memory 119 stores image data captured by the imaging unit 105 and converted into digital data by the A / D converter 106 and image data to be displayed on the display unit 118. The memory 119 has a storage capacity sufficient to store a moving image and sound for a predetermined time. The memory 119 also serves as an image display memory (video memory).

  The D / A converter 117 converts the image display data stored in the memory 119 into an analog signal and supplies the analog signal to the display unit 118. Thus, the display image data written in the memory 119 is displayed on the display unit 118 via the D / A converter 117. The display unit 118 performs display according to the analog signal from the D / A converter 117 on a display such as an LCD. The digital signal once A / D converted by the A / D converter 106 and stored in the memory 119 is D / A converted by the D / A converter 117 and sequentially transferred to the display unit 118 for display. Reference numeral 118 functions as an electronic viewfinder and can display a through image.

  The nonvolatile memory 113 is an electrically erasable / recordable memory, and for example, an EEPROM is used. The nonvolatile memory 113 stores constants, programs, and the like for operating the system control unit 114. Here, the program is a program for executing various flowcharts described later in the embodiment of the present invention.

  The system control unit 114 controls the entire digital video camera 100. The system control unit 114 implements each process of the present embodiment, which will be described later, by executing the program recorded in the nonvolatile memory 113 described above. A RAM is used as the system memory 121, and constants and variables for operation of the system control unit 114, a program read from the nonvolatile memory 113, and the like are expanded. The system control unit 114 also performs display control by controlling the memory 119, the D / A converter 117, the display unit 118, and the like.

  The system timer 120 is a time measuring unit that measures the time used for various controls and the time of a built-in clock. The mode switch 109, the recording switch 108, and the operation unit 107 are operation members for inputting various operation instructions to the system control unit 114.

  The mode switch 109 switches the operation mode of the system control unit 114 to any one of a moving image recording mode, a still image recording mode, a reproduction mode, and the like. As modes included in the moving image recording mode and the still image recording mode, there are an auto shooting mode, an auto scene discrimination mode, a manual mode, various scene modes for shooting settings for each shooting scene, a program AE mode, a custom mode, and the like. The mode changeover switch 109 can directly switch to any one of these modes included in the moving image shooting mode. Alternatively, after the mode switching switch 109 temporarily switches to the moving image shooting mode, the mode may be switched to any of these modes included in the moving image shooting mode using another operation member. The recording switch 108 switches between a shooting standby state and a shooting state. The system control unit 114 starts a series of operations from reading a signal from the imaging unit 105 to writing moving image data to the recording medium 123 by the recording switch 108.

  Each operation member of the operation unit 107 is appropriately assigned a function for each scene by selecting and operating various function icons displayed on the display unit 118, and functions as various function buttons. Examples of the function buttons include an end button, a return button, an image advance button, a jump button, a narrowing button, and an attribute change button. For example, when a menu button is pressed, various setting menu screens are displayed on the display unit 118. The user can make various settings intuitively using the menu screen displayed on the display unit 118, the four-way key in the four directions of up / down / left / right, and the SET button.

  The power switch 110 is a switch for turning on / off the power of the digital video camera 100. The power control unit 111 includes a battery detection circuit, a DC-DC converter, a switch circuit that switches a block to be energized, and the like, and detects whether or not a battery is installed, the type of battery, and the remaining battery level. The power supply control unit 111 controls the DC-DC converter based on the detection result and an instruction from the system control unit 114, and supplies a necessary voltage to each unit including the recording medium 123 for a necessary period. The power supply unit 112 includes 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 122 is an interface with a recording medium 123 such as a memory card or a hard disk, or an external output device. FIG. 1 shows a state when connected to the recording medium 123. The recording medium 123 is a recording medium such as a memory card for recording a captured image, and includes a semiconductor memory, a magnetic disk, or the like.

  Next, the internal configuration of the image processing unit 115 and the image conversion unit 124 will be described with reference to FIG. The image processing unit 115 and the image conversion unit 124 can acquire any data inside the digital video camera 100 through the system control unit 114.

  The gain adjustment unit 201 performs gain adjustment and white balance correction on the signal output from the A / D converter 106 by multiplying the RGB signals individually by gain. The matrix calculation unit 202 corrects the color tone by multiplying the RGB signal output from the gain adjustment unit 201 by a matrix. Thereby, a difference in spectral sensitivity or the like of the imaging unit 105 is corrected, and color reproduction suitable for the digital video camera 100 is realized. The gradation conversion unit 203 performs gradation conversion by applying common gradation conversion characteristics to the RGB signals output from the matrix calculation unit 202. The output from the gradation conversion unit 203 is output to the recording medium 123 through the image conversion unit 124 and the I / F 122.

  The first signal processing unit 204 individually performs gradation conversion on the RGB signals with respect to the signal input from the image processing unit 115. The first signal processing unit 204 performs gradation conversion by calculation or referring to a one-dimensional lookup table (1DLUT). In the present embodiment, the first signal processing unit 204 performs gradation conversion with reference to the 1DLUT set by the system control unit 114. The first signal processing unit 204 can perform gain adjustment when generating signals having different gradation characteristics. In addition, the first signal processing unit 204 restores the gradation characteristics after the conversion by the gradation conversion unit 203 and then adjusts the gain and applies the same gradation characteristics again to maintain the gradation characteristics. Gain adjustment can be performed without any change.

  The second signal processing unit 205 performs color gamut conversion. For example, the second signal processing unit 205 performs color gamut conversion on the entire RGB signal with reference to a three-dimensional lookup table (3DLUT) as shown in FIG. At this time, if the same RGB value as the input RGB value exists in the conversion source table, the second signal processing unit 205 converts the input RGB value into a corresponding conversion destination RGB value. When the input RGB value does not exist in the conversion source table, the second signal processing unit 205 extracts a plurality of points (entries) in the vicinity of the input RGB value from the conversion source table, and performs conversion by interpolation. The RGB value is obtained and converted. In the present embodiment, the second signal processing unit 205 performs the color gamut conversion with reference to the 3DLUT, but the color gamut conversion may be performed by calculation or the like.

In the following description, it is assumed that the image processing unit 115 generates an HDR signal, and the image conversion unit 124 converts the HDR signal into an SDR signal. In the following description, an EOTF that relates an HDR signal value and a luminance value is called EOTF _HDR , and an EOTF that associates an SDR signal value and a luminance value is called EOTF _SDR . However, the conversion processing in this embodiment is not limited to conversion from an HDR signal to an SDR signal, and this embodiment can be applied to any type of signal processing that involves gain adjustment.

  In the following description, it is assumed that the HDR signal to be converted includes an RGB signal as a color signal. However, the type of color signal is not limited to RGB signals, and the number of color signals is not limited to three. The present embodiment can be applied to a case where gain adjustment is performed for any type of N color signals (N is an integer of 2 or more). In this case, the 3DLUT in the following description may be read as an N-dimensional LUT.

  FIG. 4 is a flowchart of processing for setting the conversion characteristics of the image conversion unit 124. Unless otherwise specified, the processing of each step in this flowchart is realized by the system control unit 114 expanding and executing a program stored in the nonvolatile memory 113 in the system memory 121.

  Note that the brightness of the HDR signal is controlled to match the user's intention by setting the aperture 103, the ND 104, the imaging unit 105, the gain adjustment unit 201, and the like. The second signal processing unit 205 is configured to perform color correction processing including color gamut conversion. In the following, for the sake of simplicity, it is assumed that color gamut conversion is unnecessary. To do.

  In step S401, the system control unit 114 sets the gradation characteristics (gamma) and color gamut of the SDR signal. Here, the user may manually determine the set value, or the system control unit 114 may automatically determine the set value. In the following description, it is assumed that the set color gamut of the SDR signal matches the color gamut of the HDR signal, and the color gamut conversion in the second signal processing unit 205 is unnecessary.

  In S402, the system control unit 114 sets a gain difference between the HDR signal and the SDR signal. The gain difference may be in any unit as long as it can be converted into a magnification (gain applied to the HDR signal). Also, the user may manually determine the magnification, or the system control unit 114 may automatically determine the magnification. For example, the system control unit 114 may control the magnification according to the subject included in the video signal. In the following description, the magnification set in S402 is assumed to be k.

In S403, the system control unit 114 performs a conversion process from the HDR signal to the SDR signal (signal processing including the application of the magnification k, which is individually performed on each of the RGB signals by the first signal processing unit 204). In this case, it is determined whether saturation occurs. The saturation determination can be performed based on the setting of the HDR signal and the setting of the SDR signal. In many image pickup apparatuses, a value indicating how much reflectivity is included in a video signal is referred to as a dynamic range on the basis of a gray card having a reflectivity of 18%, and the dynamic range is determined for each gamma setting. At this time, if the conversion source dynamic range is d _src and the conversion destination dynamic range is d _dst , it can be considered that saturation occurs when k × d _src > d _dst . Therefore, the system control unit 114 determines whether saturation occurs based on whether k × d _src > d _dst . If saturation occurs, the process proceeds to S404, and if saturation does not occur, the process proceeds to S406.

  In step S <b> 404, the system control unit 114 calculates a gradation conversion characteristic that does not cause saturation as the gradation conversion characteristic to be set in the first signal processing unit 204. First, the system control unit 114 simply obtains gradation conversion characteristics for performing gradation conversion and gain adjustment based on the settings (SDR signal gradation characteristics and magnification k) in S401 and S402 without considering saturation. When the HDR signal value is x, the gradation conversion characteristic f (x) is expressed by the following formula 1.

FIG. 5 shows a gradation conversion characteristic 501 as an example of f (x). As shown in FIG. 5, the gradation conversion characteristic 501 has a saturated region. The system control unit 114 calculates a gain s for removing saturation in Equation 1. Since the output value corresponding to kd _src is EOTF _HDR ⁻¹ (kd _src ) and the output value corresponding to d _dst is EOTF _SDR ⁻¹ (d _dst ), the gain s is expressed by Equation 2.

  Here, the number of bits of the HDR signal and the SDR signal is assumed to be the same. However, when the number of bits is different, Equation 2 may be changed to compensate for the difference in the number of bits.

  Considering the gain s, the gradation conversion characteristic g (x) set in the first signal processing unit 204 is expressed by the following Equation 3.

  FIG. 5 shows a gradation conversion characteristic 502 as an example of g (x). Unlike the gradation conversion characteristic 501, the gradation conversion characteristic 502 does not have a saturated region. The system control unit 114 may calculate the gradation conversion characteristics when the image conversion unit 124 performs the conversion process, or may calculate the gradation conversion characteristics in advance and store them in the system memory 121. Good. In the latter case, the system control unit 114 selects a gradation conversion characteristic corresponding to the setting contents of S401 and S402 from various gradation conversion characteristics held in the system memory 121.

  In step S <b> 405, the system control unit 114 calculates a 3DLUT to be set in the second signal processing unit 205. Since the gradation conversion characteristic obtained in S404 includes a gain s for preventing saturation, the system control unit 114 includes a gain for compensating for the gain s in the 3DLUT characteristic. That is, the system control unit 114 includes the gain 1 / s obtained by inverting the gain s included in the gradation conversion characteristic obtained in S404 in the 3DLUT characteristic. As a result, the signal value that has been suppressed so that saturation does not occur in the gradation conversion characteristics set in S404 is restored, and a signal value with appropriate brightness is obtained. When the HDR signal value is x, and h (x) is the signal value after processing in the first signal processing unit 204 and the second signal processing unit 205, h (x) is expressed by the following Equation 4. The

  Since h (x) becomes equal to f (x) as shown in Equation 4, it can be understood that conversion to the intended SDR signal is achieved. Therefore, by multiplying the output value of the 3DLUT for processing such as color gamut conversion without gain adjustment (the RGB value of the conversion destination) by 1 / s, the first signal processing unit 204 has gradation conversion characteristics. The included gain s can be compensated. However, if the processing is simply performed according to Equation 4, saturation is performed in the same manner as in the case where gradation conversion characteristics that do not consider saturation (for example, gradation conversion characteristics 501 shown in FIG. 5) are set in the first signal processing unit 204. Hue shift due to. Therefore, the system control unit 114 includes processing for suppressing hue shift due to saturation in processing for applying the gain 1 / s to the 3DLUT. Examples of methods for suppressing the hue shift include a method of mapping to a range that can be expressed so that the color difference is minimized, and a method of mapping to a range that can be expressed to minimize the color difference while maintaining the hue. is there. These methods are one kind of methods generally known as gamut mapping, and any of them may be used.

  Note that the system control unit 114 does not need to calculate a 3DLUT that completely compensates the gain s, but may calculate a 3DLUT that compensates at least a part of the gain s.

  In step S406, the system control unit 114 calculates a gradation conversion characteristic to be set in the first signal processing unit 204 based on the settings in S401 and S402 (the gradation characteristic of the SDR signal and the magnification k). The calculation of the gradation conversion characteristics in S406 can be performed according to Equation 1 described in S404. However, unlike the case of S404, a saturation region does not occur in the gradation conversion characteristic f (x). As in S <b> 404, the system control unit 114 may calculate gradation conversion characteristics when the image conversion unit 124 performs conversion processing, or may calculate gradation conversion characteristics in advance and store them in the system memory 121. You may keep it.

  In step S407, the system control unit 114 calculates a 3DLUT to be set in the second signal processing unit 205 based on the color gamut set in step S401. In this embodiment, since it is assumed that there is no need to perform color gamut conversion, the system control unit 114 calculates a 3DLUT that performs through output. Alternatively, the system control unit 114 may store a 3DLUT that performs through output in the system memory 121 in advance, and acquire the 3DLUT from the system memory 121 when executing the process of S407.

  In step S <b> 408, the system control unit 114 sets the 1DLUT corresponding to the gradation conversion characteristic calculated in step S <b> 404 or S <b> 406 in the first signal processing unit 204. If it is determined in S403 that saturation occurs, 1DLUT corresponding to the gradation conversion characteristic g (x) is set in the first signal processing unit 204 instead of the gradation conversion characteristic f (x) in S408. As a result, the first signal processing unit 204 performs a process of converting a gradation characteristic and a process of applying a magnification (gain) smaller than the magnification k instead of the magnification k.

  Note that the system control unit 114 may set the gradation conversion characteristics in the form of a calculation formula instead of setting the gradation conversion characteristics in the form of 1DLUT. In this case, the first signal processing unit 204 converts the input signal into the output signal by performing an operation based on the set calculation formula.

  In step S409, the system control unit 114 sets the 3DLUT calculated in step S405 or S407 in the second signal processing unit 205. As described above, the 3DLUT characteristic calculated in S405 includes a gain 1 / s. Therefore, if it is determined in S403 that saturation occurs, in S409, the 3DLUT configured to compensate for the difference between the magnification of the gradation conversion characteristic f (x) and the magnification of the gradation conversion characteristic g (x) is the first. It is set in the two-signal processing unit 205.

  As a result of the above processing, the settings of the first signal processing unit 204 and the second signal processing unit 205 are completed. Thereafter, when the HDR signal to be converted is input to the image conversion unit 124, the first signal processing unit 204 individually performs signal processing on each of the RGB signals using the 1DLUT set in S408. Do. The second signal processing unit 205 performs signal processing on the RGB signals collectively using the 3DLUT set in S409.

  As described above, according to the first embodiment, the digital video camera 100 determines whether saturation occurs when the gradation characteristics of the HDR signal are converted with the application of the magnification k. When saturation occurs, the digital video camera 100 applies a magnification (gain) smaller than the magnification k instead of the magnification k when performing the process of individually converting the gradation characteristics for each of the RGB signals. . Thereafter, the digital video camera 100 collectively converts the RGB signals using a 3DLUT configured to compensate for the difference between the applied magnification and the magnification k. This makes it possible to suppress the occurrence of hue shift when applying a gain to the image signal.

  Here, the reason why it becomes possible to suppress the occurrence of hue shift according to the present embodiment will be described in detail. The signal processing in the first signal processing unit 204 is performed individually for each color signal. For this reason, even if gain is applied in this signal processing, a hue shift does not occur or a relatively small hue shift occurs unless saturation occurs. On the other hand, the signal processing in the second signal processing unit 205 is performed collectively for all color signals by using a 3DLUT. For this reason, if gain is applied in this signal processing, even if saturation does not occur, a hue shift associated with the interpolation processing may occur. However, in the case of signal processing using a 3DLUT, a hue shift caused by saturation can be reduced to some extent by a known technique. In the present embodiment, when saturation occurs, the applied gain is divided into the first signal processing unit 204 and the second signal processing unit 205. Therefore, it is possible to suppress the hue shift caused by saturation in the first signal processing unit 204 and to suppress the hue shift caused by the interpolation processing in the second signal processing unit 205. As a result, it is possible to suppress the occurrence of hue shift as a whole.

  In the above description, in S404, the system control unit 114 calculates the gradation conversion characteristic g (x) that does not cause saturation. However, it is not necessary to completely prevent the occurrence of saturation. Even if the saturation is only reduced, the effect of suppressing the occurrence of hue shift can be obtained to some extent. In this case, the system control unit 114 does not directly multiply the gradation conversion characteristic f (x) by the gain s in Expression 2, but uses the gain s ′, which is less effective from the gain s, as the gradation conversion characteristic f (x). You can multiply. Any method may be used to obtain the gain s'. For example, the effect may be weakened in the case of a subject whose hue shift due to saturation is difficult to understand. Further, according to the gradation conversion characteristic g (x), the maximum gain that does not cause saturation is applied in the first signal processing unit 204, but the gradation conversion characteristic is applied so that a smaller gain is applied. May be. Therefore, in general terms, in S404, the system control unit 114 may calculate the gradation conversion characteristics to which a gain smaller than the magnification k is applied.

  In the above description, the tone characteristics of the signal generated by the image processing unit 115 and the tone characteristics of the signal generated by the image conversion unit 124 are different. However, even if these tone characteristics are the same, Good. In this case, the gradation conversion characteristic set in the first signal processing unit 204 cancels the gradation characteristic applied by the gradation conversion unit 203 once, performs gain adjustment, and then applies the same gradation characteristic again. It becomes the characteristic to do.

[Other Embodiments]
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  DESCRIPTION OF SYMBOLS 100 ... Digital video camera, 105 ... Imaging part, 113 ... Nonvolatile memory, 114 ... System control part, 115 ... Image processing part, 121 ... System memory, 124 ... Image conversion part, 204 ... 1st signal processing part, 205 ... Second signal processor

Claims (10)

Determination means for determining whether saturation occurs when the first signal processing including processing for applying the first gain is performed individually for each of the N color signals (N is an integer of 2 or more). When,
When it is determined that the saturation occurs, the first signal processing is performed on each of the N color signals so that a second gain smaller than the first gain is applied instead of the first gain. First signal processing means to be performed individually,
Using an N-dimensional LUT configured to perform second signal processing including processing for compensating at least a part of the difference between the first gain and the second gain when it is determined that the saturation occurs. Second signal processing means for collectively converting the N color signals subjected to the first signal processing;
An image processing apparatus comprising: The image processing apparatus according to claim 1, wherein the second gain is a gain that does not cause the saturation when applied in place of the first gain in the first signal processing. The image processing apparatus according to claim 2, wherein the second gain is a maximum gain that does not cause the saturation when applied instead of the first gain in the first signal processing. The image processing apparatus according to any one of claims 1 to 3, wherein the first signal processing includes processing for converting gradation characteristics of the N color signals. 5. The image processing apparatus according to claim 1, wherein the second signal processing includes processing for converting a color gamut of the N color signals. If it is determined that the saturation does not occur, the first signal processing means individually performs the first signal processing including application of the first gain for each of the N color signals. The image processing apparatus according to any one of claims 1 to 5. When it is determined that the saturation does not occur, the second signal processing means uses the N-dimensional LUT configured to perform the second signal processing except for the compensation processing, and uses the first signal processing. The image processing apparatus according to claim 6, wherein the N color signals subjected to the processing are collectively converted. An image processing apparatus according to any one of claims 1 to 7,
Imaging means for generating the N color signals;
An imaging apparatus comprising: An image processing method executed by an image processing apparatus,
A determination step for determining whether saturation occurs when the first signal processing including the processing for applying the first gain is performed individually for each of the N color signals (N is an integer of 2 or more). When,
When it is determined that the saturation occurs, the first signal processing is performed on each of the N color signals so that a second gain smaller than the first gain is applied instead of the first gain. A first signal processing step performed individually,
Using an N-dimensional LUT configured to perform second signal processing including processing for compensating at least a part of the difference between the first gain and the second gain when it is determined that the saturation occurs. A second signal processing step for collectively converting the N color signals subjected to the first signal processing;
An image processing method comprising:   The program for functioning a computer as each means of the image processing apparatus of any one of Claims 1 thru | or 7.

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