JP6624895B2 - Image processing apparatus, imaging apparatus, control method, and program - Google Patents

Description

  The present invention relates to an image processing apparatus, an imaging apparatus, a control method, and a program, and more particularly to an image processing technique for correcting color blur caused by the influence of chromatic aberration.

  In recent years, with an increase in the number of pixels of an imaging element (increase in spatial resolution of imaging) and a reduction in the size of an imaging optical system, color blur due to chromatic aberration may occur in an image obtained by imaging. This is due to the fact that the imaging position on the image sensor changes for each wavelength of light, and the occurrence of color bleeding is easily perceived particularly in a region with high luminance. Patent Literature 1 discloses an image processing apparatus that focuses on the perceived ease of color bleeding for each luminance range, and controls the applicability of the color bleed suppression processing for reducing saturation according to the luminance range. ing.

  By the way, gamma correction for converting an input signal into an output signal based on a predetermined gamma characteristic is applied to a captured image signal in consideration of, for example, color reproducibility when displayed on a display device. . As disclosed in Patent Document 1, the conventional general gamma correction uses a gamma characteristic as shown by a solid line 401 in FIG. 4, in which the level assigned to the output signal is compressed as the signal level increases. ing. That is, the so-called knee processing for compressing the input signal level of the high luminance portion is applied in the gamma correction processing.

  On the other hand, in order to express the texture and physical characteristics of the subject, such as the brightness of metal, the transparency of water, the three-dimensional appearance of blue sky and clouds, and the skin tone, the degree of compression related to the high-brightness part is reduced or the gamma is not compressed. It is necessary to make corrections.

  For example, in a point light source 901 in a night scene scene as shown in FIG. 9, it is difficult to perform stepwise gradation expression related to light diffusion in an area around the light source due to knee processing in the gamma correction according to the conventional method. It may appear in the output signal as if it were larger than the actual shape. On the other hand, in the gamma correction in which the degree of compression of the high-brightness part is reduced or not compressed, the gradation expression is appropriately performed between the point light source and the surrounding area, so that the point light source is output in a shape close to the actual one. Appear on signal.

  Specifically, for example, in an image signal obtained by imaging a night scene as shown in FIG. 9, a luminance level corresponding to a pixel position in a peripheral area of a point light source image appears as a broken line 1001 in FIG. Consider the case as an example. A dashed line 1001 indicates that the brightness in the range of A2 to A3 corresponding to the point light source itself is high, and in the areas 1004 of A1 to A2 and A3 to A4 around the light source, A1 and below, and A4 and above, the light is diffused as the distance from the light source increases. This shows how the luminance is reduced. At this time, in the gamma correction of the conventional method, as indicated by a solid line 1003, the difference between the luminance of the area 1004 around the light source and the luminance of A2 to A3 corresponding to the light source is hardly reflected in the luminance expression after the gamma correction. As a result, the point light source appears in the output signal as a shape in the range of A1 to A4. On the other hand, in the gamma correction in which the degree of compression of the high-brightness part is reduced or not compressed, a stepwise change in luminance is expressed in the area 1004 around the light source so as to indicate diffusion of light, as indicated by a dashed line 1002. Is done.

JP 2011-010268 A

  However, when reducing the degree of compression of the high-luminance part in the gamma correction, color blur may be more easily perceived. Taking the point light source of the night scene scene as shown in FIG. 9 as an example, in the conventional method, the light source itself is expressed as being enlarged in the area 1004 around the light source, and since there is no luminance difference, color blur is perceived. It is hard to be done. That is, the gradation expression having a large contrast difference at or near the edge of the light source where the color blur is conspicuous is compressed by the knee processing in the gamma correction, so that the color blur is less conspicuous. On the other hand, when the degree of compression of the high-brightness part is reduced or not compressed, the color blur caused by the fact that the imaging position of the optical image of the point light source differs for each wavelength is combined with the brightness correction at the time of display. May be more perceptible than conventional approaches. That is, since the contrast difference is expressed even after the gamma correction, and the display device raises the peak luminance in the range of A2 to A3 so as to be equivalent to the peak luminance of the conventional method, the color blur is conspicuous in the area 1004 around the light source. It will be easier.

  The present invention has been made in view of the above-described problems, and has been made in consideration of the above-described problems, and has been made in view of the above circumstances, and has been made in consideration of the above-described problem, and has been made in view of the above. The purpose is to provide the program.

In order to achieve the above object, an image processing apparatus according to the present invention includes an acquiring unit for acquiring a first image signal related to an image to be corrected, and a color blur for the first image signal acquired by the acquiring unit. Correction means for performing a correction for suppressing the noise and generating a second image signal, control means for controlling a correction amount in the first correction means, and one of a plurality of gamma characteristics showing different characteristics. And a second correction unit that performs gamma correction on the second image signal to generate a third image signal, wherein the control unit includes a gamma characteristic used for the gamma correction , and a first image signal. Is characterized in that the correction amount is made different according to the contrast value derived from .

  According to the present invention having such a configuration, it is possible to output an image signal in which color bleeding is suitably suppressed in accordance with the gamma characteristic employed in gamma correction.

FIG. 1 is a diagram illustrating an appearance of a digital video camera 100 according to an embodiment of the present invention. FIG. 1 is a block diagram showing a functional configuration of a digital video camera 100 according to an embodiment of the present invention. FIG. 2 is a block diagram showing a detailed configuration of the image processing unit 24 according to the embodiment of the present invention. FIG. 4 is a diagram for explaining gamma characteristics used in a normal shooting mode according to the embodiment of the present invention. FIG. 4 is a diagram for explaining a gamma characteristic used in a high brightness priority mode according to the embodiment of the present invention. 7 is a flowchart illustrating a correction amount determination process according to the embodiment of the present invention. FIG. 7 is a diagram illustrating a suppression coefficient according to correction of color blur for each mode according to the embodiment of the present invention. FIG. 4 is a diagram illustrating a correction amount of color blur for each mode according to the embodiment of the present invention. Diagram for explaining how easily color blur is perceived Diagram for explaining signal level conversion characteristics in gamma correction processing for each mode

[Embodiment]
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. Note that one embodiment described below is an example of an image processing apparatus that can generate an output signal obtained by performing color blur suppression and gamma correction on an image signal obtained by imaging (digital An example in which the present invention is applied to a video camera will be described. However, the present invention is applicable to any device that can generate an output signal obtained by performing color blur suppression and gamma correction on an input image signal.

Further, in the present embodiment, a shooting mode for capturing an image signal with an extended dynamic range will be described as an example of a mode in which a difference in a correction result of color bleeding due to a difference in a gamma characteristic, which is a problem, can become apparent. More particularly, it has been extended than the dynamic range as the target gamma characteristic which has been standardized by ITU-R BT.709 or the like (the range indicated by x ₁ below 4 and FIG. 5 (a)) A mode for imaging a range will be described as an example.

Gamma characteristic indicated by the solid line 401 in FIG. 4, for example, those described above normalized gamma characteristic (dashed line 402) defined based on the dynamic range imaging signal to large x ₂ than x ₁ ( Input signal). As shown, a gamma characteristic (first gamma characteristic) indicated by a solid line 401 indicates a characteristic of compressing (knee processing) the contrast in a region of medium luminance to high luminance. In the present embodiment, it can capture an image signal of the dynamic range of up to x _2, and the shooting mode for outputting the applied signal the gamma correction using the first gamma characteristic with respect to the image signal "normal mode" Referred to as.

On the other hand, the gamma characteristic indicated by the solid line 501 in FIG. 5 (a), similarly to the normal mode dynamic range up to x ₂ is expressed in the imaging signal. The gamma characteristic (second gamma characteristic) indicated by the solid line 501 is the level of the luminance signal assigned after the conversion by the gamma correction with respect to the predetermined dynamic range, as compared with the standardized gamma characteristic (dashed-dotted line 502). The range has been extended. The second gamma characteristic has a characteristic that compression is not performed in a region from middle luminance to high luminance. In the present embodiment, it can capture an image signal of the dynamic range of up to x _2, and the shooting mode for outputting the applied signal the gamma correction using the second gamma characteristic with respect to the image signal "high luminance priority Mode ". Although the overall brightness of the image signal output by the method may be lower than that of the image signal output by the conventional method, the brightness may be ensured by increasing the peak brightness value of the display device. In addition, natural gradation, color reproducibility, and sharpness can be expressed from a low luminance portion to a high luminance portion. In this case, it is possible to present an image with a more natural gradation expression while ensuring the resolution in the high-luminance portion that has been compressed by the conventional method.

  In the digital video camera according to the present embodiment, when an output signal that has been captured in the “high brightness priority mode” and has been subjected to gamma correction is displayed on a display unit, which will be described later, a gamma characteristic for further converting the output signal into a display image signal ( The display is controlled so as to perform adjustment based on the display gamma characteristic). The adjustment based on the display gamma characteristic maintains the brightness (appearance) of the subject in a predetermined dynamic range between the normal mode and the high-brightness priority mode for the output signal to which the gamma correction related to the imaging signal is applied. Done for. As shown in FIG. 5B, the second gamma characteristic according to the high-brightness priority mode of the present embodiment is such that, when such a display gamma characteristic is taken into consideration, a difference between the imaging signal and the display image signal is obtained. In the following description, the setting is made so that a linear conversion characteristic is realized. That is, a linear gamma characteristic is realized between the input signal to be corrected and the display image signal to be displayed in the total operation of imaging, image conversion, and display in the digital video camera. However, in the embodiment of the present invention, the second gamma characteristic for adjusting the correction amount relating to color blur is not limited to this. The second gamma characteristic is such that the level range of the output signal assigned to the image signal to be corrected by the gamma correction after the gamma correction for the predetermined input signal level range is larger than the case where the first gamma characteristic is used. Any material having characteristics may be used. In the embodiment of the present invention, the gamma characteristics provided for gamma correction are not limited to the two types of the first gamma characteristic and the second gamma characteristic, and a plurality of different types of gamma characteristics are provided so as to be applicable. The first and second gamma characteristics may be just examples of these.

<< Configuration of Digital Video Camera 100 >>
FIG. 1 is a diagram showing an appearance of a digital video camera 100 according to an embodiment of the present invention.

  In FIG. 1, a display unit 28 is a display device provided to display image signals and various information shot and recorded in a plurality of shooting modes including the above-described normal mode and high-brightness mode. Further, the digital video camera 100 is provided with a recording switch 61 for giving a shooting instruction, a mode switch 60 for switching various modes, and a power switch 72 for switching power on / off. In addition, an operation member that receives various operations from the user, such as various buttons and a cross key, is provided as the operation unit 70.

  The connector 112 is a connector for a connection cable for connecting the digital video camera 100 to an external device. The recording medium 200 is a detachably connected recording medium such as a memory card or a hard disk. The recording medium 200 is connected to the digital video camera 100 by being accommodated in the recording medium slot 201, and can transmit and receive information.

  Next, the functional configuration of the digital video camera 100 will be described with reference to the block diagram of FIG. As shown in the figure, in the digital video camera 100 of the present embodiment, light from a subject is guided to the imaging unit 22 through the barrier 102, the imaging lens 103, the aperture 101, and the ND 104 in order to obtain an imaging signal. The photographing lens 103 is a lens group including, for example, a zoom lens and a focus lens, and forms a subject image. The diaphragm 101 is a diaphragm used for adjusting the amount of light. The ND 104 is a filter used for dimming. The imaging unit 22 is an imaging device including a CCD, a CMOS device, or the like that converts the formed optical image into an electric signal (analog image signal). The imaging unit 22 also has functions such as control of the amount / time of charge accumulation by the electronic shutter, control of application of analog gain, and change of readout speed. The A / D converter 23 converts an analog signal output from the imaging unit 22 into a digital signal. Note that the barrier 102 covers the imaging optical system including the imaging lens 103, thereby preventing the imaging system members including the imaging lens 103, the aperture 101, and the imaging unit 22 from being stained or damaged.

  The image processing unit 24 performs a color conversion process and a gamma correction process on the digital image signal (hereinafter simply referred to as an image signal or image data) output from the A / D converter 23 or the image data acquired by the memory control unit 15. And processing such as addition of digital gain. Further, the image processing unit 24 performs a predetermined calculation process related to exposure control or the like using the captured image signal, and transmits the calculation result to the system control unit 50. The system control unit 50 performs exposure control, distance measurement control, white balance control, and the like based on the calculation result. By operating in this manner, TTL (through the lens) type AF (auto focus) processing, AE (auto exposure) processing, AWB (auto white balance) processing, and the like are realized.

<Detailed Configuration of Image Processing Unit 24>
Here, the configuration of the image processing unit 24 will be described in more detail with reference to the block diagram of FIG. Note that each block included in the image processing unit 24 receives various data related to the operation of each block in the digital video camera 100 including various exposure parameters such as an aperture amount, ND information, and a shutter speed through the system control unit 50. Is configured to be obtainable.

  The gain control unit 301 and the white balance control unit 302 mainly adjust the signal level of the input image signal. The gain control unit 301 applies a predetermined digital gain to an input image signal, and amplifies a signal level. The white balance control unit 302 controls R gain and B gain, which are white balance gains, and corrects the color of the entire image signal.

  The luminance signal conversion unit 306 generates a luminance signal (Y signal) from the image signal subjected to various gain adjustments by the gain control unit 301 and the white balance control unit 302. More specifically, the luminance signal conversion unit 306 generates a luminance signal by extracting a G component signal from the image signal and applying an adaptive interpolation process to the G component signal. The luminance signal conversion unit 306 transmits the generated luminance signal to the gamma correction unit 304 and the brightness information generation unit 307.

  The brightness information generation unit 307 calculates an average value for each partial region in the image related to the image signal input to the image processing unit 24, and calculates the maximum value and the minimum value of the plurality of average values (by the luminance signal conversion unit 306). (A maximum value and a minimum value of a plurality of average values of the generated luminance signal). The partial region may be, for example, a region defined by a mesh frame determined to divide the entire image related to the image signal into rectangular regions having the same area. In the image processing unit 24 of the present embodiment, the maximum value and the minimum value of a plurality of average values of the luminance values obtained from each of the partial areas are used as the brightness information used for determining the correction amount of the color blur described later. Shall be. The brightness information generation unit 307 outputs the generated brightness information to the color blur correction amount determination unit 308.

  The color blur correction amount determination unit 308 determines a correction amount (amount of suppression) in the color blur correction process performed by the color blur correction unit 303 in the color blur generated in the image signal. Specifically, the color blur correction amount determination unit 308 determines a color based on a contrast value calculated from brightness information in each of the input partial areas and a gamma characteristic used for gamma correction in a gamma correction unit 304 described later. The amount of blur correction is determined. The information of the gamma characteristic used for the gamma correction in the gamma correction unit 304 may be, for example, information that can be acquired from the system control unit 50 or the gamma correction unit 304. Determined according to the mode. That is, information indicating the first gamma characteristic is obtained if the image signal is captured in the normal mode, and information indicating the second gamma characteristic is obtained if the image signal is captured in the high brightness priority mode. Is done.

  The color blur correction unit 303 performs a correction process for reducing the generated color blur on the image signal on which various gain adjustments have been performed by the gain control unit 301 and the white balance control unit 302. More specifically, the color bleeding correction unit 303 first sets the contrast value between adjacent pixels (or surrounding pixels) of each of the R component and B component signals from a partial region of the image related to the input image signal to a predetermined value. Pixels to be corrected for color blur described above are extracted. Then, the color bleeding correction unit 303 calculates the pixel of each extracted component based on the correction amount determined by the color bleeding correction amount determination unit 308 according to the contrast (R / G, B / G) of each color component. A suppression process for reducing color blur is performed. The process of reducing color bleeding may be a process of reducing the saturation of the pixel to be corrected, and the amount of correction determines the degree of reduction (saturation decreases as the amount of correction increases).

  Conventionally, the correction amount of color blur is fixedly determined based on a predetermined suppression coefficient, so that the above-described suppression of color blur may not be performed appropriately. However, in the image processing unit 24 of the present embodiment, the color blur correction amount determination unit 308 controls the correction amount based on the contrast of the image to be corrected and the gamma characteristics of the gamma correction to be performed. That is, since the image processing unit 24 of the present embodiment has the configuration of the brightness information generation unit 307 and the color blur correction amount determination unit 308, the image processing unit 24 considers the gamma characteristics defined for the imaging mode, and is suitable for the characteristics. The color blur can be dynamically corrected by the correction amount.

  The gamma correction unit 304 sets the shooting mode set when the corresponding image signal is captured with respect to the image signal subjected to the suppression processing in the color blur correction unit 303 and the luminance signal generated by the luminance signal conversion unit 306. Gamma correction is performed according to. That is, the gamma correction performed by the gamma correction unit 304 converts image signals (luminance signals, R component, G component, and B component image signals) based on gamma characteristics, which are input / output characteristics determined for the shooting mode. Do. In this embodiment, when an image signal to be corrected is captured, an image signal obtained by performing gamma correction according to a gamma characteristic predetermined for a shooting mode at the time of shooting is recorded. However, the embodiment of the present invention is not limited to this, and may be configured so that a gamma characteristic applied to an input image signal can be selected regardless of a shooting mode.

  The luminance / color difference signal generation unit 305 generates an output signal based on the image signal on which the gamma correction has been performed by the gamma correction unit 304. The output signal may be, for example, a luminance / chrominance signal related to the YRYBY space. The luminance / chrominance signal generation unit 305 outputs a RY (R component image signal−luminance signal) signal based on the luminance signal (Y signal) after the gamma correction. A BY (B component image signal-luminance signal) signal is generated.

  As described above, the output signal generated by the image processing unit 24 is directly written to the memory 32 via the memory control unit 15. The memory 32 is a storage area for temporarily storing a digital image signal captured by the imaging unit 22 and converted by the A / D converter 23. The memory 32 has a sufficient storage capacity for storing moving images and sounds for a predetermined time. The memory 32 also serves as a storage device (video memory) for storing image signals for display relating to the display unit 28. In this case, the D / A converter 13 converts the display image signal stored in the memory 32 into an analog signal and supplies the analog signal to the display unit 28. In this manner, the display image signal written in the memory 32 is displayed on the display unit 28.

  The display unit 28 is a display device such as an LCD, for example, and performs display according to the analog image signal output from the D / A converter 13. Further, the image signal once A / D converted by the A / D converter 23 and stored in the memory 32 is converted into an analog signal by the D / A converter 13 and sequentially transferred to the display unit 28 for display. Reference numeral 28 functions as an electronic viewfinder, and can realize through image display.

  The non-volatile memory 56 is, for example, an electrically erasable / recordable memory, for example, an EEPROM. The non-volatile memory 56 stores constants for operation of the system control unit 50, operation programs of each block of the digital video camera 100, and the like.

  The system control unit 50 is a control circuit such as a CPU, for example, and controls the operation of each block included in the digital video camera 100. The system control unit 50 controls the operation of each block by reading, for example, the operation program of each block recorded in the non-volatile memory 56, and developing and executing the program in the system memory 52. The system memory 52 is, for example, a RAM or the like, and functions not only as a development area for an operation program but also as a storage area for storing intermediate data and the like output by the operation of each block. The system 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 system timer 53 is used for a timekeeping function for measuring the time used for various controls and the time related to the built-in clock, and the system control unit 50 controls various processes using the timekeeping function as needed.

  The mode switch 60 receives an operation input for switching the operation mode of the system control unit 50 to one of a moving image recording mode, a still image recording mode, a reproduction mode, and the like. The modes included in the moving image recording mode and the still image recording mode include the above-described normal mode and high brightness priority mode. In addition, it may include an auto shooting mode, an auto scene determination mode, a manual mode, various scene modes for setting shooting for each shooting scene, a program AE mode, a custom mode, and the like. Information on the mode change made by the mode changeover switch 60 is transmitted to the system control unit 50 as a predetermined control signal. The recording switch 61 receives an operation input for switching between a shooting standby state and a shooting state. The system control unit 50 starts a series of operations from signal reading from the imaging unit 22 to writing of moving image data to the recording medium 200 in response to receiving a control signal related to an operation input made to the recording switch 61.

  Each operation member of the operation unit 70 is appropriately assigned a function for each scene by, for example, selecting and operating various function icons displayed on the display unit 28, and receives operation inputs related to various functions. The various functions to which the buttons are assigned may include, for example, end, return, image advance, jump, refinement, attribute change, and the like. For example, when an operation input related to the menu button is performed, a menu screen on which various settings can be made is displayed on the display unit 28, and the assignment of the operation input received for each operation member of the operation unit 70 is changed. The operator can intuitively perform various settings based on the menu screen displayed on the display unit 28 using the four-way up / down / left / right cross keys and the SET button.

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

  The recording medium I / F 18 is an interface with a recording medium 200 such as a memory card or a hard disk. The recording medium 200 is a recording medium such as a memory card for recording a captured image, and includes a semiconductor memory, a magnetic disk, and the like. In the present embodiment, the image signal output from the image processing unit 24 is recorded on the recording medium 200 in relation to the photographing operation performed in the photographing mode.

<< Correction amount determination processing >>
The specific processing of the correction amount determination processing executed in the image processing unit 24 of the present embodiment having such a configuration will be described with reference to the flowchart of FIG. The processing corresponding to the flowchart is realized by the image processing unit 24 by the system control unit 50 reading out a corresponding processing program stored in, for example, the non-volatile memory 56, expanding the program in the system memory 52, and executing the program. It can be something that can be. Alternatively, in response to an image signal (input signal) being input to the image processing unit 24, processing circuits relating to each function of the image processing unit 24 work together to realize the correction amount determination processing. Is also good. The correction amount determination process will be described assuming that imaging is started based on, for example, a shooting instruction, and is started before the color blur correction unit 303 executes the color blur suppression process on the input signal related to the imaging.

  In step S601, the color blur correction amount determination unit 308 determines whether the set shooting mode is the high brightness priority mode. If the color blur correction amount determination unit 308 determines that the set shooting mode is the high brightness priority mode, the process proceeds to S602, and if it determines that the mode is the normal mode (not the high brightness priority mode). The process moves to S606.

In step S <b> 602, the color blur correction amount determination unit 308 determines a suppression coefficient used for calculating a color blur correction amount based on the maximum luminance value included in the brightness information input from the brightness information generation unit 307. In the present embodiment, as shown in FIG. 7, the color blur suppression coefficient is determined according to the maximum subject luminance. In FIG. 7, a solid line 701 indicates the suppression coefficient in the high brightness priority mode, and a broken line 702 indicates the suppression coefficient in the normal mode. Suppression coefficient in the range of x ₁ in x ₂ in the high luminance priority mode as shown has risen in proportion to the luminance value, indicating that correction of color fringing increases. That is, as shown in FIG. 8, the correction amount of the normal mode as well as color blur in a region where the maximum luminance value is less than x ₁ is defined by the dashed line 801 in the high luminance priority mode. On the other hand, so that the maximum luminance value is determined by the solid line 802 in the region where the x ₁ or more, the correction amount to a value larger than the normal mode is controlled even with the same contrast value. In Figure 8, the maximum luminance value corresponds to the suppression coefficient when it is x _2, since showing the relationship between contrast value and the correction amount, if the maximum luminance value is in the range of x ₁ in x ₂ The correction amount is determined based on a line segment having an inclination between the broken line 801 and the solid line 802.

In the conventional color bleeding suppression processing based on the fixed correction amount determination, the image quality deterioration related to the remaining color bleeding correction between the normal mode and the high brightness priority mode is subjected to knee processing in the first gamma characteristic. It depends on whether or not there is a signal in the region of interest. That is, with respect to the image signal in the luminance range to which the knee processing is applied, in the normal mode, the influence of the color blur is reduced by the compression of the contrast and becomes less noticeable, whereas in the high luminance priority mode, the compression ratio is reduced. Therefore, the influence of color bleeding can be remarkably exhibited. In the present embodiment, x ₁ and x ₂ are matched with x ₁ and x ₂ shown in FIGS. 4 and 5, and the luminance range of the signal level at which the knee processing is performed, as shown in FIGS. The suppression coefficient is controlled so that the amount of bleeding correction is increased. Incidentally, the suppression coefficient in x ₁ and x ₂ are preliminarily various frequency components, the chromatic aberration of the characteristics are measured for a plurality of subjects having a contrast, it may be those determined on the basis of the measurement results.

  In step S603, the color blur correction amount determination unit 308 calculates a contrast value of the image based on the brightness information. In the present embodiment, the color blur correction amount determination unit 308 calculates the contrast value of the image as a difference between the maximum value and the minimum value of the average value of the luminance values obtained from the plurality of partial regions. However, in the embodiment of the present invention, the derivation of the contrast of the image does not need to be limited to the luminance signal. If the contrast of the image can be derived, it is based on brightness information based on a different definition, a histogram, or the like. Needless to say, this may be done.

  In step S604, the color blur correction amount determination unit 308 determines whether the contrast value calculated in step S603 exceeds a threshold. When the same correction amount as the correction amount of the color blur applied in the normal mode (when the first gamma characteristic is used) is used also in the case where the second gamma characteristic is used, the image quality deterioration due to the color blur is determined. May be a contrast value that is determined in advance depending on whether or not it is allowable. That is, the color blur correction amount determination unit 308 determines whether or not the correction amount can be reduced in this step, from the viewpoint that the influence of color blur is less noticeable if the contrast is low. The threshold value may be determined based on the measurement of the occurrence of chromatic aberration for various frequency components. If the color blur correction amount determination unit 308 determines that the contrast value exceeds the threshold, the process proceeds to S605 to determine the correction amount, and if it is determined that the contrast value is equal to or less than the threshold, the process proceeds to S606 to perform the same as in the normal mode. The amount of correction is determined.

  In step S605, the color blur correction amount determination unit 308 determines the color blur correction amount based on the suppression coefficient determined in step S602, that is, the suppression coefficient according to the solid line 701 in FIG. 7, and the contrast value. Transmit to 303. On the other hand, in step S606, the color blur correction amount determination unit 308 changes the suppression coefficient determined in step S602 to the suppression coefficient according to the broken line 702 in FIG. 7, and calculates the color blur correction amount based on the changed suppression coefficient and contrast value. Make a decision.

  By doing so, the amount of occurrence of color bleeding based on chromatic aberration or the like in the high-brightness priority mode is reduced, and the correction amount for ensuring the same appearance as in the normal mode is determined for signals in the level range where knee processing is performed. can do. In the present embodiment, the description has been made assuming that the correction amount of the color blur is changed based on the gamma characteristic used in the gamma correction and the contrast of the subject. However, the amount of correction for color blur, such as the average value of the gamma characteristic and the brightness of the subject, may be determined based on different parameters.

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

  24: image processing unit, 303: color blur correction unit, 304: gamma correction unit, 305: luminance color difference signal generation unit, 306: luminance signal conversion unit, 307: brightness information generation unit, 308: color blur correction amount determination unit , 22: imaging unit, 100: digital video camera

Claims (12)

Acquiring means for acquiring a first image signal relating to an image to be corrected;
A first correction unit configured to correct the first image signal acquired by the acquisition unit to suppress color blur and generate a second image signal;
Control means for controlling a correction amount in the first correction means;
A second correction unit configured to perform gamma correction on the second image signal based on any one of a plurality of gamma characteristics indicating different characteristics to generate a third image signal,
The image processing apparatus according to claim 1, wherein the control unit changes the correction amount according to a gamma characteristic used for the gamma correction and a contrast value derived from the first image signal . The plurality of gamma characteristics include a gamma characteristic in which a level range of a predetermined input signal is converted into a level range of an output signal having a different magnitude,
The control means controls the correction amount of the color blur corresponding to the level range of the predetermined input signal to a larger value as the level range of the output signal after the conversion based on the gamma characteristic used is larger. The image processing device according to claim 1.   The image processing apparatus according to claim 2, wherein the predetermined input signal level range is a range in which a signal level related to brightness is equal to or more than a predetermined value. The plurality of gamma characteristics include a first gamma characteristic and a second gamma characteristic in which the level range of the output signal after the conversion is different,
The second gamma characteristic is a gamma characteristic in which a level range of an output signal assigned after the gamma correction is larger than the first gamma characteristic,
When the gamma correction using the second gamma characteristic is performed on the second image signal, the control unit may perform the correction in accordance with a signal level related to the brightness of the first image signal. The image processing apparatus according to claim 2, wherein the amount is changed. Wherein, when the said gamma correction using the second gamma characteristic with respect to the second image signal is performed, before when Kiko contrast value exceeds the threshold value, the correction amount of the first The image processing apparatus according to claim 4, wherein the value is controlled to a value larger than when the gamma correction using the gamma characteristic is performed. Wherein, when the said gamma correction using the second gamma characteristic with respect to the second image signal is performed, prior to when Kiko contrast value is below the threshold value, the said correction amount 6. The image processing apparatus according to claim 5 , wherein the control is performed to the same value as when the gamma correction using the first gamma characteristic is performed.   The image processing apparatus according to claim 5, wherein the contrast value is determined based on a difference in signal level related to brightness of the first image signal.   8. The image according to claim 4, wherein the control unit increases the correction amount as a maximum value of a signal level related to brightness of the first image signal increases. 9. Processing equipment.   When the second gamma characteristic is combined with a display gamma characteristic relating to gamma correction applied in a display unit that displays the output signal, the second gamma characteristic is between the input signal and the output signal displayed on the display unit. The image processing apparatus according to claim 4, wherein the image processing apparatus exhibits a linear conversion characteristic. Imaging means for acquiring a first image signal related to an image obtained by imaging;
A first correction unit configured to perform a correction to suppress color blur and generate a second image signal for the first image signal acquired by the imaging unit;
Control means for controlling a correction amount in the first correction means;
A second correction unit configured to perform gamma correction on the second image signal based on any one of a plurality of gamma characteristics indicating different characteristics to generate a third image signal,
The imaging apparatus according to claim 1, wherein the control unit changes the correction amount according to a gamma characteristic used for the gamma correction and a contrast value derived from the first image signal . An obtaining step of obtaining a first image signal related to an image to be corrected;
A first correction step of performing a correction for suppressing color blur on the first image signal obtained in the obtaining step to generate a second image signal;
A control step of controlling a correction amount in the first correction step;
A second correction step of performing gamma correction on the second image signal to generate a third image signal based on one of a plurality of gamma characteristics each showing a different characteristic,
The control method of an image processing apparatus according to claim 1, wherein, in the control step, the correction amount is changed according to a gamma characteristic used for the gamma correction and a contrast value derived from the first image signal . Program for causing a computer to function as each unit of the image processing apparatus according to any one of claims 1 to 9.

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