JP4415172B2 - Image processing apparatus, image processing method, and image processing program - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is an image processing apparatus suitable for use in image contrast adjustment. , Image processing method, and image processing program About.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an electronic still camera or the like that records an image using a CCD type or MOS type imaging device, for example, the contrast shown in FIG. Processing was in progress. In this figure, KinL and KinH are set values on the low luminance side and high luminance side of the image data on the input side, KoL and KoH are set values on the low luminance side and high luminance side of the image data on the output side, In conventional contrast processing, predetermined conversion processing is performed in which the luminance values (KinL, KinH) set on the input side are set to the set luminance values (KoL, KoH).
[0003]
Each set value is a value set in advance according to the bias of the luminance distribution of the output data existing in the image sensor, the image recording method, etc.
・ KinL: Blackout side detection threshold
・ KinH: Detection threshold on the white-out side
-KoL: Reference value on the black side when generating output data
-KoH: White side reference value when generating output data
It has become.
[0004]
In such contrast processing, for example, when the luminance data is 8 bits, KinL = 32, KinH = 224, KoL = 0, KoH = 255, the input data below 32 is output as 0 and the data above 224 is 255. Is output. That is, the input data of 32 to 224 is linearly converted to 0 to 255 and output. As a result, a predetermined luminance width suitable for subsequent processing is secured in the image data.
[0005]
[Problems to be solved by the invention]
However, in the above-described contrast processing, a fixed value set in advance is used as the detection threshold value (KinL, KinH) on the input side. Therefore, the effect of the contrast processing differs depending on the luminance distribution state in the input image data. Has occurred. In addition, when important image information is present in a high-luminance portion or a low-luminance portion, there is a problem that “whiteout” or “blackout” may occur in an important portion of the image. FIG. 13 is a diagram showing an example in which “blackout” occurs in an important part in an image, where FIG. 13A shows a histogram of luminance components in the original image before processing, and FIG. 13B shows processing. It is a histogram of the luminance component in the subsequent image. An image in which “blackout” occurs is, for example, a portrait in which the face is photographed with backlight.
[0006]
The present invention has been made in view of such conventional problems, and an image processing apparatus capable of adjusting contrast suitable for the content of an image. , Image processing method, and image processing program The purpose is to provide.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 is characterized in that input means for inputting color image data and histogram data for acquiring histogram data indicating a frequency distribution of luminance of the color image data input by the input means. An output-side low-intensity value based on the restriction content of the color image data that can be expressed by the acquisition means and the output side that outputs the input color image data; Output side high brightness value Output side luminance value acquisition means for acquiring the output side low luminance value acquired by the output side luminance value acquisition means and Output side high brightness value Input-side luminance value setting means for setting the input-side low luminance value and the input-side high luminance value from the ratio of the luminance distribution in the histogram data acquired by the histogram data acquiring means, and the target average luminance on the output side Target average luminance acquisition means for acquiring a value, average luminance acquisition means for acquiring an average luminance value of the input color image data, and the target average luminance value on the output side acquired by the target average luminance acquisition means, Comparison means for comparing the average brightness value acquired by the average brightness acquisition means, input-side low brightness value and input-side high brightness value set by the input-side brightness value setting means, and comparison results by the comparison means Based on the above, the luminance is converted by selectively controlling the luminance component of the input color image data to the low luminance side or the high luminance side. Characterized in that a switch means.
[0009]
According to a second aspect of the present invention, in the first aspect of the present invention, the ratio between the average luminance value acquired by the average luminance acquisition unit and the target average luminance value acquired by the target average luminance acquisition unit is calculated. First calculation means for calculating, second calculation means for calculating a new output-side low luminance value and output-side high luminance value according to the ratio calculated by the first calculation means, and the second calculation A new output-side low brightness value and output-side high brightness value calculated by the means, the output-side low brightness value acquired by the output-side brightness value acquiring means, and Output side high brightness value And an output-side luminance value setting means for setting.
[0013]
Claims 3 The invention described is the above claim 1. Or 2 In the described invention, a calculating unit that calculates a ratio between a luminance width between the input-side low luminance value and the input-side high luminance value and a luminance width between the output-side low luminance value and the output-side high luminance value; The apparatus further comprises suppression means for suppressing the rate of change in luminance on the output side in accordance with the ratio calculated by the calculation means.
[0015]
Claims 4 The invention described is the above-mentioned claims 1 to 3 In any one of the inventions, the histogram data acquired by the histogram data acquisition means is data in one or a plurality of detection areas set in the input color image data.
[0017]
Claims 5 The invention described is the above-mentioned claims 1 to 4 In any one of the inventions, the image pickup device further includes an image pickup device, and the input device inputs color image data acquired based on the image pickup by the image pickup device.
[0019]
Claims 6 The invention described is the above claim. 5 In the described invention, the detection area includes a focus area at the time of photographing by the imaging means.
[0021]
Claims 7 The invention described is the above claim. 5 or 6 In the described invention, the detection area includes an exposure amount detection area at the time of photographing by the imaging means.
[0023]
In order to solve the problems, the claims 8 The described invention includes an input step of inputting color image data, a histogram data acquisition step of acquiring histogram data indicating a frequency distribution of luminance of the color image data input in the input step, and the input color image The output side low brightness value and the color image data that can be expressed by the output side Output side high brightness value Output-side luminance value acquisition step, and the output-side low luminance value acquired in the output-side luminance value acquisition step and Output side high brightness value An input side luminance value setting step for setting the input side low luminance value and the input side high luminance value from the ratio of the luminance distribution in the histogram data acquired in the histogram data acquisition step, and the output side target average A target average luminance acquisition step for acquiring a luminance value, an average luminance acquisition step for acquiring an average luminance value of the input color image data, and the target average luminance on the output side acquired in the target average luminance acquisition step A comparison step of comparing the value with the average luminance value acquired in the average luminance acquisition step, the input side low luminance value and the input side high luminance value set in the input side luminance value setting step, and the comparison Based on the comparison result of the step, the luminance component of the input color image data is selectively controlled to the low luminance side or the high luminance side. Characterized by comprising the luminance conversion step of performing luminance conversion.
[0025]
In order to solve the problems, the claims 9 The invention described in the above description is directed to an input unit for inputting color image data, a histogram data acquisition unit for acquiring histogram data indicating a frequency distribution of luminance of the color image data input by the input unit, and the input color image. The output side low brightness value and the color image data that can be expressed by the output side Output side high brightness value Output side luminance value acquisition means for acquiring the output side low luminance value acquired by the output side luminance value acquisition means and Output side high brightness value Input side luminance value setting means for setting the input side low luminance value and the input side high luminance value from the ratio of the luminance distribution in the histogram data acquired by the histogram data acquisition means, the target average luminance value on the output side Target average brightness acquisition means for acquiring, average brightness acquisition means for acquiring an average brightness value of the input color image data, target average brightness value on the output side acquired by the target average brightness acquisition means and the average brightness Comparing means for comparing the average luminance value acquired by the acquiring means, based on the input low luminance value and the input high luminance value set by the input luminance value setting means, and the comparison result by the comparing means , Luminance conversion means for performing luminance conversion by selectively controlling the luminance component of the input color image data to the low luminance side or the high luminance side It characterized thereby to function.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a schematic block diagram showing an electronic still camera 1 including a luminance conversion apparatus according to the first embodiment of the present invention.
[0029]
The electronic still camera 1 has an imaging lens 2, an imaging element 3, and a color processor 4. The imaging device 3 captures the subject image formed by the imaging lens 2 and outputs it to the color processor 4 as an analog color image signal. The color processor 4 performs signal processing such as gain adjustment of an analog image pickup signal output from the image pickup device 3 and generation of luminance data (Y data) and two color data (Cb, Cr data) from each pixel of the color image. , And each image signal (Y, Cb, Cr) is converted into a digital signal. The color processor 4 is connected to the CPU 6 via the bus 5, and the image data sent from the color processor 4 is sent to the CPU 6. The CPU 6 compresses the image data sent from the color processor 4 into image data having a predetermined format such as JPEG format, and records the compressed image data in a flash memory or the like connected via the bus 5. It is recorded on the medium 7.
[0030]
A ROM 8 and a RAM 9 are connected to the CPU 6 via the bus 5, and the ROM 8 stores various control programs executed by the CPU 6 and various data used when controlling each unit. And CPU6 functions as each means, such as a distribution information acquisition means of this invention, a setting value acquisition means, a setting means, by controlling each part based on the said control program. The RAM 9 temporarily stores image data for one frame output from the color processor 4, and also serves as a work memory for storing various data as necessary in accordance with image data compression work by the CPU 6 and control of each unit. used. The image data recorded on the recording medium 7 is displayed on the liquid crystal display device 10 after being decompressed by the CPU 6 during reproduction. Further, the image displayed in the shooting standby state is displayed on the liquid crystal display device 10 as a through image.
[0031]
Next, in the electronic still camera 1, a processing procedure related to contrast processing for captured image data executed by the CPU 6 will be described with reference to the flowchart of FIG. In the following description, it is assumed that the image data to be processed is VGA (640 × 480) size 8-bit image data.
[0032]
First, the CPU 6 determines the ratio (Kol / maximum luminance) of the maximum value of luminance between the dark side reference value (output side low luminance value) KoL and the bright side reference value (output side high luminance value) KoH set in the output data. KoH / maximum luminance) is calculated (step SA1). The values of the dark side reference value KoL and the bright side reference value KoH vary depending on the image processing content and output device in the subsequent stage, but when the image data that can be expressed by the liquid crystal display device 10 is limited, for example, 240 or more is white. "KoH = 240", and when 16 or less is black, "KoL = 16". If the ratio of the luminance to the maximum value is a fixed value, step SA1 is not necessary.
[0033]
Next, after detecting a luminance histogram (see FIG. 3A) in the original image (step SA2), the ratio obtained in step SA1 is regarded as a distribution ratio, and the luminance value corresponding to the ratio in the histogram is determined. (KinL, KinH) is acquired and set to the dark side reference value (input side low luminance value) KinL and the bright side reference value (input side high luminance value) KinH of the luminance data on the input side (step SA3).
[0034]
In such processing, when KoL = 16 and KoH = 240 are set,
If the luminance of the nth luminance data when luminance data before processing is arranged in ascending order is expressed as ydata (n),
KinL = ydata ((640 × 480) × (16/255))
KinH = ydata ((640 × 480) × (240/255))
And
KinL is the value of the 19275th luminance data from the bottom of the histogram.
KinH is the value of the 289129th luminance data from the bottom of the histogram
It becomes.
[0035]
Thereafter, based on KinL, KinH, KoL, and KoH, the following luminance conversion (linear in the present embodiment) is performed on the luminance component data (Y data) that is input so that KinL becomes KoL and KinH becomes KoH. Conversion) (step SA4). More specifically, the luminance value k of each pixel of the original image is converted into a new luminance value k ′ based on the following calculation, and the process ends.
(1) When k <KinL
k ′ = (k / KinL) × KoL
(2) When KinL <= k <KinH,
k ′ = ((k−KinL) / (KinH−KinL)) × (KoH−KoL) + KoL
(3) When KinH <= k,
k ′ = ((k−KinH) / (255−KinH)) × (255−KoH) + KoH
[0036]
FIG. 3C is a diagram showing tone curves before and after the above contrast processing. In such processing, the dark side reference value KinL and the bright side reference value KinH on the input side represent the luminance distribution of the original image. It changes according to the state. Therefore, unlike the contrast processing described in the prior art, a luminance distribution (see FIG. 3B) reflecting the luminance distribution of the original image (see FIG. 3A) is secured in the processed image. Can do. In other words, it is possible to perform brightness adjustment suitable for individual images, eliminate the occurrence of “overexposure” and “blackout” in important parts of the image, and always obtain a good image. .
[0037]
(Second Embodiment)
Next, a second embodiment of the present invention will be described. The present embodiment relates to an electronic still camera that performs contrast processing described below on captured image data. The electrical configuration of the electronic still camera and the image data to be processed are the same as those in the first embodiment.
[0038]
FIG. 4 is a flowchart showing the processing operation of the CPU 6 in the present embodiment. The CPU 6 acquires setting values KinL and KinH on the dark side and the bright side on the input side in the same procedure as in the first embodiment (steps SB1 to SB3). Next, after calculating the luminance average of the original image based on the histogram acquired in step SB2 (step SB4), the luminance average calculated here and the luminance average to be secured in the processed image (hereinafter, target luminance average) Are compared (step SB5). The target luminance average is a luminance value that is determined in advance, and is a luminance value in a range that is generally preferred as an average luminance of an image (approximately 128 to 192 in 8-bit luminance data), for example, “144”. .
[0039]
When the average brightness is smaller than the target average brightness, that is, when the original image is a relatively dark image (YES in step SB5), the dark reference value KoL on the output side is the same as the set value KinL on the input side. After changing to a value (step SB6), luminance conversion (linear conversion) similar to that of the first embodiment is performed. That is, luminance conversion (hereinafter, white-side contrast processing) is performed only for luminance data in a range exceeding the dark-side set value KinL on the input side (hereinafter, white-side contrast processing), and the processing is terminated. FIG. 5C is a diagram showing an example of white side contrast processing. The output side set values are KoL = 32, KoH = 235, the input side set values are KinL = 32, and KinH = 140. And the luminance average = 64. FIG. 4A shows a luminance distribution before processing, and FIG. 4B shows a luminance distribution after processing. In this case, the bright part of the image becomes brighter.
[0040]
Further, when the luminance average is larger than the target luminance average, that is, when the original image is a relatively bright image (NO in step SB5), the output-side bright reference value KoH is the same as the input-side set value KinH. After changing to a value (step SB7), luminance conversion (linear conversion) similar to that of the first embodiment is performed. That is, luminance conversion (hereinafter referred to as black side contrast processing) is performed only on luminance data of the input side set value KinH or less (step SB8), and the processing is terminated. FIG. 6C is a diagram showing an example of black side contrast processing. The output side set values are KoL = 32, KoH = 191, the input side set values are KinL = 80, and KinH = 191. And the luminance average = 155. FIG. 4A shows a luminance distribution before processing, and FIG. 4B shows a luminance distribution after processing. In this case, the dark part of the image becomes darker.
[0041]
As described above, in the present embodiment, in the case of a dark image, the bright part of the image becomes brighter, and in the case of a bright image, the dark part of the image becomes darker. The luminance distribution can be optimized without changing the linearity of the luminance change in the main image area.
[0042]
(Third embodiment)
Next, a third embodiment of the present invention will be described. The present embodiment relates to an electronic still camera that performs contrast processing described below on captured image data. The electrical configuration of the electronic still camera and the image data to be processed are the same as those in the first embodiment.
[0043]
FIG. 7 is a flowchart showing the processing operation of the CPU 6 in the present embodiment. The CPU 6 sets the input side dark side and bright side set values KinL and KinH in the same procedure as in the first embodiment. Obtain (steps SC1 to SC3). Next, after calculating the luminance average of the original image based on the histogram acquired in step SC2 (step SC4), the luminance average calculated here and the luminance average to be secured in the processed image (hereinafter, target luminance average) Are compared (step SC5). Then, according to the comparison result, calculation conditions for calculating a new dark side reference value KoL ′ and a bright side reference value KoH ′ to be described later are set.
[0044]
That is, when the average brightness before processing is smaller than the target brightness average (darker than the target),
Calculation conditions
KoL '= KoL,
KoH ′ = KoL ′ + ((target luminance average−KoL ′) × (KinH−KinL) / (average luminance−KinL))
(Step SC6),
When the average brightness before processing is larger than the target brightness average (brighter than the target),
Calculation conditions
KoH '= KoH,
KoL ′ = KoH ′ − ((KoH′−target luminance average) × (KinH−KinL) / (KinH−average luminance))
(Step SC7).
[0045]
Thereafter, based on the KoL ′, KoH ′ acquired here and the KinL, KinH acquired in step SC3, the luminance data (Y data) input so that KinL becomes KoL ′ and KinH becomes KoH ′. On the other hand, luminance conversion (linear conversion) is performed (step SC9). More specifically, the luminance value k of each pixel of the original image is converted into a new luminance value k ′ based on the following calculation, and the process ends.
(1) When k <KinL
k ′ = (k / KinL) × KoL ′
(2) When KinL <= k <KinH,
k ′ = ((k−KinL) / (KinH−KinL)) × (KoH′−KoL ′) + KoL ′ (3) When KinH <= k
k ′ = ((k−KinH) / (255−KinH)) × (255−KoH ′) + KoH ′
[0046]
FIG. 8C is a diagram showing the tone curve before and after the above contrast processing. In this embodiment, the ratio between the average luminance value of the original image and the target average luminance obtained on the output side. Accordingly, new output side set values KoL ′ and KoH ′ are obtained, and luminance conversion is performed based on the new values, so that the luminance width of the processed image is set to the luminance width of the original image (see FIG. 8A). The natural luminance width (see FIG. 8B) can be obtained. Accordingly, it is possible to prevent the brightness of the entire image from changing significantly due to the contrast processing, and it is possible to perform optimal brightness adjustment simultaneously with contrast adjustment.
[0047]
Further, the following situation which is a concern in the second embodiment described above can be avoided. That is, when the luminance average before processing is smaller than the target luminance average (for images darker than the target), the luminance average after processing greatly exceeds the target luminance average (too bright), or the luminance before processing When the average is larger than the target luminance average (for an image brighter than the target), it is possible to avoid a situation in which the luminance average after processing is much lower than the target luminance average (too dark). FIG. 9 is a diagram corresponding to FIG. 8 showing the former case.
[0048]
(Fourth embodiment)
In the present embodiment, in each of the embodiments described above, the luminance calculation gain in the final luminance conversion is set to the luminance width between the input side dark side and bright side set values (KinL, KinH) described above. The output side dark side and bright side set values (KoL, KoH, or KoL ′, KoH ′) are suppressed according to the ratio to the luminance width.
[0049]
That is, in the case of explaining in the third embodiment in accordance with the process shown in FIG.
GAINmax = (KoH'-KoL) / (KinH-KinL)
(Here GAINmax is the maximum value of the calculation gain)
More specifically, the luminance conversion is performed based on the calculation gain obtained by the following calculation.
[0050]
That is, if the calculation gain is g,
(1) When k <KinL
g = (KoL '/ KinL)
(2) When KinL <= k <KinH,
g = (KoH'-KoL ') / (KinH-KinL)
(3) When KinH <= k,
g = ((255-KoH ') / (255-KinH)
Thus, the calculation gain is obtained, and the luminance conversion is performed based on the calculation gain.
[0051]
FIG. 10C is a diagram showing the tone curve before and after the above contrast processing. In the present embodiment, the inclination of the tone curve is suppressed in a natural state in accordance with the luminance conversion processing. it can. Therefore, the noise component included in the image is not noticeable, and higher image quality can be ensured. FIGS. 10A and 10B are diagrams showing changes in the luminance distribution of the image before and after the contrast processing.
[0052]
(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described. The present embodiment relates to an electronic still camera that performs contrast processing described below on captured image data. The electrical configuration of the electronic still camera and the image data to be processed are the same as those in the first embodiment.
[0053]
FIG. 11 is a flowchart showing the processing operation of the CPU 6 in the present embodiment. The CPU 6 sets the input side dark side and bright side set values KinL and KinH in the same procedure as in the first embodiment. Obtain (steps SD1 to SD3).
[0054]
Next, when the output-side bright-side reference value KoH is larger than the input-side bright-side set value KinH, the output-side dark-side set value KoL further becomes the input-side dark-side set value KinL. If it is smaller (NO in both steps SD4 and SD6), the set value is not corrected, and luminance conversion (linear conversion) similar to that in the first embodiment is performed (step SD9).
[0055]
Further, when the output side bright side reference value KoH is larger than the input side bright side set value KinH, the output side dark side set value KoL is more than the input side dark side set value KinL. Is larger (step SD4 is NO, SD6 is YES), the dark side reference value KoL on the output side is changed to the same value as the dark side set value KinL on the input side (step SD8).
[0056]
That is, it is set as the setting value for performing the white-side contrast processing only for the luminance data in the range exceeding the input-side setting value KinL, which has already been described in the second embodiment. Thereafter, luminance conversion (linear conversion) similar to that of the first embodiment is performed (step SD9).
[0057]
Further, when the output-side bright-side reference value KoH is smaller than the input-side bright-side set value KinH, the output-side dark-side set value KoL is more than the input-side dark-side set value KinL. Is smaller (step SD4 is YES, SD5 is NO), the bright side reference value KoH on the output side is changed to the same value as the set value KinH on the input side (step SD7).
[0058]
In other words, as described above in the second embodiment, the setting value for performing the black-side contrast processing using only the luminance data not more than the input-side setting value KinH as the conversion target is used. Thereafter, luminance conversion (linear conversion) similar to that of the first embodiment is performed (step SD9).
[0059]
Further, when the output-side bright-side reference value KoH is smaller than the input-side bright-side set value KinH, the output-side dark-side set value KoL is more than the input-side dark-side set value KinL. Is larger (both steps SD4 and SD5 are YES), the process is terminated as it is.
[0060]
In this process, the process is performed only on the condition image that reliably produces the effect of the contrast process. Therefore, useless processing time and power consumption in image processing can be reduced.
[0061]
(Sixth embodiment)
On the other hand, in the contrast processing described above, the luminance histogram in the original image is acquired from the luminance data of the entire image captured by the image sensor 3, but as shown in FIG. A detection area A for detecting a detection area of luminance data (arbitrary shape) may be set in advance in 50, and a luminance histogram in the detection area A may be used in each contrast process described above. In such a configuration, by setting the detection area A in an important part of the image in advance, it is possible to perform optimum luminance processing for the important part of the image. Therefore, there is an advantage that an important part of the image and its periphery are surely clear.
[0062]
Further, if the detection area A is a focus area at the time of shooting or a range including the focus area, it is possible to reliably perform optimum luminance processing in an important part of the shot image. In addition, it is not necessary for the user of the electronic still camera to set the detection area A in advance, and the important portion of the photographed image and its periphery are sharpened without imposing a burden on the user. be able to.
[0063]
The detection area A may be an exposure amount detection area at the time of photographing or a range including an exposure amount detection area. Even in such a case, it is possible to reliably perform optimum luminance processing in an important part of the photographed image. In addition, it is not necessary for the user of the electronic still camera to set the detection area A in advance, and the important part of the photographed image and its periphery are sharpened without imposing a burden on the user. be able to.
[0064]
For example, as shown in FIG. 12B, the plurality of detection areas A1 to An are set in advance by dividing the entire image region 50 into a plurality of parts, and the above-described contrast processing is performed at the time of photographing or after photographing. Before performing, the user is allowed to select one or more detection areas (whether or not adjacent to each other) corresponding to an important part, and the luminance histogram in the selected detection area is used as described above. Contrast processing may be performed. Even in such a case, an important part of the photographed image and its periphery can be sharpened. Furthermore, not only the selected detection area but also a luminance histogram in a range including a plurality of detection areas adjacent thereto may be used.
[0065]
In each of the embodiments described above, the color processor 4 outputs luminance component data (Y data), and the CPU 6 performs the above-described processing on the luminance data (Y data). However, when the color processor 4 outputs R, G, B data as image data, the same processing as described above may be performed on these data. Further, the case where the electronic still camera 1 performs the contrast process on the image captured by the image sensor 3 has been described. However, the present invention is not limited to this, and other processes that perform the contrast process on an image source such as an arbitrary image file. The present invention may be applied to an image processing apparatus. Even in such a case, the effects described above can be obtained. Further, the description has been given of the implementation of the respective means such as the distribution information acquisition means, the set value acquisition means, and the setting means of the present invention mainly by causing the CPU 6 to perform predetermined processing operations. You may make it comprise with a circuit.
[0066]
【The invention's effect】
As described above, according to the present invention, the histogram is obtained from the input color image data, and the output side low luminance value and the output content of the color image data are expressed based on the limitation contents that can be expressed on the output side. Output side high brightness value Get this output low brightness value and Output side high brightness value Are set based on the ratio of the luminance distribution in the histogram data. Then, the target average luminance value on the output side is compared with the average luminance value of the input color image data, and based on the set input-side low luminance value and input-side high luminance value, and this comparison result, Since the luminance component of the input color image data is selectively controlled to the low luminance side or the high luminance side, it is possible to adjust the contrast suitable for the content of the image.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of an electronic still camera showing an embodiment of the present invention.
FIG. 2 is a flowchart showing a processing procedure regarding contrast processing executed by a CPU in the embodiment;
FIGS. 3A and 3B are diagrams showing the contents and results of contrast processing in the embodiment, where FIG. 3A is a histogram showing a change in luminance distribution of an image before processing, and FIG. 3B is an image of the image after processing; A histogram showing a change in luminance distribution, (c) is a diagram showing a tone curve before and after processing.
FIG. 4 is a flowchart illustrating a processing procedure related to contrast processing executed by a CPU according to the second embodiment of the present invention.
5 is a diagram corresponding to FIG. 3 and showing the content of white side contrast processing and the result thereof in the embodiment; FIG.
6 is a diagram corresponding to FIG. 3 and showing the content of black side contrast processing and the result thereof in the embodiment; FIG.
FIG. 7 is a flowchart showing a processing procedure related to contrast processing executed by a CPU in the third embodiment of the present invention;
8 is a diagram corresponding to FIG. 3, showing the contents of contrast processing and the results thereof in the embodiment. FIG.
FIG. 9 is a diagram corresponding to FIG. 3 and showing the contents of contrast processing that can be avoided in the embodiment and the results thereof;
FIG. 10 is a diagram corresponding to FIG. 3 and showing the contents and results of contrast processing in the fourth embodiment of the present invention.
FIG. 11 is a flowchart illustrating a processing procedure related to contrast processing executed by a CPU according to the fifth embodiment of the present invention.
FIG. 12 is a diagram illustrating a luminance data detection area in the sixth embodiment of the present invention.
FIG. 13 is a diagram showing the contents of contrast processing in the prior art and the results thereof.
[Explanation of symbols]
1 Electronic still camera
3 Image sensor
4 Color processor
6 CPU
7 Recording media
8 ROM
9 RAM
A Detection area
KinH Input data bright side reference value
KinL Input data dark side reference value
KoH Output data bright side reference value
KoH 'Bright side reference value of output data (after correction)
KoL Output data dark side reference value
KoL 'dark side reference value of output data (after correction)

Claims (9)

Input means for inputting color image data;
Histogram data acquisition means for acquiring histogram data indicating the frequency distribution of luminance of the color image data input by the input means;
Output-side luminance value acquisition means for acquiring an output-side low luminance value and an output-side high luminance value based on the restriction content of the color image data that can be expressed by the output side that outputs the input color image data;
The input side low luminance value and the input side high luminance value corresponding to the output side low luminance value and the output side high luminance value acquired by the output side luminance value acquiring unit are included in the histogram data acquired by the histogram data acquiring unit. Input side luminance value setting means for setting from the ratio of the luminance distribution;
Target average luminance acquisition means for acquiring a target average luminance value on the output side;
Average luminance acquisition means for acquiring an average luminance value of the input color image data;
Comparison means for comparing the target average luminance value on the output side acquired by the target average luminance acquisition means with the average luminance value acquired by the average luminance acquisition means;
Based on the input side low brightness value and the input side high brightness value set by the input side brightness value setting means and the comparison result by the comparison means, the brightness component of the input color image data is set to the low brightness side or An image processing apparatus comprising: luminance conversion means for performing luminance conversion by selectively controlling on the high luminance side. First calculation means for calculating a ratio between the average brightness value acquired by the average brightness acquisition means and the target average brightness value acquired by the target average brightness acquisition means;
Second calculating means for calculating a new output-side low luminance value and output-side high luminance value according to the ratio calculated by the first calculating means;
The new output-side low luminance value and output-side high luminance value calculated by the second calculating unit are replaced with the output-side low luminance value and output-side high luminance value acquired by the output-side luminance value acquiring unit. The image processing apparatus according to claim 1, further comprising: an output-side luminance value setting unit for setting. Calculation means for calculating a ratio between a luminance width between the input-side low luminance value and the input-side high luminance value and a luminance width between the output-side low luminance value and the output-side high luminance value;
Suppressing means for suppressing the rate of change in luminance on the output side according to the ratio calculated by the calculating means;
The image processing apparatus according to claim 1, further comprising: 4. The image processing apparatus according to claim 1, wherein the histogram data acquired by the histogram data acquisition means is data in one or a plurality of detection areas set in the input color image data. . Further comprising an imaging means,
The image processing apparatus according to claim 1, wherein the input unit inputs color image data acquired based on imaging by the imaging unit. The image processing apparatus according to claim 5, wherein the detection area includes a focus area at the time of shooting by the imaging unit . The image processing apparatus according to claim 5, wherein the detection area includes an exposure amount detection area at the time of photographing by the imaging unit . An input step for inputting color image data;
A histogram data acquisition step for acquiring histogram data indicating the frequency distribution of the luminance of the color image data input in this input step;
An output-side luminance value acquisition step for acquiring an output-side low luminance value and an output-side high luminance value based on the restriction content of the color image data that can be expressed by the output side that outputs the input color image data;
The input side low luminance value and the input side high luminance value corresponding to the output side low luminance value and the output side high luminance value acquired in the output side luminance value acquisition step, the histogram acquired in the histogram data acquisition step An input side luminance value setting step set from the ratio of the luminance distribution in the data;
A target average luminance acquisition step of acquiring a target average luminance value on the output side;
An average luminance acquisition step of acquiring an average luminance value of the input color image data;
A comparison step of comparing the target average luminance value on the output side acquired in the target average luminance acquisition step with the average luminance value acquired in the average luminance acquisition step;
Based on the input low luminance value and input high luminance value set in the input luminance value setting step and the comparison result in the comparison step, the luminance component of the input color image data is set to the low luminance side. Or a luminance conversion step for performing luminance conversion by selectively controlling to the high luminance side, and
An image processing method comprising: Computer
Input means for inputting color image data;
Histogram data acquisition means for acquiring histogram data indicating the frequency distribution of luminance of the color image data input by the input means;
Output-side luminance value acquisition means for acquiring an output-side low luminance value and an output-side high luminance value based on the restriction content of the color image data that can be expressed by the output side that outputs the input color image data;
The input side low luminance value and the input side high luminance value corresponding to the output side low luminance value and the output side high luminance value acquired by the output side luminance value acquiring unit are included in the histogram data acquired by the histogram data acquiring unit. Input side luminance value setting means to set from the ratio of the luminance distribution,
Target average luminance acquisition means for acquiring the target average luminance value on the output side;
Average luminance acquisition means for acquiring an average luminance value of the input color image data;
Comparison means for comparing the target average brightness value on the output side acquired by the target average brightness acquisition means with the average brightness value acquired by the average brightness acquisition means;
Based on the input side low brightness value and the input side high brightness value set by the input side brightness value setting means and the comparison result by the comparison means, the brightness component of the input color image data is set to the low brightness side or Luminance conversion means for selectively controlling to the high luminance side and performing luminance conversion
An image processing program characterized by functioning as

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