JP2001238129A - Image processing apparatus and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing apparatus which corrects the gradation of an input picture so that hue and saturation become appropriate while seriously considering a main object. SOLUTION: An image processing is apparatus is provided with a photographing situation estimation part 13 for estimating a photographing situation on the basis of the photometric information of a photometric evaluation part 7 and the focusing information of a focusing point detection part 8, a Y/C separation part 12 for separating an input picture into a luminance signal and a color difference signal, a luminance correction part 17 for correcting the luminance signal by a gradation conversion curve obtained by extracting an edge from the luminance signal and weighting it in accordance with a photographing situation, a color difference correction part 18 for correcting the color difference signal on the basis of the luminance signals before and after gradation correction and the theoretical unit characteristics of color reproduction, a flesh color correction part 41 for correcting a flesh color or the like in accordance with the photographing situation and a Y/C synthesis part 19 for synthesizing the luminance signal after correction and the color difference signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, a recording medium, and more particularly, to an image processing apparatus for adjusting a gradation width of an input image, and a recording program recording a processing program for adjusting the gradation width of an input image. Regarding the medium.

[0002]

2. Description of the Related Art Conventionally, in an image processing apparatus for generating a wide dynamic range image by combining a plurality of images captured under different exposure conditions, a technique for adjusting a gradation width has been used. Japanese Patent Application No. 11-338551
Each image is divided into a proper exposure area and an improper exposure area, gradation correction is performed for each appropriate exposure area, and a proper exposure area for each gradation-corrected image is synthesized. An image processing apparatus for generating a wide dynamic range image is described.

The gradation conversion processing in this image processing apparatus is performed based on histogram flattening of an edge portion. In the histogram flattening, a main subject has many edges and a non-main portion such as a background has few edges. The technology is based on this premise.

On the other hand, in a conventional digital camera, a color difference signal is also converted based on a coefficient for converting a luminance signal into a gradation. That is, assuming that the luminance Yorg is converted by the gradation conversion characteristic F as Ytra = F (Yorg), conventionally, the conversion coefficient of the luminance signal is
The gain is calculated as gain = Ytra / Yorg, and the conversion coefficient is used as it is to convert the color difference signal as Cbtra = gain · Cborg Crtra = gain · Crorg.

By the way, in a digital camera, C
It is not uncommon that the number of bits when an image signal output as an analog signal from a CD is converted into a digital signal is different from the number of bits when the image signal is processed and then recorded on a recording medium, for example.

In such a case, since the amount of information is converted, particularly the amount of information is reduced, it is necessary to adjust the gradation width even when a single input image is handled. is there.

[0007] Such a tone correction technique is not limited to the above-described digital camera, but is applied to a printer device, a monitor device, and the like.
This technique is widely used in various apparatuses that process images, and the technique described above can be applied to a case where a single input image is handled.

[0008]

However, the technique of histogram flattening based on the premise that the main subject has many edges as described above can cope with a relatively wide range of subjects. It may not be possible to handle all of them. An example that may fall under such an exception is a case where a person is relatively small in a background having a complicated shape or contour. At this time, since many edges are detected from the background portion, the background is determined to be the main subject, and the gradation width assigned to the person is reduced.

[0009] In the above-described technique of performing gradation conversion of a color difference signal using a conversion coefficient similar to that of a luminance signal, an unnatural color may be generated in a high luminance portion. That is,
Color reproduction in a color space (for example, Y, Cb, Cr space) has a theoretical limit characteristic (see FIG. 11 showing an embodiment of the present invention). The color difference range in which color reproducibility can be expanded as the value is increased, and the color difference range in which color reproducibility can be reduced after a certain luminance Y is exceeded. In other words, if the luminance is low, the color reproduction range is narrow because the whole becomes blackish, and a wide range of colors can be reproduced with appropriate luminance, and the color reproduction range is narrowed again because the whole becomes whitish when the luminance is high This is the characteristic of becoming

If gradation conversion is performed in the same manner as luminance without considering such a color reproduction range, the color after the gradation conversion approaches or exceeds the limit of the color reproduction range and becomes whitish. There was something. In order to cope with such a problem, processing for suppressing the saturation of the high-luminance part has been added in the past, but it is not sufficient, and it is desired to realize a technique for further improving color reproducibility. ing.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an image processing apparatus and a recording medium that can adaptively adjust the gradation width of a main subject in accordance with a shooting scene. I have.

It is another object of the present invention to provide an image processing apparatus and a recording medium which can adjust the saturation more optimally in consideration of the theoretical limit characteristics of color reproduction.

[0013]

In order to achieve the above object, an image processing apparatus according to a first aspect of the present invention is an image processing apparatus for adjusting a gradation width of an input image. The image processing apparatus further comprises: a photographing state estimating means for estimating; and a gradation correcting means for performing gradation correction of the input image based on the photographing state and adjusting the gradation to a predetermined gradation width.

An image processing apparatus according to a second aspect of the present invention comprises:
What is claimed is: 1. An image processing apparatus for adjusting a gradation width of an input image, comprising: a luminance / chrominance separation means for separating the input image into a luminance signal and a chrominance signal; Tone correction means, based on the luminance signal before gradation correction output from the luminance / color difference separation means, the luminance signal after gradation correction output from the gradation correction means, and the theoretical limit characteristic of color reproduction. The image processing apparatus includes a color difference correction unit for correcting a color difference signal, and a luminance / color difference combining unit for combining the luminance signal after the gradation correction and the corrected color difference signal into an original image signal.

Further, an image processing apparatus according to a third aspect of the present invention is an image processing apparatus for adjusting a gradation width of an input image, comprising: a photographing state estimating means for estimating a photographing state of the input image; A luminance / color difference separating unit that separates the luminance signal into a color difference signal, a gradation correcting unit that performs gradation correction of the luminance signal based on the photographing condition to adjust the luminance signal to a predetermined gradation width, and a gradation output from the luminance / color difference separating unit. Color difference correction means for correcting the color difference signal based on the luminance signal before tone correction, the luminance signal after tone correction output from the tone correction means, and the theoretical limit characteristic of color reproduction; And a luminance / color difference synthesizing means for synthesizing the post-luminance signal and the corrected color difference signal with the original image signal.

The image processing apparatus according to a fourth aspect of the present invention is the image processing apparatus according to the first or third aspect, wherein the photographing state estimating means includes: focusing information, photometric information, zoom position information, multi-spot information. The photographing state is estimated based on at least one of photometric information, line-of-sight input information, and flash emission information.

The image processing apparatus according to a fifth aspect of the present invention is the image processing apparatus according to the first or third aspect, wherein the photographing situation estimating means determines at least three types of landscape photographing, person photographing, and close-up photographing from the focusing information. The in-focus position estimating means for estimating the in-focus position, the subject distribution estimating means for estimating at least three types of subject distributions of the entire screen, the center weight, and the central portion from the photometric information, and the in-focus position estimating means Integrating means for integrating and estimating a shooting situation by combining the in-focus position and the object distribution estimated by the object distribution estimating means.

An image processing apparatus according to a sixth aspect of the present invention is the image processing apparatus according to the first or third aspect, wherein the gradation correction means selects an arrangement of weight coefficients based on the photographing situation; Feature value calculating means for calculating a feature value for the input image; histogram creating means for creating a weighted histogram for the feature value based on the arrangement of the weighting coefficients; and gradation for calculating a tone conversion curve based on the histogram It has a conversion curve calculation means and a conversion means for performing gradation conversion using the gradation conversion curve.

An image processing apparatus according to a seventh aspect of the present invention is the image processing apparatus according to the second aspect, wherein the gradation correction means calculates a feature quantity with respect to the luminance signal; Histogram creation means for creating a histogram, tone conversion curve calculation means for calculating a tone conversion curve based on the histogram, and brightness conversion means for performing tone conversion of a brightness signal using the tone conversion curve. It is what you have.

An image processing apparatus according to an eighth aspect of the present invention is the image processing apparatus according to the second or third aspect, wherein the color difference correcting means includes a luminance signal before gradation correction and a theoretical limit characteristic of color reproduction. First calculating means for calculating a first correction coefficient based on the above-described formula, and a second calculating means for calculating a second correction coefficient based on the luminance signal after the gradation correction and the theoretical limit characteristic of color reproduction. Means for converting a color difference signal using the first correction coefficient and the second correction coefficient.

The image processing apparatus according to a ninth aspect of the present invention is the image processing apparatus according to the third aspect, wherein at least one of the hue and the saturation of a specific color in the corrected color difference signal is corrected based on the photographing situation. The apparatus further includes a second color difference correction unit.

An image processing apparatus according to a tenth aspect of the present invention is the image processing apparatus according to the first to third aspects, wherein the gradation correcting means adjusts the gradation width by reducing the gradation width. .

According to an eleventh aspect of the present invention, in the recording medium, a step of estimating a photographing state of the input image, a step of separating the input image into a luminance signal and a color difference signal, and a gradation correction of the luminance signal based on the photographing state And adjusting the color difference signal to a predetermined gradation width, based on the luminance signal before gradation correction separated from the input image, the luminance signal after gradation correction, and the theoretical limit characteristic of color reproduction. A processing program for causing a computer to execute a step of performing correction and a step of combining the luminance signal after the gradation correction and the color difference signal after the correction with an original image signal are recorded.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 7 show a first embodiment of the present invention, and FIG. 1 is a block diagram showing a basic configuration of an electronic camera.

In the present embodiment, the image processing apparatus for adjusting the gradation width according to the present invention is applied to an electronic camera.

This electronic camera comprises a single-plate type color CCD or the like having an electronic shutter function. The CCD 4 is for photoelectrically converting a subject image and outputting it as an image signal. The CCD 4 is for forming a subject image on the CCD 4. Lens system 1
A stop 2 for controlling a passing range of a light beam passing through the lens system 1, a low-pass filter 3 serving as an optical filter for removing unnecessary high-frequency components from the light beam passing through the stop 2, and an output from the CCD 4. After that, an A / D converter 5 for converting an analog image signal, which has been subjected to noise component removal by a correlated double sampling circuit (not shown) or the like and then amplified to a digital signal, into a digital signal, and the A / D converter An image buffer 6 for storing image data for one screen digitized by the converter 5, and an image buffer 6 for reading out the image data from the image buffer 6 to obtain a luminance distribution so as to obtain an appropriate exposure at the time of imaging. Opening diameter and C
A photometric evaluation unit 7 for controlling an electronic shutter of the CD 4; a focus detection unit 8 for reading out image data from the image buffer 6 to detect a focus position and controlling an AF motor 9 described later based on the detection result And this in-focus detection unit 8
And an AF motor 9 for driving the AF lens of the lens system 1 to form a subject image on the CCD 4 and interpolating the single-plate image data read from the image buffer 6. An interpolation unit 10 for converting the image data into three image data, a work buffer 11 for storing the interpolated image data,
A Y / C separation unit 12 serving as a luminance / chrominance separation unit for separating the image data of the plate into a luminance signal Y and color difference signals Cb and Cr; photometric information output from the photometric evaluation unit 7; As will be described later in detail, based on the output focusing information, a photographing condition estimating unit 13 for estimating a photographing condition, and a luminance signal Y are first read out from the Y / C separating unit 12 to obtain an edge. The components are extracted, weighted when calculating the histogram of the edge, which is the feature amount, is calculated by referring to the estimation result by the photographing situation estimating unit 13, the conversion characteristic is calculated, and output from the Y / C separation unit 12. A gradation correction unit 14 that performs gradation conversion of the luminance signal Y and the color difference signals Cb and Cr, and converts the image whose gradation width has been adjusted by the gradation correction unit 14 into an original RGB signal or the like. After For example, while receiving the output unit 15 for outputting to a recording medium, a display device, and the like, and the detection results of the photometric evaluation unit 7 and the in-focus detection unit 8, the interpolation unit 10, the photographing situation estimation unit 13, and the gradation correction unit 14 And a control unit 16 for controlling the entire electronic camera.

FIG. 2 is a block diagram showing a detailed configuration of the photographing situation estimating unit 13.

The control unit 1 output from the in-focus point detection unit 8
The focus (AF) information input via the camera 6 is input to a focus position estimating unit 20 serving as a focus position estimating unit, and according to the subject distance, for example, landscape photography (5 m to ∞), person photography ( 1m to 5m) and close-up photography (1m or less) (Fig. 5
Reference).

Also, photometric (AE) information output from the photometric evaluation unit 7 and input via the control unit 16 is input to a subject distribution estimating unit 21 serving as a subject distribution estimating unit, and the number of luminance distributions is calculated. It is classified into crab.

More specifically, first, the photometric evaluation unit 7
The area on the CCD 4 is classified into, for example, 13 as shown in FIG. 4, and divided photometry is performed. This figure 4
FIG. 4 is a diagram showing an example of a division pattern for evaluation photometry.

That is, the middle area at the center is a1
The left neighbor is a2 and the right neighbor is a3.

Further, the upper and lower portions of the above-mentioned area a1 in the inner peripheral portion surrounding the centralmost portion are defined as a4 and a5, respectively.
The left and right sides of 4 are a6 and a7, and the left and right sides of the area a5 are a8 and a9.

In the outer peripheral portion surrounding the inner peripheral portion, the upper left is a10, the upper right is a11, the lower left is a12, and the lower right is a13.

In the photometry divided by such an area,
The subject distribution estimating unit 21 calculates the following evaluation parameters.

S1 = | a2-a3 |

S2 = max (| a4-a6 |, | a4-a7 |)

S3 = max (a10, a11) -Av Av = (Ａai) / 13

That is, the evaluation parameter S 1 indicates the difference between the left and right luminances at the center and the evaluation parameter S 2
Indicates the larger luminance difference between the upper center and the upper right and left sides of the inner peripheral portion, and the evaluation parameter S3 indicates the difference between the larger upper right and left sides of the outer peripheral portion and the average luminance of the entire screen. It has become something.

The evaluation parameters are obtained from the object distribution estimating unit 21 and the in-focus position is obtained from the in-focus position estimating unit 20. The integrating unit 22 as an integrating means as shown in FIG. Classification. This figure 5
9 is a chart showing a classification pattern of a scene from AF information and AE information.

As shown in the figure, when the AF information is 5 m to ∞, it is determined that landscape photography has been performed, and the evaluation parameter S 3 is compared with a predetermined value Th 1. At this time, if the evaluation parameter S3 is larger than the predetermined value Th1, at least one of a10 and a11 has a brightness higher than the average brightness of the entire screen to a certain extent or more, so that the scenery has an upper sky. (Type 1). On the other hand, when the evaluation parameter S3 is smaller than the predetermined value Th1, on the contrary, it is determined that there is no sky above the scenery or that there is little scenery (Type 2).

Next, when the AF information is 1 m to 5 m,
Assuming that a person is photographed, the evaluation parameter S
2 is compared with a predetermined value Th2. At this time, if the evaluation parameter S2 is larger than the predetermined value Th2, it is determined that the portrait is a portrait of one person (Type 3).
If it is smaller than h2, it is determined that the portrait is of a plurality of persons (Type 4).

Further, when the AF information is 1 m or less,
Assuming that the shooting is a close-up shooting, the evaluation parameter S
1 is compared with a predetermined value Th3. At this time, if the evaluation parameter S1 is larger than the predetermined value Th3, it is determined that the object is a close-up of a single object (Type 5).
If it is smaller than the predetermined value Th3, it is determined that the object is a close-up of a plurality of objects (Type 6).

The result of such classification is output from the integrating section 22 to the gradation correcting section 14.

FIG. 3 is a block diagram showing a detailed configuration of the gradation correction section 14. As shown in FIG.

The luminance signal Y from the Y / C separation section 12
Is input to the edge extraction unit 26 serving as a feature amount calculation unit, the edge extraction unit 26 performs edge detection based on the control of the control unit 16. Specifically, the edge extraction unit 26 is a general edge detection operator such as Laplacian or Sobel. If the strength of the edge detection operator is equal to or greater than a predetermined threshold, it is determined that an edge exists at the reference position. Otherwise, it outputs binary information that is not an edge.

On the other hand, the result of the type classification by the photographing situation estimating section 13 is used as a weighting pattern selecting section 2 as selecting means.
4, the weight pattern selection unit 24, based on the control of the control unit 16, stores a plurality of weight patterns as shown in FIG.
A weight pattern corresponding to the type is selected from M25. FIG. 6 is a diagram showing weighting factors at the time of calculating a histogram based on the classification pattern as shown in FIG. 5. FIG. 6 (A) is for Type 1, FIG. 6 (B) is for Type 2, 6 (C) corresponds to Type 3 shown in FIG.
(D) shows the Type 4 and FIG. 6 (E) shows the Type 4.
FIG. 6F shows a weight pattern corresponding to Type 6 described above.

Thus, based on the result output from the edge extracting unit 26, the histogram creating unit 27, which is a histogram creating unit, calculates an edge histogram indicating the appearance frequency with respect to the luminance level for the pixels constituting the edge and its neighboring pixels. However, when the histogram is created, the histogram is calculated by performing weighting according to the pixel position in the image as shown in FIG. Further, the histogram creation unit 27 converts the calculated edge histogram into a cumulative edge histogram by integrating the calculated edge histogram.

The conversion curve calculation unit 28, which is a gradation conversion curve calculation unit, generates a target histogram by convolving the edge histogram using a Gaussian kernel or the like. A tone curve serving as a gradation correction characteristic is calculated using the cumulative edge histogram.

The conversion section 29 as a conversion means performs gradation correction on the image data input from the Y / C separation section 12 based on the tone curve obtained from the conversion curve calculation section 28. Is output to the output unit 15. The conversion unit 29 first performs gradation correction of the luminance signal Y, and then sequentially performs gradation correction of the color difference signals Cb and Cr, and outputs the result to the output unit 15.

The output section 15 outputs a luminance signal Y after gradation correction.
And the color difference signals Cb and Cr, and generates and outputs an original RGB signal, for example.

FIG. 7 is a flowchart showing the image conversion process.

The subject image formed on the single-chip CCD 4 is converted into an image signal by an imaging operation and output.

This image signal is temporarily stored in the image buffer 6 after being converted into a digital signal by the A / D converter 5.

Based on the image data stored in the image buffer 6, the photometric evaluation unit 7 and the in-focus detection unit 8 control the AE information and the AF information as described above.
(Step S1).

On the other hand, the image data stored in the image buffer 6 is sent to the interpolating unit 10 to interpolate the R image data, the G image data, and the B image data, thereby obtaining a three-plate image. The data is converted into image data (step S2) and stored in the work buffer 11.

The Y / C separation unit 12 reads out the RGB image data from the working buffer 11 and
And the color difference signals Cb and Cr are calculated as shown in the following Expression 4 (step S3).

Y = 0.29900R + 0.58700G + 0.14400B Cb = −0.16874R−0.33126G + 0.50000B Cr = 0.50000R−0.41869G−0.08131B

The tone correcting section 14 extracts the edge component by applying a known secondary differential filter such as Laplacian to the luminance signal Y in the edge extracting section 26 (step S4). To the standard deviation of 2
The binarization process is performed by providing a threshold of about twice (step S5).

On the other hand, the photographing situation estimating section 13 estimates the photographing situation on the basis of the AF information and the AE information as described above (step S6), and the weight pattern becomes Ty.
It selects any one of pe1 to Type6 (step S7). Then, the weighting factor corresponding to the selected weighting pattern as shown in FIG.
(Step S8).

In this way, the histogram creating section 27 creates an edge histogram weighted based on the edge components binarized in step S5 and the weight pattern read in step S8 (step S9).
A cumulative edge histogram is further generated from the edge histogram (step S10). Based on the cumulative edge histogram thus obtained, the conversion curve calculation unit 2
8 calculates a gradation conversion curve (step S11).

In the conversion section 29, the Y / C separation section 1
2 output the luminance signal Y and the color difference signals Cb, Cr
Is converted by the gradation conversion curve obtained from the conversion curve calculator 28 (step S12), and the converted image data is output (step S1).
3).

In the above description, both the photometric information and the focusing information are used for estimating the photographing situation, but it is also possible to use only one of them to estimate and change the weight. Not only the photometric information and focus information but also zoom position information, multi-spot photometric information, line-of-sight input information, flash emission information, information on the detection sensor that detects the vertical and horizontal position of the electronic camera, and white balance information. By referring to one or more, it is possible to estimate the shooting situation in more detail.

Further, the above-described technique of gradation correction according to the photographing situation is not limited to being applied only to a color image, but can also be applied to a monochrome image.

Then, in the first embodiment,
Although the image processing apparatus configured as a circuit in the electronic camera performs gradation correction according to the shooting situation, such processing can be performed by a processing program of a computer. In this case, photographing information such as photometric information and focusing information is recorded in, for example, a header portion of the image file, and a computer estimates a photographing state based on the photographing information, and is suitable for the photographing state. Tone correction may be performed.

The image processing apparatus is not limited to being applied to an electronic camera, but can be widely applied to, for example, an image processing apparatus such as a printer apparatus.

According to the first embodiment, the photographing state is determined based on photographing information such as focusing information and photometric information, and weighting is performed in accordance with the photographing state when creating an edge histogram. As a result, it is possible to perform gradation correction most suitable for the shooting scene in consideration of the main subject.

FIGS. 8 to 12 show a second embodiment of the present invention. FIG. 8 is a block diagram showing a basic configuration of an electronic camera, and FIG. 9 shows a detailed configuration of a luminance correction unit. FIG. 10 is a block diagram showing a detailed configuration of a color difference correction unit, FIG. 11 is a diagram showing how color difference correction is performed in consideration of a theoretical limit characteristic of color reproduction, and FIG. 12 is a diagram showing image conversion processing. It is a flowchart shown.

In the second embodiment, the first
The same components as those of the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Only different points will be mainly described.

In the second embodiment, the Y / C separation unit 1
2, the luminance signal Y and the color difference signals Cb, Cr
Are input to a luminance correction unit 17 as a gradation correction unit and a color difference correction unit 18 as a color difference correction unit.

As shown in FIG. 9, the luminance correction section 17 receives the luminance signal Y output from the Y / C separation section 12, and performs gradation correction on luminance.
An edge extraction unit 30 as a feature amount calculation unit, a histogram creation unit 31 as a histogram creation unit, a conversion curve calculation unit 32 as a gradation conversion curve calculation unit, and a brightness conversion unit 33 as a brightness conversion unit Have been.

The processing in the luminance correction unit 17 is described in FIG.
This will be described with reference to FIG.

The luminance correction section 17 is provided with the Y / C separation section 12
The luminance signal Y output from is read (step S2).
1) The edge extracting unit 30 extracts edge components by applying a filter such as Laplacian (step S22), and performs a binarization process of comparing each pixel with a predetermined threshold value to determine whether the pixel is an edge. Perform (Step S23).

Based on the information output from the edge extraction unit 30, the histogram creation unit 31 generates an edge histogram indicating the frequency of appearance of the edge with respect to the luminance (step S24), and further integrates the edge histogram to obtain a cumulative edge histogram. Is created (step S25).

The conversion curve calculation unit 32 calculates a tone curve serving as a gradation correction characteristic as described above, using the accumulated edge histogram output from the histogram creation unit 31 (step S26).

The luminance conversion unit 33 performs gradation conversion of the luminance signal Y based on the conversion curve under the control of the control unit 16 (step S27), outputs the gradation to the color difference correction unit 18, and outputs the luminance / color difference synthesizing means. The result is output to the Y / C combining section 19 (step S28).

As described above, if the luminance signal before gradation correction output from the Y / C separation unit 12 is Yorg, and the luminance signal after gradation correction by the luminance conversion unit 33 is Ytra, The luminance signals Yorg and Ytra are used when the color difference correcting section 18 corrects the gradation of the color difference, as described below.

As shown in FIG. 10, the color difference correction section 18 outputs a color difference signal C output from the Y / C separation section 12.
b and Cr, and performs gradation correction for the color difference. The first correction coefficient calculation unit 37 as a first calculation unit
And a second correction coefficient calculator 35 as a second calculator, a ROM 36 for color reproduction limit characteristics, and a color difference converter 38 as a color difference converter.

In the color difference correction section 18, the first
The correction coefficient calculation unit 37 receives the luminance signal Yorg before the gradation correction from the Y / C separation unit 12, and receives the luminance signal Yorg.
The color reproduction range borg corresponding to org is calculated as shown in the following Expression 5 (step S31).

## EQU5 ## borg = B (Yorg)

Here, the function B (Y) is expressed in the color space (Y, C
(b, Cr space), which is a function indicating the theoretical limit characteristic of color reproduction. For example, as schematically shown in FIG. Is exceeded, the color difference range in which color reproduction is possible is narrowed.

The calculation as shown in Expression 5 is, for example,
Referring to the table data and the like stored in the color reproduction limit characteristic ROM 36 (step S30), the luminance Yor
This is performed by finding a color gamut borg corresponding to g.

The color reproduction limit characteristic ROM 36 stores the function B (Y) indicating the theoretical limit characteristic of color reproduction in advance as table data. Here, the load and the processing speed by calculation are taken into consideration. Then, the table data stored in the ROM is used, but of course, the calculation may be actually performed.

Next, the second correction coefficient calculator 35 receives the luminance signal Ytra after gradation correction from the luminance corrector 17 and receives the color reproduction range b corresponding to the luminance signal Ytra.
tra is calculated as shown in the following Expression 6 similar to Expression 5 described above (Step S32).

## EQU6 ## btra = B (Ytra)

The calculation as shown in Expression 6 is similarly performed
Referring to the table data and the like stored in the color reproduction limit characteristic ROM 36 (step S30), the luminance Ytr
This is performed by obtaining a color reproduction range btra corresponding to a.

The color difference conversion section 38 calculates a conversion coefficient gainc for the color difference signal based on borg as the first correction coefficient and btra as the second correction coefficient as shown in the following equation 7. I do.

[Mathematical formula-see original document] gain = btra / borg

Thus, the conversion coefficient ga for the color difference signal
inc is defined to be the ratio of the theoretical limit characteristic borg of color reproduction with the luminance signal Yorg before gradation correction and the theoretical limit characteristic btra of color reproduction with the luminance signal Ytra after gradation correction. Thus, it is possible to perform faithful color reproduction while maintaining saturation without causing overexposure and the like as in the case where the same conversion coefficient as luminance is used.

When the conversion coefficient gainc is obtained, the color difference signal Cb before correction is output from the Y / C separation unit 12.
org and Crorg are sequentially received (step S29),
The corrected color difference signals Cbtra and Crtra are calculated as shown in the following Expression 8 (step S33).

## EQU8 ## Cbtra = gainc Cborg Crtra = gaincCrorg

The color difference signals Cbtra,
Crtra is output to the Y / C synthesizing unit 19 (step S34).

The Y / C synthesizing unit 19 Y / C-combines the luminance signal Ytra after the gradation conversion and the converted color difference signals Cbtra and Crtra to convert them into, for example, RGB signals. Below, it outputs via the output part 15.

In the second embodiment, tone correction is performed by taking into consideration the theoretical limit characteristics of color reproduction by an image processing device configured as a circuit in an electronic camera. It is also possible to carry out by the processing program of the above.

The image processing apparatus is not limited to being applied to an electronic camera, but can be widely applied to devices that handle images, such as a printer.

According to the second embodiment, the color difference signal is subjected to gradation correction in consideration of the theoretical limit characteristics of color reproduction. Therefore, even if gradation correction of an image is performed, appropriate color correction is performed. Degree can be maintained.

FIGS. 13 and 14 show a third embodiment of the present invention. FIG. 13 is a block diagram showing the basic configuration of an electronic camera, and FIG. 14 is a flowchart showing image conversion processing. is there.

In the third embodiment, the same parts as those in the above-described first and second embodiments are denoted by the same reference numerals, and description thereof will be omitted. Only different points will be mainly described.

The third embodiment is configured to exhibit a function combining the functions of the first and second embodiments described above, that is, the gradation conversion characteristic of the luminance signal. In addition to performing weighting according to the shooting conditions when calculating, the hue and saturation are also corrected according to the shooting conditions in consideration of the theoretical limit characteristics of color reproduction when calculating the conversion characteristics of the color difference signal. It is like that.

That is, the image signal output from the CCD 4 is converted into a digital signal by the A / D converter 5 and then temporarily stored in the image buffer 6.

Based on the image data stored in the image buffer 6, the photometric evaluation section 7 and the in-focus point detection section 8 transmit the AE information and the AF information to the control section 16 as described above.
(Step S41).

On the other hand, the image data stored in the image buffer 6 is sequentially sent to the interpolating unit 10 to interpolate the R image data, the G image data, and the B image data, thereby obtaining a three-plate image. (Step S42) and stored in the work buffer 11.

The Y / C separation section 12 reads out the RGB image data from the working buffer 11 and
And the color difference signals Cb and Cr are calculated as in Equation 4 described above (Step S43).

The brightness correction unit 17 is provided with the edge extraction unit 30
In step S44, an edge component is extracted from the luminance signal Y (step S44), and a binarization process is performed on the extracted edge component (step S45).

On the other hand, the photographing state estimating unit 13 estimates the photographing state based on the AF information and the AE information as described above (step S46), and the weighting pattern is set to T.
The type is selected from type 1 to type 6 (step S47). Then, a weight coefficient corresponding to the selected weight pattern as shown in FIG. 6 is read from the weight pattern ROM 25 (step S48).

Thus, the histogram creating section 31 creates an edge histogram weighted based on the edge components binarized in step S45 and the weight pattern read in step S8 (step S4).
9) A cumulative edge histogram is further generated from the edge histogram (step S50). The conversion curve calculation unit 32 calculates a gradation conversion curve based on the cumulative edge histogram thus obtained (step S5).
1).

In the subsequent luminance conversion section 33, the luminance signal Y output from the Y / C separation section 12 is converted by the gradation conversion curve obtained from the conversion curve calculation section 32 (step S52), and the color difference Output to the correction unit 18 and output to the Y / C synthesis unit 19.

The color difference correction section 18 includes a luminance signal Y 'after the gradation correction, a luminance signal Y before the gradation correction output from the Y / C separation section 12 and the color reproduction limit characteristic ROM 36.
The first correction coefficient and the second correction coefficient are calculated as described above based on the theoretical limit characteristics of color reproduction read out from the above, and the conversion coefficient for the color difference signal is calculated based on the first correction coefficient and the second correction coefficient. The color difference signal C received from the separation unit 12
Conversion of b and Cr is performed (step S53).

The color difference signals Cb ′ and Cr ′ corrected by the color difference correction unit 18 are further input to a skin color correction unit 41 as a second color difference correction unit, and the photographing situation estimation unit 1
For example, correction of skin color is performed with reference to the photographing situation estimated in step 3 (step S54).

Here, for example, the above-mentioned Type 3 and Type
In the case of a portrait of one person or a plurality of persons as in No. 4, processing for correcting hue and saturation is performed so that the skin color looks more preferable. For example, taking Japanese skin as an example, since the skin tends to have a slightly yellow hue, processing such as moving this in the direction of a slightly red hue is performed.

In the case of a landscape having an upper sky like Type 1 described above, processing such as correcting the hue and saturation so that the sky looks bluer is performed.

Further, in the case where the landscape is estimated as in the above-described Type 1 and Type 2, and when it is estimated that there are many plants in the landscape based on other information, the hue is adjusted to make the green of the plants preferable. It is also conceivable to perform processing such as correction of color saturation or the like, and the present invention is not limited thereto, and can be applied to various subjects.

The color difference signals Cb ′ and Cr ′ corrected by the skin color correcting section 41 and the luminance signal Y ′ corrected in gradation by the luminance correcting section 17 are combined with the Y / C synthesizing section 1.
9 to convert to the original RGB signal (step S55), and then output via the output unit 15 (step S56).

In the third embodiment, the tone correction is performed as a circuit in the electronic camera. However, such processing can be performed by a processing program of a computer.

In this case, the photometric information from the photometric evaluation unit 7 and the focusing information from the focus detection unit 8 are added to the header of a file for storing the image data in the image buffer 6. For example, the data is recorded on a recording medium such as a memory card and read by the computer, and
A necessary part of the processing shown in FIG. 4 may be sequentially performed.

Such a processing program is recorded on various recording media such as a hard disk in a computer, a portable floppy disk, and a magneto-optical disk.

The image processing apparatus is not limited to being applied to an electronic camera, but can be widely applied to devices that handle images, such as a printer.

According to the third embodiment, both the effects of the above-described first embodiment and the effects of the second embodiment can be achieved, and the hue and the hue corresponding to the photographing situation can be obtained. Since the saturation can be corrected, for example, the skin of a person who is the main subject can be corrected to a more preferable skin color.

The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications and applications are possible without departing from the gist of the invention.

[0111]

As described above, according to the image processing apparatus of the first aspect of the present invention, since the photographing state is estimated and the gradation is corrected and adjusted to a predetermined gradation width according to it, It is possible to adaptively adjust the gradation width of the main subject.

Further, according to the image processing apparatus of the present invention, since the color difference signal is corrected based on the luminance signal before and after the gradation correction and the theoretical limit characteristic of color reproduction,
After the gradation correction, an image having an optimum saturation can be obtained.

Further, according to the image processing apparatus of the present invention, since the photographing state is estimated and the gradation correction of the luminance signal is performed to adjust the luminance signal to a predetermined gradation width, the main object It is possible to adaptively adjust the gradation width of the color difference signal based on the luminance signal before and after the gradation correction and the theoretical limit characteristic of the color reproduction. An image with saturation can be obtained.

According to the image processing apparatus of the fourth aspect of the present invention, the same effects as those of the first or third aspect of the invention can be obtained, and the focus information, the photometry information, the zoom position information, By using at least one of the multi-spot photometry information, the line-of-sight input information, and the flash emission information, it is possible to appropriately estimate a shooting situation.

According to the image processing apparatus of the present invention, the same effects as those of the first or third aspect are obtained, and the photographing state is determined based on the focusing information and the photometric information. It is possible to make an appropriate estimation.

According to the image processing apparatus of the present invention, the same effect as that of the first or third aspect is obtained, and the gradation correction means weights the characteristic amount of the input image. By generating a histogram and calculating a gradation conversion curve, appropriate gradation conversion in consideration of the main subject can be performed.

According to the image processing apparatus of the present invention, the same effects as those of the second aspect can be obtained, and the gradation correction means creates a histogram from the characteristic amount of the luminance signal to generate a histogram. By calculating the tone conversion curve, appropriate tone conversion can be performed.

According to the image processing apparatus of the present invention, the same effect as that of the second or third aspect can be obtained, and the color difference correcting means can control the luminance signal and the color signal before the gradation correction. By using a first correction coefficient calculated from a theoretical limit characteristic of reproduction and a second correction coefficient calculated from a luminance signal after gradation correction and a theoretical limit characteristic of color reproduction, conversion of a color difference signal is performed. Can be performed appropriately.

According to the image processing apparatus of the ninth aspect of the present invention, the same effect as that of the third aspect of the invention can be obtained, and the second color difference correcting means can correct the color difference signal after correction based on the photographing situation. Since at least one of the hue and the saturation of the specific color is corrected, the hue and the saturation can be set to be more suitable for the shooting situation.

According to the image processing apparatus of the present invention according to the tenth aspect, the same effects as those of the first to third aspects can be obtained when the adjustment for reducing the gradation width is performed.

According to the recording medium of the present invention, by executing the recorded processing program on a computer, the photographing situation is estimated, and the gradation correction of the luminance signal is performed in accordance with the estimation to obtain a predetermined gradation width. In order to make adjustments, it is possible to adaptively adjust the gradation width of the main subject, and further, to correct the color difference signal based on the luminance signal before and after the gradation correction and the theoretical limit characteristics of color reproduction. It is also possible to obtain an image having an optimum saturation after the key correction.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of an electronic camera according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed configuration of a shooting situation estimating unit according to the first embodiment.

FIG. 3 is a block diagram illustrating a detailed configuration of a tone correction unit according to the first embodiment.

FIG. 4 is a diagram showing an example of a division pattern for evaluation photometry in the first embodiment.

FIG. 5 is a diagram showing AF information and AE in the first embodiment.
7 is a table showing a classification pattern of scenes from information.

FIG. 6 is a diagram showing weighting factors at the time of calculating an edge histogram based on the classification pattern as shown in FIG. 5 in the first embodiment.

FIG. 7 is a flowchart illustrating image conversion processing according to the first embodiment.

FIG. 8 is a block diagram showing a basic configuration of an electronic camera according to a second embodiment of the present invention.

FIG. 9 is a block diagram illustrating a detailed configuration of a luminance correction unit according to the second embodiment.

FIG. 10 is a block diagram illustrating a detailed configuration of a color difference correction unit according to the second embodiment.

FIG. 11 is a diagram showing a state in which color difference correction is performed in consideration of the theoretical limit characteristics of color reproduction in the second embodiment.

FIG. 12 is a flowchart illustrating image conversion processing according to the second embodiment.

FIG. 13 is a block diagram illustrating a basic configuration of an electronic camera according to a third embodiment of the present invention.

FIG. 14 is a flowchart illustrating image conversion processing according to the third embodiment.

[Explanation of symbols]

7: Photometric evaluation section 8: Focus point detection section 12: Y / C separation section (luminance / color difference separation means) 13: Photographing situation estimating section (photographing situation estimating means) 14: Gradation correcting section (gradation correcting means) 15 ... Output unit 16 Control unit 17 Luminance correction unit (gradation correction unit) 18 Color difference correction unit (color difference correction unit) 19 Y / C synthesis unit (luminance / color difference synthesis unit) 20 Focusing position estimation unit (focusing) Position estimation unit) 21 Subject distribution estimation unit (subject distribution estimation unit) 22 Integration unit (integration unit) 24 Weight pattern selection unit (selection unit) 25 ROM for weight pattern 26, 30 Edge extraction unit (feature amount) Calculation means) 27, 31 ... Histogram creation unit (histogram creation means) 28, 32 ... Conversion curve calculation unit (gradation conversion curve calculation means) 29 ... Conversion unit (conversion means) 33 ... Luminance conversion unit (luminance conversion means) 35 ... Second correction Number calculation unit (second calculation unit) 36 ROM for color reproduction limit characteristics 37 first correction coefficient calculation unit (first calculation unit) 38 color difference conversion unit (color difference conversion unit) 41 skin color correction unit (second (2) color difference correction means)

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 5C022 AB02 AB22 AC42 AC56 AC74 5C065 BB01 CC01 DD02 GG13 GG18 GG30 5C066 AA01 AA03 AA05 CA05 CA17 DC01 EA07 EB03 EC06 FA02 GB01 JA01 KD06 KE09 KE19 KM01 KM10 KM10

Claims (11)

[Claims] 1. An image processing apparatus for adjusting a gradation width of an input image, comprising: a photographing state estimating means for estimating a photographing state of the input image; and performing a gradation correction of the input image based on the photographing state. An image processing apparatus, comprising: a gradation correcting unit configured to adjust the gradation width to: 2. An image processing apparatus for adjusting a gradation width of an input image, comprising: a luminance / chrominance separation unit for separating the input image into a luminance signal and a chrominance signal; Tone correction means for adjusting the tone width, a brightness signal before tone correction output from the brightness / color difference separation means, a brightness signal after tone correction output from the tone correction means, and a theory of color reproduction. A color difference correction unit that corrects the color difference signal based on the limit characteristics, and a luminance / color difference combination unit that combines the luminance signal after the gradation correction and the color difference signal after the correction with the original image signal, An image processing apparatus comprising: 3. An image processing apparatus for adjusting a gradation width of an input image, comprising: a photographing state estimating unit for estimating a photographing state of the input image; and a luminance / chrominance separation unit for separating the input image into a luminance signal and a color difference signal. Means, a gradation correction means for performing gradation correction of the luminance signal based on the photographing condition and adjusting the luminance signal to a predetermined gradation width, a luminance signal before gradation correction output from the luminance / color difference separation means, Color difference correction means for correcting the color difference signal based on the luminance signal after gradation correction output from the tone correction means and the theoretical limit characteristics of color reproduction; and the luminance signal after gradation correction and the correction. And a luminance / color difference synthesizing means for synthesizing a color difference signal obtained later with an original image signal. 4. The photographing situation estimating means includes: focusing information;
The photographing situation is estimated based on at least one of photometric information, zoom position information, multi-spot photometric information, line-of-sight input information, and flash emission information. The image processing apparatus according to claim 1 or 3. 5. The photographing situation estimating means includes: a focusing position estimating means for estimating at least three types of focusing positions of landscape photographing, portrait photographing, and close-up photographing from the focusing information; A subject distribution estimating means for estimating three types of subject distributions of a focus and a central part, and a shooting situation are integrated by combining the in-focus position estimated by the in-focus position estimating means and the subject distribution estimated by the subject distribution estimating means The image processing apparatus according to claim 1, further comprising: an integrating unit configured to estimate the position of the image processing apparatus. 6. A gradation correction unit, comprising: a selection unit that selects an arrangement of weighting factors based on the shooting situation; a feature amount calculation unit that calculates a feature amount with respect to the input image; Histogram creating means for creating a weighted histogram relating to the feature amount; tone conversion curve calculating means for calculating a tone conversion curve based on the histogram; and conversion means for performing tone conversion using the tone conversion curve. The image processing apparatus according to claim 1, wherein the image processing apparatus comprises: 7. The gradation correction unit includes: a feature amount calculation unit that calculates a feature amount for the luminance signal; a histogram creation unit that creates a histogram related to the feature amount; and a tone conversion curve based on the histogram. 3. The image according to claim 2, comprising: a gradation conversion curve calculation unit that performs gradation conversion of a luminance signal using the gradation conversion curve. 4. Processing equipment. 8. The color difference correction unit includes: a first calculation unit that calculates a first correction coefficient based on the luminance signal before gradation correction and the theoretical limit characteristic of color reproduction; A second calculating means for calculating a second correction coefficient based on the luminance signal after the tone correction and the theoretical limit characteristic of the color reproduction, and using the first correction coefficient and the second correction coefficient. The image processing apparatus according to claim 2, further comprising: a color difference conversion unit configured to convert a color difference signal. 9. The image processing apparatus according to claim 3, further comprising a second color difference correction unit configured to correct at least one of a hue and a saturation of a specific color in the corrected color difference signal based on the shooting situation. An image processing apparatus according to claim 1. 10. The image processing apparatus according to claim 1, wherein said gradation correction means adjusts the gradation width by reducing the gradation width. apparatus. 11. A step of estimating a photographing state of an input image, a step of separating the input image into a luminance signal and a color difference signal, and performing gradation correction of the luminance signal based on the photographing state to a predetermined gradation width. Adjusting, a luminance signal before gradation correction separated from the input image,
Correcting the color difference signal based on the luminance signal after the gradation correction and the theoretical limit characteristic of color reproduction, based on the luminance signal after the gradation correction and the color difference signal after the correction. A recording medium recording a processing program for causing a computer to execute the step of combining the image signal with the image signal.