JPH09130815A - Method and device for processing picture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To heighten the efficiency of processing by executing white balance processing and data compression processing in the same color space in a picture processor processing conversion to the color space capable of separately dealing with luminance information and saturation information in order to compress data. SOLUTION: Picture data inputted by a picture input part 1 is converted to a YUV color space by a chrominance conversion part 2, and saturation information U and V are extracted from picture data converted to the YUV color space by a data collection part 31 to obtain the average values Ua and Va of the piece of saturation information U and V. Then the average values Ua and Va are subtracted from U and V before correction by a correction part 32 through the use of a parameter (the average value) extracted by the data collection part 31 to execute white balance processing and after then compression and development processing is executed by a picture data compression and development processing part 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and an image processing apparatus for performing white balance processing on an image input by image input means.

[0002]

2. Description of the Related Art When the color of the illuminating light source is other than white,
When a certain object is photographed by a CCD camera or the like, there occurs a phenomenon that the object is not photographed as white even if it is white. Therefore, white balance processing is performed in order to extract the image data of the original color of the object regardless of the color of the light source that is irradiated.

This white balance processing is performed in consideration of a display device that displays an image, in the RGB color space or YI.
Generally, the Q color space is used. For example, a display device of a personal computer performs image data processing in the RGB color space, and therefore performs white balance processing in the RGB color space. As the method of the white balance processing,
Based on the premise that the average color of the entire screen is an achromatic color (gray), G that contains a lot of luminance information is fixed, and R and B are multiplied by a certain coefficient so that the average color becomes an achromatic color. Method,
Alternatively, there is a method of calculating the color temperature from the image information, determining the correction coefficient from the table of the color temperature and the correction count value prepared in advance, and performing the correction.

[0004]

By the way, a process of compressing image data taken in from a CCD camera or the like and then expanding it is generally performed. The image data compression in this case is usually performed by converting the RGB color space into the YUV color space. This is because the human visual characteristics are taken into consideration, and human beings are sensitive to changes in luminance (Y), but are not very sensitive to changes in saturation (U, V). The data compression ratio is increased by converting the information and the saturation information into the YUV color space, which is a color space that can be handled separately, and thinning out the saturation information to reduce the data amount.

However, as described above, the conventional white balance processing is generally performed in the RGB (or YIQ) color space in consideration of the display device. Therefore, in the image processing device when the compression processing of the image data is necessary, after converting the image data captured from the CCD camera or the like into the RGB (or YIQ) color space,
There has been a process of performing white balance processing and then repeating the conversion of the color space many times, such as converting the RGB color space into the YUV color space for data compression.

As described above, in the image processing apparatus that performs data compression by converting the luminance information and the saturation information into a color space that can be handled separately and thinning out the saturation information to reduce the data amount, a white balance is obtained. When performing the processing, in order to perform the white balance processing, the captured image data is converted into the RGB (or YIQ) color space in consideration of the display device, the white balance processing is performed, and then the data compression is performed. In addition, it is necessary to perform color conversion corresponding to each of white balance processing and data compression processing such as conversion to the YUV color space, and there is a problem that the color conversion processing is complicated and the processing efficiency is low.

Therefore, the present invention enables white balance processing in a color space in which image data is compressed, and when image data compression processing is required, white in the same color space as the compression processing is performed. An object of the present invention is to realize an image processing method and an image processing apparatus that enable balance processing, improve processing efficiency, and perform natural white balance processing that is close to appearance.

[0008]

An image processing method according to the present invention comprises a color conversion step of converting image data input by image input means into image data in a color space capable of separately handling luminance information and saturation information. In an image processing method having at least an image data compression step of performing image data compression in consideration of human visual characteristics in the color space converted by the color conversion step, white balance processing for performing white balance processing on the input image data. This white balance processing step includes a step of extracting a parameter necessary for the white balance processing based on the saturation information in the color space converted by the color conversion step, and using the extracted parameter. Then, white balance processing is performed by performing a calculation for performing white balance. According to this, the white balance process can be performed in the same color space as the data compression process, and the white balance process and the data compression process can be efficiently performed without performing color conversion many times.

The parameter required for the white balance processing is the average value of the saturation in the input image data of one screen. According to this, the parameters can be extracted by a simple process.

An example of the calculation for applying the white balance is a method of subtracting the average value of the saturation from the saturation information of the pixel before the white balance processing. According to this method, white balance processing can be performed with extremely simple processing.

A preset threshold value is set for the average value, and when the obtained average value is equal to or more than the threshold value,
The average value is not used as data for white balance processing. In this way, white balance processing is not performed for an image of a single color on the entire screen, so unnatural white balance processing is performed for an image composed of a single color. Can be prevented.

By the way, as a color space that can separately handle the luminance information and the saturation information, for example, a YUV color space is used.

Further, the image processing apparatus of the present invention is a color conversion means for converting the image data input by the image input means into image data of a color space capable of separately handling luminance information and saturation information, and this color conversion means. An image processing apparatus having at least image data compression means for performing image data compression in consideration of human visual characteristics in the color space converted by the method, comprising white balance processing means for performing white balance processing on the input image data. The white balance processing means, based on the saturation information in the color space converted by the color conversion means, a data collection unit that extracts parameters necessary for white balance processing,
It is characterized in that white balance processing is performed by performing an operation for applying white balance using the parameters extracted by the data collection unit. According to this, similarly to the above, the white balance processing can be performed in the same color space as the data compression processing, and the white balance processing and the data compression processing can be efficiently performed without performing the color conversion many times. The configuration of the processing device can be simplified.

The data collecting unit collects the saturation information in the input image data for one screen and extracts the average value of the collected saturation information as a parameter for the white balance processing. According to this, similarly to the above, the parameters can be extracted by a simple process, and the data collection unit can be realized with a simple configuration.

As an example of the correction processing, the correction unit performs the white balance processing by subtracting the average value of the saturation from the saturation information of the pixel before the white balance processing. According to this, similarly to the above, white balance processing can be performed by simple processing, and the correction unit can be realized with a simple configuration.

A preset threshold value is set for the average value, and when the calculated average value is equal to or more than the threshold value,
The average value is not used as data for white balance processing. By doing this, like the above,
Since white balance processing is not performed on an image of a single color on the entire screen, it is possible to prevent unnatural white balance processing from being performed on an image composed of a single color. be able to.

Further, as described above, for example, a YUV color space is used as a color space that can separately handle luminance information and saturation information.

[0018]

Embodiments of the present invention will be described below.

FIG. 1 is a block diagram illustrating a schematic configuration of an image processing apparatus having a function of performing compression / decompression processing of image data and a function of performing white balance processing. The conversion unit 2, the white balance processing unit 3, the image data compression / decompression processing unit 4, the inverse color conversion unit 5, and the like are included.

The color conversion unit 2 converts the image data output from the image input unit 1 (here, the image data in the RGB color space) into the YUV color space by using the conversion equation shown in the equation (1). As described above, the conversion to the YUV color space is performed in order to reduce the amount of data by thinning out the saturation information in consideration of human visual characteristics and increasing the data compression rate.

[0021]

(Equation 1)

The white balance processing section 3 comprises a data collection section 31 and a correction section 32, and the color conversion section 2
Then, white balance processing is performed based on the data color-converted into the YUV color space. A specific example of this white balance processing will be described later.

The image data compression / decompression processing section 4 is, for example, a JPEG (Joint Photographic Expert Grou).
p) and the like are used, but the invention is not limited thereto. Further, the inverse color conversion unit 5 converts the YUV color space into the RGB color space by using the conversion equation shown in the equation (2).

[0024]

(Equation 2)

Next, the white balance processing will be described. FIG. 2 is a flowchart for explaining the white balance processing of the present invention. First, from the image data converted into the YUV color space, the saturation information U of the image data for one screen,
The average values Ua and Va of V are obtained (step s1). This processing is performed by the data collection unit 31 in FIG.
The values of U and V are obtained for all pixels of the image of the entire one screen to be processed, the average values Ua and Va are calculated from the U and V of each pixel, and the average values Ua and Va are Output as a parameter for correction.

Then, in step s2, the correction is performed. This correction is performed by the correction unit 32 in FIG. 1, and specifically, the following correction processing is performed.

That is, the saturation of each pixel before correction is Uo,
Vo, the saturation of each pixel after correction is set to Un and Vn.
White balance processing is performed by obtaining n and Vn by Un = Uo-Ua ... (3) Vn = Vo-Va ... (4).

This white balance processing is performed, for example, by
When the object to be photographed is illuminated by a light source with a strong red color, the average values Ua and Va are data that include a large amount of red, so the data that includes a large amount of red is Uo and V before correction.
This is a process of subtracting from O, and Un and Vn after correction obtained by this can be data close to the original color. That is, the average values Ua, Va are considered to be values close to the color of the light source at that time, and the average values Ua, Va based on the premise that the average color of the entire image for one screen is achromatic.
If correction is performed so that 0 is set to 0, the corrected Un and Vn obtained by this will be data close to the original color. Although various correction methods are conceivable, in this embodiment, as a simple calculation method, as shown in the equations (3) and (4), the average values Ua and Va are calculated from the uncorrected Uo and Vo. The white balance process is performed by pulling.

As described above, the white balance processing can be performed in the same color space as the data compression processing, and the white balance processing and the data compression processing can be efficiently performed without performing the color conversion many times.

In the embodiment of the present invention described above, for the image data of one screen that is currently captured, an average value is obtained from the captured image data, and the above (3) and (4) are performed. Although the correction as shown in the formula was performed, the actual processing is to save the average value obtained from the captured image data for one screen and store the average value for the saved several screens. Is used to correct the image data that is currently captured, and white balance processing is performed. In this way, by using the average value obtained from the previously captured image data to correct the currently captured image data, the image data capture, average value calculation processing, and correction processing are performed. Can be performed in parallel, and the processing speed can be increased.

In the data collection performed by the data collection unit 21, the U and V values are obtained for all pixels of the image of the entire one screen to be processed, and the average values Ua and Va are calculated. However, instead of obtaining the U and V values for all pixels of the image on the entire screen, a sample point is determined and the U and V values of the pixels at that sample point are obtained, and the average value thereof is calculated. May be requested. For example, one pixel out of four pixels in the vertical direction and the horizontal direction may be set as a sample point, the values of U and V of the pixel at the sample point may be obtained, and the average value thereof may be obtained. By doing so, the processing speed can be increased.

Further, the average value obtained from the image data for one screen is compared with a preset threshold value to determine whether or not it is less than or equal to the threshold value. It is also possible to determine For example, when an average value as described above is obtained for an image of a forest or the like whose entire screen is covered with green, the obtained average value becomes a strong green value, which is used in (3) and (4) above. When the correction is performed using the formula, there is a disadvantage that the color is not green after the white balance processing although the image is originally green. To deal with this, if the calculated average value is too large, it is considered that the image is not composed of various colors but composed of a single color, and in that case, the white balance is The processing is not performed (when the above-mentioned parallel processing is performed, the average value is not used as the correction data). By doing so, it is possible to prevent an unnatural white balance process from being applied to an image composed of a single color.

[0033]

As described above, according to the present invention,
A color space that can handle luminance information and saturation information separately, for example,
Since the white balance processing can be performed in the YUV color space, the image processing apparatus that performs the color conversion processing in the YUV color space to perform the data compression processing can perform the white balance processing and the data compression processing in the same color space.
Since it is not necessary to repeat the color conversion many times, the white balance process and the subsequent data compression process can be efficiently performed, and the white balance process of the present invention can be performed by an extremely simple calculation.

Further, for example, assuming that the average color of the entire image is an achromatic color, in the white balance processing in the YUV color space, sky blue, tree green, sea marine blue, etc. are the majority of the image. Occupying (when the dominant color image exists), an effect that unnatural correction is unlikely to occur is obtained compared to the white balance processing in the RGB color space. This is because in the processing in the RGB color space, the brightness changes due to the white balance processing, but
It is considered that this is because the white balance processing in the UV color space does not change the luminance.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an embodiment of the present invention.

FIG. 2 is a flowchart illustrating processing according to the embodiment of this invention.

[Explanation of symbols]

 1 ... Image input unit 2 ... Color conversion unit 3 ... White balance processing unit 4 ... Image data compression / decompression processing unit 5 ... Reverse color conversion unit 31 ... Data collection unit 32. ..Correction section

Claims (10)

[Claims] 1. A color conversion step of converting image data input by an image input means into image data of a color space capable of separately handling luminance information and saturation information, and a human being in the color space converted by this color conversion step. In an image processing method having at least an image data compression step of performing image data compression in consideration of visual characteristics, there is a white balance processing step of performing white balance processing on the input image data, and the white balance processing step is Extracting parameters necessary for white balance processing based on the saturation information in the color space converted by the color conversion step, and performing an operation for applying white balance using the extracted parameters. An image processing method characterized in that white balance processing is performed in. 2. The image processing method according to claim 1, wherein the parameter required for the white balance processing is an average value of saturation in the input image data of one screen. 3. The image processing according to claim 2, wherein the calculation for applying the white balance is realized by subtracting the average value of the saturation from the saturation information of the pixel before the white balance processing. Method. 4. A preset threshold value is set for the average value, and when the obtained average value is equal to or larger than the threshold value, the average value is not used as data for white balance processing. The image processing method according to claim 2 or 3, characterized in that. 5. The image processing method according to claim 1, wherein the color space that can separately handle the luminance information and the saturation information is a YUV color space. 6. A color conversion unit for converting image data input by the image input unit into image data in a color space capable of separately handling luminance information and saturation information, and a human being in the color space converted by the color conversion unit. In an image processing device having at least image data compression means for performing image data compression in consideration of the visual characteristics of the image data, a white balance processing means for performing white balance processing on the input image data is provided, and the white balance processing means is Based on the saturation information in the color space converted by the color conversion means, a data collecting unit that extracts parameters necessary for white balance processing, and a white balance using the parameters extracted by this data collecting unit. Image processing characterized by performing white balance processing by performing calculations for applying Location. 7. The data collecting unit collects saturation information in input image data of one screen and extracts an average value of the collected saturation information as a parameter for white balance processing. The image input device according to claim 6. 8. The correction unit subtracts an average value of the saturation from saturation information of pixels before white balance processing,
The image processing apparatus according to claim 7, wherein the image processing apparatus performs a white balance process. 9. A preset threshold value is set for the average value, and when the obtained average value is equal to or higher than the threshold value, the average value is not used as data for white balance processing. The image processing device according to claim 7, wherein 10. The image processing apparatus according to claim 6, wherein the color space that can separately handle the luminance information and the saturation information is a YUV color space.