JPH1098624A - Image processing apparatus and image processing method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To obtain an image processing result while maintaining a light source color. SOLUTION: Based on a light source color estimation result from a light source color estimating unit 2, a conversion unit 3 into a light source color space keeps a ratio of three primary color components of a light source color, and Transform pixel data into corresponding points in RGB space. The uniform perception color space conversion unit 4 converts the image data sent from the light source color space conversion unit 3 into a uniform perception color space. The emphasis / relaxation processing unit 5 performs desired emphasis / relaxation processing on the lightness component and / or the saturation component of the image data sent from the uniform perceptual color space conversion unit 4. Then, the image data is sent to the image display unit 10 via the inverse conversion unit 8 from the uniform perceived color space and the inverse conversion unit 9 to the device space. As described above, the emphasis / relaxation process is performed while maintaining the ratio of the three primary color components of the light source color.

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 and an image processing method and, more particularly, to enhancement of a color natural image for controlling the depth, sharpness, texture and gloss of the color natural image. The present invention relates to an image processing device and an image processing method for executing a relaxation process.

[0002]

2. Description of the Related Art In a conventional image processing apparatus, image processing is performed as follows. The three primary color components R of the light source color
(Red), G (green), and B (blue) are represented by L _r ,
L _g, and _{L b, L r: L g} : L b is 1: 2: 3 Under the light source, consider the image obtained by photographing an object. This image is stored in the system (image processing device)
Is represented by the following three components. Here, RG is used as image processing.
Considering the process of expanding and contracting the dynamic range of each component of B, this process is performed in each value range of RGB inside the system. That is, L _r : L
_{Even if g} : _Lb is 1: 2: 3, for example, the ratio of the light source color to RGB is 1: 1: 1 inside the system.
If it is expressed by, processing to expand and contract under 1: 1: 1 is performed.

[0003]

As described above, the conventional
In the image processing apparatus, the ratio of the three primary color components of the light source color (L_r: L
_g: L_bIs decided by the system without considering
Image processing is performed under the RGB ratio. others
Therefore, with conventional image processing devices, images with the same light source color are maintained.
There is a problem that an image processing result cannot be obtained.

[0004] Such a problem will be described with a specific example. Image processing for expanding and contracting the dynamic range of each component of RGB (image enhancement / relaxation processing) is performed outside the system.
This corresponds to increasing or decreasing the light amount of the light source. here,
Since _Lr : _Lg : _Lb = 1: 2: 3, this light source has a strong blue color, and considering the case where the light amount of the light source is increased, the object under this light source becomes bluish. On the other hand, consider image processing inside the system corresponding to the process of increasing the light amount of the light source. This image processing is processing for enhancing an image. Inside the system, the RGB ratio of the light source color is 1: 1:
Since it is 1, the image becomes whitish when the emphasis processing is performed. As described above, the conventional image processing apparatus cannot obtain an image processing result in which the light source colors are stored.

An object of the present invention is to provide an image processing apparatus and an image processing method capable of obtaining an image processing result while maintaining a light source color. Aim.

[0006]

An image processing apparatus according to a first aspect of the present invention converts each pixel data of an image to a corresponding point in a predetermined color space while maintaining a ratio of three primary color components of a light source color. The image processing apparatus includes a conversion unit and a unit that performs arbitrary processing on each pixel data of the converted image.

According to a second aspect of the present invention, there is provided an image processing apparatus comprising:
Item 1. The ratio of the three primary color components of the light source color is defined as
L_r(Red): L_g(Green): L_b(Blue) and L_r,
L_g, L _bL is the minimum value of_min, The maximum value is L_maXWhen
Then, the conversion means is L_minAnd L_maXConvert using
Perform

According to the image processing method of the present invention, each pixel data of the image is converted while maintaining the ratio of the three primary color components of the light source color.
A conversion step of converting to a corresponding point in a predetermined color space; and performing an arbitrary process on each pixel data of the converted image.

According to a fourth aspect of the present invention, there is provided an image processing method comprising:
Item 3. The ratio of the three primary color components of the light source color is defined as
L_r(Red): L_g(Green): L_b(Blue) and L_r,
L_g, L _bL is the minimum value of_min, The maximum value is L_maXWhen
Then, in the conversion step, L_{mi n}And L_maXUsing
To perform the conversion.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image processing apparatus according to the present invention will be described with reference to the drawings. An image processing device according to an embodiment of the present invention realizes enhancement / relaxation processing of a color natural image. FIG. 1 is a block diagram schematically showing an image processing apparatus according to an embodiment of the present invention. Referring to FIG. 1, the image processing apparatus includes an image input unit 1, a light source color estimating unit 2, a conversion unit 3 for a light source color space, a conversion unit 4 for a uniform perceived color space, an emphasis / relaxation processing unit 5, Inverse conversion unit 8 from uniform perceived color space, inverse conversion unit 9 into device space
And an image display unit 10. Emphasis / relaxation processing unit 5
Includes a lightness component processing unit 6 and a saturation component processing unit 7.

The operation will be described. An image is first input via the image input unit 1. Specifically, the image input unit 1 is a television camera, a scanner, an external input unit via a line, or the like. Image data (pixel data of an image) from the image input unit 1 is sent to a light source color estimating unit 2 and a light source color space conversion unit 3. The light source color estimating unit 2 estimates the light source color and sends the estimation result to the light source color space conversion unit 3. The light source color space conversion unit 3 converts the R (red), G (green), and B (blue) space at the time of image recording into an RGB space in which the ratio of the three primary color components of the light source color is maintained. That is, the conversion unit 3 for converting to the light source color space maintains the ratio of the three primary color components of the light source color based on the light source color estimation result from the light source color estimation unit 2,
Each pixel data of the image from the image input unit 1 is converted into a corresponding point in the RGB space. The RGB space in which the ratio of the three primary color components of the light source color is maintained will be referred to as a light source color space. As described above, the conversion unit 3 to the light source color space
Converts the image data from the image input unit 1 into a light source color space.

The image data (each pixel data of the image) after the conversion to the light source color space is sent to the uniform perception color space conversion unit 4. In the uniform perceived color space conversion unit 4, the image data sent from the light source color space conversion unit 3 is converted into the uniform perceived color space. Here, the uniform perceived color space is a space arranged such that the perceived color difference is also equal if the distance between two colors is equal in any part of the space. A representative example is the Munsell HVC space. On the other hand, in a normal RGB space, it is known that even if the distance between two colors in the space is equal, it does not always seem to be perceived as a uniform color difference, and there is a considerable difference between regions. . The image data (each pixel data of the image) after conversion into the uniform perceived color space is sent to the enhancement / relaxation processing unit 5.

The emphasis / relaxation processing unit 5 performs a desired emphasis / relaxation process on the lightness component and / or the saturation component of the image data sent from the uniform perceived color space conversion unit 4. Here, the brightness component processing unit 6 performs a desired enhancement / relaxation process on the brightness component, and the saturation component processing unit 7 performs a desired enhancement / relaxation process on the saturation component. The image data (each pixel data of the image) after the enhancement / relaxation processing is sent to the inverse conversion unit 8 from the uniform perceived color space. In the inverse conversion unit 8 from the uniform perceived color space, the image data sent from the enhancement / relaxation processing unit 5 is inversely converted into the light source color space. The image data (each pixel data of the image) after the inverse conversion to the light source color space is sent to the inverse conversion unit 9 for the device space.

The inverse conversion unit 9 converts the image data from the uniform perception color space into the RGB space (device space) at the time of image recording. That is, the inverse conversion unit 9 for converting to the device space converts the image data from the inverse conversion unit 8 from the uniform perceived color space to the RG of the image input unit 1.
Inverse conversion to B space (device space). The image data (each pixel data of the image) after the inverse conversion to the device space is sent to the image display unit 10. The image display unit 10 receives and outputs the image data inversely transformed into the device space in the inverse transformation into device space 9. Specifically, the image display unit 10 is a display such as a CRT or a printer.

Next, the processing in the light source color estimating section 2 will be described in detail. In general, the spectral characteristics of the light source
(Λ) and the spectral reflectance of the object is ρ (λ), the spectral characteristic P (λ) of the color of the object is

[0016]

(Equation 1)

## EQU1 ## Usually, the color is treated as a mixture of the three primary colors. In this case, the light source I (λ) also has a component ratio of the three primary colors R (red), G (green), and B (blue), I _r (red): I _g (green): represented by I _b (blue). Therefore, when the image is subdivided into pixels, the color of the i-th pixel is

[0018]

(Equation 2)

It can be expressed as follows. Where P
_ri , P _gi and P _bi are the R, G and B components of P (λ) corresponding to the i-th pixel, respectively. Also, I _r, I _g and I _b, respectively, R of I (lambda)
Component, G component and B component. Further, ρ _ri , ρ _gi and ρ _bi are ρ _π corresponding to the i-th pixel, respectively.
The R component, the G component and the B component of (λ). By the way, in the field of image processing, the “grey hypothesis” has been often used. This means that adding all colors in the natural world results in a gray color.

[0020]

(Equation 3)

## EQU1 ## Further, since at this time the light source must naturally _{"white", I r: I g: I} b = 1:
1: 1. Therefore,

[0022]

(Equation 4)

The following holds. Therefore, now, this gray hypothesis is adopted, and if the color of the light source is not white, from Equations (2) and (4),

[0024]

(Equation 5)

Thus, the ratio of the sum of the components of each pixel of the image represents the characteristics of the light source. Furthermore, considering the effect on the brightness of the entire image, the value of each component of the light source is calculated as the average brightness of the light source.

[0026]

(Equation 6)

Is normalized by using

[0028]

(Equation 7)

As a result, an estimated value of the light source color is obtained. The desired light source color, and _{(I rs:: I gs I} bs), R component of P (lambda), the G and B components, respectively, P _r, P _g, P
_b , the RGB values (P _rt , P
_gt , P _bt ) is given by the following equation.

[0030]

(Equation 8)

Next, the light source color space conversion unit 3 and the device
The details of the processing in the inverse conversion unit 9 to the chair space are explained.
I will tell. The three primary color components RGB of the light source color are
L_r, L _g, L_bAnd The estimation result of the light source color is represented by L_r:
L_g: L_bAnd L_r, L_g, L _bL is the maximum value of
_max, The minimum value is L_minAnd the input images are RGB
It is assumed that the data is quantized by N bits. At this time,
Conversion from RBG space to light source color space at the time of image recording is as follows
(Processing in the conversion unit 3 for conversion to a light source color space).
Note that L_r, L_g, L_bAre respectively described above,
I_rt, I_gt, I_btIs equivalent to

[0032]

(Equation 9)

Here, in equations (9) to (11),
R, G, B represents a value of three primary colors components of the pixels of the image during image _{recording, R t, G t, B} t represents the value of the three primary colors components of the pixels of the image after conversion to the light source color space. The inverse conversion from the light source color space to the original RGB space (the RGB space at the time of recording an image) is performed using the following equation (processing by the inverse conversion unit 9 into the device space).

[0034]

(Equation 10)

The conversion to the light source color space as described above is performed for all the pixels of the image. Next, the conversion to the light source color space by the light source color space conversion unit 3 will be conceptually described. Here, a case is considered where an object is photographed under a light source of _Lr : _Lg : _Lb of 1: 2: 3. Such a photographing site will be referred to as the outside of the image processing apparatus. And
Consider an RGB space outside the image processing device corresponding to the RGB space inside the image processing device. FIG. 2 shows an RGB space outside the image processing apparatus, that is, an _R space under a light source having a ratio of three primary color components (L _r : L _g : L _b ) of 1: 2: 3.
It is a figure showing GB space. With reference to FIG.
Space has a rectangular parallelepiped composed of parallel sides c to L _r axis parallel sides in a, parallel to the L _g shaft side b and L _b. Here, (length of side a): (length of side b): (length of side c)
Is 1: 2: 3. The length of the side a is “1”, the length of the side b is “2”, and the length of the side c is “3”.

FIG. 3 is a diagram showing the RGB space at the time of image recording (before conversion to the light source color space). Referring to FIG. 3, this RGB space has a side d parallel to the R axis and a side e parallel to the G axis.
And a side f parallel to the B axis.
Here, (length of side d) :( length of side e) :( length of side f) is 1: 1: 1. In other words, the RG
In the B space, the ratio of the three primary color components of the light source color is 1: 1: 1. Note that the lengths of the side e, the side d, and the side f are “1”. This RGB space corresponds to the RGB space in FIG.

Referring to FIGS. 2 and 3, the ratio of the three primary color components of the light source color is 1 inside the image processing apparatus although the ratio of the three primary color components of the light source color is 1: 2: 3. 1: 1. Therefore, if the RGB space in which the ratio of the three primary color components of the light source color is 1: 1: 1 is converted into the uniform perceived color space and the enhancement / relaxation processing is performed, an image processing result with the light source color maintained can be obtained. Can not. Therefore, in the present embodiment, based on the estimation result of the light source color, the image data is stored in another RGB space different from the RGB space at the time of recording the image while maintaining the ratio (1: 2: 3) of the three primary color components of the light source color. Convert to RGB space. That is, the image data is converted to the light source color space.

FIG. 4 shows that the ratio of the three primary color components of the light source color is 1:
FIG. 4 is a diagram illustrating a light source color space in the case of 2: 3.
The light source color space corresponds to the RGB space in FIG. 2 and the RGB space in FIG.
It corresponds to the B space. Referring to FIG. 4, the light source color space is a rectangular parallelepiped including a side g parallel to the R axis, a side h parallel to the G axis, and a side i parallel to the B axis. Here, (length of side g): (length of side h): (length of side i)
Is 1: 2: 3. The length of the side g is "1/3"
And the length of the side h is “2/3”, and the length of the side i is “1”. That is, in the light source color space, the RGB of FIG.
Like the space, the maximum value of each of the three primary color components in the RGB space (FIG. 2) outside the image processing apparatus is all “1”.
Instead, the maximum value of the three primary color components in the RGB space (FIG. 2) outside the image processing apparatus is set to “1”. Thus, in the light source color space, the ratio (1: 2: 3) of the three primary color components of the light source color is maintained.

In the conversion unit 4 for converting into the uniform perceived color space in FIG.
An RGB space including a light source color space (a rectangular parallelepiped formed by sides g, h, and i with reference to FIG. 4)
(A cube consisting of a side j parallel to the axis, a side k parallel to the G axis, and a side m parallel to the B axis) into an equivalent perceived color space, and the emphasis / relaxation processing unit 5 Perform emphasis / relaxation processing. In FIG. 4, (length of side j) :( length of side k) :( length of side m) is 1: 1: 1.
And the lengths of the sides j, k, and m are “1”.

Next, the details of the processing in the emphasis / relaxation processing section 5 of FIG. 1 will be described. The dynamic range [a ₀ , b ₀ ] of the reproduced image is equal to the reproduction range [a,
b], the process of extending the reproduction range is image enhancement, as shown in the following equation. In addition,
In the following equation, the relaxation process can be performed by exchanging [a, b] and [a ₀ , b ₀ ]. Further, in the formula, x is, it indicates one of RGB values before enhancement-relaxation, x _t represents any of the RGB values after enhancement-relaxation.

[0041]

[Equation 11]

As described above, in the image processing apparatus according to the present embodiment, the image data is converted into the light source color space, and then the enhancement / relaxation processing is performed. That is, while maintaining the ratio ( _Lr : _Lg : _Lb ) of the three primary color components of the light source color,
Apply emphasis / relaxation processing. For this reason, the image processing apparatus according to the present embodiment can obtain an image processing result while maintaining the light source color. That is, when the emphasis / relaxation process is performed, color reproduction along the color tone of the light source color can be performed. Also, when the emphasis / relaxation process is performed,
There is no change in the color tone of the reproduced color at any point in the image communication / storage system.

[0043]

In the image processing apparatus according to the first aspect of the present invention and the image processing method according to the second aspect of the present invention, image processing is performed while maintaining the ratio of the three primary color components of the light source color. Therefore, it is possible to obtain an image processing result while maintaining the light source color. In other words, when image processing is performed, color reproduction along the color tone of the light source color can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically illustrating an image processing apparatus according to an embodiment of the present invention.

FIG. 2 shows an RGB space outside the image processing apparatus, that is, a ratio (L _r : L _g : L _b ) of three primary color components of a light source color is 1: 2:
FIG. 7 is a diagram illustrating an RGB space under a third light source.

FIG. 3 is a diagram showing an RGB space at the time of recording an image (before conversion to a light source color space) in an RGB space inside the image processing apparatus.

FIG. 4 shows a ratio of three primary color components of a light source color ( _Lr : _Lg : _Lb ).
FIG. 4 is a diagram showing a light source color space when the ratio is 1: 2: 3.

[Explanation of symbols]

 Reference Signs List 1 image input unit 2 light source color estimation unit 3 conversion unit to light source color space 4 conversion unit to uniform perceived color space 5 emphasis / relaxation processing unit 6 lightness component processing unit 7 chroma component processing unit 8 from uniform perceived color space Inverse conversion unit 9 Inverse conversion unit to device space 10 Image display unit

Claims (4)

[Claims] A conversion unit that converts each pixel data of an image into a corresponding point in a predetermined color space while maintaining a ratio of three primary color components of a light source color; An image processing apparatus comprising: means for performing arbitrary processing. 2. The ratio of the three primary color components of a light source color to L
_r(Red): L_g(Green): L _b(Blue) and L_r, L_g,
L_bL is the minimum value of_min, The maximum value is L_maXTo be
And the conversion means is L_minAnd L_maXUsing the
The image processing apparatus according to claim 1, wherein the replacement is performed. A conversion step of converting each pixel data of the image into a corresponding point in a predetermined color space while maintaining a ratio of three primary color components of a light source color; Performing an arbitrary process. 4. The ratio of the three primary color components of a light source color is represented by L
_r(Red): L_g(Green): L _b(Blue) and L_r, L_g,
L_bL is the minimum value of_min, The maximum value is L_maXTo be
In the conversion step, L_minAnd L_maXUsing,
The image processing device according to claim 3, wherein the conversion is performed.