JP2001257902A - Method and device for processing image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the color of an image from impressing too sharp when a gradation is made hard and to prevent the color from becoming dark when the gradation is made soft. SOLUTION: A gradation conversion factor (k) in the case of applying gradation converting processing to image data S0 is determined in a gradation conversion factor determining means 11. When the gradation of the image data S0 is converted, in a converting means 13, matrix operation for converting color saturation is simultaneously performed but the coefficient of a matrix to be used therefor is determined corresponding to the gradation conversion factor (k) in a coefficient determining means 12. Then, the image data S0 are converted in the converting means 13 by a matrix M provided thereby and processed image data S1 are provided. The processed image data S1 are outputted as a print P by a printer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image processing method and apparatus for performing image processing on image data obtained by reading an image recorded on a film or image data obtained by a digital camera. It is.

[0002]

2. Description of the Related Art To display digital image data obtained by a digital camera or digital image data obtained by reading an image recorded on a negative film or a reversal film as a hard copy such as a print or on a CRT or the like. An image processing system for reproducing a soft copy has been proposed. As described above, when reproducing an image acquired by a digital camera, a scanner, or the like, it is expected that the image has the same high-quality image quality as a photograph printed from a negative film.

[0003] For this reason, it has been practiced to reproduce an image after subjecting the digital image data to image processing for converting the gradation. For example, for an image with a narrow dynamic range, such as a landscape photograph on a cloudy day, the contrast can be enhanced to enhance the appearance of the image. Thus, an image having a soft impression can be obtained by softening the contrast.

[0004]

However, when the contrast of an image with high color saturation is enhanced, the color saturation is emphasized, resulting in an image having a stronger impression than an actual scene. Further, although the view of a fine weather scene is improved by softening, the color saturation is reduced and the color becomes dull, resulting in an image having no impact. For this reason, when the gradation conversion process is performed, it is conceivable to play back the processed image once on a monitor and correct the color saturation while observing the reproduced image. To do so requires skill and work efficiency is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an image processing method and apparatus capable of obtaining a processed image having appropriate color saturation even when gradation conversion processing is performed on the image. The purpose is to provide.

[0006]

According to the present invention, there is provided an image processing method for performing image processing on image data representing a color image to obtain processed image data. At the same time as performing the conversion processing, the color conversion processing according to the degree of the gradation conversion processing is performed to obtain the processed image data.

[0007] "Color saturation" refers to color and saturation.

[0008] "Color saturation conversion processing according to the degree of the gradation conversion processing" means that when the gradation conversion processing is a high contrast processing, the color saturation is emphasized, so that the degree of the gradation conversion processing is reduced. This is a color saturation conversion process for reducing the color saturation in response. on the other hand,
When the gradation conversion process is a softening process, the color saturation is reduced, so that the color saturation is increased in accordance with the degree of the gradation conversion process.

The gradation conversion process may be performed while the image data is displayed on a monitor or the like while the operator observes the image. However, an image having a narrow dynamic range is regarded as a low-contrast image, and the image is converted to a dynamic range. The corresponding softening process may be regarded as a high-contrast image for an image with a wide dynamic range, and the softening process according to the dynamic range may be automatically performed. Further, the gradation conversion processing may be not only linear processing but also non-linear processing.

An image processing apparatus according to the present invention performs image processing on image data representing a color image to obtain processed image data. And a conversion unit that performs a color saturation conversion process in accordance with the degree of the gradation conversion process to obtain the processed image data.

[0011]

According to the present invention, image data is subjected to gradation conversion processing and, at the same time, color saturation conversion is performed in accordance with the degree of gradation conversion processing to obtain processed image data. It is not necessary to perform the color saturation conversion processing after reproducing the image subjected to the gradation conversion processing and confirming the degree of the color saturation conversion, and thus the gradation conversion processing and the color saturation conversion processing can be performed efficiently. For example, when the gradation conversion process is a softening process, the color of the entire image becomes dull and sleepy, but by increasing the color saturation simultaneously with the softening process, an impactful and soft impression is obtained. Images can be obtained. Also, when the gradation conversion process is a high contrast process, the entire image has a sharp impression, but by reducing the color saturation simultaneously with the high contrast process, it is possible to obtain an image without a strong impression and a good appearance. Can be.

[0012] Further, since the color conversion processing according to the gradation conversion processing is performed at the same time as the gradation conversion processing, even an inexperienced operator can easily process a processed image having appropriate color saturation. Can be obtained.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an image reproducing system to which an image processing device according to an embodiment of the present invention is applied. As shown in FIG. 1, an image reproducing system according to an embodiment of the present invention is obtained by photoelectrically reading an image recorded on a negative film or a reversal film, or obtained by photographing with a digital camera. Image processing means 1 for performing image processing on the processed image data S0 to obtain a print P; an image processing means 1 for performing image processing on the image data S0 to obtain processed image data S1;
2 as a print P, a monitor 3 for reproducing the image data S0 or the processed image data S1, and input means including a keyboard, a mouse, etc. for performing various inputs to the image processing means 1. 4 is provided.

The image processing means 1 performs a linear gradation conversion process and a color saturation conversion process on the image data S0 to obtain the processed image data S1. A gradation conversion rate determining unit 11 that determines a gradation conversion rate k when performing gradation conversion on S0, and performs gradation conversion processing and color saturation conversion processing on the image data S0 based on the gradation conversion rate k. Determining means 12 for determining a 3 × 3 matrix M for calculation and coefficient determining means 1
2, the image data S is calculated based on the matrix M determined in
A conversion unit 13 for performing a gradation conversion process and a color saturation conversion process on 0.

The gradation conversion rate determining means 11 calculates a gradation conversion rate k which brings the dynamic range of the image data S0 closer to a predetermined dynamic range. Here, the gradation conversion ratio k is a value indicating how much the gradation originally included in a certain image data S0 is hardened or softened and the gradation conversion process is performed. In the case of the hard gradation, k> 1. , K <1 in the case of soft tone. Also, the gradation conversion rate k
The higher the value, the higher the degree of hardening, and the lower the gradation conversion rate k, the higher the degree of softening. Specifically, FIG.
As shown in the figure, a histogram of the image data S0 is obtained, and a density HL of a point 5% lower in density from the highlight point H0 and a density SD of a point 5% higher in density from the shadow point L0 are obtained. Concentrations HL and S
Using D, a gradation conversion rate k is calculated based on the following equation (1). The image data S0 is obtained from a color negative film, and the densities HL and SD are negative densities.

K = 0.96 × 1.2 / (HL−SD) (1) However, in order to prevent calculation of an extreme gradation conversion rate k, k is set to k> 1.2 when k> 1.2. = 1.2 and k = 0.7 when k <0.7.

Note that the gradation conversion rate k may be determined based on not only the method shown in the above equation (1) but also the skewness or the kurtosis of the histogram of the histogram of the image data S0. .

The coefficient determining means 12 calculates the color signals R0, B constituting the image data S0 as shown in the following equation (2).
Color signals R1, G1, B that have undergone a matrix operation on 0 and G0 and have undergone gradation conversion processing and color saturation conversion processing.
The coefficient of the matrix M for obtaining 1 is determined.

[0019]

(Equation 1)The coefficient of the matrix M shown in equation (2) is related to the gradation conversion rate k.
In this embodiment, the gradation conversion process is f
_RR(K) + f_RG(K) + f_RB(K) = γr = 1
(Γ is for R), f_GR(K) + f
_GG(K) + f_GB(K) = γg = 1, f_BR(K) +
f_BG(K) + f_BB(K) = γb = 1
It is determined. In addition, this allows the image to be
The gray gradation of the image data S0 is stored. This
Here, in the matrix M, γr = γg = γb = k
By determining each coefficient so that
And the color saturation conversion processing can be performed simultaneously. Also,
The coefficient of the matrix M is k <1, that is, the softening process is performed.
Then, for the diagonal term, f_RR(K)> 1, f
_GG(K)> 1, f_BB(K)> 1 and the off-diagonal term
The sum of each row is f_RG(K) + f_RB(K) <0, f_GR
(K) + f_GB(K) <0, f_BR(K) + f
_BG(K) <0, and conversely k> 1, that is, the high contrast processing
Is performed, the diagonal term is given by f _RR(K) <1,
f_GG(K) <1, f_BB(K) <1 and off-diagonal terms
Is the sum of each row of f_RG(K) + f_RB(K)> 0, f
_GR(K) + f_GB(K)> 0, f_BR(K) + f_BG
(K) is determined so that> 0. Such a coefficient f
_{i , J}(K) An example of (i, j = R, G, B) is shown below.
You.

[0020]

(Equation 2) However, for f _RR (k), f _GG (k), and f _BB (k), f _RR (k) + f _RG (k) + f _RB (k) =
_{γr = 1, f GR (k} ) + f GG (k) + f G B (k)
= Γg = 1, f _BR (k) + f _BG (k) + f
_BB (k) = γb = 1. Thereby, the matrix M can be determined by the six parameters.

The coefficients of the matrix M may be calculated sequentially using the above-described function in accordance with the gradation conversion rate k. The matrix M may be calculated in advance and stored in the memory. Also, a representative value of the gradation conversion rate k (for example, k =
1.2, 1.1, 0.9, 0.8, 0.7), the matrix M may be calculated in advance, and this may be stored in the memory. In this case, the matrix M for other values of k may be determined by linearly interpolating the matrix coefficients of these representative matrices M.

In the above description, the matrix M is determined by the six parameters. The greater the number of parameters, the higher the accuracy of the color-saturation conversion process, but the determination of the matrix M takes a long time. Conversely, the smaller the number of parameters, the easier the matrix M can be determined, but the lower the accuracy of the color saturation conversion processing. Therefore, the number of parameters may be determined depending on the accuracy of the color conversion process and the capability of the system.

The image data obtained by photographing the color patches composed of various colors is subjected to gradation conversion processing at various gradation conversion rates k, and the gradation conversion processing is performed for each gradation conversion rate k. A matrix coefficient for returning the color of the color patch to the color of the image after the conversion processing may be experimentally obtained. Here, an example of the matrix M according to the value of the gradation conversion rate k experimentally obtained as described above is shown below. Here, an example of the matrix M in the case where the number of parameters is 6 and the gradation conversion rate k = 1.2, 1.1, 0.9, 0.8, 0.7 is shown.

[0024]

(Equation 3) The conversion unit 13 uses the matrix M determined by the coefficient determination unit 12 to calculate the image data S
0, the tone signals R0, G0, and B0 are subjected to gradation conversion processing and color saturation conversion processing to obtain color signals R1, G
The processed image data S1 composed of 1 and B1 is obtained.

Next, the operation of this embodiment will be described. FIG. 3 is a flowchart showing the operation of the present embodiment. First, the image data S0 is input to the gradation conversion ratio determining unit 11 of the image processing unit 1, and the gradation conversion ratio k is determined based on the above equation (1) (step S1). The gradation conversion rate k is input to the coefficient determining means 12, where the coefficients of the matrix M in the equation (2) are determined (Step S).
2). The matrix M whose coefficients have been determined is input to the conversion means 13, where the color signals R constituting the image data S0 are converted.
The matrix operation shown in equation (2) is performed on 0, G0, and B0 to obtain processed image data S1 composed of color signals R1, G1, and B1 (step S3). The processed image data S1 is input to the printer 2, and the print P
Is output (step S4), and the process ends.

As described above, in the present embodiment, the conversion means 13 performs the gradation conversion processing on the image data S0 according to the equation (2) and simultaneously performs the color saturation conversion according to the degree of the gradation conversion processing. Processed and processed image data S
Therefore, it is not necessary to perform the color saturation conversion process after reproducing the image subjected to the gradation conversion process and confirming the degree of the color saturation conversion, thereby efficiently performing the gradation conversion process and the color saturation. A conversion process can be performed.

In the above embodiment, the gradation conversion rate k is determined by the gradation conversion rate determining means 11 as shown in the above equation (1).
The input means 4 performs a gradation conversion process to obtain a desired gradation while observing the displayed image, and obtains a gradation conversion ratio k corresponding to the performed gradation. It may be.

In the above embodiment, the expression (2)
The tone conversion process and the color saturation conversion process are performed by the matrix calculation shown in FIG. 5. The image data S0 after the tone conversion process is converted into the L ^* a ^* b ^* color space, and the L ^* a ^*
a ^* and b in the b ^* space according to the gradation conversion rate k
The value of ^* may be changed, and the changed L ^* a ^* b ^* value may be inversely converted to RGB space to obtain the processed image data S1. This processing may be performed as follows. First, the color signal R constituting the image data S0 is calculated by the following equation (3).
Convert 0, G0, B0 to CIE1931 XYZ tristimulus values.

[0029]

(Equation 4) Next, CIE1976L ^* a ^* b ^* is calculated from the tristimulus values XYZ by the following equations (4) to (6).

L ^* = 116 (Y / Yn) ^1/3 -16 (4) a ^* = 500 {(X / Xn) ¹ /3-(Y / Yn) ^1/3 } (5) b ^* = 200 {(Y / Yn) ^1/3 − (Z / Zn) ^1/3 } (6) Note that Xn, Yn, and Zn are tristimulus values for white, and can be substituted by tristimulus values corresponding to D65. it can.

Then, referring to the table shown in Table 1,
A ^* and b ^* are corrected by the following equations (7) and (8) according to the value of the gradation conversion rate k to obtain a ^* 'and b ^* '.

A ^* '= C (a ^* ) * a ^* (7) b ^* ' = C (b ^* ) * b ^* (8)

[Table 1] Then, using a ^* 'and b ^* ', the equations (4) to (6)
Is solved in reverse, and by inversely transforming equation (3),
Processed image data S composed of color signals R1, G1, and B1 subjected to color saturation conversion processing according to the degree of gradation conversion processing
1 can be obtained.

Note that the color saturation conversion processing is not limited to the matrix operation and the method of converting into the L ^* a ^* b ^* color space, but the color signals R0, G constituting the image data S0.
It is also possible to obtain the luminance and chrominance signals Y, Cb, and Cr from 0 and B0 and to perform addition, subtraction, or multiplication on the chrominance signals Cb and Cr to convert the color saturation according to the degree of the gradation conversion processing. .

In the above embodiment, a linear gradation conversion process is performed, but a non-linear gradation conversion process may be performed. In this case, the gradation conversion processing can be performed by a non-linear one-dimensional look-up table, and the color saturation conversion processing is performed by a matrix operation using a matrix determined according to the degree of the non-linear gradation conversion processing. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an image reproducing system to which an image processing device according to an embodiment of the present invention is applied.

FIG. 2 is a diagram showing a histogram of image data.

FIG. 3 is a flowchart showing the operation of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image processing means 2 Printer 3 Monitor 4 Input means 11 Tone conversion rate determination means 12 Coefficient determination means 13 Conversion means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 9/64 H04N 1/46 Z F Term (Reference) 5B057 CA01 CA08 CA12 CA16 CB01 CB08 CB12 CB16 CC01 CE11 CE17 CH07 5C066 AA11 BA20 CA05 CA17 EA05 GA01 GB01 HA03 HA06 JA01 KA12 KE04 LA02 5C077 LL19 MP08 PP15 PP32 PP36 PP37 PQ19 PQ23 SS05 TT02 TT09 5C079 HB01 LA12 LB01 MA04 NA03 NA05 PA08

Claims (2)

[Claims] 1. An image processing method for performing image processing on image data representing a color image to obtain processed image data, comprising: performing a gradation conversion process on the image data;
An image processing method, wherein a color saturation conversion process according to a degree of the gradation conversion process is performed to obtain the processed image data. 2. An image processing apparatus for performing image processing on image data representing a color image to obtain processed image data, comprising: performing a gradation conversion process on the image data;
An image processing apparatus comprising: a conversion unit that performs a color saturation conversion process according to a degree of the gradation conversion process to obtain the processed image data.