JPH07200814A - Image color correcting method - Google Patents

Abstract

PURPOSE:To correct the color of a subject image to be a desired color by a simple operation. CONSTITUTION:An image to undergo the color correction is read out of an image data storage pert 10A end shown on a display 14. At the same time, the input image data are converted into a coordinate system of HLS by a coordinate system converting part 24. Then, the optional corrected value DELTAH, DELTAL, and DELTAS are from inputted from corrected value input part 26 and added to the HLS coordinate value of the subject image at a color correction arithmetic part 32. This HLS value is converted into the RGB data and shown on the display 14. If the result of correction is satisfactory, the corrected image data are adversely converted into a CMYK coordinate system, for example, for a printing image and stored in a corrected image data storage part 10B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image color correcting method, and more particularly to an image color correcting method suitable for correcting a target image color to a target color.

[0002]

2. Description of the Related Art For example, when an image for a merchandise catalog is different from a target color, it is necessary to correct the image whose color is to be corrected (target image) so as to match the target color. .

Conventionally, in the case of making such a correction with an image for a catalog, a color photograph is redistributed and input again, or a color displayed by a halftone dot on the original plate (film) is used with a correction liquid. I responded by correcting it.

[0004]

However, there is a problem that re-disassembly for correction requires time and cost, and that there is a problem that a skilled technique is required for original plate correction.

The present invention has been made to solve the above-mentioned conventional problems, and it is possible to correct the color of the target image deviating from the target color to the target color by a simple operation. It is an object to provide a correction method.

[0006]

According to the present invention, in an image color correcting method, a target of color correction is displayed on a display, and image data of the target image is represented by H (hue), L (brightness), S ( HLS of the target image converted to the coordinate system of saturation)
The above problem is solved by adding an arbitrary correction value to the coordinate value.

According to the present invention, in the above image color correction method, an image area having a hue angle within a predetermined angle range in the positive and negative directions with respect to a specific hue angle is extracted, and only the extracted area is colored. It is intended to be corrected.

The present invention further provides, in the above-described image color correcting method, the larger the angle away from the reference hue angle is,
The correction value added to the H, L, and S coordinate values of the target image is reduced.

[0009]

In the present invention, the image data of the target image displayed on the display is converted into the H, L, S coordinate system,
Since an arbitrary correction value is added to the HLS coordinate value of the target image, it becomes possible to correct the target image to a target color with a simple operation, and to match the human color vision of H, L, and S. Since the color correction is performed using the coordinate system described above, it is possible to correct the color naturally by the human eye.

Particularly, since the present invention moves each coordinate axis of the HLS coordinate system by the correction value, it is extremely effective for correcting an image in which a color cast occurs due to the coordinate axis being displaced. Is.

In the present invention, when an image area having a hue angle within a predetermined angle range in the positive and negative directions is extracted from a target image with a specific hue angle as a reference, and color correction is performed only on the extracted area. Since it is possible to perform color correction only on a necessary area in the target image, the processing can be simplified and the processing time can be shortened.

Further, in the present invention, when the color correction is performed by extracting the specific area as described above, the correction value added to the HLS coordinate value of the target image decreases as the angle away from the reference hue angle increases. In such a case, it is possible to prevent discontinuity in hue and gradation at the boundary with other areas.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a schematic block diagram showing a correction apparatus applied to the image color correction method of the first embodiment according to the present invention.

The correction device includes a storage device 10 which is a storage medium such as a magnetic tape, a magneto-optical disk or a hard disk for storing image data decomposed by a scanner or the like, image data after color correction, and the like. A processing device 12 having a function of performing various processes to be described later with respect to image data read from the storage medium 10, and a target image of a correction target read from the storage device 10, a corrected image, and the like. And a display 14.

The processing device 12 is, as shown in FIG.
The display image reading unit 20 for reading the image data for the image to be displayed on the display 14 from the image data storage unit 10A included in the storage device 10, and the image data read by the reading unit 20 are the display image data. The image display unit 22 for converting into the image and displaying it on the display 14 and the image data displayed on the display 14 are HL.
A coordinate system conversion unit 24 for converting to the S coordinate system, and arbitrary correction values ΔH, ΔL to be added to the obtained HLS system coordinate values.
A correction value input unit 26 for inputting ΔS, an HLS addition unit 28 for adding the correction value to the HLS value of the target image,
The image data to be corrected is read again, and the conversion image reading unit 30 for converting the image data into the HLS coordinate system, and the image data of the target image converted by the conversion image reading unit 30 are input to the correction value input unit 26. A color correction calculation unit 32 for adding the correction value, and a coordinate system reverse conversion unit 34 for inversely converting the HLS system coordinate value after the calculation process and sending the same to the image display unit 22 for display on the display 14. An image writing unit 36 for writing the inversely-converted corrected image data in the corrected image data storage unit 10B included in the storage device 10.

As the correction value input section, a method of directly inputting a numerical value with a keyboard or the like, or H, L, S
An input knob or the like may be provided for each to adjust the HLS value.

Next, the color correcting method of this embodiment using the above-mentioned correcting device will be described with reference to the flowchart of FIG. The original image to be corrected is C (cyan),
It is a printing image represented by a color system of M (magenta), Y (yellow), and K (black), and here, a case where the whole is corrected will be described.

First, the display image reading section 20 appropriately thins out the target image from the image data storage section 10A according to the image size and the resolution of the display 14 and reads it (step 1). The reason for thinning out here is to prevent the image from sticking out when it is displayed on the display as it is because the image has a high resolution and a large amount of data because it is for printing.

In order to display the image read out in step 1 on the display 14, the image data is converted into RGB data for display by the image display section 22 and displayed on the display 14 (step 2).

The conversion to RGB data performed here is, for example, a printing C in which the original image data is 8 bits (0 to 255).
In the case of MY (K) data, the color of the display is generated for each value of R, G, B obtained by the complementary color conversion according to the following equations (1) to (3) using the fact that they have a complementary color relationship. In order to correct the characteristics and make them easier to see, the following (4)
This can be achieved by applying gamma correction according to the equations (6). For convenience, K is ignored here.

R = 1-C / 255 (1) G = 1-M / 255 (2) B = 1-Y / 255 (3) r = 255 (R ^0.45 ) (4) g = 255 (G ^0.45 ) ... (5) b = 255 (B ^0.45 ) ... (6)

The image data read in step 1 is converted into HLS data by the coordinate system conversion unit 24 (step 3). The conversion to the HLS data performed here is performed by, for example, converting the RGB data R, G, and B before gamma correction from the following (7) to
The luminance (Y) and color difference (Cr, Cb) data are separated by the linear conversion according to the equation (9), and then (10) to (1)
It can be realized by performing polar coordinate conversion by the equation (2).

Y = 0.299R + 0.587G + 0.114B (7) Cr = RY (8) Cb = BY (9) H = tan ^-1 (Cb / Cr) (10) L = Y (11) S = (Cr ² + Cb ² ) ^1/2 (12)

Next, the operator operates the correction value input unit 26.
Accordingly, appropriate correction values ΔH, ΔL, and ΔS for correcting the image displayed on the display 14 are input, and in the color correction calculation unit 32, the correction values are added to the HLS data of the target image converted in step 3. ΔH, ΔL, and ΔS are added, respectively, and H ', as shown in the following equations (13) to (15),
L'and S'are calculated (steps 4 and 5). This calculation corresponds to the process of moving the coordinate axis of this coordinate system by the correction value, as shown in FIG. 4 for the cylindrical coordinate of the HLS system. The perspective view of FIG. 4 (A) shows ΔL, and FIG. 4 (B) showing the state where the cylindrical coordinates are viewed from above is shown with ΔH and ΔS moved.

H '= H + ΔH (13) L' = L + ΔL (14) S '= S + ΔS (15)

Next, H ', L', obtained in step 5,
S'is converted by the coordinate system inverse transformation unit 34 from the following (16)-
After returning to the YCr Cb system by the equation (18), (19)-
It is converted back into RGB data for display using the equation (24) and displayed on the display 14 (step 6). that time,
You may display it side by side so that it can be compared with the target image before correction.

Y '= L' (16) Cr '= S' cos (H ') (17) Cb' = S 'sin (H') (18) R '= Cr' + Y '(19) ) B '= Cb' + Y '... (20) G' = (Y'-0.299R'-0.114B ') / 0.587 ... (21) r' = 255 (R '0.45) ... (22) g '= 255 ( ^G'0.45 ) ... (23) b' = 255 ( ^B'0.45 ) ... (24)

Next, the operator visually judges the color of the image after the color correction displayed in step 6 above, and
If K, proceed to step 8; otherwise, step 4
Then, a new correction value is input and the processes of steps 4 to 7 are performed (step 7).

If it is determined in step 7 that the color of the image after the color correction is OK, the conversion image reading unit 30 reads the target image data before the correction from the image data storage unit 10A without thinning it out, and the data is processed in the step. It is converted into HLS data by the same method as in 2 and 3 (steps 8 and 9).

Next, H of the original image converted in step 9
To the LS data, the correction values ΔH, ΔL, and ΔS input in step 4 and judged to be OK in step 7 are added, and H ′ is calculated by the equations (13) to (15) as in step 5.
L ′ and S ′ are calculated, and these values are calculated by the coordinate system inverse transformation unit 34.
In step S11, the original CMY (K) coordinate system is inversely transformed (steps 10 and 11). This inverse transformation method is the same as in the case of step 6 above (16) through until R ′, G ′ and B ′ are obtained.
The equation (20) is used, and then the following (25) to (28)
This is done using a formula.

C ′ = 255 (1-R ′) (25) M ′ = 255 (1-G ′) (26) Y ′ = 255 (1-B ′) (27) K ′ = K (28)

After that, C'determined in step 11 above,
M'and Y '(K') are written in the corrected image data storage unit 10B in the storage device 10 as the corrected image data (step 12).

According to the present embodiment described in detail above, the image data of the printing image is converted into the display image data and displayed on the display 14, and the image data is corrected because it matches the human sense. The result is converted into an easily predictable HLS coordinate system, and the separately determined correction values of ΔH, ΔL, and ΔS are added to the H, L, and S values of the target image to be corrected, so that the addition is simple. Natural color correction is possible through arithmetic processing.Even if the target color is similar to the target color and the color is slightly different due to differences in shooting conditions, such as in a printed image for a catalog, you can easily correct the color. You can In particular, the color correction of the present embodiment corresponds to moving the coordinate axis by the correction value of HLS, and therefore is extremely effective in correcting an image that has a color cast due to the shift of the coordinate axis.

Further, since the decomposed image data is directly corrected, the time and cost for re-disassembling is not required.

Further, using the corrected values of H, L and S,
By converting the image data for display and displaying it on the display, it is possible to correct the color only by a simple operation (input of the HLS value) while confirming the color on the display. No skill required.

Next, a second embodiment according to the present invention will be described.

This embodiment is substantially the same as the first embodiment except that the following processing is performed in steps 5 and 10 of the flowchart of FIG. 3 showing the processing operation.

In this embodiment, a representative point is designated in the target image, and the H converted by the step 3 (or step 9) is specified.
The value of H (hue angle) of the LS data is within a certain range around H _T of the representative point (for example, H _T ± 6 as shown in FIG. 6).
Only the image area within 0 ° is extracted as a color correction target.

This corresponds to extracting only the back and the seat of the same color, as shown in FIG. 6A in the case of a chair. In this way, the correction values ΔH, ΔL, and ΔS input in step 4 are added to the image data only for the region in which the value of the hue angle H is within a certain range, and the above (13)-
Each value of H ', L', and S'is calculated by the equation (15), and
As shown in (B), color correction is performed only on the extraction area.
In FIG. 6, the difference in color is indicated by the presence or absence of diagonal lines.

In the case of the region outside the above extraction range, the process proceeds to the subsequent steps without correction, the original RGB data is displayed on the display 14, and the corrected image is combined with the image of FIG. 6 (B). A composite image is created as in (C). Finally, when writing to the image data storage unit 10B in step 12, the area outside the extraction range is written with the original CMYK data.

In the case of the specific example shown in FIG. 6A,
The value of each coordinate system of the representative point of the target image is CMYK (18
0,107,10,0), RGB (75,148,24)
5), YCr Cb (137.2, -62.2, -10)
7.8), HLS (-120.0, 137.2, 12)
4.4), and in the actual processing, the extraction region is set to H _T = −
It was set to ± 30 ° with respect to 120.0 °. When the correction values were set to ΔH = −0.5, ΔL = 8.2, and ΔS = 2.7, respectively, it was possible to make a subtle correction of blue.

With the above processing, only the hue data to be corrected in the data of the target image can be targeted for color correction.

Further, since it is not necessary to perform the reverse conversion to the original coordinate system in step 6 and step 11 for the data judged to be out of the object, the processing time can be shortened.

Next, a third embodiment according to the present invention will be described.

In the case where the method for correcting the color of only a specific hue is carried out according to the second embodiment, the discontinuity of the hue or the gradation occurs at the boundary between the portion where the color correction processing is performed and the portion where the color correction processing is not performed There is. The present embodiment is a method of improving the familiarity of the boundary between the portion where the color correction processing is performed and the portion where the color correction processing is not performed in such a case.

In this embodiment, as in the second embodiment,
Only when the H (hue angle) value of the HLS data converted in step 3 (or step 9) is within a certain range around H _T , the correction values ΔH, Δ input in step 4
L, the ΔS, | H _T -H | of vary according to the value the coefficient f (|
H _T −H |) is calculated, and this value is added to the image data of the extracted region, and H ′ is obtained as in the following equations (13A) to (15A) corresponding to the above (13) to (15). , L ',
Calculate S '.

[0048] H '= H + f (| H T -H |) · ΔH ... (13A) L' = L + f (| H T -H |) · ΔL ... (14A) S '= S + f (| H T -H | ) ・ ΔS… (15A)

[0049] Also, the coefficient f (| H _T -H |) as is the function represented by the following equation (29) or (30) can be used.

[0050] _{f (| H T -H |)} = 1- (| H T -H | / 60) ... (29) f (| H T -H |) = cos (90 · | H T -H | / 60)… (30)

The coefficient of the equation (29) decreases as the hue angle deviates from H _T , as shown by a in FIG. 7 and by the equation (30) as b. In this way, by adopting a function whose value gradually decreases centering on H _T as a coefficient, the closer to the boundary of the extracted region (± 60 °
Since the correction amount can be reduced (the closer it is to), it is possible to prevent discontinuity of color tone and gradation at the boundary.

Although the present invention has been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

For example, although the original image data is CMY (K) data for printing in the above embodiment, the present invention uses other coordinate systems such as RGB data for computer graphics and YIQ data for television. Even data can be applied.

The coordinate system for color correction is HL based on the YCr Cb system used in television images.
The S coordinate system was used, but L ^* a ^* b ^*, which is a uniform color space
It is also possible to use an HLS coordinate system based on an arbitrary coordinate system having independent luminance and chromaticity, such as a system or an L ^* u ^* v ^* system. In this case, the mutual conversion between the coordinate system of the original image data and the coordinate system for color correction may be appropriately determined and the processing may be performed.

[0055]

As described above, according to the present invention,
Since the decomposed image data is directly corrected, there is no need for re-separation and cost, and the color of the target image can be changed to the target color only by the simple operation of inputting the correction value while checking the color on the display. Since it is possible to correct it,
It has the advantage that no skill is required.

Further, since the color correction is performed by the coordinate system in which the hue, lightness, and saturation are independent, which is suitable for human senses, natural correction is possible.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of a correction device applied to an embodiment according to the present invention.

FIG. 2 is a block diagram showing a schematic configuration of functional units of a processing device included in the correction device.

FIG. 3 is a flowchart showing a procedure of color correction processing executed by the method of the above embodiment.

FIG. 4 is an explanatory diagram showing an HLS coordinate system for explaining the principle of color correction.

FIG. 5 is an explanatory view showing a range of a hue angle when extracting a color correction area.

FIG. 6 is an explanatory diagram showing a processing procedure for the extracted color correction area.

FIG. 7 is a diagram for explaining characteristics of coefficients used for color correction.

[Explanation of symbols]

 10 ... Storage device 12 ... Processing device 14 ... Display 20 ... Display image reading unit 22 ... Image display unit 24 ... Coordinate system conversion unit 26 ... Correction value input unit 30 ... Conversion image reading unit 32 ... Color correction calculation unit 34 ... Coordinate system inverse transformation unit 36 ... Image writing unit

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H04N 9/64 Z H04N 1/46 Z

Claims (3)

[Claims] 1. A target image to be color-corrected is displayed on a display, and image data of the target image is represented by H (hue), L (brightness), and S.
A method for correcting a color of an image, which comprises converting to a coordinate system of (saturation) and adding an arbitrary correction value to the HLS coordinate value of the target image. 2. The method according to claim 1, wherein an image area having a hue angle within a predetermined angle range in the positive and negative directions with respect to a specific hue angle is extracted, and color correction is performed only on the extracted area. How to correct the color of the image. 3. The image color correction method according to claim 2, wherein the correction value added to the HLS coordinate value of the target image is decreased as the angle away from the reference hue angle increases.