JPH0457272B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for correcting color image information, and in particular to obtaining a copy of an original image by printing or the like from color image information given by a color image signal based on RGB three primary color data. Regarding color correction method in case.

[Background of the invention]

Conventionally, so-called printing plate-making scanners have been widely used for printing color images, but in recent years, as various data processing techniques using computers have been proposed and put into practical use, such scanners have become increasingly popular. By applying various data processing techniques to this image data after converting it into electrical image data, it has become possible to obtain even more effective printed images. There are color correction techniques.

The methods conventionally used for such color correction are mainly based on the Neugebauer equation or the photographic masking method, one example of which will be explained with reference to FIG.

The example in FIG. 2 shows a method adopted in a scanner device for printing plate making. An original image O mounted on a rotating drum 1 of a scanner S is read and scanned by the rotation of this drum 1 and the movement of the head 2. The colors are separated for each pixel by filters 3R, 3G, and 3B, and converted into electrical signals by photoelectric converters 4C, 4M, and 4Y, resulting in a cyan color signal C ₀ , a magenta color signal M ₀ , and a yellow color signal Y ₀ is output.

These color signals C ₀ , M ₀ , Y ₀ are processed by a logarithmic conversion circuit
5C, 5M, and 5Y convert the signal representing transmittance into signals representing concentration C ₁ , M ₁ , and Y ₁ , which are then sent to the adder.
It is input to the sumi version calculation circuit 7 through 6C, 6M, and 6Y, and K=min (C, M, Y)... (1) where min represents the function that gives the minimum value.

The sumi signal K is calculated and output.

On the other hand, the signals from each logarithmic conversion circuit 5C, 5M, 5Y
C ₁ , M ₁ , Y ₁ are input to the primary color correction circuit 8 and
The primary correction signals C′ ₁ , M′ ₁ , Y′ ₁ are calculated, and this primary correction signal is further input to the secondary color correction circuit 9.
Secondary color correction signals C″ ₁ , M″ ₁ , Y″ ₁ are calculated. Then, these secondary color correction signals are sent to adders 6C, 6M, 6Y.
and corresponding signals C ₁ , M ₁ , Y ₁ respectively
are added to become signals C, M, and Y, which are then supplied as output signals C, M, and Y as they are after the ink area signal K is calculated by the ink area calculation circuit 7.

The primary color correction circuit 8 functions to calculate the primary correction signals C′ ₁ , M′ ₁ , Y′ ₁ necessary for ink cloudy correction, and converts the original signals C ₁ , M ₁ , Y ₁ into The primary correction signals C′ ₁ , M′ ₁ ,
Calculate Y′ ₁ .

C′ ₁ = k ₁₁・C ₁ −k ₁₂・M ₁ −k ₁₃・Y ₁ M′ ₁ = −k ₂₁・C ₁ +k ₂₂・M ₁ −k ₂₃・Y ₁ Y′ ₁ = −k ₃₁・C ₁ −k ₃₂・M ₁ +k ₃₃・Y ₁ ………(2) However, k _ij : weighting coefficient i=1 to 3 j=1 to 3 The secondary color correction circuit 9 is selective for a specific hue. In _order to enable arbitrary color control through _{correction, secondary correction signals C″ 1 , M} ″ ₁ ,
Y″ ₁ , Y″ 1 , and the secondary color correction signals C″ ₁ , M″ ₁ , Y″ ₁ are calculated by performing a matrix operation on the primary color correction signal as shown in the following equation.

C″ ₁ =C′ ₁ +l ₁₁・ΔB+l ₁₂・ΔC+l ₁₃・ΔG+l ₁₄
・ΔY＋l ₁₅・ΔR＋l ₁₅・ΔM C″ ₁ = C′ ₁ +l ₁₁・ΔB＋l ₁₂・ΔC＋l ₁₃・ΔG＋l ₁₄
・ΔY＋l ₁₅・ΔR＋l ₁₅・ΔM M″ ₁ =M′ ₁ +l ₂₁・ΔB＋l ₂₂・ΔC＋l ₂₃・ΔG＋l ₂₄・ΔY
+l ₂₅・ΔR+l ₂₆・ΔM C″ ₁ =C′ ₁ +l ₁₁・ΔB+l ₁₂・ΔC+l ₁₃・ΔG+l ₁₄
・ΔY＋l ₁₅・ΔR＋l ₁₅・ΔM M″ ₁ =M′ ₁ +l ₂₁・ΔB＋l ₂₂・ΔC＋l ₂₃・ΔG＋l ₂₄・ΔY
＋l ₂₅・ΔR＋l ₂₆・ΔM Y″ ₁ =Y′ ₁ ＋l ₃₁・ΔB＋l ₃₂・ΔC＋l ₃₃・ΔG＋l ₃₄・ΔY
+l ₃₅・ΔR+l ₃₆・ΔM……(3) However, l _ij : Weighting coefficient i=1~3 j=1~6 ΔB, ΔC, ΔG, ΔY, ΔR, ΔM: Special color signal Therefore, this secondary color The corrected signals C″ ₁ , M″ ₁ , Y″ ₁ are converted to the original signals by adders 6C, 6M, 6Y, respectively.
By adding C ₁ , M ₁ , Y ₁ and selecting the weighting coefficient k _ij by the primary color correction circuit 8, it is possible to arbitrarily correct the deviation of the ink from the ideal color on the printed screen. , by selecting the weighting coefficient l _ij by the secondary color correction circuit 9, it is possible to arbitrarily correct the color condition on the printed screen.

Note that the correction signal K' may also be calculated for the shading signal K using the following equation, and this may be added to the shading signal K to perform the correction.

K'=K+m ₁・ΔB+m ₂・ΔC+m ₃・ΔG+ m ₄・ΔY+m ₅・ΔR+m ₆・ΔM... (4) However, m _i : Weighting coefficient i: 1 to 6 However, in this conventional method, There are problems as listed below.

(1) The number of parameters included in the calculation of the correction signal is enormous (33 in total for equations (2), (3), and (4)), and if these were made into hardware as they were, they would be adjusted as they were. Because of the number of knobs that need to be adjusted, the adjustment work required for color correction becomes extremely complicated, and extremely high skill is required to accurately obtain the required color correction in a short period of time.

(2) The current color management method is to classify colors according to human perception as hue, saturation, and lightness, and discuss the amount of each attribute (for example, ``This color is the desired color.'') (e.g., "It's too colorful than the color,""I want it to be a brighter color," etc.) However, the above-mentioned parameters do not uniquely correspond to such hue, saturation, brightness, etc., but they can be adjusted by selecting a predetermined number of adjustment knobs from among the maximum of 33 adjustment knobs as mentioned above. The hue, saturation, and brightness cannot be set as desired unless the knobs are selected and operated simultaneously, and color management is therefore extremely difficult.

(3) Color correction can be performed separately for primary and secondary color correction, and color correction for each hue can be performed quite freely with secondary color correction, but it is only possible to perform color correction for each hue at a maximum of 6
This is only a matter of color, and it is not yet possible to do this completely independently for each hue.

(4) Gradation correction and color correction cannot be performed independently, and when the gradation characteristics are changed, the hue also changes accordingly.

In other words, conventional color correction methods require an extremely large number of parameters to be considered, require a high level of skill for color correction work, and are difficult to manage colors that match the three attributes of color perception: hue, saturation, and brightness. There was a drawback.

[Purpose of the invention]

The object of the present invention is to eliminate the drawbacks of the prior art described above, and to obtain information on hue, tone, and gradation from color image information.
To provide a color correction method in which information can be easily decomposed and ink cloudiness correction or arbitrary control of hue, cloudiness, and gradation can be easily and accurately performed during printing.

[Summary of the invention]

In order to achieve this object, the present invention rearranges each of the three primary color data of color image information for each pixel to form three data arranged in order of size, and based on these three data, each pixel is The feature is that information representing each of the hue, cloudiness, and gradation of the image is obtained.

[Embodiments of the invention]

Hereinafter, the color correction method according to the present invention will be explained in detail with reference to illustrated embodiments.

FIG. 1 is an explanatory diagram of the signal processing operation in one embodiment of the present invention. In this embodiment, pre-processing of color image information is performed.

Separation conversion processing of three attribute data based on preprocessed signals.

Synthesis processing of 3 attribute data.

Post-processing consisting of sumi version calculation and UCR.

Through these four processes, color-corrected data for the original image data is obtained.

(Preprocessing) The contents of this process are as follows.

(1-1) Input color information (r, g, b) for each pixel of color image information read from the original image using a scanner or the like and stored in a memory in advance.

(1-2) Set the size of color information (r, g, b) to 0
Normalize between (low brightness) and 1 (high brightness), then complement this to obtain complementary color information (c, m,
y). That is, 0≦r, g, b≦1 c=△1-r, m=△1-g, y=△1-b.

(1-3) Sorting the complementary color information (c, m, y) and arranging them in descending order, the largest one as data a 1, the second one as data a ₂ , and the third one as data a ₁
Define a ₃ .

Here, (a ₁ , a ₂ , a ₃ ) is referred to as preprocessed data.

(Classification conversion process) This process converts preprocessed data (a ₁ , a ₂ , a ₃ )
It consists of the following three processes that proceed in parallel based on the following.

(b) Separation and conversion processing of hue information (c ₁ , m ₁ , y ₁ ).

(b) Separation and conversion processing of cloudy information (c′ ₁ , m′ ₁ , y′ ₁ ).

(c) Separation and conversion processing of gradation information g.

(Separation and conversion process of hue information (a)) This process is a process of selecting a factor that determines the hue, calculating the hue from this, and obtaining the hue information using the hue table.

(A-1) First, determine the factors necessary to determine hue.

i. When (a ₂ ≠ a ₃ ), let (a ₁ − a ₃ ) and (a ₂ − a ₃ ) be factors.

．． In the case of (a ₂ = a ₃ ) (a ₁ − a ₃ is a factor).

This is due to the following reason.

This is because the component with the smallest value among the complementary color information (c, m, y) does not become a factor that determines the hue. In other words, the component with the smallest value is
This is because adding it only makes the color closer to gray (that is, reduces the saturation, in other words, increases the cloudiness), but does not change the hue. Specifically, data a ₃ when (a ₂ ≠ a ₃ ) and data a ₂ , a ₃ when (a ₂ = a ₃ )
This is because each of these functions only as a cloudy component and does not become a factor that changes the hue.

Therefore, as mentioned above, complementary color information (c, m,
y) other than the component with the smallest value,
The hue is selected as a determining factor.

And the hue in the above case is (a ₂ − a ₃ )/
As shown in Figure 3, from (a ₁ - _{a 3} ), among the points that internally divide the real number line on the hue diagram in which hues are arranged in order of wavelength, the data is a ₁ (c, m,
y), and in the above case, it is the point where one of (c, m, y), which is data a ₁ , is located.

For example, data (c, m, y) is c=0.3,
Assuming that m=0.1 and y=0, in this case,
a ₁ = c = 0.3, a ₂ = m = 0.1, a ₃ = y = 0,
Therefore, since (a ₂ ≠ a ₃ ), (a ₂ − a ₃ )/(a ₁ −
Since a ₃ )=1/3 and a ₁ =c (cyan), point * in FIG. 3 becomes the hue of the above data.

(A-2) Next, as shown in Figure 4, the horizontal axis shows the hue in order of wavelength, and the vertical axis shows the amount of ink (called dot % or sepa density) at the highest gradation for each hue. If you prepare a completed hue table and convert it by referring to it at the hue position described above, you can obtain the amount of ink without clouding at the highest gradation required for each version of c, m, and y (separated version). Hue information (c ₁ , m ₁ ,
y ₁ ) can be obtained.

(Separation and conversion processing of cloudy information (b)) (b-1) The cloudy amount is expressed by the amount of the opposite color (complementary color) included in a certain color. In other words, when looking at a certain color,
In general, a color can be thought of as having a color unique to that color by mixing a color exhibiting the maximum saturation of the hue with a complementary color of that color.

Therefore, if the amount of complementary color mixed with a certain color is zero, then the amount of cloudiness is zero, that is, the maximum saturation, so the amount of complementary color is This is regarded as the amount by which the saturation of the color exhibiting maximum saturation is reduced, and is defined as the amount of cloudiness.

Therefore, the original data, that is, complementary color information (c, m, y) here, and the opposite colors thereof are (1-c, 1-m, 1-y).

If we sort this and arrange it in descending order, we get (a ₁ , a ₂ , a ₃ ) as mentioned above, but
Here, when we look at _a3 , which is the minimum value among them, it takes a value of 0 to a (a≧a ₁ ). Then, the color is represented by a ₁ and a ₂ , and the amount of cloudiness is represented by a 3. When a ₃ = 0, the color represented by _{a 1 and} a ₂ The saturation is maximum, that is, the cloudiness is 0. Note that in a black and white image, a ₁ = a ₂ = a ₃ , and at this time it can be considered that the amount of cloudiness is at its maximum.

As a result, given complementary color information (c, m, y)
, the color represented by that hue is the color with the maximum saturation that can be printed at that hue (c′, m′,
y'), its complementary color (1-c', 1-m', 1
−y′) can be analyzed as a color added at a ratio of a ₃ /a _1. Therefore, in this example, a ₃ /a ₁ is added to the hue information (c ₁ , m ₁ , y ₁ ). It shall be the proportion of turbidity that should be added.

(Ro-2) Therefore, by using the data (c ₁ , m ₁ , y ₁ ) obtained in the process (A-2) above and the data a ₁ , a ₃ , (c′ ₁ , m′ ₁ , y′ ₁ ) = a ₃ / a ₁ (1-c ₁ , 1-m ₁ , 1
− y ₁ ) ...(5) is calculated to obtain cloudy information (c′ ₁ , m′ ₁ , y′ ₁ ).

(Separation and conversion processing of gradation information (c)) (c-1) The gradation can be expressed by the value of the data _a1 itself. This is because in preprocessing 1, color information (r, g, b) changes from minimum value = 0 to maximum value = 1.
Therefore, the maximum gradation of the hue is always when a ₁ =1. In other words, the gradation is the data a ₁ at that time and this data a ₁
However, since the maximum value of data a ₁ is 1, the gradation is (a ₁ /1)=a ₁ .

(C-1) Next, prepare a gradation conversion table as shown in FIG. 5, and refer to this table using data _a1 to obtain gradation information g with desired characteristics.

(Synthesizing Process) This process is to obtain dot % or sepa concentration data c ₂ , m ₂ , y ₂ necessary for each separation plate other than the black plate, and the calculation process is as follows.

c ₂ = (c ₁ + c' ₁ ) x g m ₂ = (m ₁ + m' ₁ ) x g y ₂ = (y ₁ + y' ₁ ) x g ... (6) (Post-processing) Here, the sumi version Create data _k2 that represents the amount of ink required for the process, and perform processing when applying UCR (undercolor removal).

(4-1) In the sumi version calculation, data k ₂ is first defined and calculated as follows.

k ₂ =△min (c ₂ , m ₂ , y ₂ ) where min represents a function that gives the minimum value.

(4-2) Prepare the black version table shown in Figure 6, use it to convert data k ₂ to data k ₃ to be finally used, and select between full black and skeleton black by selecting characteristics a and b. can also be realized arbitrarily.

(4-3) When performing UCR, the final data (c ₃ , m ₃ , y ₃ ) is obtained by the following calculation.

c ₃ = c ₂ −α・k ₃ m ₃ = m ₂ −α・k ₃ y ₃ = y ₂ −α・k ₃ ...(7) However, α: UCR rate 0α≦1 Based on the data obtained in this way, cyan and magenta,
By exposing each of the yellow separation plates and the blackout plate, it is possible to obtain a printed matter with the desired color development.The color correction work is performed using the characteristics of the hue table shown in Figure 4 for the hue. The task is to choose,
To deal with cloudiness, the task is to adjust the size of a ₃ /a ₁ in equation (5) above for each color.
As for the gradation, the selection of characteristics in the gradation table shown in Figure 5 is the same as the selection of the characteristics of the gradation table in Figure 5, which is a mutually independent task and corresponds to the three perceptual color attributes, so it is extremely It can be done easily and accurately.

In the above embodiment, the color information (r, g, b) from the original image is read out from the memory and processed, but it may be processed in real time while being read with a scanner.

In addition, the color information from the original image data is directly transmitted (c,
m, y), it goes without saying that inversion processing in preprocessing is unnecessary.

By the way, in the above explanation, the present invention has been explained in relation to printing plate making, but the present invention is not limited to printing plate making, but is applicable to various color hard copy machines such as various printers such as inkjet type and electrostatic type, and copying machines. It goes without saying that this invention can also be applied to color correction in a production device, and that the same effects as those of the above-mentioned embodiments can be expected.

〔Effect of the invention〕

As explained above, according to the present invention, color correction is performed uniquely according to three mutually independent attributes that match human color perception, and by each control operation that corresponds one-to-one. Therefore, it is possible to easily provide a color correction method that eliminates the drawbacks of the prior art and provides the excellent effects listed below.

Color correction processing can be performed according to the perceptual classification of colors (hue, saturation, brightness), and there is no concept of parameters, so color matching can be done intuitively and easily.

Hue and brightness can be controlled completely independently, making corrections easy and accurate.

Color communication becomes smoother when multiple workers, such as designers and color separation operators, work together.

It can be implemented as either a hardware system or a software system, and has a wide range of applications.

Even when it comes to a hardware system, it can be implemented using inexpensive and highly accurate digital circuits, without requiring the precise and expensive analog circuits used in the past.

Completely independent hue control is possible for each arbitrarily set hue.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the operation of an embodiment of the color correction method according to the present invention, FIG. 2 is a block diagram showing an example of the conventional color correction method, and FIG. 3 is a hue determination process in the embodiment of the present invention. FIG. 4 is an explanatory diagram showing an example of a hue table, FIG. 5 is an explanatory diagram showing an example of a gradation conversion table, and FIG. 6 is an explanatory diagram showing an example of a blackboard table. figure. ...Pre-processing, ...separation and conversion processing, ...composition processing, ...post-processing.

Claims (1)

[Claims] 1. In a color correction method for correcting color image information to obtain printing image information, for each pixel of three-primary color image information to be color-corrected, three types corresponding to the three primary colors of each pixel are provided. determining a factor representing the hue of the color image information from the magnitude relationship of the preprocessed data; and determining a factor representing the hue of the color image information based on the complementary color information and the factor. means for obtaining hue information by determining the hue position on the diagram and referring to the hue table based on the hue position; a ratio of the data indicating the minimum value to the data indicating the maximum value among the preprocessed data; means for obtaining turbidity information based on the color information; and means for obtaining gradation information by referring to a gradation table based on data representing the maximum value of the preprocessed data; A color correction method characterized in that the hue, cloudiness, and gradation of image information can be corrected independently.