Color image information processing of the hottest

Color image information processing of electronic color separation machine

color image information processing of electronic color separation machine is completed by a special color image processing system -- color computer, which is composed of the above principles and algorithms, combined with the technological requirements of color image reproduction and people's artistic expectations. It includes five parts: color correction, level correction, black version calculation, UCR and PCR, and fine level emphasis, which are independent and restrict each other

I. color correction

color correction refers to the correction of the color deviation of the original and its reproduction process according to the purpose of reproduction in electronic color separation, that is, to correct the color difference and achieve correct color reproduction. The method of color correction depends on the image acquisition system and color recognition method of the electronic color separator. It is divided into analog color correction and digital color correction

1. The necessity of color correction

the printing and reproduction process of color originals can usually be expressed as the combination of color decomposition and color restoration of image information. The so-called color decomposition of image information refers to trying to decompose the color plate composed of subtractive primary colors such as y, m and C from the original through image transformation processing, and the color restoration of image information is trying to make the color separation image composed of subtractive primary colors such as y, m and C superimposed on the same substrate through image transformation processing, so as to reproduce the color shadow and tone of the original image. In the actual reproduction process, due to the non ideal of various pieces, the existence of color difference is inevitable, and the color difference mainly comes from three aspects. The first is the color deviation caused by the discoloration (color attenuation) of the colors and color medium caused by the photography process and materials of the original, as shown in Figure 3.28. The second is the color difference in the process of color decomposition, which is mainly the error of light source, lens, color filter, photomultiplier tube and photosensitive materials, as shown in figures 3.29 and 3.30. The third is the color difference in the process of color reduction, which is mainly the error of paper and ink. As shown in Figure 3.31

as an important part of color reproduction, the sampling of electronic color separation machine is a process of color decomposition, and at the same time, it also makes up for the color error in the reduction of subsequent processes, such as ink. Therefore, the color difference of the color separation signal input to the image information processing system (color computer) is inevitable, as shown in Figure 3.32, so it is also necessary to adopt the necessary correction means

many engineers and technicians have found through experimental research that the color difference in color image reproduction not only exists, but also is very significant, and has a regularity of 1%: c0.64. When the black mark is 100% and the white mark is 0%, we can get:

the color separation density of the basic colors y, G and R of the Y version is only black mark 6. Although the design of personalized solutions is mostly boring, the color separation density of B, C and M is 17-36% higher than the white elevation

the color separation density of the basic colors m, B and R is only 67-74% of the black mark, and the color separation density of C, G and Y is 10-36% higher than the white elevation

the color separation density of the basic colors C, G B its color separation density is only 59-83% of the black mark. On the contrary, R, m its color separation density is 17-20% higher than the white elevation, and only Y color is ideal

therefore, color reproduction is bound to cause insufficient basic colors and excessive opposite colors. Color correction is to improve the basic colors and reduce the opposite colors

2. Simulated color correction method

(1) photographic mask and electric mask

in the photographic plate making process, photographic mask is the best and most effective means of color correction: the so-called photographic mask refers to the mask with appropriate density range and tone made by photographic method, which is combined with the original or color separation film for photography or copying, so as to change the density and tone of the basic color and the opposite color of the color separation film, so as to achieve the purpose of color compensation

it can be seen from the above that the principle of photographic masking is that there is a common color error in the negative film obtained after color separation, and its basic color has a high density on the color separation negative film, which is higher than the black mark. When it is copied into a positive image, it appears that the basic color is insufficient. The density of the opposite color on the color separation negative is low, and lower than the density of the white negative. When it is copied into a positive image, it appears that the opposite color is excessive. However, according to the original and its y, m, C, BK color separations, the appropriate mask is made. After the mask is combined with it, the density ratio of the basic color and the opposite color of the negative film of the prepared color separations can be changed, that is, to increase the basic color and reduce the opposite color. There are many kinds of masks and different production methods. Here, just take M as an example to introduce a simple example

the specific manufacturing method of the mask is as follows: 1) shoot the original with an r-filter, develop it to 1/3 of the normal density, and then go to D; Then mask and register the positive onto the color manuscript; 2) Use g-filter for color separation and exposure, and control the density of color separation within an appropriate range (d); 3) Take the original with a b-filter and develop it to 1/10 of the normal density, that is, 1/10d. 4) turn over the two negative plates obtained in 2 and 3 to obtain a more ideal color separation plate. The process of other color plates is similar. The results shown in the table can be obtained through measurement. In the table × Represents basic color, √ represents phase contrast

from the above process, the following mathematical expression can be summarized, that is:

further generalizing the above formula in photographic plate making method, the following equation group can be obtained:

when expressed in matrix, it can be expressed as:

formula () and formula () are mask correction equation and mask correction matrix, in which the color correction coefficient AIJ (I, j=1,2,3) is the most concerned, and AIJ varies with different processes

the analog electronic color separation machine uses the analog voltage signal V that has a linear relationship with the original density to carry out various processing. Similarly, the following equation can be obtained:

equation () is the electric mask equation for the color correction of the electronic color separation machine, and its implementation of color correction also shows the correct selection of the color correction coefficient AIJ

in the selection of color correction coefficient, in addition to selecting three coefficients, there is color correction using neutral gray with two correction coefficients, that is:

for neutral gray:

therefore, the color correction of electronic color separation machine has two correction methods: two correction coefficients and three correction coefficients

(2) color calibration signal and color calibration signal generator

the analog color correction of electronic color separation machine is realized by the superposition of the color calibration signal obtained by the color calibration signal generator and the main signal. There are usually two kinds of color correction signals: one is the basic color correction signal, and the other is the selective color correction signal

(I) it cannot exceed the maximum bearing capacity of the key curve tester test equipment. Basic color correction and its acquisition of color correction signal

basic color correction refers to the basic color correction signal produced by a specific signal generator for the correction of three channel basic colors and opposite colors, and its purpose is to correct the basic color correction signal due to y, m The bubble size in the c-color version foam is smaller than that used by electrical appliance manufacturers in the current market, which causes the color reproduction error of basic deficiency or excessive opposite color in color reproduction

the function expression of the electric mask using the analog photographic mask method for basic color correction is:

its color correction equation is:

from the formula (), it can be seen that the basic color correction is composed of basic color correction and opposite color correction, and the key is to obtain the correct color correction signal or determine the correct color correction coefficient

the basic color correction signal generator is a special circuit that can generate color correction signals. It has two functions: (1) identifying whether the scanning part is the basic color or the opposite color, (2) generating the corresponding color correction signals

from figure 3.33, when the scanning part is the basic color, then △ V ≠ 0, and △ V increases with the increase of color saturation in the scanning area. If the scanning is not the basic color, then △ v = 0. Similarly, when the scanning part is of opposite color, then △ V ≠ 0, and △ V increases with the increase of color saturation in the scanning area. If the scanning part is not of opposite color, then △ v

the electrical principle of the color correction signal generator is shown in Figure 3.34. From the figure, it can be seen that the basic color correction signal is generated based on the response voltage of V, V and V to six pure color codes and obtained by appropriate mathematical transformation. When the response voltages of V, V and V to the six pure color codes are different, the coefficients of their mathematical transformation will also change appropriately, and the ultimate goal is to generate the correct basic color correction signal

figure 3.35 is the schematic diagram of the basic color correction circuit of the DC-300 of hell company, which is a typical basic color correction circuit. It can be seen from the figure that the mathematical expression of the basic color correction signal is:

the mathematical expression of the opposite color correction signal is:

where K and K are adjusted by the basic color correction signal strength controller

when scanning the neutral gray area of the original, the basic color correction signal has no effect on the neutral gray area

similarly:

the results of the table can be obtained from the above relationship, and the following conclusions can be drawn:

1) the basic color and opposite color correction signal voltage of each color plate plays a role in identifying the original, that is, whether the scanning part is the basic color or the opposite color, it is a sign to identify the color phase of the scanning area of the original, and the greater the voltage value, the greater the color saturation on the original

2) as an independent signal voltage, the six sign signal voltages can be used to adjust the correction amount of the basic color and the opposite color of the three color plates respectively

3) the response value of the correction voltage of the basic color or the opposite color of each color separation plate to the three basic colors or the opposite color in the color plate is different, that is, the recognition sensitivity is different, and a common correction is used for color correction