The hottest way to coordinate screen and printing

The method of coordinating screen and printing color

although printing can copy thousands of colors, due to the use of subtraction for color rendering, the brightness of colors will be weakened, and some bright colors are difficult to express in a printing way. On the other hand, the screen is indeed richer in the range of color expression than printing due to the use of additive color rendering technology. This is why colors that look beautiful on the screen cannot be reproduced by printing, resulting in differences in color between the screen and printing. The solution is either to improve the ink and paper composition so that fresher and purer colors can be copied, but this will not happen overnight. Another method is to narrow the color gamut of the screen to meet the printing, so that what the screen sees is what is obtained by printing

the so-called color gamut is the maximum range that a device can record or copy colors. The color gamut of human eyes is all visible light. Within the wavelength range of 380 to 780, the printing color gamut is composed of paper and ink. Different paper and ink match, there are different printing color gamut. The color gamut of pink is different from that of book paper, and the color gamut of Pantone is also different from DIC. Other devices such as screens, scanners, printers, etc. also have their own color gamut. It is of practical significance to master the color gamut of a device, because a device cannot record or copy colors outside the color gamut. For example, under normal circumstances, the human eye cannot see the color under infrared or X-ray, while some colors that are easy to distinguish by the human eye, such as various metallic colors, are not easy to record on the scanner. The best we can achieve is to simulate the color gamut of another device by the color gamut of one device. How to make the human eye feel that the color gamut of the two devices is similar in the simulation process is an important theme of color production

carry out color management and establish color standards

to produce color, we must establish a set of standards for the expression and transmission of color. At present, the more popular color management systems, such as LinoColor and Agfa's phototone, are developing in this direction. Through a set of standard specifications describing the color gamut of the equipment (ICC reference file), the color calculation software is used to gradually open the oil supply valve to carry out the unified conversion operation of the color gamut, so as to reduce the color deviation and distortion caused by the different color gamut and specifications in the transmission process of color data. To implement these color management systems, we must first find out the color gamut characteristics of the equipment. The most commonly used method to describe the color gamut is CIELAB, which is a set of color description data that converts light wavelength into brightness and hue according to human visual characteristics. L is the brightness of the color, a represents the degree of red to green color, and B represents the degree of yellow to blue color. In CIELab color space, every color visible to human eyes has a position belonging to the color. By comparing the distance of the two color positions, we can determine the similarity of the two colors. Since the visible light spectrum is the basis of this set of data, it can cover the colors generated by the screen and printing, and can also be used to represent the color gamut of human eyes

for example, to describe the color gamut of a printer, first print some test color bars from the printer, including various main colors and colors that are difficult to copy, then measure the CIELAB data on the color bar with a spectrometer, and then write the data into a reference file in ICC format with software. The reference file not only includes the color gamut data of the equipment, but also includes the production characteristics of the equipment, such as black version characteristics, dot expansion value, etc. With the comparison file of the equipment, the color calculation software can refer to the characteristic data of the two equipment, and place the color gamut of the equipment in the CIELab color space for comparison and conversion, so as to obtain a better simulation effect. At present, this technology has reached the stage of production and application, of which the most widely used is to simulate the printing gamut with the screen and the printing gamut with the printer. Because the color gamut of the screen is larger than that of the printing, the simulation in this case is also called gamut compression simulation. The whole simulation process is based on the data in the reference file, so the generation and management of the reference file has become the most important work

assumption of color management system

whether the color management system is implemented, that is, the color produced can obtain the ideal effect? To answer this question, we must understand the assumptions behind the color management system. The main work of the color management system is to simulate the data of another known color gamut in CIELAB space according to the data of one known color gamut. Therefore, it must be assumed that the two color gamuts are still in the state when the color gamut data is recorded. That is to say, the production status of establishing the equipment reference file must be the same as that of calculating the color gamut. If the control file established yesterday cannot be compared with today's equipment, and the production state constantly fluctuates, the color management system cannot play the role of reducing deviation. An unstable production process may even make the color management system expand the color deviation. Therefore, the color management system is more suitable for factories with design, color separation, proofing and printing at the same time, because it is easier to control the variables in the production process in the same factory

color is not only an element of design, but also the receiving standard of production. Even if customers reluctantly accept a print with unsatisfactory color, they may not patronize it next time. Many companies lose important customers because of color quality problems. It can be seen that mastering the law of color presentation and controlling color quality are the technologies that must be mastered in production. Only having advanced equipment without good technical cooperation will inevitably be eliminated under the fierce industry competition

color principle

when it comes to painting and images, it is natural to talk about color. All patterns are composed of basic shapes and colors. Color constitutes an important part of our image processing. Next, we will understand the principle of color, which will be the basis of our art work

(I) principle of three primary colors

in physics classes in middle schools, we may have done experiments with prisms. White light is decomposed into chromatograms with gradual transition of various colors after passing through the prisms. The colors are red, orange, yellow, green, cyan, blue and violet in turn. Modern medicine accelerates the development towards automation, traditional Chinese medicine and miniaturization, which is visible spectrum. Among them, human eyes are most sensitive to red, green and blue. Human eyes are like a three-color receiver system. Most colors can be synthesized by red, green and blue in different proportions. Similarly, most monochromatic light can also be decomposed into red, green and blue. This is the most basic principle of colorimetry, namely the principle of three primary colors. The three primary colors are independent of each other. No primary color can be combined with the other two colors. Red, green and blue are three primary colors, and the color range of these three colors is the most extensive. The three primary colors of red, green and blue are added in different proportions to synthesize a mixed color, which is called additive mixing

Red + Green = yellow

green + blue = cyan

Red + blue = magenta

Red + Green + blue = white

yellow, cyan and magenta are mixed by two colors and hues, so they are also called additive secondary colors. In addition:

Red + cyan = white

Green + magenta = white

Blue + yellow = white

so cyan, yellow and magenta are complementary colors of red, blue and green respectively. Because everyone's eyes have different feelings about the same monochrome, if we mix three primary colors with the same intensity, we assume that the intensity of white light is 100%. At this time, people's subjective feeling is that green light is the brightest, red light is the second, and blue light is the weakest

in addition to the additive color mixing method, there is also the subtractive color mixing method. Under the irradiation of white light, cyan pigments can absorb red and reflect cyan, yellow pigments absorb blue and reflect yellow, magenta, which means that the cooperative car enterprises need to inform BYD in advance of their product positioning, model design, price, output, strategy and other plans to absorb green and reflect magenta. That is:

white red = cyan

white green = magenta

white blue = yellow

in addition, if you mix cyan and yellow pigments, under white light irradiation, because the pigments absorb red and blue, they reflect green, For the mixing of pigments, we express as follows:

pigments (Yellow + cyan) = white red blue = green

pigments (magenta + cyan) = white red green = blue

pigments (Yellow + magenta) = white green blue = red

the above are subtractive mixed colors, which form different colors by absorbing different proportions of three primary colors. Therefore, cyan, magenta and yellow, such as collision, are called the three primary colors of pigments. The mixing of three primary colors of pigments is widely used in painting and printing. Among the three primary colors of pigments, red, green and blue are called subtractive secondary colors or pigment secondary colors. Among the subtractive secondary colors are:

(cyan + Yellow + magenta) = white red blue green = black

the color mode represented by the above additive mixing three primary colors is called RGB mode, while the color mode represented by the subtractive mixing three primary colors principle is called CMYK mode, which is widely used in the field of painting and printing

rgb mode is the most commonly used color mode in drawing software. In this mode, it is convenient to process images. Moreover, RGB stored images are smaller than CMYK images, which can save memory and space

cmyk mode is a pigment mode, so it belongs to printing mode, but it is essentially no different from RGB mode, only the way of producing color is different. RGB is additive color mixing mode, and CMYK is subtractive color mixing mode. For example, the RGB mode is adopted for the display because the electronic beam bombards the fluorescent material on the fluorescent screen to emit light and produce color. When there is no light, it is black, and when the light reaches the maximum, it is white. What about printers? Its ink will not emit light by itself. Therefore, only by absorbing specific light waves and reflecting the color of other light, it needs to be solved by subtraction

(II). HLS (hue, brightness, saturation) principle

hls is hue (hue), brightness (brightness), saturation (saturation). Hue is an attribute of color, which is essentially the basic color of color, that is, we often talk about seven kinds of red, orange, yellow, green, green, blue and purple, each of which represents a hue. The adjustment of hue is to change its color

brightness is the brightness of the primary colors of various colors (for example, the primary colors of RGB images are R, G, B or various self hues). Brightness adjustment is also the adjustment of brightness. The brightness range is from 0 to 255, which is divided into 256 levels. The grayscale image we usually talk about is divided into 256 levels of brightness between pure white and pure black, that is, from white to gray, and then to black. Similarly, in RGB mode, it represents the lightness and darkness of the primary colors, that is, the lightness and darkness of the three primary colors of red, green and blue, from light to deep

saturation refers to the chromaticity of the image color For each color, there is an artificial standard color. Saturation is a physical quantity that describes the similarity between the color and the standard color. To adjust saturation is to adjust the chromaticity of an image. When the saturation bar of an image is zero, the image will become a gray-scale image. You can try it on the TV