Although printing can reproduce millions of colors, the brightness of colors is reduced due to the use of subtraction, and some brighter colors are difficult to express in printing. On the other hand, due to the addition of color rendering technology, the screen is indeed richer in printing in terms of color expression. This is why beautiful colors that appear on the screen cannot be reproduced by printing, resulting in a difference in color between the screen and printing. The solution is either to improve the ink and paper composition to enable the reproduction of fresher, more pure colors, but this is not an overnight matter. Another method is to narrow the color gamut of the screen to meet the printing, so that what is seen on the screen is what is printed.
The so-called color gamut is the maximum range that a device can record or copy colors. The color gamut of the human eye is all visible light. Within the wavelength range of 380 to 780, the printed color gamut is composed of paper and ink. Different paper inks have different printing color gamuts and pink colors. The gamut is different from books and papers, and the color gamut of Pantone is also different from DIC. Others such as screens, scanners, printers, etc. also have their own color gamuts. It is meaningful to grasp 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 colors under infrared or X-rays, and some colors that are easily discernible by the human eye, like various metallic colors, are not easy to record on a scanner. The best we can get is the color gamut of one device, which simulates the gamut of another device. How to make people feel that the gamut of the two devices are similar during the simulation is an important theme of color production.
Perform color management and establish color standards
To produce colors, it is necessary to establish a set of standards for the expression and transmission of colors. The current popular color management systems such as LinoColor, Agfa's Phototone, etc. are all developing in this direction. Through a set of standard specifications (ICC control files) that describe the color gamut of the device, color calculation software is used to uniformly convert the color gamut Operation to reduce the color deviation and distortion caused by different color gamut and specifications during the transmission 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 that CIELab is an international lighting association that converts the wavelength of light into brightness and hue according to the visual characteristics of the human eye. L is the brightness of the color and a represents the color deviation. The degree of red to green, b represents the degree of description of the color yellowish blue. In the CIELab color space, every color visible to the human eye has a position belonging to that color. By comparing the distance between the two color positions, we can determine the similarity of the colors on both sides and three cuts. Since the visible light spectrum is the basis of this set of data, it can cover the colors produced by the screen and printing, and can also be used to represent the color gamut of the human eye.
For example, to describe the color gamut of a printer, first print some test color bars from the printer, these color bars include various main colors and colors that are more difficult to copy, then use a spectrometer to measure the CIELab data on the color bars, and then use the software to read the data The control file written in ICC format, in addition to the color gamut data of the device, the control file can also include the production characteristics of the device, such as black version characteristics, dot expansion value, etc. With the comparison file of the device, the color calculation software can refer to the characteristic data of the two devices, and compare and convert the color gamut of the device into the CIELab color space to obtain a more ideal simulation effect. At present, this technology has reached the stage of production and application. Among them, the most used is to simulate the printing color gamut with the screen and simulate the printing color gamut with the printer. Since the color gamut of the screen is larger than the printed color gamut, the simulation in this case is also called color gamut compression simulation. The entire simulation process is based on the data in the control file as the calculation basis, so the generation and management of the control file becomes the most important task.
Assumptions of the color management system
Has a color management system been implemented to achieve the desired effect of the colors produced? To answer this question, one 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 on the CIELab space based on the data of a known color gamut. status. That is to say, the production status of the equipment control file and the production status when calculating the color gamut must be the same. If the comparison file established yesterday cannot be compared with today's equipment, the production status is constantly floating, and the color management system cannot play a role in reducing deviations. An unstable production process may even cause the color management system to expand color deviations. 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 various variables in the production process in the same factory.
Color is not only an element of design, but also a standard for the receipt of production. Even if the customer barely accepts a print with unsatisfactory color, it may not be patronized next time. Many companies lose important customers because of color quality issues. It can be seen that mastering the law of color presentation and controlling the color quality are the techniques that must be mastered in production. With advanced equipment alone and without good technical cooperation, in the fierce industry competition, the fate of being eliminated is inevitable.
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. Below we will understand the principle of color. It will be our art. basis.
(1) The principle of three primary colors
In the middle school physics class, we may have done experiments with prisms. After passing through the prisms, white light is decomposed into a chromatogram of gradually changing colors. The colors are red, orange, yellow, green, cyan, blue, and purple. . Among them, human eyes are most sensitive to red, green, and blue. Human eyes are like a system of three-color receivers. Most colors can be produced by combining the three colors of red, green, and blue in different proportions. Most monochromatic light can also be decomposed into three colors of 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, and any one primary color cannot be synthesized with the other two colors. Red, green and blue are the three primary colors, and these three colors have the widest range of colors. The three primary colors of red, green and blue are added and mixed in different proportions, which is called additive color mixing.
Red + Green = Yellow Green + Blue = Cyan Red + Blue = Magenta Red + Green + Blue = White
Yellow, cyan, and magenta are all made up of two kinds of mixed colors, 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. Since each person's eyes have different perceptions of the same monochromatic color, if we use three primary colors of the same intensity to mix, assuming that the intensity of the white light is 100%, the subjective feeling of this person is that the green light is the brightest Red light is second, and blue light is the weakest.
In addition to the additive color mixing method, there is the subtractive color mixing method. Under the irradiation of white light, cyan pigments can absorb red and reflect cyan, yellow pigments can absorb blue and reflect yellow, and magenta pigments can absorb green and reflect magenta. That is:
White-Red = Cyan White-Green = Magenta White-Blue = Yellow
In addition, if two pigments of cyan and yellow are mixed, under the irradiation of white light, since the pigment absorbs red and blue, and reflects green, we express the mixing of pigments as follows:
Pigment (yellow + cyan) = white-red-blue = green pigment (magenta + cyan) = white-red-green = blue pigment (yellow + magenta) = white-green-blue = red
All of the above are subtractive color mixtures. Subtractive color mixtures form different colors by absorbing the different proportions of the three primary colors. Therefore, cyan, magenta, and yellow are called pigment primary colors. 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 three primary colors of additive mixing is called RGB mode, and the color mode represented by the principle of subtractive three primary colors is called CMYK mode, and they are widely used in painting and printing.
The RGB mode is the most commonly used color mode for drawing software. In this mode, it is more convenient to process the image, and the image stored in RGB is smaller than the CMYK image, which can save memory and space.
The CMYK mode is a pigment mode, so it belongs to the printing mode, but it is essentially the same as the RGB mode, only the way of generating colors is different. RGB is the additive color mixing mode, and CMYK is the subtractive color mixing mode. For example, the display uses the RGB mode because the display emits bright light by bombarding the fluorescent material on the fluorescent screen with an electron beam to produce color. It is black when there is no light, and white when the light is maximized. And the printer? Its ink does not emit light by itself. Therefore, only the color that absorbs a specific light wave and reflects other light is used, so it needs to be solved by the subtractive color method.
(2), HLS (hue, brightness, saturation) principle
HLS is Hue (hue), Luminance (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, cyan, blue, and purple, each of which represents a hue. Hue adjustment is to change its color.
Brightness is the brightness of the primary colors of graphics in various colors (such as RGB images with primary colors of R, G, B or various colors), and brightness adjustment is the adjustment of brightness. The brightness ranges from 0 to 255 and is divided into 256 levels. The grayscale image we usually talk about is to divide 256 levels of brightness between pure white and pure black, that is, from white to gray, and then to black. Similarly, in the 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 dark.
Saturation refers to the chroma of image colors. For each color, there is an artificially specified standard color. Saturation is a physical quantity that describes how close the color is to the standard color. Adjusting saturation is adjusting the saturation of the image. When the saturation bar of an image is zero, the image becomes a grayscale image. You can try the saturation button on the TV.
Although printing can reproduce millions of colors, the brightness of colors is reduced due to the use of subtraction, and some brighter colors are difficult to express in printing. On the other hand, due to the addition of color rendering technology, the screen is indeed richer in printing in terms of color expression. This is why beautiful colors that appear on the screen cannot be reproduced by printing, resulting in a difference in color between the screen and printing. The solution is either to improve the ink and paper composition to enable the reproduction of fresher, more pure colors, but this is not an overnight matter. Another method is to narrow the color gamut of the screen to meet the printing, so that what is seen on the screen is what is printed.
The so-called color gamut is the maximum range that a device can record or copy colors. The color gamut of the human eye is all visible light. Within the wavelength range of 380 to 780, the printed color gamut is composed of paper and ink. Different paper inks have different printing color gamuts and pink colors. The gamut is different from books and papers, and the color gamut of Pantone is also different from DIC. Others such as screens, scanners, printers, etc. also have their own color gamuts. It is meaningful to grasp 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 colors under infrared or X-rays, and some colors that are easily discernible by the human eye, like various metallic colors, are not easy to record on a scanner. The best we can get is the color gamut of one device, which simulates the gamut of another device. How to make people feel that the gamut of the two devices are similar during the simulation is an important theme of color production. [next]
Perform color management and establish color standards
To produce colors, it is necessary to establish a set of standards for the expression and transmission of colors. The current popular color management systems such as LinoColor, Agfa's Phototone, etc. are all developing in this direction. Through a set of standard specifications (ICC control files) that describe the device's color gamut, color calculation software is used to perform unified color gamut conversion Operation to reduce the color deviation and distortion caused by different color gamut and specifications during the transmission 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 that CIELab is an international lighting association that converts the wavelength of light into brightness and hue according to the visual characteristics of the human eye. L is the brightness of the color and a represents the color deviation. The degree of red to green, b represents the degree of description of the color yellowish blue. In the CIELab color space, every color visible to the human eye has a position belonging to that color. By comparing the distance between the two color positions, we can determine the similarity of the colors on both sides and three cuts. Since the visible light spectrum is the basis of this set of data, it can cover the colors produced by the screen and printing, and can also be used to represent the color gamut of the human eye.
For example, to describe the color gamut of a printer, first print some test color bars from the printer, these color bars include various main colors and colors that are more difficult to copy, then use a spectrometer to measure the CIELab data on the color bars, and then use the software to read the data The control file written in ICC format, in addition to the color gamut data of the device, the control file can also include the production characteristics of the device, such as black version characteristics, dot expansion value, etc. With the comparison file of the device, the color calculation software can refer to the characteristic data of the two devices, and compare and convert the color gamut of the device into the CIELab color space to obtain a more ideal simulation effect. At present, this technology has reached the stage of production and application. Among them, the most used is to simulate the printing color gamut with the screen and simulate the printing color gamut with the printer. Since the color gamut of the screen is larger than the printed color gamut, the simulation in this case is also called color gamut compression simulation. The entire simulation process is based on the data in the control file as the calculation basis, so the generation and management of the control file becomes the most important task.
Assumptions of the color management system
Has a color management system been implemented to achieve the desired effect of the colors produced? To answer this question, one 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 the CIELab space based on the data of a known color gamut. Therefore, it must be assumed that the two color gamuts are still maintained when recording color gamut data. status. That is to say, the production status of the equipment control file and the production status when calculating the color gamut must be the same. If the comparison file established yesterday cannot be compared with today's equipment, the production status is constantly floating, and the color management system cannot play a role in reducing deviations. An unstable production process may even cause the color management system to expand color deviations. 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 various variables in the production process in the same factory.
Color is not only an element of design, but also a standard for the receipt of production. Even if the customer barely accepts a print with unsatisfactory color, it may not be patronized next time. Many companies lose important customers because of color quality issues. It can be seen that mastering the law of color presentation and controlling the color quality are the techniques that must be mastered in production. With advanced equipment alone and without good technical cooperation, in the fierce industry competition, the fate of being eliminated is inevitable.
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. Below we will understand the principle of color. It will be our art. basis.
(1) The principle of three primary colors
In the middle school physics class, we may have done experiments with prisms. After passing through the prisms, white light is decomposed into a chromatogram of gradually changing colors. The colors are red, orange, yellow, green, cyan, blue, and purple. This is the visible spectrum. . Among them, human eyes are most sensitive to red, green, and blue. Human eyes are like a system of three-color receivers. Most colors can be produced by combining the three colors of red, green, and blue in different proportions. Most monochromatic light can also be decomposed into three colors of 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, and any one primary color cannot be synthesized with the other two colors. Red, green and blue are the three primary colors, and these three colors have the widest range of colors. The three primary colors of red, green and blue are added and mixed in different proportions, which is called additive color mixing.
Red + Green = Yellow Green + Blue = Cyan Red + Blue = Magenta Red + Green + Blue = White
Yellow, cyan, and magenta are all made up of two kinds of mixed colors, 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. Since each person's eyes have different perceptions of the same monochromatic color, if we use three primary colors of the same intensity to mix, assuming that the intensity of the white light is 100%, the subjective feeling of this person is that the green light is the brightest. Red light is second, and blue light is the weakest.
In addition to the additive color mixing method, there is the subtractive color mixing method. Under the irradiation of white light, cyan pigments can absorb red and reflect cyan, yellow pigments can absorb blue and reflect yellow, and magenta pigments can absorb green and reflect magenta. That is:
White-Red = Cyan White-Green = Magenta White-Blue = Yellow
In addition, if two pigments of cyan and yellow are mixed, under the irradiation of white light, since the pigment absorbs red and blue, and reflects green, we express the mixing of pigments as follows:
Pigment (yellow + cyan) = white-red-blue = green pigment (magenta + cyan) = white-red-green = blue pigment (yellow + magenta) = white-green-blue = red
All of the above are subtractive color mixtures. Subtractive color mixtures form different colors by absorbing the different proportions of the three primary colors. Therefore, cyan, magenta, and yellow are called pigment primary colors. 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 three primary colors of additive mixing is called RGB mode, and the color mode represented by the principle of subtractive three primary colors is called CMYK mode, and they are widely used in painting and printing.
The RGB mode is the most commonly used color mode for drawing software. In this mode, it is more convenient to process the image, and the image stored in RGB is smaller than the CMYK image, which can save memory and space.
The CMYK mode is a pigment mode, so it belongs to the printing mode, but it is essentially the same as the RGB mode, only the way of generating colors is different. RGB is the additive color mixing mode, and CMYK is the subtractive color mixing mode. For example, the display uses the RGB mode because the display emits bright light by bombarding the fluorescent material on the fluorescent screen with an electron beam to produce color. It is black when there is no light, and white when the light is maximized. And the printer? Its ink does not emit light by itself. Therefore, only the color that absorbs a specific light wave and reflects other light is used, so it needs to be solved by the subtractive color method.
(2), HLS (hue, brightness, saturation) principle
HLS is Hue (hue), Luminance (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, cyan, blue, and purple, each of which represents a hue. Hue adjustment is to change its color.
Brightness is the brightness of the primary colors of graphics in various colors (such as RGB images with primary colors of R, G, B or various colors), and brightness adjustment is the adjustment of brightness. The brightness ranges from 0 to 255 and is divided into 256 levels. The grayscale image we usually talk about is to divide 256 levels of brightness between pure white and pure black, that is, from white to gray, and then to black. Similarly, in the 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 dark.
Saturation refers to the chroma of image colors. For each color, there is an artificially specified standard color. Saturation is a physical quantity that describes how close the color is to the standard color. Adjusting saturation is adjusting the saturation of the image. When the saturation bar of an image is zero, the image becomes a grayscale image. You can try the saturation button on the TV.
Another concept is contrast. Contrast refers to the difference between different colors. The greater the contrast, the greater the difference between the two colors and vice versa. For example, a gray-scale image will increase its contrast to be more black and white, and when adjusted to the limit, it will become a black and white image. On the contrary, we can get a gray canvas.
We understand the principle of color, we will not be at a loss in image processing, and can adjust the color faster and more accurately. Another concept is contrast. Contrast refers to the difference between different colors. The greater the contrast, the greater the difference between the two colors and vice versa. For example, a gray-scale image will increase its contrast to be more black and white, and when adjusted to the limit, it will become a black and white image. On the contrary, we can get a gray canvas.
We understand the principle of color, we will not be at a loss in image processing, and can adjust the color faster and more accurately.
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