The principle of color printing reproduction in color space
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Device-independent color spaces are mainly used for color modules and for converting between RGB and CMYK modules.
Each color display has its own color gamut due to different RGB phosphors even if it is manufactured by the same manufacturer in the same year.
The reason is that it is suitable for printing presses and CMYK toners. It usually has more color gamut restrictions than most monitors, because the colors produced by the two different formats of RGB and CMYK will vary from device to device. The characteristics of the color space to which the device belongs.
Some color spaces allow for color to be expressed in a device-independent manner, and color does not depend on any particular device, but rather on humans.
A true color statement after the eye perceives. These color statements, called device-independent color spaces, were developed by the International Standards Board (CIE) in 1931 and are therefore called the CIE-based color space.
The goal of CIE is to create a standard system for repeatable color communication for paint, ink, dye and other colorant manufacturers.
The most important function of these standards is to provide a monolithic architecture of color matching. The device independent color space is used to convert color data from one device-specific color space to another device-specific color space, and those representing the entire visible color range are conversion spaces. , which means that any color selected on the display is the color gamut of this neutral color space.
CIE L*a*b* is a three-dimensional color space based on human color. It is the most widely used color space for CIE. L*a*b* color space is based on a color that cannot be both green and red at the same time. It is a blue and yellow theory that results in a single shade that can be used to describe red/green and yellow/blue properties. The CIE L*a*b* space represents the color associated with the reference white point, and as a specific meaning of white light, it is usually based on the whitest light that a device can produce. The CIE color space constitutes a device independent color basis for color management.
Although it is possible to copy colors in the way that comes to mind, there are only two basic methods - the additive method and the subtractive method, both of which are commonly known as the three-color method, which are based on the different principles of the three primary colors to create full color. Understand these two systems to understand the principles of many color reproduction jobs in printing. It is the basis for understanding the tone reproduction, gray balance, and color correction of halftone color reproduction, for proper contrast, color balance, and hue. It is decisive.
Printing is based on subtractive methods and is usually printed on white, near-white paper, or any other white object due to the "white" paper surface.
The light waves are all reflected in the same amount and appear white. When the color is copied, we intuitively think that the color is in the paper. In fact, after printing on the surface of the paper using transparent ink (cyan, magenta, yellow), it is multi-filtered. When the red, green, and blue waves are dropped, color appears, and the paper itself does not change color. Considering transparent four-color inks, such as the red, green, and blue wavelengths that our eyes feel, rather than those that combine on paper to replicate color, we find that by combining two ink waves and subtracting the other.
In theory, combining all three color inks can avoid all reflected light waves, producing black, even the best four-color ink will not
It absorbs light waves. When cyan, magenta, and yellow inks are combined, the wavelengths absorbed by the combined three-color inks are inconsistent, and the red portion of the spectrum reflects more. The result will be brownish instead of black, in order to make up for printing. This shortcoming requires the use of black ink in the color printing process.
Paper has a significant effect on color reproduction. Paper reflects unwanted unabsorbed light waves to the viewer, and the coated paper has a strong anti-reflection.
The shot surface produces a wider range of colors than uncoated paper, and the rough, non-coated surface diffuses light, reducing the amount of reflection to the viewer and thus feeling darker in color.
The problem that has been explored since the previous color reproduction. Before the 1970s, most of the color separations were placed in front of a plate-making camera or a magnifier lens with red, green, and blue color filters. The skilled technicians used their own experience to obtain a good color reproduction. The original, the color-changing film, the color separation film, and the mesh are produced from the original through multiple processes, and then subjected to dot etching to obtain an ideal halftone mesh. Later, some manufacturers used the contact exposure method to change the size of the dot. After many adjustments, it took a long time, and it may not be able to obtain the desired color.
After the 1970s, high-end electronics or laser scanners used countless knobs and buttons to make color adjustments. Although these expensive analog scanners lack computer memory and digital devices to store images, later models converted RGB digital color signals into CMYK color separations for the computer, the original is mounted on a transparent roller, and the other roller is The color separation film is installed, and the scanner is corrected by the experts who have been trained in advanced technology and makes the best input and output settings. However, re-scanning is still quite common, especially for prints with special colors. If the colors are not matched, the adjustment of the scanner or the knowledge of the operator is usually not a limiting factor, but is affected by the quality of the ink and paper.
With the addition of complex color controls on the scanner, printing has been converted from process to pre-press, printing or post-press, from the use of visual adjustment to color control via several densitometers, quality control charts, ink and paper tests. Technology.
In the 1980s, advances in minicomputers, memory, and storage devices enabled the color electronic prepress system (CEPS) to be used for storage, display, color correction, and image matching. For example, Scitex Response and Hell Chromacom's tens of millions of systems can get high-quality color reproduction, but it also takes a long time to learn.
In the 1990s, a powerful electronic prepress system on the table appeared. Innovative page description output (PostScript), image platforms such as Apple, Microsoft, and publishing software such as Adobe Photoshop, Quark Xpress can use desktop hardware to make high-end color quality, and its ease of use, low-cost combination system quickly replaces Expensive independent system.
Scanning and color separation, once required to be highly trained experts, become popular, anyone including photographers, designers, typesetting and computer operators can operate a computer, scanner and printing press to complete the color separation Full-time work. The desktop computer uses an open system and theoretically unlimited support for various color computer peripheral devices. Today, many of these color publications work consistently, but still face the same problem, how to make accurate colors.