Color vision and digital color equipment management points (on)

Color is a powerful and attractive aspect of the world we know. It forms our concept, explanation and memory of everything. Life needs color because nature itself is colorful. Color realistic architectural renderings, structured satellite imagery, reproducible crystal prints, and vivid color photographs, all closely related to color, require an input device such as a scanner or digital camera to capture images. The monitor's screen looks at the color of the image, and then uses a large format color inkjet printer or a printer to achieve color reproduction.

The use of digital color devices (referred to as color devices), such as high-resolution color display, scanners, digital cameras, color printers, etc., has become more and more popular. They are popular with people because of their simple operation methods and bright and bright color effects. Favored, and they brought about such as the complexity of data exchange, reproduce color cast and other issues have also been increasingly valued by people. The use of reasonable methods to organize and manage color devices and reduce system color errors is the key to ensuring the normal operation of the entire computer color system.

Color management from the color prepress system into the country has been of concern. However, color management is a very complicated issue. Because in a sense, color management is the feeling of managing people. How large the range of colors can be seen by a person's eyes, and how large the original's color range is, how to compress the original's color range according to the characteristics of different devices to the range of colors that the printing can reflect is a very complicated matter.

1. The principle of color vision

Color is the perception of light of different frequencies. It has both its objective properties and its close relationship with the construction of human eyes. The color vision, which is an important function of the human eye, is the result of physiological activity of the cone retinal cells in a bright environment, and has the ability of color discrimination in the visible spectrum with a wavelength of 390 to 760 nm. Retinal cone cells contain photosensitive pigments that sense red, green, and blue primary colors, namely red, green, and blue pigments. Each of the pigments excitates a spectrum of light and produces a variety of color perceptions. The most sensitive wavelengths corresponding to the three photopigments were 580 nm, 540 nm, and 440 nm, respectively. The wavelengths experienced by the three sensitizing pigments have a partial overlap, and this overlap is more pronounced at long and medium wavelengths. Human eye color perception occurs because these three types of photoreceptors combine a certain proportion of the three primary colors perceived at a certain wavelength to form a specific color.

The researchers found that the ratio of the number of conical cells in the human eye to the three primary colors is 40:20:1 for red, green, and blue, indicating that the human eye is much less sensitive to blue than to red.

V(λ), a spectral brightness effect map defined by the CIE (International Commission on Illumination), describes the relative sensitivity of the human eye to a single color light across the entire visible spectrum. The peak of the V(λ) plot (555 nm) corresponds to a greenish yellow color.

2. The effect of color devices on color

It is very difficult to maintain the original color in the entire flow of the digital image from the input device to the monitor to the output device or the final image file. Because each related hardware or software has its own color processing features, it also represents different color reproduction characteristics. So the scanned, the image on the display, the color proofing or the printed manuscript will show different colors. The root cause of this situation is that the color space of different devices in the color flow is different, ie different colors are used to produce the colors. For example, monitors and scanners are based on an "additive" coloring system using RGB, while printers and printing are based on a "subtractive" coloring system, which uses four colors of CMYK as the base color. The RGB mode of the screen display color based on the additive method cannot completely match the CMYK mode based on the subtractive color method used for printing and printing. Therefore, the color of the RGB mode can be well expressed during printing and printing. , we must use certain methods to manage the differences on these devices.

Even with the same kind of equipment, there will be a difference in color. When you enter an appliance store and see a wall made up of multiple television sets, you will know that no two television screens are truly the same in terms of image color and quality. For computer monitors, the same thing happens, and no matter how they are adjusted, they can't be exactly the same. When you use a printer, the problems you encounter will increase dramatically. A host of factors, such as the condition of the printing equipment, the color of the ink, the relative humidity, and the type of substrate, will all affect the print quality. The mechanical equipment itself is not perfect. Over time, year after year, day after day, the performance of the equipment tends to be unstable and abnormal work occurs.

3. Common color devices

(1) Scanners, digital camera scanners, digital cameras are digital image acquisition devices

Scanners use photoelectric coupling devices (CCDs, mainly for flatbed, hand-held scanners) or photomultiplier tubes (PMTs, mainly for drum scanners) to convert photos, prints, reversals, and negatives into direct scans. For digital images. In recent years, CCD-based flatbed scanners have been welcomed for their low cost, fast scanning, and good results. Not only can it scan images for printing, printing, web publishing, but also for character reading (OCR), it gradually enters the office and becomes an indispensable office product. Digital cameras were first formed in the late 1980s because of their rapid imaging but low resolution, low memory, and high prices. A new generation of digital cameras use external memory, high resolution, rapid imaging, shooting images can be used directly for printing, printing. The remaining acquisition equipment also includes extensions and video capture cards.

(2) color display, printer

Monitors and printers are the most commonly used output devices. Displays used for color management should be capable of displaying at least 800×600 resolution with progressive color display. The remaining output devices include film recorders.

Different color devices in the prepress system work in different color spaces. Monitors, digital cameras, and scanners all work in the RGB color space: printers and printers work in the CMYK color space. The output color of an image on different types of devices or the same type of device may be different, that is, these color spaces are related to the device. Therefore, the color management of the device is first of all a problem of the color space, ie, which color space is used for color control.

4. Common color system

At present, almost all computers use the GUI (Graph User Interface) as a human-computer interaction method. This method makes the computer a combination of a large number of data processing, complete graphics, and graphical user interfaces. In order to express rich image resources, a great deal of involvement of color devices becomes inevitable. Leaving aside the intangible data flowing in computer systems, we can regard the entire computer system as a tangible system for generating, exchanging, copying, and displaying graphics, images, and data for the purpose of generating, exchanging, copying, or displaying visible graphics. image. Color devices play a mediating role among people and machines.

The color device is connected with the host through the network interface and the cable. They can exchange data with each other. This causes the entire computer system to have a uniform color attribute, and the problem arises. Due to the hardware principle and the difference in color description methods, the performance of different devices on the color varies greatly, and when the image data flows from one device to another device, there is a possibility that the data reproduction distortion occurs. The main causes of this distortion are: