At present, in the color management technology, the so-called color feature connection space adopts the color space of CIE1976Lab. The color on any device can be converted to this space to form a “universal†description mode, and then the color matching conversion is performed. . Within the computer operating system, the task of implementing color matching conversion is accomplished by the "color matching module". It is of great significance to whether the color conversion is reliable or not, and whether or not the colors match.
So, how to achieve the color in the "universal" color space transmission, to achieve the loss of color or as little loss as possible?
This requires each device to generate a profile, the device's color profile. We know that different devices, materials, and processes will exhibit different characteristics when presenting and delivering colors. In color management, the colors presented on one device are presented on another device in high fidelity, which requires us to understand the color rendering characteristics of colors on various devices. Since the device-independent color space has been selected, that is, the CIE 1976Lab color space, the color characteristics of the device are expressed as the correspondence between the description value of the device and the chromaticity value of the “universal†color space, and the correspondence relationship is: The color description file for the device.
Device Color Profiles In the color management technology, the most common device color profile has three types. The first type is a scanner profile, which provides Kodak, Agfa, Fujitsu's standard manuscripts and standard data of these manuscripts. These manuscripts are input using a scanner. The difference between the scanned data and the standard manuscript data reflects the scanner. The second category is the characteristics of the display file, which provides some software, can measure the color temperature of the display, and then generate a color block on the screen, these color block information reflects the characteristics of the display; the third category for the printing device The feature file, it also provides a set of software, the software generates a graphic containing hundreds of color blocks in the computer, and then output the graphics on the output device, if the printer is directly proofed, the printer will be the first out of the film , Proofing and then printing, measuring these output images reflect the characteristics of the printing device file information.
The generated profile, the color profile, is composed of three parts: the file header, the tag table, and the tag element data.
File header, which contains the basic information of the color profile, such as file size, type of color management method, version of file format, device type, device color space, color space of profile, operating system, device manufacturer , color reproduction target, original media, light source color data, etc., the file header occupies a total of 128 bytes. Tag table, which contains the name of the tag, storage location, data size information, does not contain the specific content of the tag, the tag name name occupies 4 bytes, and each item of the tag table occupies 12 bytes . Marking element data, it is in accordance with the description of the mark table, in the prescribed location to store various information required for color management, according to the complexity of the mark information, the amount of data in the mark varies.
For the color profile of the equipment in the printing company, there are two ways to obtain the information and information processing operators.
The first way is to purchase the device, the profile provided by the manufacturer along with the device, it can meet the device's general color management requirements, when installing the device's application software, the profile is loaded into the system.
The second way is to use a special profile creation software, according to the actual situation of the existing equipment to generate a suitable color profile, the resulting file is usually more accurate, but also more in line with the actual situation of the user. The state of equipment, materials, and processes can change or shift with time. Therefore, it is necessary to re-create the profile at intervals to adapt to the color response at the time.
Colors are passed in the device
Now let's take a look at how colors are transmitted in various devices.
First of all, for a manuscript with normal colors, it is first scanned with a scanner. Due to the profile of the scanner, color (ie, red, green, and blue tristimulus values) from the scanner is provided to the CIE 1976Lab. The corresponding relationship of the space, so the operating system can obtain the color value Lab of the original color according to this conversion relationship.
The scanned image is displayed on the monitor screen. Because the system has mastered the correspondence between the Lab color value and the red, green, and blue drive signals on the display, the red, green, and blue color values ​​of the scanner are not used directly in the display. According to the conversion relationship given by the profile of the monitor in the Lab color value of the previous manuscript, the display driving signals of the red, green, and blue colors that can correctly display the original color on the screen are obtained, and the display is driven to display the color. This ensures that the colors displayed on the display match the colors of the original.
After observing the accurate image color display, the operator can perform image adjustment processing according to the screen color according to the customer's request. Since the profile of the printing apparatus is included, after the image separation, the correct color after printing can be observed on the display. When the operator is satisfied with the color of the image, the image is separated and stored. During color separation, the correct percentage of dots is obtained according to the color conversion relationship carried by the profile of the printing device. After RIP (Raster Image Processor), recording and printing, printing, proofing, and printing, a printed copy of the original can be obtained to complete the entire process.