At present, in color management technology, the so-called color feature connection space uses the chromaticity space of CIE1976Lab. Colors on any device can be converted to this space to form a "universal" description method, and then color matching and conversion are carried out. Within the computer operating system, the task of implementing color matching conversion is completed by the "color matching module", which is of great significance for the reliability of color conversion and color matching. So, how to achieve color transfer in a "universal" color space, achieving lossless or minimal color loss?
This requires each set of devices to generate a profile, which is the device's color feature file.
We know that various devices, materials, and processes exhibit different characteristics when presenting and transmitting colors. In color management, to present the colors presented on one device with high fidelity on another device, we must understand the color presentation characteristics of colors on various devices.
Since a device independent color space, CIE1976Lab chromaticity space, has been selected, the color characteristics of the device are represented by the correspondence between the device's description value and the chromaticity value of the "universal" color space, which is the device's color description document.
1. Device color feature description file
In color management technology, the most common types of device color feature description files are:
The first type is the scanner feature file, which provides standard manuscripts from Kodak, Agfa, and Fuji companies, as well as standard data for these manuscripts. These manuscripts are inputted using a scanner, and the difference between the scanned data and the standard manuscript data reflects the characteristics of the scanner;
The second type is the feature file of the display, which provides some software that can measure the color temperature of the display, and then generate a color block on the screen, which reflects the characteristics of the display; The third type is the feature file of the printing device, which also provides a set of software. The software generates a graph containing hundreds of color blocks in the computer, and then outputs the graph on the output device. If it is a printer, it directly samples, and the printing machine first produces the film, samples, and prints. The measurement of these output images reflects the feature file information of the printing device.
The generated profile, also known as the color feature file, consists of three main formats: file header, tag table, and tag element data.
· File header: It contains basic information about the color feature file, such as file size, type of color management method, version of file format, device type, color space of the device, color space of the feature file, operating system, device manufacturer, color restoration target, original media, light source color data, etc. The file header occupies a total of 128 bytes.
· Tag Table: It contains information about the quantity name, storage location, and data size of the tags, but does not include the specific content of the tags. The quantity name of the tags occupies 4 bytes, while each item in the tag table occupies 12 bytes.
· Markup element data: It stores various information required for color management in designated locations according to the instructions in the markup table, and varies depending on the complexity of the markup information and the size of the labeled data.
For the color feature files of equipment in printing enterprises, operators of image and text information processing have two ways to obtain them:
· The first approach: When purchasing equipment, the manufacturer provides a profile along with the equipment, which can meet the general color management requirements of the equipment. When installing the equipment's application software, the profile is loaded into the system.
· The second approach is to use specialized profile creation software to generate suitable color feature description files based on the actual situation of existing devices. This generated file is usually more accurate and in line with the user's actual situation. Due to changes or deviations in the state of equipment, materials, and processes over time. Therefore, it is necessary to remake the profile at regular intervals to adapt to the color response situation at that time.
2. Color transmission in the device
Now, let's take a look at how colors are transmitted across various devices.
Firstly, for a manuscript with normal colors, a scanner is used to scan and input it. Due to the scanner's profile, it provides a corresponding relationship from the color (i.e. red, green, and blue tristimulus values) on the scanner to the CIE1976Lab chromaticity space. Therefore, the operating system can obtain the chromaticity value Lab of the original color according to this conversion relationship.
The scanned image is displayed on the display screen. Since the system has mastered the correspondence between the Lab chromaticity values and the red, green, and blue driving signals on the display, it is not necessary to directly use the red, green, and blue chromaticity values of the scanner during display. Instead, from the Lab chromaticity values of the previous manuscript, according to the conversion relationship provided by the display profile, the display driving signals of red, green, and blue that can correctly display the original color on the screen are obtained, Drive the display to display colors. This ensures that the color displayed on the monitor matches the original color.
After observing the accurate image color display, the operator can adjust the image according to the screen color according to customer requirements. Additionally, due to the profile containing printing equipment, the correct color after printing can be observed on the display after image color separation. After the operator is satisfied with the color of the image, the image is color separated and stored. During color separation, the correct percentage of dots is obtained based on the color conversion relationship carried by the printing device's profile. After undergoing RIP (Raster Image Processor), recording and printing, printing, proofing, and printing, a printed copy of the original document can be obtained, thus completing the entire process.
Post time: Nov-23-2023
