Color Management Implementation Method and Experience (4)

1. Display Correction and Description At present, the Desktop system uses the display as a pre-proofing method and relies on the screen color to adjust the image color. Therefore, one of the keys to the color management system is to bring the display effect of the display close to the output proofing or printing effect. However, since the display is based on the principle of R, G, and B coloration, although the display effect of the general color display is still acceptable, the effect of various factors such as the output proofing or the physical characteristics of the printed color material is different, which makes the display. Colors are difficult to match well with proofing or printing ink colors. As a result, operators are often misled by actual production, and many reworks are favored. Therefore, we should try our best to adjust the color of the display to the effect similar to the color of the proof or printing, which is very important for the accuracy of adjusting the color of the image.
1) Display... The display has been calibrated at the factory, but over time, the use environment, manufacturing reasons, etc. still need to be corrected frequently. The variables that the display needs to correct include brightness, gamma, and white balance (color temperature).
A. determine the color temperature: general computer system monitor color temperature of about 9300K, but the prepress system in order to make the operator see the image color on the screen and output image color on the paper as close as possible, requires the monitor's color temperature is 5000K -6500K, Mac default is 6500K, which is the color temperature value of standard illumination body D65 recommended by CIE in colorimetry. The color temperature reflects the white area color balance on the screen (cold and warm), the color temperature is low, the screen color is yellow, and the high color temperature is blue.
B. Determination of gamma: This value affects the aspect of the highlights and shadows of the image (in the absence of color management, the gamma may be adjusted against the final print and screen image of the same document so that their contrasts are similar). When using color management, the system sets a typical gamma value. For example, EFI's RGB calibration standard specifies a display gamma value of 2.20, and Mac machines generally set 1.8.
2) Adjust the screen color A. Use ISO IT8 color scale to adjust the screen color to simulate the proofing or printing effect. If using IT8 reflection color scale, it must be of good quality and cannot be placed for too long because it is made of photosensitive paper. Easy to fade. IT8 color standard principle and data, can be in WWW. Checked on the Ehongnet website.
B. Use the IT8 color standard, output the film, and play standard color proofs.
C. Use the IT8 color sample proof on the screen to calibrate the IT8 color standard. There are two methods: One is the automatic calibration method: the software and the spectrophotometer or screen correction instrument are used to complete the software. The 928 colors are passed to the screen. The spectrophotometer then returns the measured data to the computer. Based on the comparison correction, the software creates a standard Color Profile to drive the display. With this profile file, we can know the conversion relationship between the monitor's color space RGB and the CIE Lab standard color space.
The other is a manual correction method: dig a small white hole in the middle of the seven hue of C, M, Y, MY, CY, CM, and CMY in the IT8 color proof sample, and paste each color block on the screen separately. Corresponding color blocks, and then use Photoshop software's Color Picker dialog box color axis to adjust the hue, drag the gradient color to select the small circle in the figure, respectively, adjust the hue saturation, brightness, make it reach The effect is similar to the 7 color proofs.
3) Add a black cover at the top and left of the screen to prevent interference from ambient light and make the color of the viewing screen more accurate.
4) In the actual production, it should focus on correcting the monitor separation and the adjustment of the monitor with the monitors of the 3 workstations, and the monitors used for the repair of the dirty and the composite panels can be corrected normally.
If you use the PC image workstation P II400-512MB, display 1280 product 024, true color, 16.7M, after fine tuning the display effect is very close to the proof ink effect, so the screen color has a certain reference.
5) Since the current screen can also completely simulate the ink proofing and printing effects, it can be used as a reference for the pre- proofing color, and at the same time further rely on the dot value of the CMYK four-color ink displayed by the color separation software to make precise adjustments. The combination will be more accurate.
2. Scanner Calibration and Profile Creation
The scanner shoulders the most important mission of the color management system. Whether the scanner can realistically reproduce the key to the color level in the image art in the process of color management and digitization. Therefore, the characteristic management of the scanner is the most important, and now some high-end professional platform scanners have developed a color management system with its own characteristics, so that the scanning color separation technology is more standardized and the color reproduction is more accurate. (To be continued)