How to implement effective color management
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1. How to make an ICC profile? Where can I find the programs used for color management and these feature files?
For color management, each device (including scanners, digital cameras, monitors, printers, etc.) requires its own profile. Each profile of these devices associates the device's color data with a standard color space and combines them to produce a complete conversion process. In order to generate these profiles, a target image for measurement is required. For example, a scanner can use a medium-sized photo, but it is best to use the IT8.7/2 standard color scale for scanning reflexes using IT8.7/1. The standard color scale is used to scan the transmission. The printer uses prints containing color patches, preferably IT8.7/3, which contains 928 color patches. The display requires a target image of more color patches.
The feature file creation software is provided with the test image. In order to generate the printer and display profile, we should evaluate the transmissive and reflective film of the scanner and digital camera. There should also be a specific color code provided by Macbeth for evaluation of the digital. Camera system. Then, a color management device is needed to measure this printed image, and through these measurements, the measured data is provided to the software for making a profile.
Feature file creation software is available from Agfa, Fuji, Gretag-Macbeth, Heidelberg, Kodak, Monaco and others. Measuring equipment is available from companies such as Gretag-Macbeth, X-rite, Alwan Color Expertise, Color Savvy.
In order to combine the profile files of different devices, a color management module (CMM) is required. The CMM allows images to be converted between devices in different color spaces and produces predictable colors. The most important CMM is the interpolation engine for combination table insertion (LUT). The CMMs produced by different manufacturers are different. ICC does not explicitly recommend which CMM to use, because some CMMs pick up the special tag information in the profile. , more meaningful as a special application. Many high-end RIPs include a CMM and a Photoshop program that allow people to use a simple combination of feature files, as Photoshop also includes a CMM. The CMM in Apple is an integral part of the operating system, called ColorSync, and the CMM in Windows is the ICM. Most software vendors that make profile files can also use their software to create specific CMMs.
2. What color management space is mainly used in color management? What is PCS?
In color management, the color data of an image is converted from one color space to another, and there are two main categories of application. One is a device-independent color space, mainly CIE XYZ, CIE Lab color space (see Figure 1). The other is the color space associated with the device, mainly RGB (see Figure 2), CMYK color space.
PCS (Profile Connection Space), which is a feature file connection space, can be defined by XYZ space or Lab space, and is a device-independent color space. The purpose of PCS is to serve as an intermediate color space for color space conversion when color conversion between different devices is used as a link. For example, the RGB image of the scanner is displayed on the display screen. First, the color management system converts the RGB image of the scanner to the Feature File Connection Space (PCS). The color management system then uses the information stored on the display in the color profile of the display to convert the image from the feature file connection space to the color space of the display to see the image displayed on the display.
3. What is the rendering intent?
The color space of different device image data is different. For example, the image scanned by the scanner is RGB data, and the image printed by the printer is CMYK data, and the CMYK color gamut is much smaller than the RGB color gamut. For color management, the characteristics of various devices can be described by supporting the color profile between media devices, including the ICC profile of the scanner, the ICC profile of the display, the ICC profile of the printer, and the ICC profile of the device connection. Wait. Color space conversion between the device color space and the PCS space is performed by establishing an ICC profile, and color matching is performed because the color gamut of the color space used by the two is different. The mapping method of converting image data from one color space to another is called color matching.
4. How many color matching methods are there? Which color matching method should I use?
When copying images of different color gamuts to one type of media, the color matching method defines how the color gamut obtained on the media is corrected. The ICC standard provides four color matching methods, namely, sensation, relative chromaticity, saturation, and absolute chromaticity.
The sensation method is to adjust the conversion ratio according to the color range displayed by the output device to obtain the consistency of the color in the sense. The relative chromaticity method is to change the white point calibration. All colors are changed according to the change of the calibration point, but the color gamut compression is not performed, and the color beyond the color space range is replaced by the color with the closest color gamut boundary. The saturation method is to nonlinearly compress the saturation, not necessarily faithful to the original, and pursue high saturation if the equipment conditions permit. The absolute chromaticity method is that the color in the output gamut remains unchanged after being converted, and the color beyond the gamut is replaced by the color of the gamut boundary.
Which color matching method to use depends on the gamut of the original and the copy medium. The scanned ordinary photo image is copied into a print or used for display, usually using a sensory method. The main reason is that the color gamut of the printed or displayed is usually lower than the original. For high color gamut printing, it may be more appropriate to use the chromatic method (trying to produce an accurate color matching). However, in other cases, such as proofing (one device emulation of another device, such as display analog printing), when there is no color gamut matching, a colorimetric method is required; when the output color gamut is close to the input color gamut You can use the absolute colorimetric method. Saturation is commonly used in commercial images to produce higher vividness on prints and to make images more powerful.