How to perform effective color management

1. How to make ICC profile? Where can I find the programs used by color management and these feature files?

For color management, each device (including scanners, digital cameras, monitors, printers, etc.) needs its own profile. Each profile of these devices associates the device's color data with the standard color space and combines them to produce a complete conversion process. In order to generate these profiles, a target image for measurement is needed. For example, the scanner can use a medium-sized photo, but it is better to use the IT8.7/2 standard color code for scanning reflection texts. IT8.7/1 is used. The standard color code is used to scan the transmitted document. The printer uses prints containing color patches, preferably IT8.7/3, which contains 928 color patches. The display requires more color target images.

The profile creation software is provided with the test image. In order to be able to generate printer and display profile files, the transmissive and reflective films of the scanner and digital camera should be evaluated. There should also be a specific color scale provided by Macbeth for evaluation of digital data. Camera system. Then, a color management device is required to measure this printed image, and through these measurements, the measured data is provided to software for making a profile.

Profile creation software is available from companies such as Agfa, Fuji, Gretag-Macbeth, Heidelberg, Kodak, and Monaco. Measurement equipment is available from companies such as Gretag-Macbeth, X-rite, Alwan Color Expertise, Color Savvy, and others.

In order to combine the profiles of different devices, a color management module (CMM) is required. The CMM transforms the image between devices in different color spaces and produces predictable colors. The CMM is the most important interpolating engine for combination table insertion (LUT). The CMMs produced by different vendors are different. ICC does not explicitly recommend which one to use, because some CMMs pick up special tag information in the profile. It makes more sense as a special application. Many high-end RIPs contain a CMM and a Photoshop program that allow people to use simple feature file combinations because Photoshop also includes a CMM. The CMM in the Apple computer is an integral part of the operating system called ColorSync. The CMM in the PC is the ICM. Software vendors that make most feature files can also use their software to make specific CMMs.

2. What color management space is used mainly 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 types 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), the connection space of the profile, can be defined by XYZ space or Lab space and is a device-independent color space. The purpose of the PCS is to serve as a link between the color space used for color space conversion when the color conversion between different devices. For example, the scanner's RGB image is displayed on the display screen. First, the color management system converts the scanner's RGB image to a profile connection space (PCS). The color management system then uses the information about the display stored in the display's color profile to convert the image from the profile's connected space to the display's color space and see the image displayed on the display.

3. What is a rendering intent?

The color space of image data of different devices 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. In order to perform color management, the characteristics of various devices can be described in terms of color profiles supporting media devices, including the scanner's ICC profile, the monitor's ICC profile, the printer's ICC profile, and the device's connected ICC profile. Wait. By establishing the ICC profile, the color space conversion between the device color space and the PCS space is performed. Since the color space of the color space used by the two is different, the color matching is performed. The method of mapping image data from one color space to another is called the color matching method.

4. What are the color matching methods? Which color matching method should I use?

When the images of different color gamuts are copied to one kind of media, the color matching method defines how the color gamut obtained on the media is corrected. The ICC standard provides four types of color matching methods: sensory method, relative colorimetry, saturation method, and absolute colorimetry.

Sensing is based on the color range displayed by the output device to adjust the conversion ratio so as to obtain a sense of color consistency. Relative colorimetric method is to change the white point calibration, all colors change according to the change of the calibration point, but does not do color gamut compression, the color beyond the color space range is replaced with the color with the closest color gamut boundary. Saturation method is the nonlinear compression of saturation, not necessarily faithful to the manuscript, the pursuit of high saturation under the conditions of the equipment. Absolute chromaticity method is to keep unchanged after the color conversion in the output color gamut, and the color beyond the color gamut is replaced with the color of the gamut boundary.

Which color matching method to use depends on the color gamut of the original and the copy media. The scanned ordinary photo image is copied into a print or used for display, usually using a sensation method. The main reason is that the printed or displayed color gamut is usually lower than the original, and for high color gamut printing, using chroma (trying to produce an exact color match) may be more suitable. However, in other cases, such as proofing (a device emulates another device, such as displaying analog prints), a colorimetric method is used when no color gamut is matched; when the output gamut is similar to the input gamut Absolute colorimetry can be used. Saturation method is usually used for commercial images, which can produce higher vividness in prints and make the rendering effect of the images stronger.