The structure and working principle of the color profile

The ICC International Color Consortium, established in 1993, established a cross-computer platform device color profile file format for the purpose of color management through color profiles to achieve color transfer consistency. The device-independent color space (PCS) Profile Connection Space, the standard format of the device color profile, the ICC Profile, and the color space conversion method (CMM) are the system-level color management frameworks of the Color Management Module. This article mainly discusses the structure and working principle of the device color profile to analyze the significance and role of the color profile in the color management system.

1 device color profile structure

The ICC standard color profile consists of a file header, a tag table, and tag element data.

(1) File header Profile Header

The file header records the basic information of the color profile and is 128 bytes in length. Including the color profile size, category, version number, CMM type, data color space type, color profile generation time, operating system platform, CMM and distributed processing mark, device manufacturer, device model, device characteristics, copy Intent, XYZ values ​​of the illuminant space illuminator, markers of the color profile generator, and the like.

(2) Tag Table

The length of the tag table is  4 + 12 × N 字节 bytes, where N is the number of tags? The first 4 bytes of the start record the number of tags in the tag table, followed by the content of each tag index, each tag index The content is 12 bytes, which respectively record the tag name  4 bytes , size  4 bytes , offset address  4 bytes.

(3) Tag element data î—¤ Tagged Element Data

The tag element data is used to provide complete information and data for color conversion by the color management module. There are dozens of tags in the ICC color profile. The definition, use, and byte length of each tag are different. The content and number of tags in different profiles are also different.

2 How Device Profiles Work

The color management module (CMM) converts between the PCS and the device color space based on the information and data of the color profile. The ICC standard specifies three types of basic device characteristic description files, ie, an input device characteristic file, a display device characteristic file, and an output device characteristic file. The three basic characteristic files are further divided into monochrome and color device characteristic files.

(1) The input device characteristics file works.

1 monochrome input device profile (see Table 1

).

The PCS value corresponding to the device value can be obtained by reading the gray copy curve label. The mathematical calculation formula is:

Profile connection space value = grayTRC [device value] î™…

The inverse process is expressed as:

Device value = grayTRC-1  profile file connection space value 

(to be continued)