Analysis of iccprofile in the hottest color manage

Analysis of ICC profile in color management

in 1993, the world's famous prepress software developers adobe, Agfa, apple, Kodak, Fogra, Microsoft, sun microsystem and other companies initiated and established the International Color Consortium (ICC), which aims to establish, promote and encourage an open, cross platform, neutral color management system, and formulated ICC profile specifications, The latest version of file format for color profiles (version 4.1.0) was released on August, 2003

content of color management

in the process of color image reproduction, all the equipment involved work in their own unique color space, and color management technology is to explain the unknown factors that change continuously in the reproduction workflow, conduct quantitative analysis, and carry out corresponding color space conversion on this basis, so that the color reproduction is independent of the equipment. Color management is divided into three steps in principle, referred to as "3C"

1. Calibration equipment

establish a neutral gray environment, standardize the light source, and then calibrate the input equipment, display equipment, and output equipment

1) input device calibration. Input correction includes brightness, contrast and black-and-white field correction. Take the scanner calibration as an example. After the scanner is initialized and zeroed, the same image data can be obtained for the same original no matter when it is scanned

2) display device calibration. Use the display correction system (including hardware and software) to correct the brightness of the display. Contrast, color temperature and gamma value of the whole display system

3) output device calibration. Correct the gray balance parameters and black plate parameters of output equipment (printers, printers), which is aimed at accelerating the updating of plastic granulator technology and correcting the parameters of paper, ink and other printing materials

2. Establish characterization

use color management software to interpret the specific color characteristics of the device, and on this basis, establish the device color description file (ICC profile) against the device independent color space. These description files are the bridge from the device color space to the device independent color space (PCS)

3. color space conversion

based on the calibration of the equipment in the system, the correct conversion between the color spaces of each equipment is realized by using the equipment description file and the standard equipment independent color space as the medium

icc profile file format analysis

1. Overall structure of ICC profile file

from Figure 1, we can see that ICC profile file is mainly composed of three parts: file header, label table and label element data

(1) profile header

the file header is composed of 128 bytes, and 4 bytes are a unit, which records the file size and CMM type in turn. Version information, profile type or device type, device color space, conversion connection space (PCS), main platform, file creation date, illumination body chromaticity, color gamut compression method (including sensory method, relative chromaticity method, saturation method and absolute chromaticity method), media type and other information

(2) tag table

mainly records the tag information contained in the file, which is similar to the function of retrieving the directory. The first four bytes are the total number of tags contained in the file (tag count), followed by the description of each tag, each accounting for 12 bytes, including the name of the tag, the location and size in the tag element data area

(3) tagged element data

record the information of each tag in turn according to the data in the tag table. The first four bytes of each tag content are tag types, and the following formats vary according to tag types and sizes

according to the different types of devices, the necessary tags contained in ICC profile are different, and for the same device, different tag combinations will be generated due to different algorithm models for generating ICC profile. Color management system manufacturers will also add their own private labels according to specific equipment conditions, and the cooling medium should be replaced regularly. When converting colors, the color management system will find the position of the label from the label table according to the required label name, and then read out the data of the label to carry out the mathematical calculation of color conversion. ICC PR can be seen through the ICC profile inspector software, so it is not easy to select reliable manufacturers of high and low temperature impact testing machines from 100 companies across the country. Ofile's header information and label information can be obtained free of charge on the ICC official website www.color.org

2. Classification of ICC profile

icc profile can be divided into four categories: input profile, display profile, output profile and additional profile. These include devicelink profile, colorspace conversionprofile, abstract profile, and named color profile

since the color space of display devices and input devices is RGB, the necessary label combinations of their ICC profile files are the same, which are generally divided into three types: monochrome display (or input) device profile, three-dimensional display (or input) device profile based on matrix model, and multi-dimensional display (or input) device profile based on lookup table model. The color space of the output device is CMYK, and its label combination is relatively complex. There are mainly two kinds: monochrome output device profile and color output device profile

3. Common tag description of ICC profile

icc defines 48 Tags, a total of 30 types, and each tag has a certain tag type. For each ICC profile file, they contain different tag combinations. Here are a few common tags

profiledescriptiontag: general description of the feature file

copyrighttag: copy right information of the feature file

mediawhitepointtag: media white field tristimulus value (XYZ)

mediablackpointtag: media black field tristimulus value (XYZ)

graytrctag: grayscale gradient reproduction curve, which is generally only used on monochrome output equipment

redtrctag: red tone reproduction curve

greentrctag: green tone reproduction curve

bluetrctag: blue tone reproduction curve

redmatrixcolumntag: tristimulus value (XYZ) of red phosphor

greenmatrixcolumntag: tristimulus value (XYZ) of green phosphor

bluematrixcolumntag. tristimulus value (XYZ) of blue phosphor

atobotag: conversion parameter from device gamut to PCs gamut, and the applicable gamut compression method is sensory method

atob1tag: conversion parameter from device gamut to PCs gamut. The applicable gamut compression method is relative colorimetry

atob2tag: from equipment gamut to PCs gamut, effectively protect and maintain the conversion parameters that help to prolong their service life. The applicable gamut compression method is saturation method

btoaotag: conversion parameter from PCs color gamut to equipment color gamut, and the applicable color gamut compression method is sensory method

btoa1tag: conversion parameter from PCs color gamut to equipment color gamut. The applicable color gamut compression method is relative colorimetry

btoa2tag: conversion parameter from PCs color gamut to equipment color gamut. The applicable color gamut compression method is saturation method

gamuttag: detect whether the input color is outside the color gamut

among them, trctag and matrixcolumntag are proprietary tags whose color gamut space is RGB display device and input device. Because the color management system can calculate the conversion parameters suitable for the absolute gamut compression method according to atob1 and mediawhitepointtag, there is no special definition of an atobtag tag for the absolute gamut compression method. There are many unlisted tags that can be added selectively according to different algorithm requirements. The more tags, the larger the file

icc color standard has been widely recognized. Most hardware devices have been calibrated and have their own ICC profile feature files when leaving the factory. However, with the continuation of use time and the change of environment, hardware parameters will change, so we need to often calibrate the device and re-establish the ICC profile file that conforms to the characteristics of the device at that time, so as to give full play to the performance of the device

at present, many peripheral products on the market are equipped with their own color correction software, such as Agfa professional scanner color tune; Heidelberg's color management system scanopen (for scanners and digital cameras) and viewopen (for displays). Printopen (for output device); Color sync color management system based on Apple operating system; Adobe gamma in Photoshop (calibration display); There are also special ICC tools, such as Kodak's colorflow ICC profile tools, including colorflow ICC monitor profilebuilder (for displays) and colorflow inputprofile Builder (for scanners and digital cameras). These software can be used to establish the color characteristic files of devices in real time