ICC profile

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An ICC profile (also: color profile ; ICC:  International Color Consortium ) is a standardized data set that describes the color space of a color input or color reproduction device, e.g. B. a monitor , printer or scanner .

The aim of a consistent use of color management is that a template that was captured with any input device is reproduced as similarly as possible on other output devices.

Color management systems can coordinate devices such as scanners, digital cameras , monitors, printers as well as film and platesetters . The color is z. B. displayed according to the printing conditions .

ICC is the abbreviation for the International Color Consortium , an association of many manufacturers of graphics , image processing and layout programs , founded in 1993 with the intention of standardizing color management systems.

Color transfer

Colors that the printer or monitor may not be able to display (they are outside its gamut ) are shifted depending on the type of color transfer (the rendering intent ) so that they are as close as possible to the original. This process is called gamut mapping . The color transfer must be stored in the color profile as a table.

Profile classes

In terms of content, there are mainly the following profile classes:

  • Monitor (mntr): Display devices such as monitors
  • Input (scnr): input devices such as scanners , digital cameras
  • Output (prtr): Output devices such as inkjet printers, printing machines or printing processes.
  • Link (link) for directly clearing two similar output devices, eg. B. two printing processes such as gravure and sheet-fed offset. These profiles contain CMYK-to-CMYK tables and are e.g. B. used in the conversion of print templates (especially PDF / X-3 ).

ICC profiling

For accurate color reproduction in the image processing process, it is important to profile all devices involved.

Monitor profiling

The monitor should be calibrated before profiling. This means first of all to reset the settings of the monitor. Then the values ​​for gamma correction (usually 2.2) and color temperature (usually 5000 Kelvin are set according to the viewing conditions for the graphic industry and photography (ISO 3664: 2009), or 6500 K). This is followed by any necessary measurements with the colorimeter . Now the actual profiling begins. A series of characteristic colors (target values) is displayed on the monitor and measured by the colorimeter (actual values). The ICC profile is then calculated from these target and actual values.

Scanner profiling

IT8.7 / 1 target
A so-called IT8 target is required for ICC profiling of a scanner . This target (a slide for film scanners or a larger template for flatbed scanners) shows a whole series of reference colors that the scanner reads. Special software compares these measured color values ​​with the target values ​​specified in a reference table and thus determines the ICC profile.

Printer profiling

Profiling a printer is similar to that of a screen. A number of characteristic colors (actual values) are printed out on a so-called test target, which are then measured with a spectrophotometer and compared with the target color values ​​by the computer. If you don't want to buy an expensive spectrophotometer, you can hire a service provider to create an output profile. Another solution here is the ICC printer calibration with the help of a scanner, which is used in the SilverFast software . If you have high demands on a profile, you cannot avoid a spectrophotometer.

Digital camera profiling

Similar to the scanner profiling, a special target with reference colors is required here that has to be photographed without reflections and with uniform lighting. The image file obtained in this way is loaded into special profiling software, which then, as before, is made up of target and actual values ​​to create a DCP profile (Digital Camera Profile for Adobe Camera RAW / Lightroom and other DCP-compatible RAW converters) or a ICC profile (for Capture One) created.

Interoperability (PCS)

Color profiles with a reference from the color space to be described to one of the two standardized contact color spaces (Profile Connection Space, PCS), CIE * Lab or CIE * XYZ, and back are fully interoperable. These include the profile classes monitor (mntr), input (scnr), output (prtr) and individual colors (ncl2). In principle, these profiles can be easily combined, in contrast to device link profiles (link).

technical structure

Two types of ICC profiles are distinguished according to their technical structure:

  • Matrix profiles contain 3 × 3 matrices and curve definitions for the primary valences (e.g. definition of a gamma curve for a screen). They are usually very small (around 1 KByte) and are suitable for describing standard color spaces and output devices in which the primary valences do not influence each other (e.g. monitors).
  • LUT profiles (look-up table) are often output profiles (i.e. profiles of specific devices). They are usually relatively large (rarely less than 1 MB) and may contain a. a table of direct assignment of values ​​of a so-called Processing Color Space (XYZ or L * a * b * are defined) in the color space of the output device (e.g. CMYK printer). Complex conversions are possible, e.g. B. also the response of 10-color printers.

Visual representation

2D representations, for example from dye manufacturers, often neglect the lightness axis in order to be able to show all process colors at once. This can lead to problems, as color tones appear to be in the color space that are not at all. 3D models, on the other hand, can be visualized very well on the computer. Mac OS X has an option included with ColorSync , Microsoft on Windows XP offers something similar for separate download with the “Color Control Panel Applet”. In addition, there are z. B. the very extensive program "ColorThink Pro" from Chromix for the visualization of color data.

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