ICC Profiles

What is an ICC profile?

A. ICC profiles help you to get the correct colour reproduction when you input images from a scanner or camera and display them on a monitor or print them. They define the relationship between the digital counts your device receives or transmits and a standard colour space defined by ICC and based on a measurement system defined internationally by CIE. Thus, if you have a profile for each of your scanner, camera, display and printer, the fact that they refer to a standard colour space lets you combine them so that you obtain the correct colour as you get images from the scanner or camera and print or display them.

An ICC profile is one that conforms to the ICC specification. By conforming to this specification profiles may be exchanged and correctly interpreted by other users. The two main types of profiles are source (input) and destination (output) profiles and essentially consist of tables of data that relate the device co-ordinates to those of the standard colour space defined by ICC. There are various relationships defined in each profile (known as rendering intents ? see a later question). Special types of profiles (devicelink, and abstract) are defined for special workflow applications.

What is spectrophotometry?

A. Spectrophotometry is the measurement of the reflectance or tranmittance of a sample at discrete wavelengths. Spectrophotometers usually provide illumination of the sample by white light and then contain a diffraction grating to refract the reflected light and enable measurement of the amount of light reflected at discrete wavelengths.

What are the limitationss of spectrophotometers?

A. Different spectrophotometers are more or less accurate than others. Most of the cheaper instruments available today are reasonably accurate for reflecting media without steep changes in spectral reflectance, which is the case for most pigments.

Although measurement typically takes a second or so on a hand-held device, if you have a large number of colour patches to measure this can add up to long time. Some manufacturers offer automated devices which move the measuring head across the chart automatically, or allow you to 'swipe' the instrument across a strip of patches.

How do I implement ICC colour management on my system?

A. To apply colour management, you need a profile for each of your scanner and/or digital camera and another for your monitor and/or printing device. Each of these relates the device colour data to the standard colour space which allows them to be combined to produce an overall transformation.

To combine profiles you need a Colour Management Module (CMM). At its most basic this is nothing more than an interpolation engine for combining LUTs. ICC do not specifically recommend a single CMM as some CMMs attempt to 'add value' for specific applications by picking up private tag information in the profile.

Many colour management-aware applications such as high-end RIPs and Adobe Photoshop contain an internal CMM. CMMs are also built in to the OS on the Mac (ColorSync) and Windows (ICM and WCS).

 Where can I find profiles for my devices?

A. Most often these are available from the manufacturer of the device.

How do I make ICC profiles?

A. The main requirement is a software application that will generate profiles from measurement data. For output profiles, you also need a measurement instrument to measure your prints or display. For more details, see making profiles. For a list of software and instruments available from ICC members, see profiling tools.

What is an output profile?

A. Output profiles are of the LUT type, and are used in conjunction with hard copy output device, such as printers and film recorders. Output profiles translate between the PCS and the output colour encoding. In the case of a printer profile, the output colour encoding might be monochrome, CMYK, RGB or n-colour, where n can be up to 16 (although in practice is rarely greater than 6 or 7).

In some workflows there is a further conversion from the output colour encoding of the profile to the actual colorants used by the printer, which is usually performed in the printer driver.

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