Why we need colour management

The digital revolution has introduced new technology: digital cameras, scanners, ink-jet printers and high-powered computers have become widely used tools. Photographers and designers are now doing a lot of the tasks previously performed by the “Professionals”; however, there are hurdles to overcome when tying to harmonise various different types and makes of equipment.

In 1993 a group of industry experts recognised these problems and set up the ICC – the International Color Consortium (www.color.org) They devised the ICC profile specification as a cross-platform method of translating colour from one device to another.

Original ( input from camera/scanner )

Displayed on Computer Screen

Printer Output

The examples above indicate how this can affect your images

What is an ICC Profile?

ICC profiles contain information about the colour rendering ability of a device. During profile creation the device is given a set of known colours to display/scan/reproduce and then the results are read back into the profiling software. You are then given a “what I’ve got compared to what I should have” comparison.

There are three classes of profile: input (scanner and digital camera), monitor (for the screen), and output (inkjet and press). An ICC profile is a small text file (about 1mb) containing numbers in table format. When opened in a text editing software a profile looks a bit like this…

BEGIN_DATA_FORMAT
SAMPLE_ID XYZ_X XYZ_Y XYZ_Z RGB_R RGB_G RGB_B
END_DATA_FORMAT
BEGIN_DATA
1 8.060 8.390 31.480 0 100 100
2 10.490 12.530 41.060 10 100 100
3 13.950 18.650 51.430 20 100 100
4 18.280 26.010 59.710 30 100 100
5 23.200 33.020 64.150 40 100 100

…but the lines go on and on for ages. Profiles contain a lot of information, such as the class of profile, the colour space of the device and the creator application. The numbers refer to the colour values of defined colours in a colour space and are used as a look-up table for colour conversion.

ICC colour management uses profiles to convert colours into or out of a theoretical colour space (referred to here as CIELab) Every colour is plotted to a point in the CIELab colour space and is represented by a three-value number.

CIELab is a mathematical 3D colour model used as a translation reference. It is a numerical model of human colour sensitivity based on a sample of individuals with normal colour vision. It’s origins date back to Sir Isaac Newton’s colour experiments in 1730.

When a scanner profile is made you get the RGB to CIELab conversion values, and when a press profile is made you get the CIELab to CMYK conversion values. The removal of a direct RGB to CMYK table means you don’t have to know where an image is going to end up when you are shooting or scanning it.