August 2008

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So What is the Problem ?
Lack of feedback is the main problem. The computer has no way of knowing how a colour actually appears on the screen or printer after it has sent the colour information out. There are also colour balance, contrast, and brightness controls on the average computer screen. Each of these will change how a colour appears on the screen even though the colour numbers stored inside the computer remain the same. So, the same colour information (e.g. the HVS numbers) stored on a computer but sent to two different screens with different colour balance, brightness, and contrast settings will result in different colours on the screen.

In addition to this the colour reproduction of a computer screen may change through time and the computer has no information to allow it to compensate for this colour drift.

The colour printer however has no such colour adjustment. Assuming that the printer is functioning correctly then it should produce the same colour on the page when sent the same information from the computer. So, whereas the colour on the computer screen is dependent upon different colour adjustments beyond the control of the computer, the printer colour is relatively fixed and stable.

The Simple Solution
The cheap solution involves a two-stage colour matching procedure. Each colour is matched into the computer twice - once for the screen and again for the printer. The computer holds two sets of numbers for each colour.

Screen colour matching is done visually on the screen usually with slider bars representing the three colour numbers available. A colour sample area is observed on the screen and the slider bars are adjusted until the desired colour is attained. The numbers required to reproduce this colour are then held.

In order to match a colour to the printer you must first print out a "colour atlas" on that printer. This is a series of printed pages with a range of colour "chips" on each page. Each colour chip has a code number to identify it. Since the pages are printed using the colour printer they represent true colours that the printer is capable of printing. Matching a colour to the printer therefore is simply a case of choosing a colour chip from one of the colour atlas pages and entering its reference code into the computer. The computer uses this code to reproduce the same colour as on the colour chip when printing. The reference codes may be arbitrary codes printed on a page or may be more universal for example "Pantone" codes.

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