Representing printing colours or paints on a display screenAs already explained, the additive RGB colour system used on displays and the subtractive CMYK system of paints are inherently opposed models that lack completely accurate equivalence. Even so, display screens can provide a fairly good idea of what colours look like in various conditions, outdoors for example. This is made possible by yet another property of the eye, which may equally be seen as a deficiency or strength: the eyes adapt extremely well to changing viewing conditions. Our perceptual system can also “recall” several colours and processes its observations accordingly. For example, the colour of the skin, the greenness of the grass and the whiteness of paper are perceived more or less identically in vastly different lighting conditions. Analyzers indicate that a sheet of white paper illuminated by an incandescent lamp indoors reflects a significantly different range of wavelengths when compared to outdoors in sunlight. However, to us it appears white in both situations.
Once the eyes have become adjusted to the colours displayed, they perceive colours to be relatively natural. When colours are viewed on screen, perhaps the most important question is to ensure that the surroundings are neutral and lighting intensity is moderate. While normal and somewhat dim indoor lighting is perfectly adequate, problems may arise if large amounts of natural light are mixed with it. The area around the display should be fairly neutral in colour without any brightly coloured surfaces or rich colours to confuse the eye. The more colourless and grey the surroundings are, the easier it is for the eye to adjust to the screen’s colour system.
While currently popular flat screens offer few colour adjustments, in fact they are not necessary. With a CRT display, correct adjustment should be made before its colours are critically analysed. Grey neutrality provides a good point of reference: for example, if you know a pixel on the display to be grey, but it is clearly some other colour, then adjustments should be made. Image processing software is often supplied with display adjustment applications and may prove to be useful. Calibration carried out with specific display tools is only useful for image processing software that can make use of the calibration data.
|Portions of colours perceived by the eye reproducible with various techniques.
Text and images: Sakari Mäkelä, M.A.
(Article in the Tikkurilan Viesti Newsletter, Issue no. 2, November 2004)