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Colour Adjustment - Part 1 - part 1 of 1 2 3 4

by Mike McNamee Published 01/10/2002

One of the most potent features of digital imaging is the ability to colour correct before output. This strength comes from two quarters, the ability to measure within the image and the ability to correct using numerical values. Both add great precision to the procedure, so much in fact that you can colour correct with impaired colour vision, providing you know the target numbers of various parts of the image.

Colour Blindness are you seeing clearly? Most of us take colour for granted although it has not always been so. Primitive cultures tended not to bother about colour and had a limited vocabulary of colours (that is they did not assign names to specific colours). Colour is in any case a conceptual thing that only really exists in the mind of the viewer. It ceases to exist in a darkened room. Animals see in colour quite differently to humans; dogs for example are limited in their colour discrimination. Our New World cousins have different colour to us Old World types. Forty million years ago primates developed an additional skill that enabled them to differentiate green and red - pretty handy if you are up a tree trying to decide which fruit is ripe and which is not. Colour vision works a bit like your scanner. In the scanner, the detector looks for Red, Green and Blue light and mixes them together to define the colour of the pixel. The eye works in a similar way. "Cones", which are situated close to the central axis of the eye have pigments which are (each) one of three colours. They are usually thought of as red, green and blue although they are, in reality, not too close to those colours, being more accurately described as Yellow-Green, Green-Yellow and Blue. This does not inconvenience us as the brain does clever tricks and makes red look like red etc. The cones are the source of our colour vision and it was a 3rd cone type that formed those 40 million years ago to give us our enhanced 24-bit vision. Dogs have 16 bit vision (2 by 8-bits of colour!). Some poor Aussie nocturnal creatures have poor old 8-bit vision and see in monochrome. Poor vision does not however seem to be suffered by Aussie batsmen.

While the cones are the source of our enhanced colour vision they can also be the downfall of some people. If your genetics are mixed up you could end up with one of your cone sets missing or perhaps with cones that are too similar to each other in their colour detection. The genetic basis of colour vision is what makes men more vulnerable to colour vision defects, 16 times in fact (0.43% of women 8.14% of men to be precise). Girls take X chromosomes from each parent while boys take one of the mother's X's and one of the father's Y's. As the X chromosome carries the pigment making signals for the cones, the boys are disadvantaged.

If you are colour blind or defective there are certain occupations that you are barred from. You won't be much use in a photographic laboratory, an electronics company or as a Police Officer. The first is obvious, the second is because you would mix up all those wires and the third is because the judge will want a better description of the getaway car than "it was a reddy, greeny-grey colour".

Assuming you are not a colour defective i.e. something biologically wrong such as a missing pigment, how do you measure up when judging colour? This is an important question because experience tells us that some people seem to be better at judging colour than others. We spoke to one of the UK's leading experts in this subject, Jennifer Birch of the City University and then got her book from the reference library. In this she says "most people with normal colour vision can acquire superior colour-matching skills if they are sufficiently motivated"

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1st Published 01/10/2002
last update 09/12/2022 14:52:34

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