[COLOR=darkgreen][B]No.12[/B][/COLOR]: Coordinate your colour.

It would be ridiculous to attempt to explain [B][COLOR=darkgreen]colour management[/COLOR][/B] in any detail via this blog; a team of researchers could end up writing volumes on the subject. But it's an important concept to grasp if you are going to be moderately serious about your photography, and even if you simply want good, consistent, colour.

So today's Daily photo tips blog will briefly introduce the concept of colour management, finishing up tomorrow.

[B][COLOR=darkgreen]Standardising colour[/COLOR][/B]

Colour is perceived by us through our eyes and our brain. Sometimes, two people will not actually agree on the colour of something. Even worse, the colour of an object will appear different according to the light shining on it, and colours that surround it. So colour is a very tricky thing!

It's the same with colour images. When you take a picture, your aim is usually to reproduce the same colours you saw when you pressed the shutter button... on a print, or on a computer screen.

[B][COLOR=darkgreen]Reflected colour[/COLOR][/B]

When you view a print you are seeing light reflected off the surface of the paper. The colour you see is the component of the colour spectrum of the light that hasn't been absorbed by the surface of the paper, of the print. This is reflected colour.

[COLOR=darkgreen][B]Transmitted colour[/B][/COLOR]

A computer or a TV screen, or a colour transparency, for example, transmits colour through a medium that filters the light. Once again, the colour you see is the result of an elimination process, so you see the colour from the spectrum of the light source that hasn't been filtered our or absorbed by the transparency medium.

[B][COLOR=darkgreen]Emissive colour[/COLOR][/B]

And then we have materials that emit light of just one colour. Examples of which are LEDs and luminous substances.

[COLOR=darkgreen][B]Additive and subtractive colour[/B][/COLOR]

When dealing with transmitted light, mixing the primary colours red, green, and blue results in intermediate colours via an additive process:

[IMG]http://dpnow.com/images2/daily_tips/colour1.png[/IMG]

[COLOR=black][B]Additive colour model (above)[/B][/COLOR]

[B][COLOR=darkgreen]Additive colour for mixing light[/COLOR][/B]

Shine a beam of red light onto a surface where green light is already shining and the sum result is yellow. The energy of the different light sources light add up, which is why yellow is brighter than either red or green. Shine red, green, and blue light of equal brightness onto the same spot and you will get white.

Look at the dots on your TV or computer monitor, for example. By varying the relative brightness or intensity of each of these primary colours, you can create all the other colours of the visible spectrum, from black (all dots off), to white (all dots on and at their brightest).

When using colour in a reflective form, in painting or printing, the convention is to use cyan, magenta, and yellow dyes or pigments in the ink or paint to create intermediate colours. This is subtractive colour:

[IMG]http://dpnow.com/images2/daily_tips/colour2.png[/IMG]

[B]Subtractive colour model (above)[/B]

[B][COLOR=#006400]Subtractive colour for mixing colour materials[/COLOR][/B]

Consider that an object that looks cyan, for example, is absorbing the red from the white light shining on it and reflecting the green and blue that you see added together as cyan. Something that looks magenta is absorbing the green part of the spectrum from the white light it reflects.

With subtractive colour, if you mix materials that are cyan and magenta, the result is a material with that looks blue colour. Half the material is absorbing red, and half is absorbing green. That leaves just blue being reflected to your eye.

This colour model works really well at this simple level, but in reality the colour mixes are much more complicated.

Colour management is designed to equate additive colour image sources with subtractive colour printed results. It also attempts to ensure that the colour mix is the same for one device as it is for another. Without colour management, we would all be seeing radically different colour in our images to everyone else.

Sleep on that and come back tomorrow for more on colour management.

[I]Incidentally, please don't hesitate to post a question about this Daily photo tip if you have one![/I]