Colour space

 A big challenge in photography is controlling colour. This is true of both digital and film photography. The simple fact is that no camera, film or sensor can record colour in the way that we can see it. We can sense a greater variety of colour, and the way that we sense it varies from person to person, as it is a function of the eye and brain's interpretation of stimulation by wavelengths of light.

Camera equipment can record some of the information that we can see, and a typical 8-bit digital image can record 16.7 million colours, which is a lot. With colour film, each type of film has a slightly different response to light. Fuji Velvia for instance favours warm, red tones; Provia is neutral to cool toned, but neither will show the colours exactly as we see them because that is impossible.

So what we are doing is 'mapping' some of the real world's colour into the available colour space of the film, or the digital sensor - shrinking it to fit the technology's ability to record it.

With digital data, colour is described using the RGB colour model, mixing number values of red, green and blue to create all of the other colours. Because this model uses three dimensions (red, green and blue), the mapping of resulting values creates a 3D space, called the colour space. The range of colours available within that colour space is called the gamut.

The picture above shows a colour space. This can be found in Macs by going to the utilities folder and opening Colorsync, and viewing profiles.

The picture above is a comparison of two colour spaces. The greyed out area shows the wide-gamut space called Epson Wide Gamut. The coloured area inside shows sRGB colour space. It is much smaller, displaying a reduced range and variety of colours.

When you shoot, you probably use a colour space like sRGB or Adobe RGB. When you print, your printer, paper and ink can combination will have a different colour space. Prints have a limited range (gamut) of colours, so all of the information from the camera's colour space has to be mapped to the printer's colour space using software. 

When you print, and choose the paper type from the printer's menu, you are instructing the software to map values from one colour space to another to help to produce a more controllable and pleasing result. 

This a difficult idea to understand, but it is important to start to try to grasp the concept of 3D colour space.

If your pictures have a named colour space, eg sRGB or Adobe RGB, then it is easier to translate the known colour values from one device to another. It is often compared to the idea of having a language dictionary when you go from one country to another.

If you scan a picture, and forget to set a colour space, then colour values can be random and uncontrollable. 

A colour space is often also referred to as a profile.

90% of printing problems come when you select the inappropriate printer profile, causing the colour values to translate inaccurately for that paper. Choosing another profile often fixes it. If you are using a particular paper, ink and printer combination, the light reflecting off the print can be measured accurately using a profiling device which creates a colour space for that paper. This can make printing much more accurate. Some printing labs offer this type of service. However if you then change the ink, or the paper, the colour space will not be as accurate and another profile needs to be created.

There are many links in the chain to produce accurate and appealing colours. The process is in part technical and in part creative.

Key points are: accurate exposure when shooting; setting white balance; using fill-flash to balance light sources; using grey cards when shooting; calibrating the computer screen; using colour profiles; working in colour neutral rooms when using computer screens; using the info palette in Photoshop to measure colour values when editing; using printer profiles when printing or use a lab with colour synchronised workflow eg Loxleys, Printlab or A&M.

If your exposure control is loose and sloppy, your flash use is vague and you forget to pay attention to colour profiles, then your colours will be goosed too.

Photobox, the photographic printers, provide guidance on colour calibration:
http://www.photobox.co.uk/content/quality-advice/calibration

Photo Net guide to colour management:
http://photo.net/learn/digital-photography-workflow/color-management/101-basics/

More from Photo Net:
http://photo.net/learn/digital-darkroom/

*Colour Confidence:
https://shop.colourconfidence.com/section.php?xSec=10322

*Colour Tools: http://www.colourtools.co.uk/
 
*Colour Spaces: http://dx.sheridan.com/advisor/cmyk_color.html

Computer Darkroom: http://www.computer-darkroom.com/

Bruce Lindbloom: http://www.brucelindbloom.com/

Digital Dog: http://www.digitaldog.net/