…but were afraid to ask.

You’ve probably often heard about colour management, but wondered why you need to manage your colours. You’ve probably heard of AdobeRGB, but wondered what difference it made to your life. You’ve possibly heard about Colour Space, but ignored it because it’s sounds like something techy you don’t need to worry about. Well, the good news is that these are all easy things to understand.

Colour is funny stuff

For years, people have told you that there are 256 or 16,384 shades of Red, Green, and Blue on a computer making up all the colours you’ll ever need. This is commonly known as 8-bit or 16-bit RGB. This is really all you need to know when messing about with colour. These people have been lying to you.

The colour system you have been using all these years is called sRGB (standard RGB), and it was only named in 1996. sRGB is one way of translating three values of Red, Green, and Blue into real colours. A pixel on a screen or in a digital photo contains three numbers, and this “code” is translated to colour you can see. You know all this; why am I telling you again? Notice I said “one way”. There are other ways of translating RGB pixels into colour too.

If you could print every colour available in sRGB accurately on a big sheet of paper, and compare it with some real objects, like flowers, you might notice that these objects have shades of colour missing from your sheet. There’s a good historical reason for this: when sRGB was invented, scanners, printers and monitors were very limited in the colours they could reproduce (and most still are), so there seemed little point in having a code for a colour you couldn’t make.

Moving goalposts

Adobe produced its own version of RGB in 1998. The idea was to expand on the palette of colours in sRGB, and include the colours available in cutting-edge printers too. Again, your pixels have three values of Red, Green, and Blue, but the end result is different. AdobeRGB translates the numbers into a wider range of colours than sRGB, with noticeably deeper hues.

Modern digital cameras can actually record colours well outside those available in sRGB and AdobeRGB colour spaces. Kodak invented ProPhotoRGB to include these colours, but it isn’t widely supported. Naturally, as technology progresses, devices (like monitors, printers, and projectors) will support a wider range of colours, and ProPhoto RGB will come into its own — much like AdobeRGB has done recently (10 years after its introduction).

Make your mind up!

Oh dear, this is starting to sound tricky. “Different results?!” It’s not a big deal. Whenever you provide a digital image, it just needs to be tagged with the name of the colour system used. This is that Colour Space you keep hearing about. Your photo software does this automatically. See, it’s easy, isn’t it? Every colour image has an associated Colour Space (sometimes called “ICC Profile”), and the image can’t contain any colours outside that Colour Space.

So, you’re probably now wondering why you need to know any of this. Well, if you don’t much care how the colours in your photos come out, then you don’t need to know — go and watch telly. If you’re concerned with faithful colour reproduction, then it helps to understand what’s going on.

Shoe-horning colour

Many monitors and printers (and newer projectors) support colours outside the sRGB colour space. If you want to show off that red rose, lush meadow, or heavenly sea in your photos, you need to use the best tool for the job — which means choosing your colour space appropriately.

JPEG shooters should be using the biggest possible colour space available (usually AdobeRGB) if they think they will ever need to display more colours than those available to sRGB monitors and projectors. Maybe, in 10 years’ time, all display devices will be AdobeRGB-compatible. It’s fairly likely. Those sRGB photos will look a bit dull by comparison.

For now though, AdobeRGB images usually need to be converted to sRGB for reliable display. This means losing colour. Generally, there are two ways to do this: a Perceptual conversion squashes all the colours to fit, giving the best variety of colour, but compromising accuracy; and a Relative Colorimetric conversion picks the nearest colours to the “lost colours” just inside the new colour space, giving better overall accuracy but less variation.

Thinking outside the box

So, starting with the best colour space will guarantee that you can future-proof your images. Shooting “raw” neatly side-steps the whole issue — raw camera files have no colour space — the colour space is applied only when the raw data is processed into a digital image.

A digital image with a big colour space stands a better chance of producing a good print on a posh printer, and will look better on a so-called “wide-gamut” monitor or projector, when you eventually upgrade.

Keeping it all under control

That’s all there is to it. Sorry, I lied. Some software is like you might have been at the start of this article — unaware of the different types of colour space. Windows’ Internet Explorer and Picture & Fax Viewer are two popular applications which don’t understand colour space, and assume all images are sRGB images and all monitors are sRGB monitors. But, hopefully, you use “colour-managed” software (like Photoshop) and you calibrate your monitor, printer, projector and camera …
What do you mean, “no”?

Keith Nuttall, 2009