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"If you think you understood me, it's because I mis-spoke", Alan Greenspan.

Colour Management is the process of setting up a computer system to be colour- and luminance-neutral. In other words, the system alone must have no influence on the variables within an image, it must not, of itself, change those things in an image which can be changed by the user.

If you take an image into a colour-managed computer system then, if the user changes nothing, the image should come out looking the same as when it went in.

This can't happen perfectly in practice but we should be able to get close.

The business of colour management is thus about getting consistent, reliable and repeatable results without the need for trial-and-error.

Why Colour Manage?

If accurate colour processing is to be done there must be some method to match the way different devices see colours. A scanner may see red better than blue so an image coming from this scanner would appear abnormally red on a monitor which wasn't able to compensate. If the printer's green ink was a brighter than its blue then this would contribute to more colour inaccuracies. Whilst it is quite possible to balance these factors out and make good prints on a single system it is a difficult calibration process to carry out and one which needs constant supervision.

Colour Management provides a method by which this calibration process can be largely ignored by the user whilst also providing the opportunity to move images between different computer systems with a reasonable expectation that the image can be rendered the same on each.

Why isn't this simple...what is the problem?

Devices and variability

The trouble is that all colour 'devices' do see or produce light differently. You only have to go around any TV shop to be aware of this. All those tellys show the same picture from the same signal and no two of them are the same colour or brightness. This shows the variation across a range of devices which are, nominally, very similar. Much more variation is apparent when comparing, for example, a scanner and a printer. Somehow a system has to be found to balance colours across a whole range of very different devices.

This can be done by trial and error much in the way that a lot of colour work was done in the darkroom. The more expensively-equipped darkrooms had colour analysers to do the job by the numbers but still one relied on trial-and-error and experience to get a good colour print.

There are some disadvantages to this method. Experience shows that it is hard to set up right and takes a lot of adjustment to maintain. Once the settings have been made they are then only right for that set of circumstances; if you change any element, say a monitor, then the whole thing has to be done again.

Again, any image produced using this system is unlikely to ever display the same on another system. So, even if you can get good colour from your printer, when you send away to get an outside printer to print your image you will be lucky to get the same result.

ICC Colour Management

The way to avoid these problems is to use a system which standardises all colour devices. If a monitor, scanner or a printer can come with a description of how they 'see' colour with reference to a common standard then it becomes easy to add new devices without disturbance and easy to export images knowing that, if the system receiving your image is managed the same way, the image will look the same. However, the most important advantages are the easier setting up and the easier maintenance. Easy is a relative term!!!

System Calibration using ICC Colour Management

There are three distinct areas where calibration is necessary. These are:

  • The Monitor
  • The Printer
  • The Input Devices

Links to these can be found in the menu.

These are set out in the order in which they should be tackled. The crucial elements are the first two. Click on the items in the list for futher information.

There are other factors involved with our peception of colour and brightness which, although they don't fall strictly into the colour management framework, have an effect on the process. A couple of these are:

  • Ambient Lighting. The viewing conditions around the monitor are important.
  • Colour Temperature, White Balance and Eyes. How do we see colour?

Links to these can be found under the 'Lighting' menu.

copyright © tony cropper 2006-2011

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