"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. |