Colour Management

Introduction

The problem we face in ensuring consistency in colours is that not all graphic equipment is perfectly built. Nor are we humans perfectly built either. At some point, when you were young, you probably had your eyes checked to see if you needed glasses. That is to do with focusing rather than colour correction, but the basic idea is the same - we need to be checked.

In that sense we need to send all our equipment to the 'opticians' to see what needs to be corrected. Your biggest problem will be your computer screen as you will be using that every day. Are your reds being displayed on screen a little too orange? Are your blue skies being shown as slightly purple? If you do not have your screen corrected then you will end up 'correcting' your images instead so that the oranges become more red, and your skies become more blue. Your images may now look correct on YOUR screen, but when viewed on other screens they will look different. You will have just corrected colours for your screen that may not have been incorrect in the first place.

Below there is more information about correcting, or 'calibrating' your monitor and, just as importantly, how to deal with the lighting in your working envioronment.

Screen calibration

FIGURE 1 There are several makes of calibration hardware, with two of the most commonly used being the EyeOne from 'GretagMacbeth' and the Spyder from 'ColorVision'.

Hardware calibration is done by attaching a measuring device to the monitor, and then running a series of colour and greyscale patches. The software knows what the colour values are for each patch. The hardware measures what values the monitor actually displays, and so the differences between the two sets of values are calculated. The result is a colour profile for the monitor which is saved into the appropriate folder and activated automatically every time the computer is switched on. The profile does not change the image itself, but it does alter the pixel colour values that are sent to the graphics card and then onto the monitor.

Calibration takes just a few minutes and so is of little inconvenience to run on a regular basis. Monitors do change over time and should be checked on occasion. How often will depend on how important the colour accuracy is to you; but usually once a month is quite enough. Warnings are set to inform you when the time allocated has been reached, though this can be switched off if you do not want to be bothered with reminders.

Do not worry too much about how to run this calibration equipment. The software that comes with it will have a step by step guide that tells you what to do at each stage. The resulting colour profile for correcting the monitor will automatically be saved into the correct folder within your computer system, which will then be activated every time you switch on the computer.

NOTE 1:  The resulting monitor colour profile is ONLY intended for the monitor that the calibration equipment was run on.  If you have more than one monitor then the same process will have to be repeated for each of them.

NOTE 2:  Calibrating your monitor, and activating colour management, will NOT make a poor quality computer screen into a good quality one; it will only correct the monitor to within the limits of its abilities. In other words: If you have a crap monitor, then expect to see crap colours, no matter how many times you wave the calibration equiment at it.  This is particulary true of cheap laptops.

Bright light

FIGURE 2 You are likely to be spending a lot of time in front of your computer looking at images, so you will need to make sure you are comfortable and not straining your eyesight.

Avoid sitting directly in front of a window where the outside daylight is brighter than the monitor you are working with. Bright lights that fall directly within your line of sight will cause you to squint and make the images harder to concentrate on. Direct lighting should also not shine onto the monitor as that too will dull the image and often create reflections.

Clearly, the computer shown above is not a graphics machine, but these rules also apply to anyone who works with computers. It is not just graphics people who suffer from eye strain.

The pot plants are optional.

Discoloured lighting

FIGURE 3 If you have photographed in rooms lit with florecent lighting you may recognise the excess green colour problem here. No camera filtration was used so this is how the film recorded the colours. However, this is NOT how the people in the room would have viewed the colours. The human brain does a very good job of trying to neutralise colours and making white those colours that it thinks ought to be white.

FIGURE 4 This is the same image after it has been colour corrected and is close to how the scene would have been viewed by those who were there. 

As helpful as the brain is in trying to neutralise colours, it is actually causing us a problem when we try to do colour correction. Let us assume that the woman in the image above is working on a graphics computer and that she is working with Photoshop to correct some images. Let us assume that the monitor is a good quality graphics screen and that colour management is being used. Clearly, the computer in the image above is not intended for graphics; the photograph even predates the invention of Photohop by quite a few years.

But bare with this a little bit. Now assume that the woman is colour correcting an image on screen which has a lot of green in it, such as a view with trees and grass. As her brain filters out a good deal of the green from within the room (that was recorded in the top image), she will be doing the same with any greens that she sees on the computer monitor. The greens in the image she is trying to correct will appear to her as being very weak and she will naturally try to improve those green tones to make them more realistic.

One final step. If she were to pass the corrected image to you, and let us assume you then view the image under correctly controlled room lighting, then you will wonder what on earth she had been doing with the image as all the greens would look over-saturated and far too bright. The image will look 'correct' to her as she is viewing the image under poor lighting conditions and her brain will dampen down the excess green colour. You, on the other hand, will view the colours differently as you will be working under different lighting conditions.

It is possible to alter the colour correction profile being used in the monitor to take account of the local lighting conditions. Good quality monitor calibration equipment will not only measure the colours on the screen, but also the room lighting as well. But we should not be straining our eyes with having to deal with bad lighting conditions. Get rid of the flourescent lighting and put in a few upward pointing lights instead. Most ceilings are white and so will spread the light well without discolouration.

However, if you happen to work in an office where the lighting is not just covering your area, and turning off the lights will cause complaints from other workers in the office, then a bit of direct action is called for. Climb up onto your desks and remove the offending light bulbs, then switch on your own lighting that is powered from your desk or from the wall sockets. 

Quick summary

1.  Do make sure you get the best quality computer monitor that your budget can afford, and make sure that it is a decent size so that it is comfortable to work with.

2.  Get hold of colour calibration hardware and have your monitor checked about once a month.

3.  Avoid sitting in direct sunlight. Find a possition to sit so that no direct light falls in your eyes or onto the screen, and make sure there are no reflections in the monitor.

4.  Cover up bright paintwork behind the computer that comes within your line of vision. If nessacary, cover the lower half of the window next to you if your desk gets flooded with direct sunlight.

5.  Turn off flourescent lighting in the room. Get rid of it if you can and replace with softer indirect lighting. Think of it like your home. You would not dream of flooding your living room with flourescent lighting (well, hopefully), so why should you put up with it where you work?

6.  Take regular breaks so that you can rest your eyes from becoming strained.

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