A study in colour - Part 7 - The colour wheel in photography and white balance

The three primary colours (RGB) and secondary colours (CMY) make up the colour wheel.

The colour wheel in photography involves all the colours you can make with the three primary colours red, green, and blue (RGB).  There is an excellent image showing the relationship between the primary and the secondary colours (YMC) here.

If you look at the image above, you can see the colour cast I added to the surrounding images.  Opposite colours are diagonally located (green and magenta are opposites).  Combining two of the primary colours produces a secondary colour.  For example, if you combine red and blue, you get magenta.  The same is true for red and green (yellow) and green and blue (cyan).  If you subtract opposite colours, you get the opposing colour (if you subtract cyan, you get red).  Adding opposite colours cancels them out and produces white (gray).

I used the colour wheel all the time when printing photos in the lab I worked in.  Altering the colour balance of the photo to be printed involved either increasing the amount of red to get red or decreasing the amount of red to get cyan.  There were only three channels to work with and you could get whatever colour you wanted by increasing or decreasing the values as needed.

The issue then becomes compensating for luminosity.  A few points of change here and there will make little difference, but significant adjustments may require an increase or decrease in exposure.

The above illustration also indicates something about white balance.  You will notice that the off-whites cause very different results to the images.  Warm vs cool colours.  Some of the off-balance shots are more appealing than the others.  It is always a good idea to correct for white balance in an image - we will look into this more when I do a section on white balance and skin tone.  Soon.

Thanks for reading.

Eric Svendsen     www.ericspix.com