Exercise: Managing Colour

For this exercise I have chosen two images that have a significant colour cast. I have chosen to correct one jpeg image and one raw image. The requirements of the exercise means one of these images must contain something grey, therefore for the first photo I have chosen a picture I took of some aluminium chairs on concrete. The software I use is an open source photo editor called GIMP.


I chose this image as it is mostly grey and therefore answers that requirement of the exercise. It will also be useful to test the GIMP software to see how it handles a range of grey tones.

grey chairs

In GIMP the grey dropper tool is located in the ‘adjust colour cast’ dialogue box. I selected the areas that are supposed to be grey. I selected a couple of point on the aluminium chair which seemed to make no difference to the picture, then I selected the concrete floor which change the overall tone of the picture.

grey chairs2

I then used the sliders on the ‘Adjust colours’ dialogue box. Using the mid point grey slider I could increase or decrease the overall contrast of the image.

I decreased the contrast in this image.

I decreased the contrast in this image.

In this image the constrast was increased.

In this image the contrast was increased.


For the raw image part of this exercise I have chosen this picture I took of a room in Greece, the light coming in through the window combined with the colour of the wall gave the room a distinctly yellowish hue. The sheets on the bed for example were not yellowish but a brilliant white.


I opened the picture in the ufraw converter, and the first thing I did was to use the white balance/colour temperature slider to adjust the white balance. Then I used the exposure compensation slider to brighten the image and selected the highlight clipping icon. I then used the manual curve to adjust the colours of the room still further. Then I increased the contrast slightly.

The end result is much closer to the original colours of the room without the yellowish cast. The walls of the room are still yellow but they do not influence the colour of the bedsheets. The light coming in from the window is overexposed and ufraw does not allow editing of a specific area.



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