Monday, 22 October 2012

Exercise: Managing Colour

To judge colour cast and correct using software. Both JPEG and RAW files can be corrected for colour cast, but the options for JPEG are more limited, and in effect it is ‘post-processing’, whereas the WB is not set for the RAW file and can be chosen from the drop-down list in Lightroom.

For this exercise I have chosen three images from my archive with noticeable colour cast.

The first one (IMG_1171) (which has a large area of known ‘grey’, but is only a JPEG) was taken during a photography course of a light-table with products on it. The test at the time was to compare WB, so this is a good example to use. I think the WB was ‘daylight’ and the colour cast is quite clear. It appears yellow. I select the ‘grey-dropper’ next to the WB selection pane and simply select a point where I know it is grey (the foreground in this case). The image immediately corrects to the right colour and no further adjustments are needed, though it is possible to use the WB sliders if further refinements are felt necessary.
Before and after images are displayed below.

The second image (IMG_0437) was taken at last year’s BOGI fair and was photographed under a blue tent. This has given an obvious blue cast to the image. I used the WB dropper again and clicked on the back wall of the tent which looks to be grey to me. This does a good job – now the grass looks green and the jam jars look to be correct. Once again the dropper has done a good job and no more adjustment is needed.
Before and after images are displayed below.

The third image (IMG_0763) was also taken at the BOGI fair, inside the hall, the walls of which are yellow. This has resulted in a yellow colour cast on the image. I selected the floor this time, and the colour cast has disappeared. Skin tones look much more natural and the hat in the foreground (for example) looks white! The difference is great! I chose to slightly increase the green (decrease magenta) to make the skin tones and vegetation in the background more accurate.
Before and after images are displayed below.

Whilst it is better to shoot RAW and avoid problems with colour cast, it is still essential to know how to remove casts such as those shown above, which are not caused by just choosing the wrong WB (but instead by coloured light from walls/tent etc.). Using the dropper is effective and generally accurate, though as the course notes point out, sometimes it’s necessary to search hard for a grey point! This is the first time I have used the dropper in LR, so it was certainly a worthwhile exercise for me!

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