01.01.09
Using Levels to correct colour in Photoshop Elements
If you’ve ever just played around with Elements’ Levels adjustments, then you may have already noticed that applying an Auto Levels correction can shift the colour balance of the picture. But rather than leaving it to chance, its possible to take control by tweaking the levels of each colour channel (red, green or blue) individually.
Looking at the Colour Wheel, should give you a clue as to how it’s possible to add or subtract red, yellow, green, cyan, blue and magenta, using just the red, green and blue channels.
A colour wheel is a convenient way of thinking about the relationship between colours. Red green and blue are known as additive primaries; cyna magenta and yellow are known as subtractive primaries. In the colour wheel, each additive primary is opposite it’s complimentary subtractive primary: red–cyan, green–magenta, and blue–yellow.
Increasing the amount of a primary colour in an image also reduces the amount of its compliment. For example the amount of yellow in an image is affected by making changes in the blue channel, because adding blue is the same as subtracting yellow.
Going back to the Levels dialogue box, choosing the red channel from the pop-up menu at the top will let you add or subtract red or cyan from the image by moving the middle slider left and right. Likewise selecting the green channel will let you add or subtract green and magenta, and the blue channel add or subtract blue and yellow.
Having a go this will actually reinforce the concept of additive and subtractive primary colours. It isn’t anywhere near as complicated as it sounds, and it gives a lot more control than resorting to Elements’ automatic Remove Color Cast command, which quite honestly only works well for us one time in ten.
This picture of the church of Santa Maria del Mar in Barcelona was taken using the interior lights as the only source of illumination. As these were mostly tungsten flood lamps, it’s not surprising that the shot has a pretty warm colour cast.
To remove the cast using Levels, either select Image > Adjust Lighting > Levels", or better still insert a Levels adjustment layer (Layer > New Adjustment Layer > Levels). In this case we’ve removed the yellow cast by selecting the Blue channel from the drop-down menu and moving the middle (grey) slider to the left.
We’ve also removed a bit of Red cast by selecting the red channel and moving the middle slider to the right. The good thing about adjusting colour in this way is that you can see the consequences of your actions in real time. And if you get in a complete mess, click Reset to start again.
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