Photoshop basics

This is an easy technique for correcting a colour cast in Adobe Photoshop. It is not always successful and will not give you the desired results 100% of the time. But as it is quick and easy it is certainly a good place to start.

AWB failure

My photo from Goðafoss has a distinct blue cast. This was a long exposure in low light, so to the camera, this scene was very much darker than it appears. My Canon couldn’t really see well enough to calculate the correct white balance and I was in AWB (Auto-White Balance). I could have corrected this at the RAW stage, or selected a better white balance manually, but for the benefit of this tutorial, I am making this adjustment to the photo it as it came out of the camera.

The first step is to duplicate the layer.
First duplicate the layer.

The Average Blur

Duplicate the layer. Then apply an ‘average blur’ to the top layer. This is like putting your photo through a washing machine were all the colours run into each other – making an ‘Average’.

Apply an 'average blur' to the top layer.
Apply an ‘average blur’ to your copy layer.

You will see the top layer converted into a big blue smudge (or whatever colour cast you are dealing with).

Adjustment Layer

An adjustment layer allows to to make changes to your picture without directly affecting your picture. Then the effect can be faded in or applied to a particular part of your image with a Layer Mask. You can create an ‘curves adjustment layer’ by clicking on the adjustment layer button on the layers pallet. Alternatively you can create a ‘curves adjustment layer’ from the layer menu. See more info about photoshop adjustment layers.

Create a 'curves adjustment layer'.
Create a ‘curves adjustment layer’ by clicking on the “Ying Yang” icon and selecting “Curves” from the list.

The curves dialogue box will open and you simply select the middle eye-dropper tool and click anywhere on your picture.

Click anywhere on the top layer.
Click anywhere on the top layer with the middle eye-dropper tool.

Final steps

When you click on the blurred layer, you should see the layer turn grey. This is what the middle eye-dropper has corrected. The final step is to get rid of the top layer so that the curves adjustment layer can affect the original photo.

Delete or make the top layer invisible.
Turn off the Background copy.

Then simply delete or make the top layer invisible so that you can see the effect of the curves adjustment layer. You can see the effect of this simple curves adjustment compared with the original image below.

Left = before, right = after.

*Note: the same effect can also be achieved with the middle eye-dropper on the ‘Levels adjustment layer’.