Removing colour casts from old scanned photos.
by Peter Dennis
After scanning open image in PhotoShop and make a copy layer of the original image (Ctrl-j) and then do whatever repair work you want to do to the photo. (Cloning damage areas for example).
Then make another copy of it, which will put it in a new layer. If you already have several layers that you’ve been working on, you can make copy of all these layer and combine them into one new layer by pressing Shift-Ctrl-Alt and e. You have to be a bit of a contortionist for this one but it’s possible.
Now for the removal of the colour cast. Make sure the new copy you’ve just made is selected. Go to the top menu, Filters>Blur>Average. This will change your layer into an average colour of the image. Whilst keeping this layer selected press Ctrl-i. (‘I’ for invert). This changes the layer’s colour to its inverse colour.
Next we change the Blend Mode. Look at the top of the Layers palette. You will probably see ‘Normal’. Click the little arrowhead (triangle) to reveal other blend modes. Select ‘Soft Light’ to start with. You can also play with other blend modes such as ‘Overlay’
But try ‘Soft Light’ to start with. This should have removed all the colour cast. If you think it has gone too far then adjust the Opacity slider at the top of the Layers palette until you find something that you like.
And there you have it.
There is also another technique that I’ve found useful when the above is not so successful. Add a ‘Curves’ layer. You will see a diagonal line from bottom left to top right. At the each end of this line you can see a small square. These can be dragged left or right or up and down.
The default is RGB for all colours. Select one colour at a time from the menu on the Curves palette. Drag each of the little squares left and right (you can also use the little triangles at the bottom of the graph to move the diagonal line) so that the diagonal line starts approximately where the histogram graph starts. If you have a heavy colour cast at least one of the colours will start well in from the left or right. Play around with each colour until reach a satisfactory result.
Hope this all makes sense. Give me a shout if you would like more details.