Introduction to Adding Colour

The purpose of these notes is to discuss a process of adding colour using a Gradient Adjustment Layer. The idea for this arose when I noticed that when using levels to add colour to a picture the resulting histogram has many gaps whereas if Photo Filter is used the resulting histogram was free of gaps.

Although, Photo Filter gives an unbroken histogram, unlike Levels it cannot be used to brighten the image and the result is often lacking in contrast. Increasing the contrast of course leads to the dreaded gaps in the histogram.

I set myself the task of taking an image for which I wanted to alter the colour balance, adding colour to achieve the effect I wanted and having control over brightness and contrast at the same time and without producing a histogram with gaps in it. What I came up with has probably been done before but I have not yet found the technique described elsewhere.

The obvious choice, and luckily one that did what I wanted was to use a Gradient Map Adjustment layer to create the colours that I wanted to add and then using the linear dodge blending mode to add the extra colours to the original image.

There is always a dilemma when preparing notes for general use; do you aim at the experts or the beginners. The result is that there will be parts of these notes for which some of you may think that I am trying to “teach you to suck eggs” and other bits that you may wish to skip over as quickly as possible as being of irrelevant academic interest only to “geeks” like me.

I have included most of the things that I have discovered about how Photoshop does what it does while I have been preparing these notes. Just in case anyone else is interested.

To aid the newcomer to photo editing there are descriptions of the Colour Picker, The Gradient Editor, the Gradient Tool, the Gradient Map Adjustment layer as well as how I used these tools to add colour to an image.