Eish!

There is a little understood component in working with digital images that involves blending between layers.

Blending dictates, essentially, how one layer interacts with or affects another layer (below it). Photoshop and its many little ugly cousins provide us with a miriad of possibilities from blending brightness to contrast to colours to plain weirdness. You probably won’t ever need more than about 5 of the basic blending modes but the one that I find the most useful is the “Luminosity” blending mode.

When increasing contrast in an image, whether you use Levels, Curves or any other contrast enhancing tool, it is important to note that it affects contrast across all of your colour channels. This can be easily remedied by simply changing your contrast enhancing layer or adjustment layer [1] to use a Luminosity blending mode.

To illustrate this point, I’ve taken a crop of picture of a man running on water in a weird fashion. Ignore his rather odd gait for a moment and cast your eyes towards the surrounding greenery.

Clearly, the picture needs a little help. Slapping on simple Levels based contrast adjustment we see things spring out a bit.

I’ve exaggerated the contrast to show you what happens to the green. Note that the greens have saturated a bit? This is because blanket use of the contrast enhancing tool (and it doesn’t only apply to Levels) has applied itself to the colour channels as well.

Now this may be exactly what you are looking for. Perhaps your audience is colour blind, were born in the sixties or like green a lot. I like to keep natural colours in some shots to show things as they were. Let’s assume this is one of those situations and the unnatural greens just have to go. Switching the blending mode on the Levels Adjustment Layers to Luminosity has the effect of the adjustment being applied to only the Luminosity channel. [2]

Again, I’ve exaggerated things a bit to really highlight the contrast increase without the associated colour change.

This is a very simple technique and one which I use quite a bit with great effect with many different adjustment tools. Remember kids, Blending Modes are your friends.

—-

[1] You are using layers right? Tell me you are…

[2] Just for reference, Luminosity in this context refers to the “V” in HSV and is also referred to as Lightness or Value. Either way, it is a colour component that describes the gradations of image information.