Saturation Out and In

I've seen several tutorials about using a Luminosity mask. To date, I've only seen one tutorial on a Saturation mask. Rather than show the joys of Sat masking, I'm going to show an easy way to to extract Sat to greyscale and put it back into the original photo.

First, the photo:

It's got some high saturation and some low saturation. Not too shabby for our purposes here.

One easy way of extracting Sat to greyscale is with a Selective Colour Adjustment Layer. Once you add an SC Ad-Layer, use the drop-down to select the major hues and bring the Black slider all the way over to -100%.

Use Black = -100% for Red, Yellow, Green, Cyan, Blue, and Magenta.

That leaves White, Neutral, and Black. For these, use Black = +100%.

Once you get all of that done, you will be left with is Sat in greyscale. At this point, I like to Copy Merged and Paste. Then I'll trash the SC Ad-Layer. Also, might be a good idea to save an *.asv file for easy retrieval.

Tada. I'm going to call this layer SatBW.

Now, depending on various things, the final Sat mask may be jaggie, noisey, or have lots of stair-stepping. For the most part, I leave it and only fix nastiness when it becomes a problem. There are lots of ways of fixing said nastiness, but outside the scope of this little tutorial. "Smoothifying" is a whole new can of techniques.

Now that you have your Sat mask, what you do with it is up to you. One of my personal favorite uses is to adjust just the low sats while leaving the hues alone. Or you can mess with blending modes for funky effects. Use your imagination.

Now we are going to put the Sat back in using our greyscale Sat mask. This is a bit tricky. You see, greyscale has Sat=0, so using Saturation blending mode won't work without some cleverness. What you have to do is put the Sat back into the mask itself. That is, the highs will have to mapped to high Sat.

Sounds like a job for another Ad-Layer, this time a Gradient Map.

When you add a G-Map Ad-Layer, one side will have to be Sat=0. This could be pure black, pure white, or any shade inbetween. The other side will have to be Sat=100%. This could be any pure hue that you like. Personally, for visual reasons, I prefer Black - Yellow.

Add the G-Map Ad-Layer, set the stoppers, and clip it to SatBW.

Very important: the Smoothness should be set to 0%. If you don't use Smoothness = 0%, you will get anomalies.

Once you have it setup like that, set the blending mode of the SatBW layer to Saturation. You should now be looking at the original photo. If you feel up to it, go ahead and do some comparitive tests. In the tests that I've done, the error has always been well under 0.5%.

With this setup, you can tweak the Sat in a more "pure" manner. All you have to do is add an Adjustment Layer of your choice between SatBW and the G-Map. My personal favorite is a Levels Ad-Layer. This method is different than using an Ad-Layer and setting to Saturation. Different.

Lots of fun in there. But, like I said, Sat out and in. The uses and creativity is up to you.