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Doing Even More with Luminosity Masks

Blocked up shadows are a common problem in photography since the subject brightness range capable of being captured on digital or film is so much less than what our eyes can see. Luminosity masking and Contrast masking can each be used to improve this problem considerably in the digital darkroom. But because Luminosity masking creates an actual layer mask you can use it for so much more. Here's but one example to get you thinking.

Original image of Palouse FallsI present here an image of the canyon below Palouse Falls in eastern Washington State. It was late in the afternoon, but the "magic hour" colors weren't cooperating. I knew though from previous attempts that if I waited much later the sun would dip low enough that the shadows would engulf the canyon so I went ahead and took this before it was too late. It does a good job of conveying what things looked like, but not what I wish that it had looked, and not how it felt.

In the right circumstances, the warm glow of sunset would have bathed the canyon on one side, while the other took on the much cooler color temperature seen in shadows and open shade. To achieve this, I did a bit of image optimization using luminosity masking.

To begin with though, I added a curves adjustment layer to improve the overall contrast of the image. A slight "S" curve to create a steeper slope in the mid-tones can help most images and this one was no exception. Still, the colors that I had hoped to capture were somewhat lacking so I continued in my efforts.

What I wanted was for the shadows to be cooler while at the same time for the highlights to be warmer. Adjustment layers using opposing cooling and warming Photo Filters would do the trick nicely, but I needed a good way to select the areas I wanted to affect for each. This is where luminosity masking came in.

If you're a regular reader here, you already know how to select the highlight areas in an image. All you have to do is to click on the small dotted-circle icon at the bottom of the Channels palette or use the equivalent keyboard shortcut Ctl-Alt-~ (tilde) on Windows, or Command-Option-~ on Mac OS. This will result in an image being covered in the "marching ants" pattern surrounding any highlight areas. The actual selection though is much more than just what we can see from this. In fact, every point in the image will have been selected proportionally to how bright it is as we saw last week.

After doing so on this image, I converted the luminosity mask selection into a layer mask on a new Photo Filter adjustment layer by clicking on the half-black half-white circle icon at the bottom of the Layers palette. I selected the "Warming Filter (81)" option from the Filter dropdown list since I wanted to emulate the effects of a traditional 81-series warming filter. Leaving all other options at their defaults, I then clicked on "OK" to finish creating the new layer. I wanted to tweak the layer mask a bit before turning my attention to the optimal level of warming for the filter.

By Alt-clicking on the layer mask to the right of the Photo Filter rectangle on my new layer (Option-clicking for those of you on Mac OS) I was able to see the mask itself as a grayscale image, temporarily replacing the main image window display. I then used Image >> Adjustments >> Levels to severely increase the contrast of the mask. To prevent bleed over of the warming effect into the shadows, the black point was considerably raised and the mid-point slider adjusted accordingly to taste. I then also used a soft brush to paint over the sky with black so as to constrain the warming color to just the highlights of the canyon itself.

By then double-clicking on the Photo Filter rectangle itself I returned to set the options for the warming filter. Because the layer mask was controlling where the effect would be applied, I could safely increase the Density far more than one might ordinarily do.

Layer mask used for warming adjustment layer
Layer mask used for warming adjustment layer
  Final setting for warming Photo Filter
Final setting for warming Photo Filter
  Affect produced by warming adjustment layer and mask
Affect produced by warming adjustment layer and mask

To create a similar Photo Filter adjustment layer for the shadow, I used essentially the same series of steps with one notable difference. Since I wanted to affect the shadows and not the highlights, I used Select >> Inverse as described last week.

I also obviously picked "Cooling Filter (80)" from the Filter dropdown list when initially setting the options for the new layer. As before though, I left the Density alone to begin with so I could take a look at the layer mask before deciding on just how much cooling seemed appropriate. Again, I severely clipped the shadows in the mask. These actually represent the highlights of course since I inverted the selection and was thus working on a negative version of the Palouse Falls canyon.

Layer mask used for cooling adjustment layer
Layer mask used for cooling adjustment layer
  Final setting for warming Photo Filter
Final setting for cooling Photo Filter
  Cooling adjustment layer result (warming layer temporarily turned off to show just cooling)
Cooling adjustment layer result (warming layer temporarily turned off to show just cooling)

Returning to the Photo Filter settings by double-clicking on the adjustment layer icon for my cooling layer I ended up pushing the Density all the way to 100% to accentuate the blue in the water in the bottom of the canyon. The far distance of the canyon picked up a bit too much of the cooler color temperature though so I then went back to the layer mask and used a moderate opacity soft brush to paint with black over that part of the mask. To see the effect in real time, a selected the mask by regular single-clicking on it this time rather than alt-clicking. This selects the mask but retains the view of the image itself rather than the black and white mask image. Alt-clicking (Option-clicking on Mac OS) selects the mask and shows it to you as a mask; regular single-clicking selects the mask but still shows the image while you work on the mask. It's good to be familiar with both ways of selecting an existing layer mask.

By the way, it's also good to know what to do if you accidentally paint with black or white on your image itself rather than one of the masks. There's nothing more startling than seeing a big white swatch show up on your image when you are trying to make s subtle change to a mask. This is easier to do than you might suspect and sooner or later you will do it. But don't panic. Just back up in the History palette and you will be back where you were. Photoshop designates the layer or mask that is active by means of the border around its thumbnail in the layers palette but it can be easy to miss this cue sometimes while you are working. Thank goodness for the History palette.

Shown here are side-by-side before and after images of Palouse Falls canyon. The "after" image is much closer to what being there actually felt like.

Palouse Falls before optimization
Palouse Falls before optimization
  Palouse Falls after optimization with cooling and warming adjustment layers
Palouse Falls after optimization with cooling and warming adjustment layers

Date posted: November 26, 2006


Copyright © 2006 Bob Johnson, Earthbound Light - all rights reserved.
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Contrast Masking in Photoshop
Another Photoshop Masking Technique: Luminosity Masking
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