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Contrast Masking in Photoshop

Contrast masking is a traditional "wet" darkroom technique used to help bring the contrast range of a film image into line with what can be printed on paper. A black and white negative is made from the original positive slide and sandwiched together with it for printing. The negative will be darker in areas that are lighter in the slide and lighter in shadow areas. When combined, the result will add density to the slide proportional to the brightness of each part of the original. Digital darkroom techniques allow us to achieve a similar effect and much more.

Here's a great way to approach the problem that makes use of an Overlay blending mode layer much like the dodge and burn method I wrote about back in July 2005. In Overlay mode, anything darker than medium tone will darken or dodge the layers underneath while anything above 50% gray will lighten or burn it. The effect is proportional to how far below or above medium each point in the dodge and burn layer is. As we saw back then, we can directly paint on such a layer to selectively adjust brightness, but what we want to do here is to create a dodge and burn layer based on an inverse of the image itself.

To do so, first create a duplicate of your image layer. If you have a just a single layer, you can do this by means of the Layer >> Duplicate Layer menu option (or drag your image layer to the "New Layer" icon at the bottom of the layers palette). If you already have multiple layers that make up your image, you can instead click on the top visible layer in layers palette, then select the entire canvas and use Edit >> Copy Merged followed by Edit >> Paste. Either way, you should now have a new layer containing a composite copy of your photo on top of the other layers that make up your image.

Next, use Image >> Adjusts >> Desaturate to convert this new layer to grayscale. If you'd prefer to more heavily weight certain channels, the Channel Mixer can be used instead but for this purpose destaturating the image is generally sufficient. You should now see a black and white rendition of your image completely covering up the original color version underneath. This new layer will become our contrast mask.

Original capture of Echo Basin in eastern Washington
Original capture of Echo Basin in eastern Washington
  Duplicated and desaturated version
Duplicated and desaturated version

Now use Image >> Adjustments >> Invert to convert this black and white layer to a negative. Yes, it will probably look less than appealing at this point, but we're not done yet so bear with me.

Now go to the top of the layers palette and change the blending mode on this negative layer to Overlay. The color image will now show through, modified by the dodging and burning being done by the Overlay mode. This will still be somewhat harsh looking, but there's one more important step to go.

After inverting to create a negative version
After inverting to create a negative version
  After changing the blending mode to Overlay
After changing the blending mode to Overlay

Using Filter >> Blur >> Gaussian Blur, add a small amount of blur to the contrast mask layer. Depending on how big your image is, an amount somewhere under 30 should suffice, but you can feel free to adjust things to taste. If the entire effect is too pronounced, you can also lower the opacity of the contrast mask until you get what you like. If you are feeling adventurous, you can also apply Levels or Curves directly to the mask layer just as you would a regular layer to adjust black point, white point and contrast within the mask itself. Indeed, many of your favorite filters and other adjustments can be brought to bear on the mask layer if you feel they will create a better mask. Whatever your creativity leads you to try.

What the final contrast mask looks like
What the final contrast mask looks like
  The final image of Echo Basin after adjusting opacity
The final image of Echo Basin after adjusting opacity

Users of Photoshop Elements aren't left out either. While Adobe hid some of the needed commands in Elements, they're all there. Desaturate is hidden under Enhance >> Adjust Color >> Remove Color, while Invert is at Filter >> Adjustments >> Invert. Everything else is pretty much where it is in the full version of Photoshop.

Under harsh lighting, contrast can be extreme with both lost shadow detail and burned out highlights. Similarly, a subject that looks great when sufficiently lit can often appear rather drab and dull in dimmer light. Such problems are to be expected of course, but now they needn't get in your way of creating great images.

Date posted: November 12, 2006


Copyright © 2006 Bob Johnson, Earthbound Light - all rights reserved.
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Previous tip: Three Cheers for the Gold-N-Blue Return to archives menu Next tip: Another Photoshop Masking Technique: Luminosity Masking

Related articles:
Dodging and Burning in the Digital Darkroom
Another Photoshop Masking Technique: Luminosity Masking
Doing Even More with Luminosity Masks
Using an Image as its Own Photoshop Layer Mask

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