Friday, June 29, 2007

Contrast Masks

Take control of the contrast in your images with precision using these Photoshop controls


This Article Features Photo Zoom


Contrast Masks The relationship between highlights and shadows is a critical aspect of any image. Photographers have been trained to become highly sensitized to these relationships. Today, we have more control and greater precision than ever before over these key visual elements using the digital darkroom. In Photoshop, the type of adjustment chosen will provide very specific control. The specificity of an adjustment can be further refined by using a mask. One type of mask yields extreme precision and is derived directly from the light and dark relationships within an image—a luminance or contrast mask.

A contrast mask allows you to target a specific range of tones without affecting the others—highlights, shadows and even midtones. In the analog darkroom, it's challenging and time-consuming to make contrast masks; in the digital darkroom, it's quite easy to quickly make contrast masks. And you can refine or modify them infinitely and indefinitely.

Creating A Contrast Mask

I'll say it extremely simply: Load a channel as a selection and then create a layer mask. Now, I'll go into a little more detail.

Go to the Channels palette and at the top click-hold and drag a channel (RGB, R, G or B) to the Load Channel As Selection icon (dotted circle) at the bottom. This creates a selection based on the luminance (light and dark) values of the channel you choose. The active selection outline appears complex; a dotted line appears at all 50% gray values, but the whole image is affected to varying degrees based on the density of the values used to make the selection. As values grow darker the effect reduces, and as values grow lighter, the effect increases. Remember this mantra, “Black conceals, white reveals.” You can turn a selection into a mask in one of two ways: 1) Make an adjustment layer—Layer > New Adjustment Layer; the selection automatically becomes an adjustment layer mask; 2) Make a layer mask—Layer > Layer Mask > Reveal Selection.
The Color Range Feature

You can quickly make a contrast mask that aggressively targets highlights or shadows using the Color Range feature (Select > Color Range) in Photoshop. Once the dialog box has been activated, use the Eyedropper to sample the range of colors you wish to target (in this case, highlights or shadows). Then use the Fuzziness slider to increase or reduce the number of values selected.

The Color Range feature has the ability to target highlights, midtones and shadows in an image, but these features don't allow you to customize the results with a slider, as you can if you sample the values first. Because the Color Range feature includes distinctions in separate hues, it can be difficult to use it to select midtones for all hues and customize the results. You quickly can accomplish this task with this tool if you first reduce the saturation of the image to zero by using an adjustment layer. Next, use Color Range to select the midtones. Then turn off the adjustment layer and use the active selection (midtones for all hues) as you wish.

Contrast masks are extremely useful for making adjustments to a specific range of tones without affecting others.

BELOW: To make a contrast mask, you can select a color channel (here, we selected the Red Channel); then you can adjust the contrast within that channel to refine the mask as we have in the Red Contrast image. To make adjustments to shadows instead of highlights, simply invert the mask as we have done in the Red Inverted image. Defining a complex contour is easily achieved with the Contour contrast mask.


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The Magic Wand Tool

You can quickly make a very rudimentary contrast mask using the Magic Wand tool in Photoshop.
1. Set a low tolerance for the tool (try 11).
2. Click on a near-black area of the image.
3. With the selection active, make an adjustment layer correction to lighten the shadows, classically Curves; the selection becomes the adjustment layer mask.
4. Introduce a few gray values for smoother transitions by blurring the mask with the filter Gaussian Blur.



 

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