Contrast masking is a technique initially used in the wet darkroom. Essentially this technique balances the tone across an image. In the darkroom, contrast masking is a very difficult and time-consuming task. Using Photoshop it takes only a few minutes.
Contrast masking will not work on all images. This technique is usually employed where distinct areas are significantly brighter or darker than others, images that lack definition or looks flat. It only takes a few minutes to apply contrast masking, and it doesn’t hurt to try you can always ‘undo’ or adjust it if it doesn’t look right. Experiment with all types of images to get used to the effects of contrast masking.
I recommend applying contrast masking after adjusting setting the Black and White points, prior to any color adjustments, cropping, or manual touching up the image.
Open your image in Photoshop and make sure that your layers palette is visible. Duplicate the background player of the image. You will now have two layers in your layers palette. Double-click Layer 1 and rename it Contrast Mask.
With the Contrast Mask layer selected in your layers palette, set the blending mode for this layer to Overlay. You will notice that the image gains in excess of contrast and loses a lot of detail.
Set the opacity to 80%. The opacity of this layer can be changed later on in order to adjust the strength of the contrast mask. The higher the opacity, the stronger the contrast mask. For right now 80% will do.
Now Desaturate the contrast mask layer. Desaturate is found in the image menu under Adjustments. This will remove all color from the contrast mask layer making it now black and white.
Under the same menu, choose Invert or press Command I. This will invert the layer, and now your image will show much more detail than the original.
What you did up to this point was to use an Overlay layer to apply contrast to the whole image, using a duplicated, saturated and inverted copy of the original image to apply the overlay to just the right spots. The problem is that your Contrast Mask layer is much too detailed for this contrast improvement to make the image look better. It’s bringing out too much detail. It needs to be softened.
In the final step you will need to apply Gaussian Blur to the Contrast Mask layer. Gaussian Blur is found under the filters menu. Adjust the Radius between 20 and 200. Keep an eye on the image preview to see which Radius works best for your image. Images with more resolution will need a higher Radius.
Applying a blur applies the contrast mask effect to the general area instead of the exact detail of the image. The the trade-off is that you lose some detail gained in the previous steps, but the result is a more realistic photo. You may further adjust the Opacity of the contrast mask layer to tweak its strength.