Contrast Masking

Out of The Wet Darkroom

The December, 2000 issue of PCPhoto magazine had an article by Richard Pahl called Digital Contrast Masking. It describes how to use a technique that experience darkroom workers have used for ages and has brought it into the Photoshop age. Thanks Richard.

I was excited to see this technique brought up-to-date because though its use in the wet darkroom was tedious at best, in the dry darkroom it's simple, quick and even more effective. It now forms part of my Photoshop repertoire and I have adapted it to my own way of working.

  Figure 1

The screen shot above shows a photograph taken in Antelope Canyon in 1998. This photograph was part of my Photo Technique magazine Featured Portfolio in the Fall of 2000 and I sold a large number of prints of it. It also happens to be one of my most difficult to print images. While I have used numerous techniques to tame it, the masking technique detailed here is the one that produces the highest quality results.

The challenge of this photograph is the combination of a huge dynamic range together with ultra-saturated colour. Antelope Canyon is a place of extremes of light, and while capturing it on film is always a joy, it's a real challenge as well.

Figure 2

Original Scan                                                        Corrected with Levels and Curves

Final Image using Contrast Masking

These three shots tell the tale. The first is the raw scan (done with an Imacon FleXtight). The second is with standard contrast, brightness and colour adjustments done using Photoshop's Levels and Curves. (Please see my tutorial called Instant PhotoShop for a photographer's guide to Photoshop for beginners). The third image is the final one, corrected as well with a Contrast Mask. 

I was able to bring down the very hot sky portion at the top of the frame to a manageable degree and to also open up the shadow areas, while still retaining saturated colour. Let's see how it's done.

How To Make a Contrast Mask

Using a contrast mask is a lot like taken a patent cold medicine — it's good for whatever ails you. It can be used to reign in burned-out highlights and also to open up shadows. It can also do both at once, (as illustrated in this example) or just one or the other.

Step 1

On the Layers Palette highlight the background layer and then select Layer / Duplicate Layer. Name it Contrast Mask. If you have any existing Adjustment Layers ( see Instant PhotoShop ) then move the new Contrast Mask Layer above them on the Layers Palette. Don't worry if you lose your adjustments, they'll come back soon.

 

Step 2

With the Contrast Mask layer selected use Image / Adjust / Desaturate. The layer will now become monochrome, as will everything below it (for the moment). 

Step 3

Now use Image / Adjust / Invert. This turns the Contrast Mask later into a negative. Think about what's about to happen. Everything that was dark in the original photograph is now light, and everything that was light is now dark. All that needs to happen is to apply this layer properly for it to be effective.

Step 4

Double-Click on the Contrast Mask layer on the Layers Palette and select Layer Options.

In the Mode box select Overlay. Looks a bit ugly, but there's one more step to go.

Step 5

We need to blur the mask layer so that it doesn't fight with the detail of the original layer. This is accomplished with Filter / Blur / Gaussian Blur and usually a value of between 10 and 30. You can see the changes that you make so as to be able to fine tune the amount of blur. 

On a large file this can take quite some time so it's always a good idea when experimenting to work with a 72 dpi version. When you've achieved the effect that you want you can reload the original file and repeat your steps, either with a Photoshop Action or manually.

Lot's More

Well, actually there's a whole lot more. You can use the Opacity box in the above window to reduce the effect. You can also now create additional Adjustment Layers to further fine-tune what you need.

Here, I've created a Curves Adjustment Layer to open up the shadows a bit more. 

An additional enhancement would be to use one of the available masking tools to isolate just one section or colour or brightness range within the image and then to apply the Contrast Mask just to it, rather than the entire image. This is what we used to do in the wet darkroom with Litho film masks.

As always with Photoshop there are endless opportunities for experimentation. I hope that this tutorial helps you discover this useful technique from the wet darkroom and apply it to your work in Photoshop.

February, 2001

Reader Åke Vinberg has written a very informative report on the effect of varying the amount of Gaussian Blur when using this technique.