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Post-production: Luminosity masking

From our digital-only Photography Magazine, we look at adjusting shadows and highlights with luminosity masking

Post-production: Luminosity masking
Image: Steve Davey

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A digital DSLR has a far greater dynamic range — the ability to record both shadows and highlights — than was ever possible when shooting film, especially when shooting in the RAW format, which can record far more detail than a JPEG file. A JPEG recorded in 8bit will effectively be able to record 256 shades, from black to white; a RAW file shot in 14bit can render 16,384. This extra detail can hold enough information in both the shadows and the highlighted areas to rescue even the most contrasting subject. It’s all very well having this available but many photographers struggle with the techniques needed to bring it out.

If the part of your image which is too light, or too dark, is a large area with a straight line join — such as the sky or foreground, then you can use the very flexible virtual graduated filter in Adobe Lightroom to selectively lighten or darken the corresponding areas.

In Adobe Photoshop (and many other image manipulation programs) you’ll find dodging and burning tools to selectively lighten and darken various areas of the image. These emulate the techniques used in a photographic darkroom, but it’s all but impossible to make anything other than very subtle changes using these tools.

You can get more control by creating a mask, which allows you to incrementally paint over an area using the painting tool, and then convert this mask to a selection, which can then be lightened or darkened. This technique will require a lot of fine control when masking edges — especially if they’re intricate, such as with hair or foliage. Luckily, there’s a virtually automatic way to darken areas of the image, and it only takes a few seconds to achieve quite profound results, using a luminosity mask.

Creating the constituent parts

The first step is to create two different versions of the image in question in Adobe Lightroom. Create a virtual copy of the RAW file, and process a lighter version to bring out the shadow and midtone details; process a darker one to correctly render the highlighted areas. Don’t try to balance the opposite tones — this is all going to be done in Adobe Photoshop afterwards.

If you’re going to apply any cropping or profile corrections, then make sure to apply them equally to both images, so they’ll line up with each other exactly. Export these two images as 16-bit TIFFs and then open both files in Adobe Photoshop.

Pasting everything together

Copy the darker of the two images and paste it over the lighter image. As the two images are identical, they’ll fit exactly. In the layers palette, select the lighter layer and then move to the Channels palette. On later versions of Photoshop there’ll be a circular, dotted Load Channel As Selection icon at the bottom of the palette. This will create a dotted ‘marching ants’ selection around parts of the image.

Click on the top, darker image in the Layers palette, and then click on the Add Vector Mask icon: this is the third icon from the left at the bottom of the palette, and looks like a circle in a rectangle. This will add a mask over the top, darker layer, causing most of it to be masked out; only the darker highlight areas will be visible, and the light shadow and midtone areas from the bottom image will show through the masked off areas.

Finishing touches

To get a better result, you can select the mask in the Layers palette and either apply some blur using the Filter > Blur > Gaussian Blur… filter. This will soften the edges of the mask. A value of up to 50 should be enough. If you have a more recent version of Photoshop, you can double-click on the Mask to open the Mask Properties options, and add some feathering to the mask. A value of up to 10 will soften the edges of the mask, and make any effect a little more natural.

Make sure to view your image at 100% when you make either of these changes, though, to judge the effect. Too much blurring or feathering can create a fringe to the masked areas. If you do too much, simply undo this using the History palette. If you want to make the effect more pronounced, with the lighter areas of the image even darker, then duplicate the top masked layer, which will have the effect of making the highlighted areas darker.

If you want to make the effect less pronounced, select the masked layer and reduce its opacity. As you move closer to 0% opacity, the effect of the top layer will fade to nothing. If you’ve duplicated the masked layer for a more pronounced effect, you can still reduce the opacity of just one of these layers for more precise control. If you want to work on the image further, save the image as a Photoshop document with the Layers intact. If not, then flatten the layers to make the file size smaller and save.

 

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Filled with previously unpublished images from our photographers around the world, along with tips, tricks and tutorials from industry experts, the Photography Magazine covers everything from equipment to post-production touch-ups.

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Published in issue 9 of National Geographic Traveller (UK) Photography Magazine