An Introduction to Luminance/Luminosity Masks in Digital Blending

Article by Jimmy McIntyre

Introduction to luminance/luminosity masks

Luminance masks, otherwise known as luminosity masks, is a buzz term around the HDR community right now. A great number of photographers have mastered the use of luminance masks (LMs) as a way to ween themselves off their dependence on HDR software and give themselves more control over their imagery. By using LMs we in no way alter the quality of our original images, which is a welcome break from the artifacts that are sometimes left over from the HDR process.

Please note, you can now download the Easy Panel for free, which will create the luminosity masks for youEasy Panel for Photoshop.

And for those wishing to really master luminosity masks, feel free to check out our Luminosity Mask Tutorial.

What are Luminosity Masks?

Luminosity Masks masks are of particular interest to us as HDR photographers because they allow us to make specific selections based on luminosity, or in other words, the brightness of a pixel.

For a working example, try this-

1. Open Photoshop and import any image.

2. Go the Layers Palette to the bottom right and click on Channels, which contains your colour channels. You’ll see 4 channels, RGB, Red, Green and Blue.

3. Click on any of the black and white channels, so that the other channels are deselected. Now, while hovering the cursor over the thumbnail of that channel hold down ctrl and press the left mouse button. You’ll see marching ants appear.

4. Now go back to your Layers palette and and click on the background layer so that the main image returns to colour format (You may have to double click on the background layer and press ‘Okay’ if a dialogue box appears).

5. Now open a Curves adjustment layer. You’ll see that the marching ants have disappeared and the Curves layer now has a mask exactly the same as the channel you selected earlier. To view the mask press alt and left mouse button on the mask.

6. Press ctrl and left mouse button again to return and this time make some contrast changes to the Curves layer. If your image has particularly dark areas, they will not be affected at all. This selection is targeting only bright pixels according to the chosen channel. The darker the pixel the darker the area on the mask.The darker the area on the mask, the smaller the adjustment effect.

What does this mean to HDR and digital blending?

Assuming you have your own actions, or have downloaded the actions at the top of this article, import the actions by extracting them from the zip file and double clicking on the file. Or you can go the the Actions panel in Photoshop, click on the top right menu and choose Load Actions (See image below).

As you can see in the image above, you will now be given a new option called JM Luminance Masks. If you click on the arrow next to that you’ll see another option become available called Generate Luminance Masks. Click on that and then the Play button at the bottom of that panel (The triangle button next to the circle).

Once Photoshop has finished working, go back onto the Channels panel as you did earlier. This time you’ll see a lot more channels – 18 new channels, to be exact. Scroll through them to see how each is different. Starting with Brights 1 and scrolling down to Brights 6, you’ll see that they become progressively darker, which means that they are make more and more specific selections based on brighter luminosity values.

The Darks channels are exactly the same, but this time they are inverted so that they select only the darker pixels. The Midtones are something entirely different and beyond the scope of this article.

I’m working with the two exposures below. The goal is to recover lost information in the blown out sky around the tree of the 0 exposure. I’ll do this by making a selection of the Brights 3 and masking in some of the -2 exposure which is almost perfectly exposed in that area.

0 exposure

 -2 exposure

The Brights 3 selection

In the image above, you can see that Brights 3 is targeting mainly the blown out area around the tree, without affection any of the correctly exposed areas.

Firstly, in the Layers palette I will place the -2 exposure on top of the 0 exposure and apply a black layer mask to make it invisible. Then in the Channels palette I’ll go to the Brights 3 channel and left click on the thumbnail while pressing ctrl. The marching ants will appear. Press ctrl and H to hide them.

Now I’ll return to my Layers palette and choose a large brush with an opacity of around 50%. Make sure the colour is set to white. With the layer mask selected I will simply run the brush once around the area I want to recover. This will bring through enough of the darker exposure so that we end up with an evenly exposed sky.

And that’s it!

How it looks in Photoshop

After that I will continue to use LMs but this time to make fine contrast adjustments and specific changes to the image.

So what does it all mean?

Well, ultimately, armed with knowledge of luminance masks we can make images, just like this, in a matter of minutes and with no extra noise or softening of pixels. However, I don’t want anyone to come away from this article with too much confidence. Mastering LMs is a challenge worth taking on. Working on more complex images you really get an understanding of how tricky the whole process can be. And, if you’re anything like me, you’ll get a strange satisfaction or sense of achievement from working with complex luminance masks in your workflow – not to mention the awesome benefits it will bring to your imagery.

I hope you’ve found this information useful. For more tips and HDR photos, feel free to join me on facebook or Google+.