Layer masks are the key to nearly all great images created with Photoshop. They let you make targeted adjustments, blend images, composite, work non-destructively, and are probably the most important component of using layers. Masks have two properties which are designed to help you get more natural-looking results. You may already be familiar with mask feathering, which allows you to soften the edges of your mask for a more gradual result. But the other property, “density“, is one that I almost never see other photographers take advantage of. It’s incredibly useful in certain scenarios, but it isn’t obvious and most photographers never realize it can help improve their images.
We’ll cover several great ways you can use density, but it’s important to first understand what it actually does. Layer masks control the visibility of individual pixels of a layer (including images and adjustment layers). The basic principle is that as you paint on the layer mask: “black conceals”, “white reveals”, and gray gives some proportional results. There are times when it would be helpful to ensure a minimum visibility (gray) in the layer mask, and that’s what density does. At the default 100% density, the layer mask looks exactly as you painted it. But as you slide reduce density, the dark values in the mask are lightened. If you slide all the way to 0% density, the mask becomes pure white (even if you have true black in your mask)! Let’s explore a couple scenarios where you could benefit from adjusting density.
Using density for more natural-looking transitions
Filters often look best when you apply them in a targeted way that affects some parts of the image much more than others. For example,a noise reduction filter works best if you apply it more aggressively in smooth areas (such as sky and water) than in areas where you wish to retain detail. You can paint a layer mask that will help do that using white to cleanup the sky/water while using darker greys elsewhere to strike a balance of noise reduction and detail. Because you probably want at least some minimum effect everywhere in the image, the mask is going to have a minimal gray – and that’s exactly what density offers. So rather than spending too much time painting a very fancy mask, you can simply paint white on the sky/water areas that need the most smoothing. Then just adjust the mask density to reveal some noise reduction everywhere else. With minimal effort, you’ll get a perfect result with no obvious transition edges. It’s fully non-destructive, so you can readjust the density anytime you need.
You can use this approach when using a layer mask on an adjustment layer, such as for color grading or color overlays. Anytime you want the effect to show more in some places than others but need to show a little bit everywhere to look natural, density is a great solution. I show this in the video to improve a color overlay, which could just as easily been any form of color grading.
It works very well with smart filter masks, such as for sharpening and noise reduction. You could also use it to improve complex filters such as Nik Color Efex Pro or Luminar. Just apply a filter to your Smart Object, invert the filter mask to black, paint white where you need the filter most, then adjust the density to balance out the effect across the whole image. It’s the same workflow I showed in the video above to reduce noise.
One thing to keep in mind is that this control is separate from the master layer opacity, BlendIf, and vector masks. So even if you make the mask white via density, these other factors can still hide your pixels.
Using density to help blend a layer
Exposure blending, time blending, compositing and other forms of combining layers with different content typically involve painting white on a black layer mask to reveal each layer. Until you’ve revealed your subject, it can be hard to know exactly where you should brush on your image. In other words, you need a bit of a “sneak peak” to know how to paint the mask. You can <shift>-click the mask to disable it, but this reveals the layer entirely and obscures everything below it. Mask density offers a way to get something in-between to let you see everything at once. Just slide the density to around 50%. This will show the blend layer enough to know where to paint, while showing the underlying content at the same time. And as you paint, the blend layer will become more and more opaque so you still get a good sense of the blended result. Once you no longer need the visual aid, just slide density back to 100%. Be careful to slide all the way to 100%, so that you don’t allow unwanted portions of the layer to create unwanted ghosting.
Controlling density via Lumenzia
The sliders in Lumenzia allow you to not only adjust Lumenzia’s previews and BlendIf, but also the sliders for layer masks including feather and density. When you click on a mask to make it active, the precision slider in Lumenzia will show white to indicate that it is ready to adjust the feather on that layer or filter mask. To adjust density instead, just <alt/option>-click the slider and it will turn yellow to indicate that it is ready to adjust the density on that mask.