Photoshop has been around for a long, long time, yet there’s one feature that’s been underappreciated more than any other. You’ll have seen it before, hiding at the bottom of a much-used dialog box, but probably ignored it. What is it? It’s Blend If, and it can save you from a world of painful background removal tasks.
So what does Blend If do? It hides part of an image based on the color values of the pixels within it. The easiest example is a shot of lightning; you could choose to hide the background quite easily. Not every image is suitable, but the good news is that Blend If works best when other options fail. Let’s dig deeper.
Note: download this great Creative Commons photograph (by Matvey Andreyev) to follow along with this article.
Blend If is part of the Blending Options dialog. Since that dialog only affects regular layers, not Background layers, you’ll have to promote your Background layer to a regular layer. Option-double-click on the Background layer, just to the right of its name, to instantly promote it to Layer 0. (The Option key skips the dialog you’d usually see.)
No longer the Background layer.
Release the Option key, and double-click again, just to the right of the name. You’ll see the Blending Options dialog, which you might have used previously to access Layer Styles such as Drop Shadow. At the bottom of the dialog is the Blend If section we’re looking for. Think of it as “Display the pixels on this layer if…”.
Layer Style, with Blend If at the bottom
At the moment, we’re seeing all the pixels on this layer: light, dark, and everything in between. Blend If can limit the pixels you see, based on the RGB or Luma values of this layer, or of layers below the current layer. Try something simple: under This Layer, drag the Black slider at the left of the gradient to the right. You’ll see the darker areas disappear from view first, followed by more and more of the area around the (brightest) lightning.
Blend If, with the darkest pixels on the top layer hidden.
So far, so good, but the edges of the selection are rough. Drag all the way to 209 on the 0-255 range. To see just how rough the background is, you’ll need to import a background to place the lightning against. The easiest way to do this is to use File > Place, then navigate to your image, resize it, then finally drag it below Layer 0.
Now, to soften the edges, hold the Option key, and drag the right-hand-side of the black slider towards the white slider on the right. By doing this, you’re defining a falloff between visible and invisible, interactively deciding how fuzzy the edge should be. Move the right-hand-side of the now-split control to 246 to give a soft edge to the lightning.
Blend If, with a falloff applied and Underlying Layer adjusted.
Blend If results with Ambleside (UK) behind.
There are many more options here. We’ve adjusted Gray (i.e. Luminance) but you can limit visibility based on individual component channels (R/G/B) as well. Most useful in my example (where a slight dark edge is visible over the sky of the background image) is to pull the Underlying Layer’s white control just a little to the left, then soften it slightly. Now, none of the lightning layer will be visible where the layer underneath is bright.
Another tweak that can produce unexpected results is to play with the Underlying Layer controls for individual channels. If you’re lucky, you can use this to force the blended layer in and out of the layer below, as shown in this example after changing the Red controls.
Blend If, with Red adjusted for Underlying Layer.
Use a Blending Mode such as Screen (or Multiply for darker images) can sometimes more seamlessly integrate the overlaid layer. You may also want to add a Layer Mask to paint out any pesky areas that just can’t be blended automatically.
Blend If is a great feature. Even if it’s not usually the first port of call for a cut-out, it can really help to finish one off — or perform a trick that’s almost impossible any other way. Best of luck exploring it!
Blend If results with red adjustment above, no layer mask applied yet.