Understanding Adobe Photoshop’s Advanced Blending Options
Yeah, these suckers here. You know, there’s not a lot that I don’t know in Adobe Photoshop, but every so often I come across something that I’ve been, well, avoiding to have to learn properly. Something I’ve always been able to muddle through without really understanding the why and the wherefore. Not often. And I hate when it happens. The layer Advanced Blending Options has been one such thorn, and in a recent UI experiment that I document with some video tutorials, I hit the wall and had to mess around randomly with these options until I found the magic combination and permutation that actually worked. I was content. Until I had to do said video tutorials. That’s where I look like a fool if I can’t explain something properly. “Don’t be an ass,” I said to myself. “You either know or you don’t. Don’t fake it.”
So I turned to Google. And you know what? no-one (least of all Adobe) had a satisfactory explanation for the phenomenon I was experiencing. Was it a bug? Unlikely. So I had to figure it out the hard way. I’m documenting my findings here, to create the definitive record on the web for how this shit works. I can only hope that my SEO + your Google-fu gets you to this article when you’re in need of enlightenment.
The Advanced Blending Options are found either by double-clicking the layer in the Layers Palette (but you can’t double click on the name of the layer – ’cause that renames the layer, and you can’t double click on the swatch of a shape layer, ’cause that invokes the colour picker dialog), or, perhaps more reliably, you can select the layer, then go down to the f/x menu and choose Blending Options… You get this beauty:
In this post, I’m focusing on the little group of checkboxes in the middle section called Advanced Blending. Specifically, in this first post, I’m looking at the synergy between Blend Interior Effects as Group and Blend Clipped Layers as Group. Oh there’s synergy all right.
But let’s look at them individually, first. We’ll worry about the cross-mojonation later.
Blend Interior Effects as Group
Okay, this one works as advertised. Sorta. By default this checkbox is off. The so-called “Interior Effects” are:
- Inner Glow
- Color Overlay
- Gradient Overlay
- Pattern Overlay.
Any documentation you will read says that “Interior Effects” refers to any and all f/x that are applied to the interior of the layer they are effecting, namely, the opaque pixels of the layer. This is not true, as this post will bear out.
So, sadly, you will need to refer to the list above to know which f/x are affected by this option.
Okay, moving on. Let’s figure out what the “Blend Interior Effects as Group” option actually does.
When we’re not blending the interior f/x as a group (the default behaviour), each f/x has its own Blend Mode (e.g.: Multiply, Screen, Overlay, Hard Light etc…) and each f/x’s Blend Mode is applied individually after ( or “on top”, if you prefer) the layer’s fill itself is applied against the background. Perhaps an illustration would, uh, illustrate this more clearly:
Here we have a simple background gradient, on top of which sits a green layer. Currently the Blending Mode of the layer is set to Normal. So nothing special going on here. Moving on…
Now, we’ve set the layer’s Blend Mode to Multiply. As you know, Multiply invariably results in a darker composite, as the RGB values of the layer, expressed as a decimal from 0 to 1 (where 0 is OFF and 1 is completely ON) are multipled with the RGB values of the underlying image. Multiplying a fraction by a fraction invariably results in a smaller number. Smaller numbers are darker values (less light), so we get a darker result, except in the case where the layer’s colour is white (1, 1, 1) – as you know, multiplying anything by 1 doesn’t change the original value, so using the Multiply Blend Mode on a white layer effectively makes that layer transparent (or at least the white parts of that layer). But I digress. A lot.
Now we’ve turned on the Gradient Overlay interior f/x, We’ve chosen a simple gradient with Black and the top and White at the bottom, and we’ve set the Blend Mode of this f/x to Screen. Screen is basically the opposite of Multiply and will only result in a brighter composite.
At first you might not be surprised by the results. We’ve turned on Screen, and sure enough, the Black parts of the gradient are being ignored as they should, and then the image gets gradually brighter as we move down through the gradient to White.
And then if you think about it again, you might. “Wait,” you might say to yourself. “I thought this Layer’s Blend Mode was set to Multiply! Shouldn’t we be blending against the background? Why the White at the bottom?” The Gradient Overlay is certainly not acting as though it were part of a Multiply Blend.
That’s because, by default, each interior f/x is applied to the filled pixels of the layer after the layer itself has been composited to whatever is below it. So:
- The green layer is Multiplied against the background,
- Then, the Gradient is overlayed on top of this “new” background that was darkened by the layer, and the Screen Blend Mode of the Gradient Overlay is applied, allowing us to get the pure white at the bottom of the gradient.
This will all be more clear when you see what the other option is, when we turn on Blend Interior Effects as Group:
Here, we’ve turned on the Blend Interior Effects as Group Advanced Blending option. All Interior Effects are blended to the layer first, and then the layer’s Blend Mode is applied to whatever sits underneath it.
So here’s what happens in this scenario:
- We start with a Green layer.
- The Gradient is overlayed on top of that with Screen mode: this results in a layer that is now Green at the top and White at the bottom.
- This new result is then composited over the background with Multiply. Remember that Multiply essentially “ignores” white – so as our Green layer becomes more White toward the bottom, the visual result is that it becomes more transparent.
And that’s what the evidence bears out in the screenshot above: the Green hexagon appears to fade out, as though it had some kind of layer mask, because it’s actually no longer a Green hexagon, but a hexagon with a gradient on it from Green at the top to White at the bottom.
The “Missing” Interior Effects
As I mention in the first paragraph of the previous section, the list of so-called “Interior Effects” is deceiving. Technically this should apply to all f/x that have an effect on the opaque pixels of the layer (as opposed to those f/x that affect the transparent pixels surrounding the layer, such as Drop Shadow or Outer Glow).
There are a few f/x however that do affect the interior pixels, but are exempt from this list, and therefore will not be affected by the setting of the Blend Interior Effects as Group checkbox. These are:
- Bevel and Emboss
- Inner Shadow
It actually works out in our favour, because most use cases for this f/x really don’t want them blending with the base layer under any circumstance. Nonetheless, you’ll want some proof that what I’m saying is correct. Well, the two images below should bear that proof:
This gawd-awful construction was specifically build to demonstrate which f/x are considered “Interior Effects” and are subject to the Blend Interior Effects as Group option. Working our way from the outside of the hexagon inward you will see: 1. a red Stroke, 2. a green Inner Shadow, 3. a cyan Inner Glow, 4. a high-contrast Bevel and Emboss, and 5. a diamond-shaped Satin f/x. Currently Blend Interior Effects as Group is turned off, so we’re seeing each of these composited on top of the blended result of the layer, Multiplied against the underlying image.
The image above throws the kitchen sink at the layer f/x stack, with each f/x being highly tweaked to be as high-contrast and obvious as possible. Let’s take a look at which ones change as a result of turning the Blend Interior Effects as Group option on:
In the screenshot above, we can clearly see that the cyan Inner Glow, the white Satin and the high-contrast Pattern Overlay are being composited against the base layer first, and then the resulting composite is blended against the underlying image. Because the Blend Mode of the base layer is Multiply, the parts of the resulting layer (after the layer f/x are applied) that are White become transparent. It becomes immediately obvious which f/x are being affected by the Blend Interior Effects as Group option.
Blend Clipped Layers as Group
Let’s make things more interesting. Let’s add a new layer to the mix, and let’s make it part of a clipping group – that is, a group of layers that are all clipped (or close-cropped) by the shape (the transparency) of the base layer. You do this by Option (Alt on Windows) clicking on the dividing line that separates two adjacent layers in the Layers palette. Both of those layers can’t already be part of some other Clipping Group in order for this to work. Once in a clipping group, it’s the layer at the bottom of the group that becomes the “base layer” and determines the overall transparency of the group. Think of the base layer as the “window” through which all the other clipped layers are seen. In Adobe Illustrator, this sort of thing is called a “clipping mask” with the difference being that the mask itself is the topmost layer. Who could accuse Adobe of being consistent?
In this screenshot, we’ve added a rectangular layer, coloured in Red, that runs across the middle of our hexagon. We’ve made them into a clipping group, with the green hexagon as the base layer.
The base layer’s layer f/x sit on top of all the clipped layers and their layer f/x.
Let me repeat that, because it’s totally counter-intuitive and will seriously mess you up if you don’t remember it. All the clipped layers, even though they appear to be visually stacked above the base layer in the Layers Palette, will be visually rendered before (and therefore under) the layer f/x of the base layer.
Yes, this sounds totally messed up.
But actually A) it kinda makes sense and B) it’s pretty cool.
Let’s pretend that we wanted to make our hexagon base layer really look like a “window” that you can see through, and through that window we want to see all those clipped layers. That’s pretty much the use case for clipping groups right there. Well, to make that more realistic we want to a) use an Inner Shadow to make the “window” appear to have some depth, and then b) use a gradient to make it look like our window is made out of glass, thus partially lightening the clipped objects “behind” the window to give us the effect of looking through glass.
If the base layer’s f/x were composited underneath the clipped layers, we would have to create another layer on top of all the others, that covered the entire area of the base layer, just to create those effects. But, because the base layer’s f/x are composited after (on top) of the clipped layers (and their f/x), this is not necessary. Take a look:
In this modification, we’ve added an Inner Shadow f/x to the base layer – note how the inner shadow covers not only the green hexagon, but also is overlayed on top of the red stripe – the clipped layer – so clearly it’s being rendered last. I’ve also altered the base layer’s gradient (still with Screen mode on) to look like more of a “reflection” or “highlight” and I’ve put it on an angle. Otherwise, it’s basically the same. Again, this clearly overlays on top of everything, including the clipped layer. A final note about this screenshot: I’ve turned the Blend Interior Effects as Group option off, just so we can more clearly focus on what’s happening inside the clipping group.
All the Layer f/x are rendered above the clipped layers? Always?
Actually, as it turns out, no. So here’s the rule:
- The “exterior” layer f/x (Drop Shadow, Outer Glow) are exempt from this rule. Completely. Since they will never overlap the clipped layers.
- The “interior” layer f/x obey this rule when Blend Interior Effects as Group is turned off. This makes sense, because if the option is on, we’re compositing those f/x against the base layer; we can’t do that if they’re rendered after everything else.
- The “missing f/x”, as I’ve documented above (Bevel and Emboss, Inner Shadow and Stroke) will always render above the clipped layers. Always.
And that’s the rule. At least as of Photoshop 13 (CS6).
So, with that information in our back pocket, let’s turn our attention to the Blend Clipped Layers as Group option. It has a similar role to the Blend Interior Effects as Group option, in that it controls whether or not the clipped layers are applied to the base layer before the base layer’s Blend Mode is applied to the underlying image, or after. Let’s look at what happens when this option is off, first.
Here I’ve turned off the Gradient Overlay on the base layer for clarity, and I’ve gone and turned off the Blend Clipped Layers as Group. What we see, therefore is the full Red colour of the clipped layer. Note that this option doesn’t really deal with the layer f/x so much as with the layers themselves, so I haven’t bothered to put any layer f/x on the Red rectangle layer.
When this option is off, the rendering order is as follows:
- The base layer is composited against the underlying image using the base layer’s Blend Mode (in this case, Multiply, as before)
- Then each clipped layer (from lowest to highest) is then applied, using that layer’s Blend Mode (in this case, just the Normal default). Each clipped layer is composited against the result of blending the base layer against the underlying image.
- Finally, the base layer’s layer f/x are applied on top of everything.
This explains why the Red of the rectangle shows through perfectly. Contrast that with the screenshot below:
In this screenshot we see that when Blend Clipped Layers as Group is turned on, all the clipped layers are composited against the base layer first, and then the result is composited against the underlying image using the base layer’s Blend Mode.
Notice how the Red of the clipped layer is a lot darker? That’s because it was composited against the Green of the base layer first, and then the new Green-and-Red shape was Multiplied against the underlying image. Both the Red and the Green were used to darken the underlying image, as you would expect from Multiply mode.
Note that, regardless of the setting of the Blend Clipped Layers as Group option, the Inner Shadow of the base layer is still composited on top of everything else.
In the next post
In the next post we will look at what happens when you play with these two options together. This can be a make-or-break combination depending on what effect you’re trying to achieve, so be sure to stay tuned.
Author’s note: to the best of my Google-fu, this is the only post out on the interwebs that properly explains these two very important options. Help get the word out to other Photoshop users by sharing, linking and Tweeting this post. Let’s get it done. Thanks for reading. – Tom