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When we were working with the Continuous Rasterization in the previous two movies, you might have noticed that this switch had a second name attached to it, Collapse Transformations, and that's what we'll discuss in this movie. I want to go ahead and close all my comps, I'm still in Render Order.aep, and I'm going to open up the comp Collapse Transformations, Collapse*starter. Here we have a very simple composite of a watch face over a background. The watch face has been set to Overlay mode, so it has an interesting interaction with the background. This is the composite in Normal mode and here's the composite in Overlay mode. And we also, see that we have an effect applied, namely a drop shadow, and the transforms are pretty much at their defaults including a 100% scale. So After Effects is following it's normal order of applying a drop shadow, calculating the transforms, then using the blending mode to composite this layer on top of those underneath. Let's play a couple of games here. And let's set the scale down to a small value such as 10%, one tenth of the original size. Then I'm going to take this scaled and affected layer and pre-compose it. I'm going to right-click on it and choose Pre-compose, and select the option Move all attributes into the new composition; that means the effect, the blending mode, and the transforms will all be moved into this pre-comp, and I'm even going to name it watch face pre-comp. I'll click OK, and then I say, well it's too small. Let's scale it back up again. So I'll press S, and put the scale up to 1000%, ten times the original scale compared to the one tenth scale I have on the pre-comp. Press Enter and the result is something that looks pretty ugly. Not at all like our original composite. Two things are wrong: one, the watch face is looking very pixelated and very aliased, and two, we're not seeing our blending mode, and in fact we don't have a blending mode set here. Let's understand what's going on. I'm going to tap Shift to bring up my mini comp navigator and go into the pre-comp. In this pre-comp, the effect and the scale are being calculated, as well as the blending mode. And you can press F4 to toggle in between the switches and modes columns. If I turn on my Transparency Grid you'll even see a very slight drop shadow off of this scaled-down layer. When you have a chain of compositions, normally After Effects will calculate the pre-comp, convert the results into a pixel-based image which is the same size as the pre-comp, then pass that pixel-based layer onto the master composition, where it's used as a normal layer. Now the rules of normal pixel-based layers apply. One, scaling past 100% results in a drop in quality and some pretty nasty aliasing. Second, the blending mode is back here in the pre-comp, and since there is no layers to interact with we're not seeing its result. And up here in main comp, we don't get the results of the overlay set in the base comp. We can change it to overlay here, but we still have a very pixelated layer. Well there is a workaround for some of this. I'll set it back to Normal for now. I'm going to press F4 to bring forward the Switches column again. For pre-comp layers, this little sunburst icon becomes the Collapse Transformations switch. Not continuously rasterized. That's just for vector-based layers, but collapse transformations. And when I enable it, watch what happens. We get back a resolution. We get back a blending mode. Well, what's going on? Continuous Rasterization means that one of the rasterization or convert to pixel steps is being skipped. I'll tap Shift key. Previously the pre-comp was converted to pixels at this stage, then passed on to our master comp, but with Continuous Rasterization, the layers in the pre-comp are brought forward directly into the master comp. There's no conversion to pixels at this middle stage. As an additional benefit, any transformations you have applied in the master comp are combined with any transformations happening in the pre-comp. So 1000% scale times 10% scale equals 100% scale. This operation is performed only once in the master comp. So we don't have any scaled-down layer being scaled back up again, and therefore we get a cleaner image. Also, since the layers in the pre-comp are being brought directly forward to the master comp, any blending modes set up in the pre- comp will be used for that layer in the master comp, and indeed if I tap F4 to bring up the Modes column, you'll see that the Modes popup has this little dash in it saying, you can't set any modes here, modes have already been set in the pre-comp. And if I had multiple layers, all of those layers will be brought forward each with their own mode and composited in this master composition. I'll tap F4 again, you'll also notice that the quality and motion blur switches have dashes through them, meaning that the settings in the pre-comp are what's going to be obeyed. Now if you got your head wrapped around that, there are exceptions and complications. For example, what would happen if I would then apply a mask or an effect to this Pre-comp layer? Normally, any layers in this pre-comp are brought forward and calculated in the master comp, including their masks and effects. However, if you go ahead and do something like apply say Blur > Box Blur, After Effects has to do a new set of calculations. It has to convert the pre-comp into pixels before it can apply the Box Blur. The transformations are still being sent back to the pre-comp so that they're calculated only ones and we get a higher quality image, but now I'll tap Shift, some conversion of pixels need to take place here before you can apply effects to this layer or before you can mask this layer. And as a side effect of that any blending modes set in the pre-comp get ignored in the main comp because they have to be composited and converted to pixels before you can mask and apply effects. The main thing I want to get across here is if you do have nested compositions, I'll delete my mask for now, and you need to do any additional transformations, particularly scale to that pre-comp and the master comp, quite often you can buy back more image quality by enabling the Collapse Transformations switch. You can also use the pre-comp as a way of grouping multiple layers together, and treating the result as one layer in the master comp. This is particularly handy in 3D space which we'll cover in a later lesson. However, don't blindly turn the switch on for all pre-comps, because sometimes unexpected things will happen, particularly if you decide to apply additional effects or masks to this pre-comp layer.
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