The Arithmetic Effect

The Arithmetic effect allows you to combine channels of a layer with itself using blend modes. Hopefully that definition makes at least some sense. It’s probably better than Adobe’s own definition of the Arithmetic effect, which you can find by clicking the effect’s About button at the top of the effect in the Effect Controls panel.

Open the Arithmetic.aep project in the Chapter 5 folder of the exercise files. Apply the Arithmetic effect to the orb layer.

In the Arithmetic effect, we have three color parameters, one for each color channel. We can increase the amount of color from any of the three channels, and blend that effect back onto our layer using one of the modes in the Operator drop down. For example, I’ll increase the Red Value property to 100, and take

the Operator to Add. This will add red color using an Add blend mode, producing a brighter result.

If we kept the Red Value the same, but changed the operator to Subtract, we get a completely different result. The result is cyan, because the Red Value now specifies how much red to subtract from the final result.

Unless you have a specific purpose in using the Arithmetic effect, the results of your experimentation will most likely seem psychedelic. In this case, I’ll increase the green and blue values a little and take the Operator value back to its default value of Xor (short for “eXclusive or,” a mathematical formula). The results are just plain weird.

The Blend Effect

The Blend effect is like a really weak version of the layer blend modes in the Timeline panel. There are only five of them here, and one of them is Crossfade, which basically blends two layers together using opacity. There are two benefits with this effect. The first is that you can animate the change of blend mode. It doesn’t smoothly interpolate from one to another, as it can only create Hold keyframes. But it’s possible to animate them with the Blend effect, while it isn’t possible in the Timeline panel (although you could also split the layer and change the blend mode to create the illusion of animated blend modes). The other benefit is that you can use the Blend effect to blend together any two layers in the Timeline panel, even if they aren’t next to each other in terms of layer stacking order.

Apply the effect and chose the layer to blend with from the Blend With Layer drop down. Then choose the blend mode from the Mode drop down. To see your results, you will need to reduce the Blend With Original value.

The Calculations effect (coming up next) is much more powerful, and does both of these blend mode tricks, but it does them much better. We’ll save our look at these features for our upcoming coverage of the Calculations effect. For all intents and purposes, you probably should be using the Calculations effect instead of the Blend effect anyway.

The Calculations Effect

The Calculations effect is another effect from Photoshop, and it’s perhaps the most powerful effect in this chapter. It basically allows you to blend a channel (or the entire composite) of the layer you’ve applied it to with a channel (or the entire composite) of any other layer in the same composition. You can also composite them using any of After Effects’ blend modes, and can animate the changes between them.

Open the Calculations.aep project from the Chapter 5 folder of the exercise files. It’s important to note that the comp in this project contains three layers—two Artbeats video clips and some more medieval art from my friend, Will Kindrick. Take special note that the two Artbeats clips are separated by the knight layer.

Select the layer CED113.mov and apply the Calculations effect to it. At first, these options may seem a little baffling. But they’re actually organized very well, and make sense once you understand what this effect is trying to do.

The section at the top—Input—is for defining how the current layer will be affected. Basically here, you specify which part of the current layer (CED113.mov) will be used in the final blend. The default setting uses all of the channels, including the alpha.

The next set of options are the Second Source options. Here you define the other layer that will blend with the current layer, and how they will blend together. Choose another layer from the Second Layer drop down in the Second Source area. Herein is one of the great benefits of this effect. Any layer in the comp can be used for the final blend, regardless of where it is in the layer stack.

To keep things simple at first, let’s choose the current layer (CED113.mov) as the Second Layer. For now, we’ll also leave the Second Layer Channel value set to RGBA, to blend the layer with the full version of itself. Increase the Second Layer Opacity value all the way up to 100%. All that’s left now is to specify how this layer should blend together with itself. Let’s pick the standard blend mode for self-blending—Overlay. This creates the same results as duplicating the layer and changing the blend mode of the duplicate, but we’ve kept our Timeline cleaner.

Another difference between this and blending with layers is that we can selectively choose which channel to blend. Take the Second Layer Channel value to Red to blend this layer with its own red channel in the Overlay blend mode.

Now let’s take this up to the next level. In the Second Layer drop down, select the UW225.mov layer. This is the other Artbeats video clip of slow motion water splashing. Note that this layer is not next to the current layer in the layer stack, and yet the Calculations effect still allows us to blend them together. Change the Second Layer Channel back to RGBA, and leave the Blending Mode value at Overlay. These two layers are now blended together using the Overlay blend mode.

The Calculations effect can also be good for reflections of other layers. I’m going to change the Second Layer drop down to the knight layer. I’m then going to take down the Second Layer Opacity value to 50%, and then change the Blending Mode to Add. By default, the second layer is stretched to fill the boundaries of the layer. You can offset this behavior by deselecting the Stretch Second Layer to Fit, but I like the skewed results here, so I’m leaving it selected. We now have something that is starting to look a little like a reflection. I’m also going to drag the actual knight layer on top of the current layer, and turn on its visibility. This will help create the illusion that the knight is casting a reflection on the buildings behind him.

The Channel Combiner Effect

The Channel Combiner effect is like Arithmetic and Calculations, in that it performs these really abstract channel calculations. But we can use the Channel Combiner effect to create some extreme color and luminance changes that might be difficult—or even impossible—without it.

If you’d like to follow along with me here, open the Channel Combiner.aep project from the Chapter 5 folder of the exercise files. There are several comps already setup for you here. Let’s start in the Channel Combiner Start comp. This contains the 3D garage scene we’ve been using in this book. Apply the Channel Combiner effect to this image.

The default results are usually garish beyond description. This is because the default settings convert the current layer’s RGB values to HLS values.

This effect allows you to remap colors from one channel or aspect of the layer to another. In the From drop down, you’ll see a list of all of the source attributes that you can use. Right below that, the To parameter specifies how the From attribute will be mapped to the current layer. The top five settings here already contain the attribute that they’re going to remap to. So, when one of these top five options is selected, the To parameter is grayed out and unavailable.

Take the From value to Red to unlock the To property. This is where it starts getting a little abstract, but stay with me here, folks. This is (potentially) good stuff. By default, the To value is set to Lightness. So then, our results now map the red channel to the lightness channel. Huh? To understand this, let’s take a look at only the red channel of the original layer.

By remapping the red channel to the lightness channel, we’re telling After Effects to control the lightness of this image using these grayscale values (in the red channel). You can even use the attributes of a second layer by enabling the Use 2nd Layer option, and selecting a layer from the Source Layer drop down.

So what cool stuff can you do with this? To see some more practical examples of this, hop on over to the Darken/Change Color comp. It basically contains another instance of the same comp, with the 3D garage scene and the Channel Combiner effect. But the effect has already been setup for us here. In this case the From value is set to the blue values in this image, and the To value is again set to the lightness values. This is far more interesting because yellow and blue are opposites. That means that the car is very dark in the blue channel because not much blue light is needed to make a yellow car. So, when we use the

blue channel to control the lightness of the image, we get a very dark car. Turn on the visibility of the Channel Combiner effect in the Darken/Change color comp to see the results.

This is a very unique result. It would be very challenging to recreate this with a luminance adjusting effect, like Levels or Curves, because of all the intricate highlights, reflections, and other details on this car. But they have not been dimmed at all in this case because it took a lot of blue light to make those bright highlights as well, so they remain bright when the lightness is remapped.

Very little changed much besides the car, which is another impressive aspect of this result. Areas that had lots of blue to begin with (like the blue sky background, or the teal-colored post on the right), are brightened, and areas with warm tones (like the table in the foreground) were darkened a little. But overall, the scene is relatively unchanged.

Let’s look at one more example. Switch over to the Intense Reflections comp. Let’s say that we wanted to isolate this car to use in a movie poster. In the garage scene, the car looks realistic. But on a movie poster, it would seem to plain and dull. Even isolated by itself, the car seems lonely and in need of some enhancement.

Now turn on the Channel Combiner effect here, which is mapping the saturation values to the lightness values. This creates a much more intense car.

The results have much more punch and flash (and other Hollywood-esque adjectives) to them than the original. But if this is really for Hollywood, we can’t let this alone without adding yet more intensity. The top layer is already in the Overlay blend mode in the Timeline panel. Turn on the duplicate layer underneath it to combine these two layers in the Overlay blend mode, making a very flashy final product. Now the car is ready for Mr. DeMille’s proverbial close-up.

The Compound Arithmetic Effect

The Compound Arithmetic effect is exactly like a watered down version of the Calculations effect. It allows you to combine different attributes from two different layers.

Use the Second Source Layer drop down to select a second layer to blend with the current layer. Choose a blend operation with the Operator drop down, and a few other self-explanatory properties. For more control, use the Calculations effect.

The Invert Effect

In Photoshop, there is an Invert adjustment. For this adjustment, there are no options. You simply apply it, it inverts the colors of your layer and you’re done. Boom. End of story. The Invert effect in After Effects is much more exciting because it allows you to invert all kinds of stuff, not just the composite colors. However, if a simple inversion is what you’re looking for, then just apply it and walk away.

For this look at the Invert effect, open up the Invert.aep project in the Chapter 5 folder of the exercise files. This project contains a logo I created in Adobe Illustrator.

Apply the Invert effect to this, and instantly the colors of the logo are inverted. If you’re looking for the standard Photoshop Invert adjustment, there you go.

The great thing about this effect is that taking it to the next level is very simple. Other than the ubiquitous Blend With Original setting (basically the opacity of the effect), there is only one setting here—Channel. In the Channel drop down, you specify which attribute of the current layer gets inverted. And that’s all there is to it.

Let’s take the green channel, for instance. Change the Channel value to Green. This inverts the green channel, and the green channel only. Because there is no green light used to make black, all black areas become 100% green. So, the red and blue channels remain as they were, and all that is inverted is the green channel. I’m not sure of a practical use for this, but creatively, it’s great to see some completely different color variations of a layer.

You could also get a little more adventurous than just inverting a single color channel. I’m going to change the Channel drop down to Hue. This will invert the hues of the image, but will maintain the same saturation and lightness values. Note the differences

between this and the default result. The default result inverts everything (black becomes white, and so forth). This result only adjusts the hue.

The Minimax Effect

The Minimax effect might be the Channel effect used most often. From a technical aspect, the Minimax effect looks at each pixel and forces it to become either the minimum or maximum value of the pixels in a specified radius. In layman’s terms, the Minimax effect is typically used to expand or contract the edges of a layer. This can be helpful in polishing up keyed footage, removing strokes, cleaning up noisy edges, and other such purposes.

Open the Minimax.aep project up from the Chapter 5 folder of the exercise files. We’ll start in the Creepy Stranger comp. This contains a simple Illustrator graphic with a thin stroke around its edges.

Apply the Minimax effect to the Creepy Stranger graphic. The Operation drop down at the top is really the key here. The two main behaviors are Minimum and Maximum. Let’s first look at the default value—Maximum. To see what this value does, increase the Radius value. I used a value of about 20.

Let’s examine this a little bit. Remember that this effect looks at neighboring pixels (within a 20 pixel radius, according to our Radius value). It then causes them all to be the maximum value in that search area (because of the Operation setting of Maximum). Because the value with the highest RGB values is white, the 20 pixel area all becomes white. If the stroke were black, then it would have been completely replaced by blue, because blue has the greater of the RGB values.

If we take the Operation to Minimum, then it replaces those same 20 pixels with blue, because blue has the minimum RGB values here. For practical purposes, we could have used this setting to remove the white stroke. The edges are clean, and no one would have ever suspected that this layer ever had a white stroke.

You can also use a couple settings in the Operation drop down that perform both Minimum and Maximum calculations in order. For example, The Maximum Then Minimum setting performs the Minimax calculations with the Maximum value and then the Minimum value. The results are quite different from what we’ve seen so far.

Click the Reset button at the top of the Minimax effect in the Effect Controls panel. We’re now going to look at the Channel drop down. So far, we’ve been looking at obtaining the minimum and maximum color values. But we can change this setting to process individual color channels, or the alpha channel. Change the Channel value to Alpha. Now, when you increase the Radius value with the Operation value set to Maximum, the alpha channel expands.

Likewise, changing the Operation setting to Minimum will shrink the alpha channel. This can be helpful for removing aliased edges, or edges that didn’t quite key out properly when working with blue and green screen footage.

That covers what you need to know about using the Minimax effect for practical purposes. But some people also use Minimax for creative effect, in the same way that you might use an effect in the Stylize category. It can be used to enhance the size of reflections or specular highlights using the Maximum operation. Or it can be used to create a painterly effect.

Switch over to the self-portrait comp. This is a self-portrait painting I did in Corel Painter. Apply the Minimax effect to this layer.

Increasing the Radius value with the Operation set to Maximum will thin the black lines and create dreamlike highlights.

We can also thicken the black lines and create thicker lines in general by changing the operation to Minimum. To demonstrate the effects of the Minimum operation on this image, I’ve used a Radius value of 2.

With these results, the edges start getting eroded, as if we had applied a blur effect. To restore the edges, select the Don’t Shrink Edges option at the bottom of the Minimax effect in the Effect Controls panel.

The Remove Color Matting Effect

The Remove Color Matting effect basically does the same thing that After Effects does when using the Premultiplied option when interpreting an alpha channel. This is probably best done in the Interpretation Settings dialog in the Project panel. Regardless, let’s look at how color matting works, and how the Remove Color Matting effect can remove it.

Open the Matting.aep project in the Chapter 5 folder of the exercise files. This project contains a plant image that I rendered from 3DS Max. When I created this file, I rendered it out using a premultiplied alpha channel, which means that there is some residual background color in the alpha channel. Then, when I imported this image into After Effects, I falsely labeled the alpha interpretation as Straight. This leaves stray pixels around the edges of the object. I’m going to magnify this layer to 200%, so that we can see them more clearly.

If you want to see this image without its alpha channel, you can change the Show Channel and Color Management Settings option at the bottom of the Composition panel to RGB Straight. Hopefully now, it will be easier to see the fringe blue pixels in Figure 5.47.

If you haven’t done so already, switch the Show Channel and Color Management Settings option to RGB, so that we can see our alpha here. Apply the Remove Color Matting effect to this layer. At first the results look bad because the default color it’s trying to remove is black. That default doesn’t work for us here, but black is perhaps the most common background color in premultiplied alphas, and it’s usually the most offensive when left uncorrected.

We need to change the Background Color value to the same blue background on this plant layer. That will tell the Remove Color Matting effect which fringe edge pixels need to be removed. You can do this in a few different ways. You can change the viewed channels back to RGB Straight and click the background color with the eyedropper. Or, you can click the Background Color swatch and enter the RGB values 90, 197, 255. This will then remove all of the speckles of color along the edges of this plant. Remember that you could have also achieved the same results by interpreting the alpha channel as Premultiplied.

The Set Channels Effect

The Set Channels effect is perhaps the most esoteric effect in this category. Honestly, I haven’t found a practical use for this one yet. It basically allows you to recreate a layer using attributes from other layers. This sounds similar, but is very different from say, the Calculations effect. The Calculations effect (and others we’ve looked at so far in this chapter) blend other attributes into the current layer. The Set Channels effects just completely replaces the current attributes.

Open the Set Channels.aep project from the Chapter 5 folder of the exercise files. This project contains three of the Artbeats video clips we’ll be looking at in this book.

Select the CJ121.mov layer, and apply the Set Channels effect to it. Basically, this effect allows us to rebuild this layer based on the attributes of other layers. We can select which layer to use for the red channel, for example, and then which attribute of that layer to use to create the red channel.

In the Source Layer 1 drop down, change the layer to the CED113.mov layer (the one that shows city buildings). In the Set Red to Source drop down, you can specify which attribute of the city video that you’d like to use to make the red layer. I chose the blue channel. In the results shows in Figure 5.45, the green and blue channels are taken from the original layer, but the red values are created from the blue channel of the CED113.mov layer.

As you can see, the effect is an interesting blend of the two layers. However, when we start using more layers for additional channels, things get out of hand. In the Source Layer 2 drop down, change the value to the UM230.mov layer (the layer with the falling leaves in front of a green screen). Change the Set Green to Source drop down to Blue to use the blue channel of the leaves layer to create the green channel of the current layer.

If at this point you’re scratching your head, wondering how this could ever come in handy, I’m right there with you. It’s an interesting ability, but I only see it being helpful in creating weird blends of layers.

I should point out that you can use the current layer as the source layer, which means that you can also mix and match channels. This essentially turns the Set Channels effect into the Shift Channels effect. There is an interesting example using the Shift Channels effect later in this chapter that you may want to see.

The Set Matte Effect

The Set Matte effect is similar to the Set Channels effect, only that the Set Matte effect allows you to use the alpha channel of another layer as the alpha channel of the current layer. The After Effects help documentation suggest that this effect is obsolete; replaced by the alpha and track matte options in the Timeline panel. However, I think this effect is viable for two reasons. First, it allows you to use any layer in the composition as a matte, as opposed to mattes in the Timeline panel, which require that matte layers be adjacent to the layer they’re masking. This effect is also viable because it allows you to use other attributes from another layer— not just the alpha channel. If you do a lot of work with luma or alpha mattes, this effect can open up all new doors of possibility for you.

Open the Set Matte.aep project in the Chapter 5 folder of the exercise files. Our project here consists of one composition with three layers. Our main layer here will be some computer generated lava.

There are also two other layers that we’ll be using to control the transparency of the lava layer—a layer of lightning and a layer of fractal fire.

Apply the Set Matte effect to the lava layer. In the Take Matte From Layer drop down, choose the lightning layer. By default, the alpha channel of the lightning layer now becomes the alpha channel of the lava layer. This is basically the same results that we would have achieved had we used this lightning to create an alpha matte. The problem is that the glow around the lightning creates an ugly halo.

However, with the power of the Set Matte effect, we don’t have to be stuck only using the alpha channel of the lightning. Change the Use For Matte drop down to Red Channel. This will use the grayscale values of the red channel only to create transparency. The result is that there is much less of the glow around the lightning used here, which creates a tighter matte.

If you selected the Invert Matte checkbox, then the lightning would cut a transparent hole in the lava layer. This lightning has already been animated. If you preview this comp, you’ll see that this inverted matte is actually a traveling matte.

Now let’s adjust the Take Matte From Layer drop down to select the fractal fire layer. Change the Use For Matte drop down to use the luminance of the fractal fire to create the alpha channel (matte) of the current layer.

The results seen in Figure 5.53 resemble what would be created by making a luma matte with these two layers. Notice that these layers are not next to each other in the layer stacking order in the Timeline panel. And it doesn’t have to end here. We could use the green channel, or the saturation, or a whole host of properties from our second layer to create a matte on the current layer. Remember that if you’re going to use effects to control the alpha channel with the Set Matte effect (as I’ve done here with the Advanced Lightning and Fractal Noise effects), then you’ll need to precompose the layers that they are applied to first.

The Shift Channels Effect

The Shift Channels effect seems like another weird channel effect without any usefulness. But I actually have an interesting example, using one of the 3D Channel effects that we looked at back in Chapter 2. The purpose of the Shift Channels effect is to take channel data from a layer and use it in other channels on the same layer. This is similar to the Set Channels effect, except we’re only allowed to use the attributes of the current layer.

Open the Shift Channels.aep project. This contains the familiar 3D garage scene we’ve been using as an example in this book. We’re going to be relighting the scene using the Shift Channels effect. Note that we’re not going to be lightening the scene, as with an effect like Levels, but we’re actually going to be changing the current lighting, as if we had this image back in its original 3D rendering application.

The first step is actually to apply the 3D Channel Extract effect to this garage scene. Then, change the 3D Channel value in the 3D Channel Extract options to Surface Normals. I realize that this creates a weird looking result, but just go with me on this one.

This display of surface normals is showing us which direction each polygon is facing. Notice that the red areas tend to be facing right, green areas tend to be pointing upwards, and blue areas tend to be facing the camera. Areas that face a direction between them have blended colors.

Here’s the magic, folks. Because the polygons facing upwards are green, if we can extract that green data and remap it, we can relight the scene. And that’s exactly what we’re going to do.

Duplicate this layer and delete the 3D Channel Extract effect from the bottom copy only. On the top copy of this garage scene, apply the Shift Channels effect. In the Shift Channels effect, change the Take Red From, Take Green From, and Take Blue From values to Green. This will create a grayscale result that displays the amount of green light in the surface normals in this scene. Note that the areas with the most green light are white.

Then, in the Timeline panel, place the top copy of the garage layer into the Overlay blend mode. This will remove the gray areas of the image, and brighten the areas that are white on the top copy, which adds more light to the scene.

To really see the power of what just happened, I’m going to zoom in closer to the car, and do a split screen. What we did here couldn’t be accomplished by another luminance adjusting effect, because we just increased the lightness of the objects pointing upwards. This isn’t possible without 3D data. Even the crevasses

of the hubcaps that are pointing upwards have been relit in a very natural way.

Notice in Figure 5.58 that only the pixels that are facing upwards were relighted. The side of the car has very little change to it. But the hood of the car and the shop floor are brightened considerably.

The Shift Channels effect is a key ingredient in this recipe. Using the Shift Channels effect, we turned the multicolored surface normals display into a grayscale map of the green channel that we could blend with other layers.

The Solid Composite Effect

We finish out this chapter with a simple effect—the Solid Composite effect. The purpose of this effect is to save you the step of creating a solid layer to blend with another layer. You can create an area of color and blend it into the current layer. Let’s see how this works.

Open the Solid Composite.aep project from the Chapter 5 folder of the exercise files. The project contains a photo of a little girl interacting with a llama. Apply the Solid Composite effect to this layer.

The controls here are simple. Just change the Color value to essentially create a new solid. I’m going to select a vibrant blue color. This is a little confusing initially, because you don’t see anything different. But what’s happening is that this effect has created a virtual solid “layer” beneath your footage. You can then see this blue color by lowering the Source Opacity value, which lowers the opacity of the Source Layer. Be aware that the Opacity value adjusts the opacity of the color, but only after it is made visible by lowering the Source Opacity value, or by changing the Blending Mode. Note that the Blending Mode value blends the source footage and the virtual solid together by treating the source layer as the top layer, so to speak.

Try taking the blend mode to Hard Light, which creates a blend result that is less dependent on layer stacking order.

At the end of the day, the Solid Composite effect is a quick and easy way to blend source material into a solid color.