The Role of Grain

Beyond lens effects, you will need to consider another attribute of images shot with a real camera: grain. Grain is essentially high-frequency noise that occupies every channel of your shot to some degree. And grain is your friend, as long as you give it the proper amount of attention.

Grain can give texture and life to images and help to conceal a multitude of small details, enabling compositors to get away with illusions. Just like depth of field and motion blur, grain can be a problem or the key to a whole cinematic look.

The day may come when digital cameras are capable of delivering moving footage that has no grain whatsoever. Already, high-definition video cameras used to shoot movies pick up clearer detail than film cameras, all other things being equal. For example, miniatures for Star Wars, Episode One: The Phantom Menace, the first big-budget film to be shot on digital video, had to be created with greater detail than typical film miniatures because of what the digital camera exposed.

For compositors, perhaps the most important role of grain is its role integrating a flat, static layer with moving footage, adding life to an element that otherwise looks oddly suspended out of the time and place of the rest of the scene (Figure 9.26).

Figure 9.26. Solid areas of color are always the best for examining grain, and it always appears, even on perfectly shot 2 K film plates (here zoomed in to 400%). Drop in a solid the same color as the plate, and you see that it fails to blend with its surroundings. The effect is even more pronounced with moving footage, especially at film resolution.

Proper grain is not simply switched on or off, however; it needs to be carefully adjusted. You can become quite theoretical about all this, but really you need to concern yourself with only two basic factors:

• Size of the grain

• Amount of grain, or amount of contrast in the grain

The trick is that these factors typically vary from channel to channel. Blue is almost universally the channel likeliest to have the most noise; happily the human eye is less sensitive to blue than red or green, but this can be bad news for blue-screen shoots.

How much grain is enough? As with color in Chapter 5, "Color and Light: Adjusting and Matching," your goal is typically to match what's there already. If your shot has a background plate with the proper amount of grain in it, you match your foreground elements to that. In the case of a fully computer-generated scene, you might have to match surrounding shots that have plate reference, which you would match in the same manner.

Grain is often the result of a low amount of light coming through the lens combined with a low-quality image-gathering medium, such as 8 mm film or miniDV, that has poor light-gathering abilities or large silver particles (typical of faster, cheaper film stocks).

Grain Management Strategies

After Effects 6.5 Professional includes a suite of three tools for automated grain sampling, grain reduction, and grain generation: Add Grain, Match Grain, and Remove Grain. Add Grain you adjust entirely manually, but Match Grain and Remove Grain sample a noise source layer to give you an initial result that you can then adjust.

If you've been reading closely up to this point, you know I'm not a fan of using the automated solutions. Not so in this case. The Match Grain effect does not seem to be appreciably slower due to grain sampling than Add Grain, which does not perform any sampling and includes all of the same controls. Therefore, I recommend you see what Match Grain can come up with as a starting point, and then work from there. In either case, the steps are the same:

1.	Look for a section of your source footage that contains a solid color area and little or no motion for 10 to 20 frames. Most clips have this, and those that don't tend to let you be a bit more fast and loose with grain anyhow.
2.	Zoom to 200% to 400% on the solid color area, and create a Region of Interest around it. Set the Work Area to the 10 or 20 frames with little or no motion.
3.	Add a solid that is small enough to occupy part of the Region of Interest. Apply a Ramp effect to the solid, and use the eyedropper tools to select the darkest and lightest pixels in the solid color area of the clip. The lack of grain detail in the foreground gradient should be clearly apparent (Figure 9.27). Figure 9.27. Inserting a small solid with a Ramp effect, and then using the eyedropper tools in Ramp to sample the brightest and darkest areas of the background will give you a much clearer idea of how good a grain match you're getting once you apply the Match Grain or Add Grain effect.
4.	Apply the Match Grain effect to the foreground solid. Choose the source footage layer in the Noise Source Layer pull-down. As soon as the effect finishes rendering a sample frame, you have a basis from which to begin fine-tuning. You can RAM preview at this point to see how close a match you have. In most cases, you won't be done yet.
5.	Twirl down the Tweaking controls for Match Grain, and then twirl down Channel Intensities and Channel Size. You can save yourself a lot of time by doing most of your work here, channel by channel.
6.	Activate the red channel only in the Composition window (Alt+1/Option+1) and adjust the Red Intensity and Red Size values to match the foreground and background (Figure 9.28). Repeat this process for the green and blue channels (Alt+2/Option+2 and Alt+3/Option+3). RAM preview the result. Figure 9.28. As with color matching, channel by channel is the way to go to refine your grain match. Match Grain is the best type of automated plug-in. It is really only semi-automated, giving you easy access to control and improve upon its result.
7.	Feel free to adjust the overall Intensity, Size, or Softness controls under Tweaking according to what you see in the RAM preview. You may also find it necessary to reduce Saturation under Color, particularly if your source is film rather than video.

In most cases, this is all you need to do for a result that will work. You can copy the effect and paste it to any foreground layers that need grain. If the foreground layer already contains noise or grain, you may need to adjust the Compensate for Existing Noise percentage for that layer.

Obviously, I left a lot of other controls alone (Figure 9.29); the Application category, for example, contains controls for how the grain is blended and how it affects shadows, midtones, and highlights individually. Typically these are overkill, as are the Sampling and Animation controls, but how far you go in matching grain before your eye is satisfied is, of course, up to you. This is one more case in which slamming the result can help ascertain its effectiveness (Figure 9.30).

Figure 9.29. Match Grain clearly has a lot of controls, and yet the ones you will use most often are in the highlighted region, mostly under the Tweaking and Color categories. It is best to go top to bottom, first adjusting overall Intensity, Size, and Softness, then refining the individual Channel Intensities and Channel Size (as in Figure 9.28).

Figure 9.30. How good a match? As always, slam the resultwith an adjustment layer containing a Levels effect with its Gamma and Output Black raisedand behold. Adjust Match Grain as needed. Not bad in this case.

Grain Removal

Using Noise for Grain

Prior to the addition of Add Grain and Match Grain to version 6.5 Professional, the typical way to generate grain was to use the Noise effect. The main advantage of Noise effect over Match Grain is that it renders 20 times faster. The downsides are that After Effects doesn't make it easy for you to separate noise channel by channel, nor can you hold out noise to foreground elements only while viewing the background. Scaling it requires a separate effect. But adding grain is one of those areas where you can often get away with less than 100% accuracy.

You can use three solid layers, with three effects applied to each layer: Shift Channels, Noise, and Transform. You use Shift Channels to set each solid to red, green, or blue, respectively, set their Blending Modes to Add, and set their Opacity very low. Next, set the amount of noise and scale it in the Transform effect.

If the grain is meant to affect a set of foreground layers only, hold them out from the background plate either using pre-composing or track mattes. If this sounds complicated, it is, which is why Match Grain is the better choice if it's available.

Removing grain, or sharpening an image in general, is a completely different process from adding grain. Typically on a production that has been well shot, however, you'll rarely have a reason to reach for the Remove Grain tool.

If you do, your reason will probably be unique to your particular footage. In such cases, you may very well find that Remove Grain at the default settings gives you a satisfactory result. If not, check into the Fine Tuning and Unsharp Mask settings to adjust it.

Remove Grain is often most useful sort of "behind the scenes," in other words not across the whole final shot (Figure 9.31), or in combination with other effects. If you're using Remove Grain to improve the likelihood of a clean blue-screen or green-screen key, apply the resulting matte back to your source footage as an alpha track matte. That way you get the best of both worlds: a clean matte channel and realistic grain on the source color layer.

Figure 9.31. Although it may look nice for a still figure in a book, the results of Remove Grain applied to the whole shot at the default settings are rarely what you want. The solid with the Ramp effect now matches quite well with no grain applied to it whatsoever, but in full motion the grain-reduced shot looks a bit strange and retains a certain soft lumpiness. Still, it's a powerful tool if you need it, and you can certainly dial it back.

When to Employ Grain Strategies

Chapter 10, "Expressions," offers a unique and highly effective strategy for removing extreme amounts of grain from a locked-off shot using expressions.

The most obvious time to add grain to a layer is in cases where the layer is computer-generated or a still image. In either case, it will lack any of the moving grain that you would find in film or video footage. Pixar does not add grain to its final shots because they are internally consistent; none of the shots originated on film or video, so they all lack appreciable grain. As soon as your shot has to match anything that came from a camera, and particularly if it's going to be projected, you need to manage grain.

You also may have to add grain to an element if it has blur applied to it. Blurry source shots can still contain quite a bit of grain over the blur because the grain is an artifact of the medium recording the image, not the subject itself. Elements that are scaled down in After Effects also have the grain scaled down, another case in which it may be necessary to restore it.

Blue-screen footage that has been keyed may also need grain added. Remember, the blue channel contains more grain, typically, than red or green. Suppressing the blue channel in a color key operation, therefore, can also suppress grain too much for it to match other footage.

Other compositing operations can enhance the grain of an element. Sharpening, if it is not done via the Remove Grain tool, can strongly emphasize grain contrast in an element, typically in a not-so-desirable manner. Sharpening also brings out any nasty compression artifacts that come with footage that uses JPEG-type compression, such as miniDV video.

Lack of grain, however, is one of the big dead giveaways of a poorly composited shot. It is worth the effort to match the correct amount of grain into your shot even if the result isn't apparent as you preview it on your monitor. Especially when outputting to film, but even with video, elements with the wrong amount of grain stand out unpleasantly and fail to look natural.