In previous editions of this book, I dutifully explained and made recommendations about the controls below Screen Colour: Screen Gain and Balance, Despill and Alpha Bias, and Screen Pre-blur. There’s more informa- tion about these later in the chapter, but on the whole my advice is, don’t touch these. They all have one thing in common—they change the way the matte itself is
Figure 6.12 You can’t see it in a still figure, but by Alt-dragging (Opt-dragging) around the blue area of Layer view on the right, which is set to not render, a real-time update of Status view on the left allows you to discover the optimum back- ground color.
ptg calculated—and I have come to believe that manipulat-
ing them does more harm than good.
Skip down to Screen Matte and twirl down those con- trols. From here down, all of the Keylight controls are working with the matte after it has already been gener- ated. In other words, adjusting these controls is no dif- ferent than applying a separate effect after Keylight to refi ne its matte, and that’s a good thing in this case.
Raise Clip Black by dragging to the right across the value to bring it upward. Stop when you see all of the gray pixels in the background turn black in Status view.
(Even though you’ll also see some of the gray pixels around the hair—the ones you want to keep gray—
turn black as well. We’ll deal with those next.) In my attempt, I ended up with a value of 26.0, and as a rule of thumb, anything above 20 is a bit high—another rea- son to take more care with this matte than just pulling the key in one pass.
Now lower Clip White by dragging to the left across that value to bring it downward. Here you may fi nd that you have to go pretty far—like down into the 50s—in order to see all of the gray or green pixels in the torso become white. I ended up with a value of 57.0. You’ll also see some green pixels remaining around the edges of the fi gure, particularly around the wisps of hair.
The green pixels in Status view are Keylight’s signal that the color values of those pixels have changed in the keying process. Focus on the wisps of hair on the light side, and switch between Final Result and Intermediate Result in the View menu. The former suppresses that blue spill that you see in the latter to the natural hair color as part of the keying process.
Intermediate Result shows the source footage with the matte applied as an alpha channel but no alteration to the RGB pixels at all, while Final Result adds color sup- pression as a natural by-product of Keylight’s method of removing the background color. Final Result seems to be the one you want, but there’s an unfortunate side effect to watch out for: It can dramatically enhance graininess in the result. Figure 6.13 shows a before and
ptg after in which the suppression process clearly pushes
pixels to a much contrastier shade even though the source is well lit footage from the RED camera. For this reason, don’t let Keylight do your spill suppression for you.
Spill suppression will have to wait until after we’re done with this key, and at this point, we’re not even close.
Getting that shirt to key has ruined the detail in the hair and motion of the hands. Had the talent been wearing a different costume and not moved around as much, the steps taken to this point might have resulted in a completed key, but with anything more complicated—and most effects shots seem to be much more complicated—it’s now necessary to break this operation into component parts (or be painted into a corner.) Neither holes in the matte nor crunchy edges on the hair are acceptable, and right now the two are fi ghting one another (Figure 6.14).
4. This is the moment to separate the plate for multiple passes. In every case there are two basic ways to do this.
. Separate one part of the foreground from the rest with a mask or other selection. For example, in this case you could rotoscope a mask around the hair, and possibly another one around the moving hands.
. Create multiple passes of the same matte: one as a gar- bage matte (or gmatte), one as a core matte (or cmatte),
Figure 6.13 Flashing the image with the exposure control at the lower right reveals a horrific amount of grain in Final Result view of this Keylight oper- ation (left). Intermediate Result (right) omits any alteration to the source color, revealing that the original image, even flashed like this, is nicely shot, with smooth, tolerable grain.
Figure 6.14 Closing all those little gaps in the foreground will mean destroying that hair detail if this matte is attempted in one pass.
ptg In this case, we know that there are prominent holes
in the foreground, so the latter approach—to create at least a core matte so that the interior areas are isolated from the all-important edge—is the way to go.
This method of breaking down the shot would work with any software keyer, but we’re sticking with Key- light, as it is the most powerful keyer included with After Effects and this maximizes what it can do.
a.Duplicate the layer to be keyed.
At this point, our bluescreen shot has a garbage mask and an instance of Keylight applied to it. Leave these on the upper of the two layers, rename that layer “edge matte,” and turn off its visibility—we’ll deal with it later.
b.Rename the lower layer “cmatte” and refi ne the core matte (Figure 6.15).
To begin, reset Clip Black by right-clicking on that property in the Effect controls and choosing Reset.
We’re keeping our Screen Colour selection, but will now crush the matte. Switch back to Status view and lower Clip White until the torso and hair are com- pletely fi lled in with white (around 66.0 may work).
Now raise Clip Black all the way to one unit below the Clip White value (65.0 if the previous value was as specifi ed).
You now have the worst matte possible, with no edge subtlety whatsoever. What possible good is this?
Switch to Intermediate Result. Yep, horrible matte.
Now close the Keylight controls and apply the Simple Choker effect. Toggle Alpha Channel view in the Composition viewer (Alt+4/Opt+4) and take a snapshot (Shift+F5 or F6,F7, or F8 all work).
Raise the Choke Matte value into the low double digits—say, around 15.00. The matte shrinks. Press F5 to toggle back and forth with the un-choked matte, and make sure that all of the choked matte’s edges are several pixels inside that of the unchoked matte. This is important: There must be no edge pixels in the core matte that overlap with those of the edge matte.
Switch a RAM preview to Alpha Channel view (Alt+4/Opt+4) and the cache is preserved; you can watch a real-time preview of the alpha channel without re-rendering the preview.
Figure 6.15 A heavily choked source matte, turn- ing all areas of the alpha channel either white or black, makes a good core matte to sit behind the edge matte.
ptg This matte may behave better if it’s softer—for now, you
can take my word for that, since we’re not yet putting it into use. As an extra precaution, apply Channel Blur and raise Alpha Blurriness to 15.0. This provides an extra threshold between the chunky core and the fi ne edge (Figure 6.16).
c.Kill the spill.
Leaving the View on Intermediate Result is great for avoiding side effects such as enhanced graininess, but the layer almost always then requires some sort of spill suppression. More often than not, you have to do this anyway.
There’s a Spill Suppressor effect in After Effects; how great it would be if all you had to do was sample the color, change Color Accuracy from Faster to Better, leave Suppression at 100, and be done. But heck, you can crank Suppression up to 200 if you want (who knew?) and still see your talent looking green (or in this case, blue) around the gills (Figure 6.17).
You could also use the Edge Colour Correction in Keylight, but it has no effect other than in Final Result mode, and—gotcha—that’s likely to mess with your foot- age too much, remember?
Spill suppression is a big enough deal that it merits its own section below. The key (please excuse the pun) is not to simply suppress or desaturate it but in fact to bring it back around to its natural hue. For that you need an effect a lot like Hue/Saturation and the skills to use it (coming up).