Keying> Correction group

Once you have generated your matte, the Correction group will tweak it to a great composite. These tools perform most of the same functions as the Fine Tune sliders, but with a greater degree of automation.

Whether to use the Correction or Fine Tuning tools largely depends on the particular keying situation you are facing. Once you get the hang of using all of the tools available to you in Primatte Keyer you will know when to use Correction and when to use Fine Tuning. Generally speaking, these controls should be used before attempting a Fine Tuning operation, but this is not a requirement. There are four main components to the Correction tools.

Correct> Spill Sponge button

The Spill Sponge tool is used, as its name suggests, to 'sponge away' color spill from the foreground area. Unlike the Spill control in the Fine Tuning tool, the Spill Sponge does not have any sliders or other controls. When removing spill from your foreground objects it is a good idea to try using the Spill Sponge first, then follow up with a Fine Tuning operation if necessary.

Sample areas of spill with the Spill Sponge and they disappear like magic. If you sample too much of a non-spill area your image will take on a magenta or yellow tint. In this case, simply undo the sample stroke and try again using the Spill Minus tool (found in the Refinement group) which gives you more control over the spill removal.

At left, the woman's cheek has some blue spill. At right, sample it using the Spill Sponge and the spill disappears.

Correct> Matte Sponge button

Retains spill suppression while bringing back pixels that were turned transparent. The Matte Sponge is used after the keying operation is mostly completed and some transparent pixels have appeared in the foreground area; these pixels can be seen in the matte as gray areas in the 100% foreground region. With the Matte Sponge selected and the Matte View visible, click on the unwanted gray or black pixels and they will become white (100% foreground) while still retaining the spill suppression information for that color region.

NOTE: This same operation can be achieved manually by using the Fine Tune sliders. Sample the offending pixels and move the Transparency slider to a lower value.

Correct> Restore Detail button

Brings back detail in areas that have been fully keyed out by the sampling process. Black background pixels (100% transparent) sampled in the image window become translucent. Restore Detail is useful for restoring lost detail in semi-transparent objects like hair, clothing or smoke.

NOTE: This same operation can be achieved manually by using the Fine Tune sliders. Sample the offending pixels and move the Detail slider to a higher value.

At left, much of the edge detail and the 'fullness' of the center of the smoke column has been keyed out.
At right, sampling the transparent edge pixels brings them back into visibility, which improves the overall detail and realism of the keyed smoke.

Correct> Decrease Opacity button

Makes opaque foreground areas slightly less opaque. This tool is useful for the subtle tuning of foreground objects which are otherwise entirely obscured, like smoke, clouds, or other wispy or semi-transparent items.

Defocus Matte

Determines the defocusing level being applied to the matte. It blurs the matte in both the inward and outward direction and is useful when you end up with a 'hard edged' foreground object and results in softer, cleaner edges on the foreground objects.

You will probably never need to use a very high Defocus. Try using values between 0.5 and 3.0 to begin with.

When using this tool, some noise may appear around the edges of the foreground object. To avoid this problem, enable the Inward Defocus checkbox. Also when using this feature, foreground details and smoothness of motion blur may be adversely affected.

At left, the original matte. At right, the same matte with a 15 pixel defocus applied.

Inward Defocus checkbox

This checkbox works in conjunction with Defocus Matte. When this is not enabled, the blur will be applied in both the inward and outward directions from the edge of the foreground object as in the large image above. This can sometimes cause a 'halo of light' to appear around the foreground objects. When this checkbox is enabled, the defocus operation will start at the outside matte edge and blur only in an inwards direction and eliminates that 'halo' artifact

At left, the original matte. At right, the same matte with a 15 pixel Inward Defocus.

Shrink Matte

Chokes in the foreground areas of the matte by lowering the brightness levels of the pixels that make up the matte edge. You can use this control to get rid of unwanted edge artifacts on troublesome images.

Shrink Matte is a gamma correction, identical to the input gamma value in the standard Levels filter in After Effects. A value of 99 translates into a reduction of 50% in the gray levels. Why 50%? Because unlike the input gamma value in the AE Levels filter, which defaults to the middle and allows you to push values towards either white or black, the Shrink Matte function starts in the middle but only permits values to be pushed to black.

Let’s put this in simpler terms. When using the Shrink Matte filter, pixels that are 100% black will stay black and pixels that are 100% white will stay white. This correction affects only pixels that range between pure black and pure white. The more you increase the value of the slider, the more those pixels will be pushed towards black. The pixels that were originally closer to black will become black first as the slider value increases.

The darkest pixels are pushed towards black while the brighter pixels are left unchanged. Decreasing the brightness levels will decrease the perceived transition between the foreground and background, and can make the matte edge rough. If this happens, you can use Defocus Matte to soften the matte and lessen the effect of the harsh edges.

At left, a keyed matte with a large degree of semi-transparent detail. The darkest, most transparent pixels are in the wispy strands of hair poking out to the left.
At right, the matte with the Shrink Matte at 40, which equals a 20% reduction in the luminance values of the edge pixels.

Edge Color Replace pop-up

Lets you re-color the edges of the foreground area. The menu gives you three color replacement options.

- Complement: The default spill replacement mode. This uses the complement of the backing screen color to replace the spill. Essentially Primatte finds the matte edge, then uses the color of the corresponding pixels in the background element. This spill replacement mode is best used when maximum detail must be retained.
- Color: Lets you select a solid color to be used in replacing spill. It is useful when the foreground object is white and replacing spill with the complement color of the backing screen introduces strange colors or artifacting. The Color mode works in conjunction with the Replace Color button. The default replacement color is a 50% gray value (R:128 G:128 B:128).
- Defocus: Uses a defocused copy of the background image to determine the spill replacement colors. Replacement colors are selected from an area on the blurred background image that corresponds to the selected area on the foreground image. This mode works well on diffuse transparent objects like glass. For a translucent candelabra in the images below, you can see the results using the Complement and Color replacement methods and the more natural results you would get using the Defocus method.

Left to right, the original object, the spilled composite, Complement option, Color (yellow) option, Defocus option.

Replacement Color

Works with Color mode of Edge Color Replace. To change the solid replacement color, click the Replacement Color swatch to select a color value, or select a color with the eyedropper.

This mode is problematic if the foreground object has multiple colors. For those situations, try the Defocus mode.

BG Defocus Layer pop-up

Works with Defocus mode of Edge Color Replace. Selects the background layer to defocus. It will display all of the layers in the composition and you must choose the one that will give you the best results. That is usually the layer directly below the foreground object.