Alpha Controls group

The Alpha Control group lets you make adjustments to the Primatte matte to achieve a superior composite. The interface is comprised of two sections, Gamma and Alpha Cleaner.

Gamma group

The Gamma group lightens, darkens or adjusts the gamma curve of the matte using a standard Levels interface. The controls in Gamma are identical to those found in the standard After Effects Levels filter.

Histogram

Displays the amount of pixels with each luminance value in the matte. The Matte mode in the View pop-up is a helpful visualization tool when working with the Histogram features.

Because this chart is depicting our matte, a monochromatic alpha channel, the transparent pixels are represented as black at the left end of the grayscale chart. The opaque pixels that make up our foreground image are represented as the white on the right of the grayscale.

Numerics> Input Black, Input White

Semi-transparent pixels are found in the middle range of the Histogram. Raising the Input Black Numeric makes the semi-transparent pixels more transparent by crushing up the darkest end of the scale.

Conversely, bringing down the Input White Numerical value lowers the threshold to accept more semi-transparent 'gray' pixels in our matte as fully opaque whites.

Numerics> Gamma

The Gamma changes the distribution of the values in the matte by altering the exponential power curve when you change the numerical control. The Gamma strength is divided by its number, which means a higher numerical value will display less strength.

Gamma affects the contrast of the matte on the grayscale. When the control is at 0.0, the Matte will display the highest level of contrast between black and white, making the semi transparent pixels 'black', or totally transparent.

Changing the Gamma control to a higher number will show more of the variance within the grayscale of the matte, leading to more semi-transparent pixels.

Numerics> Output Black, Output White

Set Output Black to its maximum of 100% to raise the transparent pixels in the luminance scale up to opaque, revealing the RGB straight channel and no transparencies.

Set Output White below 100% to make the opaque pixels in the matte transparent. A value of 0% makes the pixels completely invisible.

Alpha Cleaner group

A big part of getting a successful key involves having good source footage. Unfortunately, this doesn't always happen. Quite often your source image has wrinkles, discoloration, uneven lighting or other problems, all of which can create a problem key. Primatte is able to handle many of these problems but you will still run into issues. Alpha Cleaner is designed to help in these situations, and you can read a great example in Keying Difficult Footage.

Alpha Cleaner zaps grain or noise, fills holes in the foreground matte, and fixes other problems that would otherwise require a separate matte touch-up in a paint program. Alpha Cleaner works by applying a clean-up pass to your matte and identifying dirt and other artifacts based upon a combination of values like their size, alpha level, and proximity to the principle element in your matte.

There are six Threshold controls for the threshold values for controlling the operations of Alpha Cleaner. These are broken into three pairs of operations, with each pair treating specks or holes or both.

Alpha Cleaner> Cleaning Mode pop-up

Designates which cleaning operation you want Alpha Cleaner to perform.

- None: No cleaning detection is applied.
- Remove Specks: Removes specks and noise from the background. (White noise in black areas.)
- Plug Holes: Removes holes from the foreground object. (Black holes in white areas.)
- Both: Lets you remove both Remove Specks and Plug Holes in one pass. This mode has the same effect as making two passes, but is more efficient since some internal buffers can be reused, speeding up the render process.

Alpha Cleaner> Size Threshold

Determines which pixels will be removed based upon their proximity to each noise or chatter area. The value controls the size of the clean-up area, with 100% representing the largest area of cleanup (roughly 1/5 of the image size) and 0% representing no cleanup. Increase this value to get rid of larger areas of noise, such as larger specks in the black areas or larger holes in the white areas. Noise outside of the Threshold range is left unaffected.

Alpha Cleaner> Level or Alpha Threshold

Determines which pixels will be removed based upon the pixel’s luminance value. Noise pixels with a luminance value below the Level/Alpha Threshold will be set to 0 (black) or 100 (white), depending on whether you are removing specks or filling holes. The higher the Level/Alpha Threshold value, the more pixels will be set to either solid white or solid black.

When you look at your matte, if you have areas of your background or foreground (pixels which should be 100% black or 100% white) which appear gray, this control will allow you to remove them. However, if you have any areas of your matte that are supposed to be semi-transparent, such as hair, smoke, or motion-blurred edges, this operation will remove the transparency in these areas also. In these situations, you should first isolate the areas that need to be cleaned with a garbage matte, then using Alpha Cleaner only on those areas.

Note that only pixels within the range of the Size Threshold value will be affected by Level/Alpha Threshold.

Alpha Cleaner> Connection Threshold

Determines which pixels to remove based on their proximity to major objects in the alpha. The higher this value, the more non-essential pixels will be removed. Increase this value if you find your alpha growing 'tendrils' after cleaning.