Ultimatte-9 Operations Manual
March 1, 2000
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VI.
UNDERSTANDING BASIC CONTROLS
To generate a composite image using the Ultimatte-9 requires some understanding of the way an
Ultimatte-9 matte signal is generated and how it functions in compositing the FG and BG images. It is
also important to have some understanding of FG processing methods, including Flare Suppression
techniques.
1. Matte Density
The matte signal, in its most general form, is a function of the difference in level between the main
backing color and the higher of the other two colors in the FG signal. With a blue backing, normally the
green content is higher than the red. For illustration purposes, one can start by thinking of the matte
signal in the backing area as the difference between blue and green. With an Ultimatte Blue backing, the
separation between the blue and the green at peak intensity of the backing should be around 40 video
units (viewed on an RGB waveform monitor).
The object of the circuits which create the matte signal from this difference signal is to generate a signal
which will be 100 units at peak intensity of the backing where the BG is to be fully turned on, and 0 units
wherever the FG is supposed to be completely opaque. In other words, the matte signal, when viewed on
a picture monitor, will be a silhouette of the FG subject against a white field.
The most important step in generating the matte signal is controlling the density of the matte. The Matte
Density setting determines what level of separation will correspond to the point at which the FG is
opaque. The default setting for the Matte Density is such that a neutral area in the FG will be opaque, i.e.
when both green and red are equal to blue.
The effect of the Matte Density control is easily seen by activating the Matte button in the View Menu to
view the matte signal on a video monitor. As Matte Density is decreased, black areas of the matte
corresponding to opaque FG objects will become gray in the matte signal. Increasing the Matte Density
above its default setting causes pastel blue areas of the FG to become black in the matte signal.
Advancing the Matte Density control too far will cause dark edges on the FG subject in the composite
image. Any edge on the FG subject is a transition area during which the image consists of a mix of FG
subject and backing, and the composite image should consist of a mix of the FG subject and the BG
scene.
The object in setting the Matte Density is to keep it as low as possible in order to prevent darkening of the
edges. Keeping the Matte Density setting as low as possible is achieved by setting the control right at the
threshold where the FG becomes opaque. In addition, there are three controls, which can help in setting
the density of the matte properly: the Black Gloss control, the Green Density control, and the Red Density
control (for blue backing).
2. Black Gloss
If there is a black glossy object in the FG that is reflecting color from the backing, the camera may see it
as a dark area of the backing, and no amount of Matte Density adjustment will make it possible to
distinguish it from the backing. The Black Gloss control introduces a negative offset to the main backing
color channel in the matte generation circuitry so that the difference between this main channel and the
other two channels will be zero, thus interpreting the object as an FG object.