Field and Frame Rendering

You can render interlaced or progressive frames. If you select the Interlaced option in the Rendering box, the Keyer combines the two fields and renders each frame. If you select the Interlaced option, the Keyer renders each field separately. Use the Interlaced option if the two fields in the image are not properly aligned and if the filters you are using are not applied to the proper pixels.

A third option, As Front (or As Input if you have accessed the Keyer from Action), renders using the mode that corresponds to the source clip (or the scan mode attribute of the Action media).

Punch Mattes Options

When you pull a key, a matte is created for both the front and back images. If you modify the luminance curves for both mattes, you can specify whether both mattes are used in the generation of the composite clip, or only the back matte. To do this, use the Punch Mattes options:

• Punch F & B uses both the front and back mattes. This is appropriate for clips that do not contain a pre-multiplied alpha channel, such as clips originating from CG applications.
• Punch Back uses the back matte only. The luminance curve for the front matte is ignored, resulting in an additive key. Use Punch Back when you are using a CG clip with a pre-multiplied alpha channel in which the area to be keyed out is black. On these clips the front matte has been previously applied to the front image. If the front matte is applied a second time, an unwanted black fringe may result along the edges of the matte subject.

When the front matte is not used, the entire front image is used, and the curves calculation maps all the black areas of the front clip as transparent. For complete details about the Blending menu, see Using the Luminance Curves.

Displaying the Key while Processing

In the Setup menu, enable the Display Process button to view the composite clip as it is processed. When this button is disabled, the image window remains at frame 1 during processing. You can reduce processing time by disabling Display Process.

Slip Synching

You can offset the front, back, and key-in clips using the Slip fields in the Setup menu. You can delay the start of a clip or start anywhere in a clip; this way you do not have to exit the Keyer to edit the length or sequence of a clip.