Using Linear Keying
Summary
This article addresses the concept and configuration of the linear keying capability as it pertains to Spyder. This article is intended for any user with an intermediate or advanced skill level in working with Spyder and the Vista Control Suite 2005 software platform.
More Information
As of software version 2.5, Spyder can accept a two channel linear key signal. A linear key consists of two video sources, known as a cut signal and a fill signal. The fill signal contains a video image which is to be displayed on screen, while the cut signal contains a video mask which is used to select regions of the fill signal to be removed from the final display. Combining the cut and fill signals allow user defined, non-rectangular images to be displayed in Spyder's final output. Since both the cut and fill signals are video inputs, both signals can be in motion while on screen.
Spyder uses 7 bits of the green channel of the fill signal to determine the alpha value to be combined with the fill source. The 7 bit value allows each pixel to have any of 127 alpha values which can be used to generate gradiated edges on the cut signal, allowing soft edges to be generated as part of the cut signal.
Displaying a Linear Key in Spyder:
Follow the steps below to configure spyder to display an existing linear key source. Note the linear key function requires the use of two Spyder inputs when in use (any two adjacent layers can be used).
- Create a new source for the fill signal, and call this source 'Linear Fill'. In the input configuration for this source, set the 'Key Mode' property to Fill.
- Create a new source for the cut signal, and call this source 'Linear Cut'. In the input configuration for this source, set the 'Key Mode' property to Cut.
- Add layers one and two to any PixelSpace, placing the 'Linear Cut' source on layer one and the 'Linear Fill' source on layer 2. Note that when configuring layers for linear keying, the cut layer is always the first of two adjacent layers.
- Cut and fill layers must be manually positioned over each other to display the linear key effect. One simple way to accomplish this is to right-click layer 1 and select 'Copy Keyframe', and then right-click layer 2 and select 'Paste Keyframe'. Once layers one and two are positioned equally, the linear key effect will be visible.
- Learn a new command key from the screen to persist the linear key look for easy recall later.