Pre Multiplied Key - Blackmagicdesign ATEM Live Installation And Operation Manual

Pre multiplied Key

A modern graphics system or character generator that offers fill and key outputs will most likely
provide what is known as a pre-multiplied or shaped key. A pre-multiplied key is a special
combination of the fill and key signal where the fill signal has been pre-multiplied with the key
signal over a black background. Photoshop generated images that contain an alpha channel are
pre-multiplied.
ATEM switchers have an auto key adjustment for pre-multiplied keys so that when the pre-
multiplied key setting is enabled, the clip and gain parameters are automatically set by
the system.
When using a Photoshop generated image, generate graphics over a black background layer
and place all content on the upper layers. Add an alpha channel in your Photoshop document
that the ATEM can use for blending the graphic over the live video. Then, when saved as a
Targa image file, or downloaded direct to the media pool, you can select pre-multiplied in the
keyer and you should have a great key!
Photoshop documents are pre-multiplied by nature, so you should always use the pre-
multiplied settings on the ATEM switcher when keying them.
Performing an Upstream Luma/Linear Key
Since luma and linear keys use the same parameters, they are set up on the software control
panel and advanced panel using a common menu, called the luma key menu. What defines the
key as being either luma or linear is in the selection of fill and key sources. In a luma key, fill and
key sources are the same. For a linear key, fill and key sources are different.
The Upstream Key palette has a menu for resetting parameters at the top of each tab.
Select the sections you wish to reset from the menu.
Luma Key Settings
Keying using ATEM Switchers 135