Keying using ATEM Switchers
Preview Transition
ATEM switchers have a powerful feature which allows you to review and adjust a transition
on the preview output. The preview transition feature can be performed using the 'prev trans'
button in ATEM Software Control's transitions block, and lets you verify a transition before
actually performing it on air.
To preview a transition:
1 On the preview bus, select the video source that you want on the program output.
2 Select the transition type using the transition type buttons in ATEM Software Control,
or on your switcher's built in control panel.
3 Press the PREV TRANS button to put the switcher into preview transition mode.
The PREV TRANS button will illuminate red and the preview output will change so that it
is a copy of the program output.
4 Manually move the fader bar from one end to the other to preview the transition on the
preview output. The program output will remain unchanged.
5 Press the PREV TRANS button or return the fader bar to its starting position to
turn off preview transition mode. Returning the fader bar to its starting position will
automatically disable preview transition mode and turn off the red light on the PREV
TRANS button. Moving the fader bar after the light is off will take the transition on the
program output.
Keying using ATEM Switchers
Keyers are a powerful production tool that allow the arrangement of visual elements from
different sources on the same video image.
To do this, multiple layers of video or graphics are stacked on top of the background video.
Altering the transparency of various parts of these layers allows the background layer to be
visible. This process is called keying. Various techniques are used to create this selective
transparency and these correspond to the different types of keyers available on your switcher.
The following section explains luma and linear keyers, which are available either upstream or
downstream, and chroma, pattern and DVE keys, which are upstream keyers.
Understanding Keying
A key requires two video sources; the fill signal and the key or cut signal. The fill signal contains
a video image which is to be stacked on top of the background, while the cut signal is used to
select regions of the fill signal to be made transparent. The fill and cut signals can be selected
from any of the switcher’s external inputs or internal sources, allowing both still and moving
images to be used as fill or cut sources.
Fill and cut signals are selected on the software control panel from drop down lists in the
upstream and downstream key palettes. In your switcher’s LCD menu, you can select fill and cut
signals in the upstream or downstream key menus.
There are two types of keyers used in your switcher; upstream keyers and downstream keyers.
One upstream keyer, also known as an effects keyer, plus two downstream keyers are available
via the switcher's control panel and LCD menu, or via ATEM Software Control. The upstream
keyer can be set up as a luma, linear, pre-multiplied, chroma, pattern or DVE key. Two
downstream keyers are available in the dedicated DSK block. Each downstream keyer can be
set up as a luma or linear key.
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