Keying Using Atem Mini; Understanding Keying; Luma Key - Blackmagic Design ATEM Mini Manuel D'installation Et D'utilisation

Keying using ATEM Mini

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.

Luma Key

A luma key or self key consists of one video source containing the video image that will be
stacked on top of the background. All of the black areas defined by the luminance in the video
signal will be made transparent so that the background can be revealed underneath. Since only
one image is used to define the areas to be cut out, a luma key uses the same signal for the fill
and key. The following images are an example of what background, luma key signals and the
resulting combined image might look like.
Combining a background and fill/key in a luma key
Background
A full screen image, often a camera source.
Fill
The graphic you plan to display on top of your background video. Notice that the final
composition does not retain any black from the graphic because all of the black parts have
been cut out of the image.
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