Blackmagic Design SWATEMTVSTC/HD08ISO User Manual

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Chroma Key

Chroma key is commonly used for weather broadcasts, where the meteorologist appears to be

standing in front of a large map. In the studio the presenter is actually standing in front of a blue

or green background. In a chroma key two images are combined using a special technique and

a color from one image is removed, revealing another image behind it. This technique is also

referred to as color keying, color-separation overlay, green screen, or blue screen.

A very common use for chroma keys for backgrounds is computer generated graphics. It’s

simple to connect an external computer to your ATEM switcher using the HDMI output of the

computer or a video card such as the Blackmagic Design DeckLink or Intensity range and

then play back video clips to your ATEM switcher. If you render a green background on your

animations, you can then key this green to create fast and clean animations of any length.

Keying is easy as the green is computer generated so it’s a very flat color that’s easy to key.

Background Fill Key Mask Combined Output

Combining a background with a fill and chroma key/cut

Background

A full screen image; in the case of a chroma key it is often a weather map.

Fill

The image you plan to display on top of your background video. In the case of a chroma key,

this is video of the meteorologist in front of the green screen.

Key/Cut

In the case of a chroma key the key/cut signal is generated from the fill signal.

Performing an Advanced Chroma Key

Your ATEM switcher features advanced chroma keying, with more detailed chroma sampling

and adjustment options. These controls help you achieve the best key, improving the blend of

foreground and background so you can create a more convincing visual effect.

To set up a chroma key on upstream keyer 1 on ATEM Television Studio HD8:

1 Press the ‘key 1’ button to enable keyer 1 on the preview output. This automatically selects

the keyers menu on the system control LCD, but you can also press the ‘keyers’ button to

enter the menu directly.

2 Select the ‘chroma’ key type using the corresponding ‘key type’ control knob.

3 Select your fill source by turning the corresponding LCD control knob. Typically, this source

would be from a camera facing a presenter in front of a green screen, or a graphic loaded in

a media player. You can also select a fill source by pressing the corresponding button in the

source select bus.

4 Use the ‘right’ arrow buttons to access the chroma adjustments screen.

5 Click the ‘sample chroma’ button.

109Keying using ATEM Switchers

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Blackmagic Design SWATEMTVSTC/HD08ISO ATEM Television Studio HD8 ISO