Chroma key

A chroma key makes a green or blue screen behind a presenter transparent, so they can stand in front of something else. Open the camera’s settings and go to its Key tab, then switch on Key this input.

The key belongs to the input, so it goes everywhere the input does:

• Inside a Composite, over a background layer: the usual way to use it.
• Over Program, as an overlay: the presenter stands in front of whatever is on air.
• On its own on Program, where it was keyed shows as black, which is rarely what you want.

Setting it up

The Setup section shows a frozen frame from the camera. Result shows it keyed over a checkerboard, and Matte shows it in black and white: white is kept, black is keyed, and grey is the edge between them. The matte is the quickest way to find holes in the presenter and green left in the background. New Frame freezes the current picture again.

1. Pick the screen’s colour. Click the screen in the frozen frame; the pointer is an eyedropper there. Or press Green or Blue for the standard chroma-key paint colours. Clicking is better: it takes the colour your camera actually sees.
2. Tolerance is how far from that colour still keys. Raise it until the whole screen goes, shadows and creases included, and stop before the presenter starts to go.
3. Softness is how wide the edge between keyed and kept is. More softness gives gentler hair and edges.
4. Spill takes the screen’s colour out of what stays: the green that reflects onto hair, shoulders and edges. It turns a green fringe grey without darkening it, and leaves skin alone.

Each slider has its own reset arrow. A shadow on the screen keys with the lit part, since the key looks at colour, not brightness.

To cut away lights, stands and the edges of the screen, crop the input in its Picture tab: the crop is the garbage matte.

With colour correction

The key works on the camera’s own picture, first. White balance, exposure, grading and a LUT from the Colour tab then apply to what the key keeps, so you can match the presenter to the background without changing the key. Reset All in the Colour tab leaves the key alone.

Switching Key this input off keeps every setting, so switching it back on brings the key back as it was.

Next

Composite inputs, to put the keyed presenter over a background.