14: Chroma Key

Overview

Paint comes with a built-in chroma keyer. There are two types for keyers, Adaptive and Gauss. The type of the keyer can be set in the Config editor, User Interface tab.

Adaptive

The Adaptive keyer is only used in a Paint Live configuration (although it can use the Gauss keyer too). Using the Adaptive keyer in recorded cameras is not supported.

The Adaptive keyer is fully automatic. An initial key is computed when the application is started. Then the algorithm maintains and adapts the key as the match continues and the light conditions change.

You can check the current key at any time. Just open the Chroma Key Editor and choose Mask or Preview mode. All other functions in the editor will be disabled.

Gauss (manual)

This type of keyer is fully user-operated. Open the Chroma Key Editor and pick the colors you want to be part of the key.

Chroma Key Editor

The editor is accessible from Administration menu on the Clear button. Open the popup using a right mouse button click and select “Edit Chromakey”. Dialog with chroma key controls appears:

The dialog contains several buttons:

• Reset: Removes the current chroma key.
• Undo: Restores to the state before the very last pick in the preview.
• Original video: No chroma key visualization. In this option you see the state before activation of the chroma key dialog. If there are any drawings, they are visible. This is useful to see the graphics with current key.
• Mask: Shows only the mask. The mask is black-and-white image. When the key is correctly set, you will see a white pitch with sharp black pitch lines and outlines of the players.
• Preview: This is a mix of mask and the original video. You can see the input video and preview of the mask.

The mouse cursor changes to a square defining the area, from which the chroma key is computed.

Select the area in the video to be keyed. Repeat this step until the mask fits. The mask should look like:

Adjust the size of the pick area

Use the Pick size slider in the Chroma key dialog to adjust the size of the pick area. Alternatively you can use CTRL + mouse wheel to change picker size.

Automatic refinement

Each time you create a new drawing, a new sample of the chroma key is taken and added to the current key. Only samples that don't cause significant changes to current key are taken into account. All refinements are discarded:

• When the Chroma key editor is opened
• When the Clear button is pressed

Automatic key refinement can be enabled/disabled by check box in the Chroma key editor. The value is saved and used next time the application is launched.

Automatic refinement is available only when Live input is selected.

Automatic (adaptive) Keyer

If Adaptive keyer has been enabled in the Config Editor, the Chromakey editor will only show the key that has been placed automatically, it is not possible for you to add or remove Chroma when Adaptive keyer is enabled.

Chroma key stored in a clip

Each clip can have its own chroma key, which will be loaded when the clip is selected and unloaded when the clip is deselected. The stored key can be deleted or redefined later.

When a new clip is created, the current chroma key setting from Live cameras is copied and saved with the clip. Clips with no stored key inherit their key from the Live input. A stored key can be redefined. Just select the clip, open the chroma key editor and redefine the key.

A chroma key stored in a clip can be deleted. Select the clip, open the chroma key editor and press 'Clear'. From then, chroma key for the clip is inherited from the Live input again.

Tools using chroma keyer

Most tools support the chroma keyer. You can change the keyer settings in the popup invoked for a tool.