Mattes and Keying

While a "Mask" usually refers to a shape you manually draw (like a polygon), a Matte usually refers to transparency information generated mathematically from the image itself.

The most common example of generating a matte is Chroma Keying (removing a green screen).

Generating a Matte (Green Screen Keying)

When you key out a green screen, the software analyzes the color green and changes its Alpha channel to 0.0. This generates a black-and-white Matte, where white represents opaque areas (the actor) and black represents transparent areas (the green screen).

To pull a professional key in Oraphim:

1. Ensure your green screen footage is piped into a DeltaKeyer node.
2. Select the DeltaKeyer node.
3. In the Inspector, click and drag the eyedropper icon from the "Background Color" swatch directly onto the green screen in the Viewer.
4. The green screen will vanish, revealing a checkerboard pattern (transparency).

Refining the Matte

A one-click key is rarely perfect. You must inspect the matte to fix holes and edges.

1. While selecting the DeltaKeyer, press M on your keyboard, or select "Matte" from the view mode dropdown in the top-left of the Viewer.
2. Your viewer will change from the full-color image to a high-contrast Black and White image.
   • Ensure the actor is solid, bright white (no gray holes).
   • Ensure the background is solid, pitch black (no gray static).
3. In the Inspector, navigate to the Matte tab.
4. Adjust the Threshold Low slider to crush gray static in the background into pure black.
5. Adjust the Threshold High slider to boost gray holes in the actor into pure white.
6. Once the matte is solid, switch the viewer back to the color view to check the edges.

Using External Mattes (Luma Mattes)

Sometimes you receive a matte from an external 3D program. For example, a 3D artist might render a spaceship as an RGB color pass, and provide a separate black-and-white video file representing the matte.

To use an external matte:

1. Bring the Color file and the Black-and-White file into the node graph using two MediaIn nodes.
2. Add a Channel Booleans node to the Color pipe.
3. Connect the Black-and-White file into the Foreground (Green) input of the Channel Booleans node.
4. In the Inspector for the Channel Booleans, set:
   • Operation: Copy
   • To Alpha: Foreground Luminance
5. The Channel Booleans node has now successfully injected the black-and-white data into the alpha channel of the color image, cutting out the spaceship perfectly.

Use Mattes in a production project

1. Open Composition workspace and select the intended layer, mask, matte, effect, or composition graph item.
2. Establish the correct input state first—timing, media link, layer/node enable state, project settings, or source selection as relevant.
3. Apply or adjust Mattes with one clear goal. Change the smallest set of controls needed to reach that goal so the result remains understandable and reversible.
4. Review the complete affected range in context. Scrub difficult frames and also play at normal speed when motion or audio is involved.
5. Save a named milestone before moving into another major operation, especially after graph changes, tracking, AI processing, relinking, simulation, or delivery setup.

Practical guidance

A matte is data that controls visibility or processing. Inspect the matte directly, then inspect the composite for edge contamination, holes, chatter, and premultiplication problems.

A useful test is a short 5–10 second section containing both an easy case and a difficult case for this feature. Tune against the difficult moment without breaking the easy one. If two approaches are plausible, duplicate/version the project state and compare them rather than stacking both together blindly.

Verify the result

• Scrub the shot, inspect edges and timing, then render a short review range.
• Toggle/bypass the operation where possible and make sure the change you intended is actually responsible for the result.
• Check selection, visibility/mute/solo state, node connections, track locks, range, and source identity when the result appears missing.
• Save and reopen before treating a complex setup as reusable.
• If this feature changes final pixels or audio, render a short review and inspect the file outside Oraphim.

Related guides

• Adjustment Layers
• Effects
• Compositing Overview
• Layers