Build a composite in the Compositor

Open the Compositor

Choose Compositor on Lumina's editing rail or in the Tools panel, or open /app#compositor directly. A link like /app#compositor=green-screen opens it with a preset. The Compositor runs on your device in a background worker; your images are not uploaded.

The window has three columns. On the left are Images, Nodes, Canvas and Problems. In the middle you see the preview with a histogram, the status line and the Graph diagram. On the right is Node settings for the selected node and Export.

Load images and a preset

Under Images there are three slots: Main image, Background image and Extra image. When a photo is open in the editor, it becomes the main image automatically; Use the edited photo takes it again after you changed it. Load image reads a PNG, JPEG or WebP file into a slot, and Remove empties it. Large images are scaled to about 4 megapixels for the Compositor.

Pick a Preset in the toolbar — Green-screen composite, Product shot on a gradient, Colour grade with a LUT or Sky replacement with a luma key — and choose Load preset. Preset with samples also loads synthetic sample images made for that preset, so you can see it working before you use your own photos.

Read and edit the node list

Every row in Nodes is one node: its category (for example Keying or Masks), its name and id, and after a run its size or mask coverage. Click a row, or use the keyboard:

• Up and Down arrows move between nodes.
• Alt+Up and Alt+Down move the focused node in the list. The order is only for you; the picture follows the connections.
• Delete removes the node. Where possible its input is connected straight through to the next node.

The ↑, ↓ and × buttons next to each row do the same with the mouse. Undo and Redo in the toolbar (or Ctrl+Z and Ctrl+Y) step through your changes.

Add and connect nodes

Select the node after which the new one should go, pick a type in Node type to add and choose Add node. A new filter or colour node is inserted into the existing link, so the picture keeps flowing.

In Node settings, the Inputs box has one menu per input, such as Image input, Foreground (A), Background (B) or Mix mask. Each menu lists only nodes that fit — an image input never offers a mask, and nodes that would create a loop are left out. The Settings box below holds the node's parameters. Node name gives the node your own label.

If something is wrong, Problems says so in a full sentence, for example that a node needs a connection or that two nodes form a cycle. Choose a problem to jump to the node.

Key, grade and mask

• Chroma key removes a green or blue screen. Set Screen colour, then Clip black and Clip white to clean the matte. Spill suppression removes green light on the subject.
• LUT (.cube) grades with a 1D or 3D LUT. Choose Load .cube file or Use the warm fade sample LUT, and lower Strength to soften the look.
• Shape mask, Mask from image, Combine masks, Invert mask, Grow or shrink mask and Blur mask build masks. Connect a mask to Limit to mask of a colour node to grade only part of the picture.
• Merge puts the Foreground (A) onto the Background (B) with an Operator such as A over B and a Blend mode such as Multiply or Soft light.

Preview, check and export

Show switches the preview between Output and Selected node; Preview this node in Node settings does the same. The histogram below the preview shows the red, green, blue and luma distribution and how many pixels are transparent. The status line reports how many nodes were evaluated and how many came from the cache — only nodes after your change are recomputed.

Use Download PNG, Download JPEG or Download WebP to save the result; JPEG is flattened on white. Open in photo editor continues with the composite in Lumina.

Reuse the graph

Save graph downloads a .lumina-comp.json file, and Open graph reads one back. Copy graph JSON puts the graph on the clipboard: paste it into the lumina-compositor tool to run it through the API or MCP, or into the Composite graph (Lumina) step of a Reelcraft recipe to apply it to many images or to short clips. Clips come back as MP4 (opaque) or, if the graph's output is transparent and you choose WebM VP9 with transparency or ProRes 4444 MOV with transparency, with their alpha channel kept. The format is described in /static/apps/lumina/compositor.schema.json.