16.01.2024 – Projection

Week 12 – Projection in Nuke

Projection is essential to create 3D patches, allowing you to seamlessly insert or remove elements in your footage post-matchmoving. The following nodes prove instrumental in executing these steps:

• Project3D (Shader): This node projects the image of a patch onto a 3D object through the camera. Generally, you won’t need to alter its settings except in specific situations.
• MergeMat (Shader): Similar to the Merge node, this is specifically designed for 3D space operations.

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Projecting on Matchmove Geometry: Freeze a frame using the FrameHold node and roto (paint) at this frame.(Ensure you choose a frame closest to the camera and clearest in the scene. Selecting a blurry frame can result in unnatural visuals.)

Freeze the frame once again to minimize unnecessary calculations of the RotoPaint node. If you haven’t performed rotopaint, there’s no need to freeze again. Freeze the camera obtained from the CameraTracker node. Connect the camera and patch using the Project3D node, and link it to the card created in the matchmove stage. Finally, merge it with the original camera.

This approach involves holding two frames, one far and one close to the camera. By projecting the same image at different distances, the result appears more natural.

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Projecting Roto: Project the plate onto a card created in the matchmove stage and connect it using the ScanlineRender node with a held frame. This stabilizes the plate, facilitating easier roto work. Project the Roto node onto the same card and connect it to the ScanlineRender node with the original camera. This process yields an alpha channel where roto work was performed.

It can be a more efficient and faster alternative to traditional roto methods.

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Projecting UV: Project the plate onto the card by adjusting the ScanlineRender node’s knob from ‘Render camera‘ to ‘UV.’ Reformat the scene to a square. After this stage, perform patchwork and set the roto’s lifetime to cover all frames. Reformat the premultiplied patch to its original ratio and texture it onto the card using the ScanlineRender node.

This technique proves helpful when dealing with plates that undergo changes in lighting.

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27.01.2024 added

LensDistortion node can be resource-intensive. It’s advisable to render it into the .exr format, ensuring an uncompressed format to preserve the quality of the original plate.

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Types of projection

• Patch Projection: The conventional approach involves setting the texture for replacement and a camera fixed on a specific frame. Project these elements onto the scene.

• Nested Projection: This technique involves a projection within another projection, as exemplified in the case of a brick wall patch.

• Coverage Projection: Ideal for sky projection, it seamlessly projects multiple images onto a sphere, creating a natural sky or environment.

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Projection Artefacts

• Smearing: Occurs when an image smears or streaks across the glancing angle of an object.
• Doubling: Manifests when a matte painting projects onto multiple geometries.
• Resolution: Arises when the painting lacks sufficient resolution due to the camera getting too close.

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ModelBuilder node (NukeX Only): Connect the source (plate) and camera (cam) to the ModelBuilder node.
Before creating shapes, ensure the camera is set in the viewer and locked(the camera icon turned red.)
In the ‘Shape Defaults’ tab, create shapes. Right-click to change modes (align, edit / edge select, vertex select, etc.).
Select an edge, right-click, and choose extrude/bevel/subdivide (similar to Maya operations).
To export data, select your object in the Scene knob, go to Export – Selected geometry – Bake.