Wiki · Autograph / Lens distortion / Compositing

Autograph lens-distortion, undistort, and redistort checklist

Published 2026-07-16 · Wiki · Lens distortion / Tracking / Workflow

A production checklist for using Autograph in a plate-based VFX workflow where footage is undistorted for tracking or compositing, then redistorted to match the photographed lens.

Why this page exists

Lens distortion is a geometric property of the photographed plate, not a look that can be approximated safely at the end. Tracking, paint, projections, CG alignment, and edge filtering can all fail when some elements are created in distorted plate space and others in an undistorted working space. Autograph supports OpenFX plug-ins, including products whose vendor pages list Autograph as a host, but each host and plug-in combination still needs a controlled round-trip test before production use.

Choose one working-space contract

• Distorted plate space: work directly over the original plate. This can be acceptable for simple 2D work, but planar tracking, camera solving, projections, and CG integration may be harder near curved edges.
• Undistorted working space: remove lens distortion first, perform tracking and compositing in rectified space, then apply the inverse distortion once at the end.
• STMap exchange: store the forward and inverse mappings as images so different applications can reproduce the same transformation. Confirm channel convention, direction, resolution, and data treatment.
• Do not mix these contracts inside one shot without naming the space of every plate, render, matte, and track.

Before undistorting

1. Preserve the original plate unchanged and record its resolution, pixel aspect ratio, framing, frame range, and any crop or stabilization already applied.
2. Identify whether the distortion model is static or animated. Zoom lenses, focus breathing, stabilization, and in-camera correction can make a single fixed model insufficient.
3. Use calibration imagery when available. Otherwise, evaluate long straight features across the frame and confirm that the chosen model improves geometry without introducing new curvature.
4. Record the model, coefficients, center, scale, and plug-in version. A screenshot is not a reliable interchange format.
5. Decide the undistorted output bounds before tracking. Removing barrel distortion often requires extra canvas area; cropping it away can remove pixels needed after redistortion.

Autograph and OpenFX validation

• Confirm that the exact lens plug-in and version loads in the installed Autograph version. A vendor host listing establishes intended support, not complete production equivalence.
• Create a synthetic grid and a real plate test. Render undistort and redistort through Autograph, then compare the round trip against the original.
• Test full resolution, proxy resolution, non-square pixels if relevant, and the actual delivery bit depth.
• Check whether the plug-in expands image bounds or clips to the project frame. Inspect all four corners and any overscan region.
• Verify parameter animation, motion blur interaction, caching, and final render behavior rather than trusting only the interactive viewer.
• Keep lens maps and geometric data outside display-color transforms. An STMap or coordinate map is data, not a viewable color image.

Tracking and compositing order

1. Undistort the source plate.
2. Track, solve, paint, key, project, and composite in the agreed undistorted space.
3. Render CG with matching undistorted camera framing or transform it into that space explicitly.
4. Merge all elements that belong in the photographed scene.
5. Redistort the completed composite once, using the inverse of the approved undistortion.
6. Apply final crop, delivery resize, grain matching, and output transforms according to the production specification.

Some operations may need a different order for technical reasons, but the exception should be documented. Repeated undistort/redistort cycles add resampling and make edge diagnosis harder.

Round-trip acceptance test

• Compare original plate versus undistort → redistort at 100% and with a difference operation.
• Ignore small interpolation noise only after checking that straight features, corners, and high-contrast edges return to the correct position.
• Check the first, middle, and last frames, plus zoom, focus, or stabilization changes.
• Place a tracked marker or CG object near the center and near each corner. Edge agreement matters more than a good center match.
• Verify alpha and RGB together. A geometric transform can expose hidden RGB or create fringes if the element's premultiplication state is mishandled.
• Re-import the rendered result into the intended receiving application and repeat the comparison.

Common failure patterns

• Center aligns, corners drift: wrong distortion model, incomplete calibration, or an incorrect distortion center.
• Round trip crops the image: insufficient undistorted bounds or a host/plug-in frame-clipping difference.
• Track works until a zoom or focus change: a static model is being used for animated lens behavior.
• CG bends differently from the plate: CG was rendered in one camera space and composited in another, or redistortion was applied twice.
• Edges soften after delivery: repeated resampling, low-precision maps, proxy-derived calibration, or an unnecessary resize between transforms.
• STMap produces a color-management warning or wrong geometry: the map was treated as color rather than raw data, its channels were interpreted incorrectly, or the map direction was reversed.

Minimum handoff note

• Original plate specification and whether it contains in-camera correction.
• Distortion model, coefficients, center, scale, and whether parameters animate.
• Undistorted resolution, overscan policy, pixel aspect ratio, and frame range.
• Forward and inverse map filenames, map direction, channel convention, precision, and color-management bypass.
• Application and plug-in versions used for the approved round-trip test.
• Reference frames or difference renders proving the handoff.

Practical rule

Treat lens distortion as shared shot geometry. Approve one model, one mapping direction, and one image-bound convention; then test that Autograph and every receiving host reproduce the same undistort/redistort round trip before creative work accumulates.

Useful next pages

• Autograph OpenFX plugin compatibility note
• Autograph alpha and premultiplication troubleshooting checklist
• Autograph frame-rate and image-sequence handoff checklist
• Autograph to Nuke EXR and OCIO handoff checklist

Sources checked

• Maxon Autograph product page — checked 2026-07-16. Used for Autograph's compositing, camera, OpenFX, OpenEXR, and 2D/3D workflow context.
• RE:Vision Effects RE:Lens product page — checked 2026-07-16. Used for the vendor's Autograph host listing and lens-correction workflow context.
• Foundry Nuke lens-distortion documentation — checked 2026-07-16. Used as a pipeline reference for undistorting plates, working in rectified space, and restoring distortion.
• OpenEXR Technical Introduction — checked 2026-07-16. Used for data-window, display-window, channel, and high-precision image-storage context relevant to overscan and data maps.