Wiki · Autograph / Alpha / Compositing

Autograph alpha and premultiplication troubleshooting checklist

Published 2026-07-14 · Wiki · Alpha / Compositing / Troubleshooting

A practical checklist for diagnosing dark fringes, bright halos, dirty transparent pixels, broken glows, and inconsistent edges when media moves through Autograph, OpenFX plug-ins, EXR files, and downstream compositing tools.

Why this page exists

Alpha problems are often misdiagnosed as color-management, antialiasing, or codec problems. The image may look correct over black and fail over a bright background, or it may survive inside one host and break after an OpenFX effect, resize, blur, color correction, or EXR handoff. The core question is whether RGB values are stored independently from alpha or already multiplied by alpha, and whether every stage treats that relationship consistently.

Establish the alpha contract

Straight or unassociated alpha: RGB describes the underlying color independently of transparency. Fully transparent pixels may still contain meaningful RGB.
Premultiplied or associated alpha: RGB has already been multiplied by alpha. Edge pixels therefore become darker as coverage falls.
Opaque media: do not invent an alpha workflow for files that are meant to be fully opaque. Confirm that the host is not deriving alpha from luminance or another channel.
Data channels: depth, normals, motion vectors, IDs, and masks are not automatically color channels and should not be premultiplied merely because they are stored in an EXR beside RGBA.

Fast diagnostic test

Place the element over black, middle gray, white, and a saturated color.
Inspect a soft edge at 200–400% zoom and compare RGB and alpha separately.
Temporarily unpremultiply, inspect or process the RGB, then premultiply again before the final over operation.
Render a short test to the intended delivery format and re-import it into Autograph and one receiving application.
If the fringe changes with the background, suspect alpha association or hidden RGB before blaming the display transform.

Symptom map

Dark outline: premultiplied RGB may be treated as straight, or a color operation may have been applied directly to premultiplied edge pixels.
Bright or colored halo: straight RGB may be treated as premultiplied, or transparent pixels may contain a matte color that leaks during filtering.
Edge changes after blur, resize, transform, or defocus: filtering may be happening in the wrong alpha state, or the plug-in may use a different association assumption from the host.
Glow or additive element becomes weak: the element may have emission in RGB with little or zero alpha. Treating it as ordinary premultiplied coverage can suppress the intended energy.
Correct in viewer, wrong after export: the file writer or receiving application may interpret alpha differently from the working graph.

OpenFX and effect-order checks

Test the plug-in on a small synthetic image with a hard shape, soft edge, semitransparent gradient, colored transparent border, and an additive highlight.
Compare three paths: effect on straight RGB, effect on premultiplied RGBA, and unpremultiply → effect → premultiply.
Check whether the effect modifies RGB outside the visible alpha. Those values may become visible after a transform, blur, key, or later unpremultiply.
For color corrections, sharpening, denoising, and spatial filters, verify edge behavior explicitly rather than assuming the plug-in follows the host's internal convention.
Keep a known-good test project per plug-in version. Host support alone does not guarantee identical alpha behavior across effects or updates.

EXR handoff checks

Record whether beauty RGBA is expected to be associated or unassociated. Do not rely on the filename or the presence of an A channel to communicate that decision.
Inspect channels independently. Arbitrary EXR channels can carry color, masks, vectors, depth, IDs, or other data with different processing rules.
Do not premultiply utility passes such as normals, position, depth, or motion vectors unless the pipeline specification explicitly requires it.
Check data window and display window behavior. Cropped or overscan EXRs can reveal unexpected RGB at boundaries when transformed or reformatted.
Re-import the exact written file and compare it over multiple backgrounds before delivery.

Color-management boundary

Alpha is normally coverage or opacity data, not display-referred color. Color transforms should generally affect RGB, while the alpha relationship must remain coherent before and after the transform. When debugging, separate two questions: whether the RGB values are in the intended color space, and whether those RGB values are straight or premultiplied. Solving only one can leave the edge wrong.

Minimum handoff note

File format, bit depth, channel names, and alpha presence.
Straight or premultiplied expectation for beauty RGBA.
Any matte color or meaningful RGB outside alpha.
Whether glows, fire, sparks, or other additive components are embedded or supplied separately.
Which application and background colors were used for verification.

Practical rule

Do not fix a fringe by crushing, eroding, or color-correcting the edge until the alpha association is known. First identify the representation, process RGB in the appropriate state, restore the intended association, and verify the written file over more than one background.

Useful next pages

Sources checked

Maxon Autograph product page — checked 2026-07-14. Used for Autograph's compositing, multi-channel EXR, OpenFX, video, and 2D/3D workflow context.
OpenEXR Technical Introduction — checked 2026-07-14. Used for EXR channel, alpha, data/display-window, floating-point, and production-image context.
Foundry Nuke Premult documentation — checked 2026-07-14. Used for the operational distinction between multiplying RGB by alpha and processing imagery before compositing.
Adobe After Effects alpha channels, masks, and mattes — checked 2026-07-14. Used as a receiving-host reference for straight and premultiplied alpha interpretation.