EXR → sRGB

Turn ACES-linear EXR renders into display-ready images — without opening your compositing app.

Batch convert to PNG / JPEG / TIFF, view .exr files by double-clicking them, pull cryptomatte mattes, and write scene-linear 32-bit TIFF when the destination is a comp rather than a screen.

Installs in seconds. No admin needed. · All releases

_{Double-click any .exr to open it in the viewer. The probe reads the linear scene value and the display colour side by side.}

_{Or skip the app entirely — right-click any .exr and convert it in place.}

Colour is done with OpenColorIO's built-in ACES configs — the same engine your renderer uses — so the output matches your viewport instead of a gamma guess. The ACES output transform (RRT + ODT) is applied properly, not approximated.

Tested against Blender Cycles, C4D Redshift and C4D Octane output, and checked frame-for-frame against Nuke conversions of the same renders.

Run EXRtoSRGB_Setup_v<version>.exe. It installs like any other application:

• No admin prompt. Installs per-user to %LOCALAPPDATA%\Programs\EXRtoSRGB, the same as VS Code or Discord. Nothing is changed for other accounts.
• Appears in Add/Remove Programs, with a Start menu entry and a working uninstaller that takes the file association and right-click menu with it.
• Offers to open .exr files and to add the right-click convert menu, both ticked by default and both changeable later under the ⚙. If another application already owns .exr, setup opens the page where you can hand it over — Settings → Default apps on Windows 11, the "Open with" chooser on Windows 10. Only you can set a default file handler on Windows; an installer cannot do it silently, whatever it claims.
• Upgrades in place. The app lives at a fixed path, so the association keeps working across versions.

The app itself is self-contained — OpenImageIO, OpenColorIO and every ACES config are compiled in. Windows supplies the webview, so there's no bundled browser.

The installer is unsigned, so Windows SmartScreen shows a warning the first time. More info → Run anyway. Code signing is a paid annual certificate rather than anything that can be fixed in the source.

There's a sample render in docs/sample_render.exr if you want something to drop on it straight away — the frame in the screenshots above. Scene-linear ACEScg, 1600 × 1000, with highlights up past 10.0, so it actually shows the ACES roll-off rather than looking the same through any curve.

pip install OpenImageIO OpenColorIO pywebview
python exr2srgb.py

Drag .exr files or folders anywhere onto the window, or use Add files / Add folder. Whatever you just added is selected automatically.

Sequences collapse into one row. A folder of shot_010.0001.exr … .0240.exr reads as shot_010.####.exr · 240 frames · 1–240. Drop a single frame and the whole run comes with it — matching stem, frame padding and extension, so a differently padded render or a stray .png never joins by accident.

Only one converter window opens at a time; launching again focuses it. Viewers are unrestricted.

The _srgb suffix is on by default, so converting in place never drops a .png next to its .exr with the same stem.

The Alpha setting picks the edge-pixel convention, and the two "keep" entries are both correct — they answer different questions. Nothing but antialiased edges changes; opaque pixels are identical either way.

If you are diffing this tool's output against a Nuke or After Effects export and finding edges a few levels apart, that setting is the reason — the default now matches both to the bit, measured on a 4000px production render.

On the CLI: --alpha keep (default), keep-straight, black, white.

Save the combination you actually use — config, display, format, depth — and pick it next launch. Presets deliberately don't store the output folder: a preset is how to convert, not where to put it.

Tick Convert every layer, one file each and a multi-AOV render writes one image per layer in a single pass, each named for its layer.

Multi-layer EXRs name channels <layer>.<component>. The beauty is auto-detected by ranking layer names — never by matching the component suffix, which is how a tool ends up exporting Ambient Occlusion as the beauty and nobody notices.

Data layers — normals, position, depth, motion vectors, cryptomatte — are excluded from auto-detection, since running them through a view transform is meaningless. You can still select them explicitly.

Multi-part EXRs work. Blender's File Output node writes one part per slot rather than one channel group per pass, so a custom AOV export is a multi-part file by construction. Every part is listed as a layer, the beauty is still auto-detected across all of them, and cryptomatte is read from whichever part carries it.

OCIO configuration — eight ACES configs are compiled in:

Default is ACES 1.3 · CG v2.2, which matches the output transform in current Blender, Octane and Redshift ACES setups. ACES 2.0 is a different look, not a newer version of the same one — the tone curve genuinely changed.

ACES 1.2 is not a built-in. It predates OCIO's built-in registry and only exists as a downloadable config.ocio. Use Custom config.ocio… and point at it.

Worth getting right, because the wrong pick silently skips the ACES curve.

With an ACES 1.3 CG/Studio config (fn-nuke_cg-config-v2.2.0_aces-v1.3_ocio-v2.4 and friends), the output transform is a display + view pair, not a colorspace:

Don't pick the colorspace sRGB Encoded Rec.709 (sRGB). It's a plain transfer function — identical to the Un-tone-mapped view — and highlights clip instead of rolling off. The give-away is the ladder below: 1.0 lands on 255 instead of 207.

With an ACES 1.2 config.ocio, color_picking (Output - sRGB) is the full RRT + ODT, so that setting is correct as-is.

Tick premultiplied on the Write node. Renders carry associated alpha; without it the display transform is applied to already-premultiplied pixels and antialiased edges come out with a dark fringe.

Use the ACES 1.3 · CG v1.0 or Studio v1.0 entry — those are the config versions After Effects ships with.

These are correct ACES values. If 1.0 lands on 255, the ACES curve isn't being applied — the view has resolved to a plain transfer function.

Blender Cycles and C4D Redshift renders, converted here and in Nuke, compared pixel-for-pixel. Mean 8-bit error:

The test suite asserts those bounds, so a colour regression fails the build rather than shipping.

Double-click any .exr and it opens. The installer offers this, or tick Open .exr files with this viewer under the ⚙ in the title bar. The association is per-user, needs no admin rights, and unticking hands the file type back.

.exr files also get their own aperture icon, distinct from the app's, so a file and the app that opens it don't look identical in Explorer.

If Photoshop, After Effects or another viewer already owns .exr, ticking the toggle usually still wins it — but Windows has the final say, and where it refuses, only you can override it. In that case the toggle opens the right page for your Windows:

• Windows 11 — Settings → Apps → Default apps, at the EXR → sRGB entry. Set .exr there. (Windows 11 removed the ability for apps to show the old one-click chooser; it now answers with a message pointing at Settings.)
• Windows 10 — the "How do you want to open this?" dialog. Pick EXR → sRGB.

The toggle reports what Windows actually resolves .exr to, not what the app asked for — so if it reads off after you ticked it, the default really is somewhere else.

The window opens centred and sized to the image, up to 1:1, capped to your screen. Move or resize it and that's remembered.

• Zoom and pan — scroll to zoom at the cursor, drag to pan. F fits, 1 is actual pixels. Past 1:1 the visible region is re-rendered at source resolution, so 100% means real pixels rather than an upscaled preview.
• Exposure and gamma — exposure in stops before the display transform, so it behaves like a camera stop; gamma after, like a compositor's viewer gamma.
• Channel isolation — R G B A, C back to colour.
• Layer switching for multi-layer and multi-part files.
• Pixel probe — linear scene values, plus a colour chip and the hex of what's on screen. Every value copies on click. The eyedropper (E) locks one reading so it stops following the cursor.
• Convert — the same presets as the right-click menu, applied to the layer you're looking at.

Load a second EXR with Compare… and flip between them, wipe, or look at the difference. \ cycles the four modes.

The difference is taken in linear, before the tone curve — a difference of 0.01 then means the same thing in the shadows as in the highlights, and exposure works as the gain control for reading small ones. The two images must be the same size; a resized comparison would partly be measuring the resampler.

Read the cryptomatte manifest, pick objects, export mattes.

Pick straight off the ID view: Ctrl-click adds, Alt-click removes. Ticked objects stay lit and everything else dims, so the selection builds up on the image instead of being hunted through a list.

• Type — CryptoObject, CryptoMaterial, and whatever else the renderer wrote. Selections are remembered per type.
• Filter a long list; Select all acts on what the filter shows.
• One file per object or combine into one.
• White silhouette (premultiplied) or flat white RGB. The second forces TIFF, because PNG always associates alpha and would turn flat white back into coverage.

Enable it under the ⚙ to add a convert submenu to .exr files in Explorer: PNG 8/16-bit, JPEG, TIFF 16-bit, and TIFF 32-bit scene-linear. Conversion runs headless — no window ever opens. It's pictured at the top.

The verbs are registered under SystemFileAssociations\.exr, so they show up whatever application owns the file type, and .exr files get their own aperture icon once the association is on.

Set Look to Scene-linear and the file is data rather than a picture: no display transform, no clamp, alpha untouched, and 32-bit float TIFF regardless of what else is selected.

Three things it deliberately does not do:

• Clamp. Linear values run past 1.0 and that's the point.
• Touch alpha. Un-premultiply is skipped, so the output is bit-identical to the source layer.
• Claim to be sRGB. The file is tagged colorspace=Linear, written to ImageDescription as well as the EXIF tag because TIFF can only express sRGB natively and OIIO silently drops an unrecognised value. A linear file labelled sRGB gets a transfer function applied twice downstream.

The preview stays display-referred in this mode and says so — raw linear renders as a near-black smear.

EXRtoSRGB.exe --cli shots/ --format png --bits 16 --out out/

Exit codes: 0 fine, 1 some frames failed, 2 nothing to convert, 3 bad arguments. --config refuses an ambiguous match rather than guessing.

Press ? in either window, or open the ⚙ in the converter.

Converter — ↑ ↓ previous / next file · Ctrl+O add files · Ctrl+↵ convert · Esc cancel · E eyedropper · , . step frames · Ctrl/Alt-click matte picking

Viewer — F fit · 1 actual pixels · + − zoom · R G B A channels · C colour · E eyedropper · \ cycle A/B · Esc close

build_exe.bat

Runs EXRtoSRGB.spec with PyInstaller. The spec carries the parts that are easy to get wrong: the OIIO/OCIO DLLs, the ui/ folder, and pywebview's WebView2 backend. The exe lands in the repo root; PyInstaller's scratch goes to %TEMP%.

core.py is the conversion — colour pipeline, layer resolution, alpha handling, sequence grouping, cryptomatte. It imports no UI and is what the test suite exercises, so colour behaviour is verifiable without opening a window.

exr2srgb.py is a pywebview window: Python stays the application and the interface is HTML and CSS rendered by the OS's own webview (WebView2 on Windows), which is why there's no bundled browser and the download is around 37 MB rather than 150.

MIT — see LICENSE. Made by VISOR for 3D/CGI/VFX production, and free for anyone to use.

OpenImageIO, OpenColorIO and pywebview are bundled into the built .exe under their own licenses (Apache-2.0 / BSD-style); this repository's MIT license covers the Python sources, ui/, and the build scripts.