OpenEXR
by @oumad
Work with OpenEXR files — inspect channels, extract beauty/RGB passes, decode cryptomatte segmentation (material, object, asset), convert color spaces (ACESc...
clawhub install exr📖 About This Skill
name: exr description: > Work with OpenEXR files — inspect channels, extract beauty/RGB passes, decode cryptomatte segmentation (material, object, asset), convert color spaces (ACEScg to sRGB), and batch process EXR directories. Use when working with EXR files, render passes, AOVs, or cryptomatte. compatibility: Requires Python packages (pip install -r requirements.txt). Pin OpenEXR==3.2.4. metadata: author: oumad version: "1.0" clawdbot: '{"requires":{"bins":["python3"]}}'
EXR Skill
Work with OpenEXR files — the multi-channel, high dynamic range format standard in VFX, CGI rendering, and compositing. EXR files typically contain beauty renders, AOV passes (depth, normals, motion vectors), and cryptomatte segmentation data, all stored as 32-bit float channels.
Setup
Install dependencies before first use:
pip install -r requirements.txt
Dependencies: OpenEXR==3.2.4, numpy<2, Pillow.
> Note: OpenEXR 3.2.4 is pinned because later versions (3.4+) can segfault on some platforms. numpy<2 is required for OpenEXR 3.2.x compatibility.
Ready-Made Tool
scripts/exr_extract.py is a general-purpose CLI for common EXR tasks:
python scripts/exr_extract.py info
python scripts/exr_extract.py beauty [--colorspace CS] [--output-dir DIR] [--force]
python scripts/exr_extract.py crypto [--type TYPE] [--bg-color COLOR] [--suffix TEXT] [--no-suffix] [--output-dir DIR] [--force]
python scripts/exr_extract.py channels --channels R,G,B [--colorspace CS] [--output-dir DIR] [--force]
Use this tool first. Fall back to custom Python only for edge cases.
Channel Inspection
Always start by inspecting what's in the EXR:
python scripts/exr_extract.py info render.exr
This shows:
Common channel patterns:
R, G, B, A — beauty/RGBA passdepth.Z or Z — depth passN.X, N.Y, N.Z — world-space normalscrypto_material00.R, .G, .B, .A — cryptomatte rank 0-1crypto_object00.R, .G — object ID cryptomatteBeauty / RGB Extraction
Extract the rendered beauty image as a tone-mapped PNG:
python scripts/exr_extract.py beauty render.exr --colorspace acescg
Color space options:
acescg (default): ACEScg AP1 primaries → linear sRGB via 3x3 matrix → sRGB OETF. Standard for most VFX renders.linear: Already linear sRGB primaries → apply sRGB OETF only (gamma encoding).srgb: Already sRGB-encoded → clamp and save directly.The ACEScg→sRGB pipeline applies the AP1-to-Rec.709 matrix then the piecewise sRGB OETF. See ${CLAUDE_SKILL_DIR}/references/color-spaces.md for exact values.
Cryptomatte Extraction
Extract material, object, or asset segmentation masks as color-coded PNGs:
python scripts/exr_extract.py crypto render.exr
python scripts/exr_extract.py crypto render.exr --type crypto_material
python scripts/exr_extract.py crypto ./renders/ --bg-color black --output-dir ./masks/
How it works:
1. Reads the top-ranked cryptomatte ID from {prefix}00.R (float-encoded uint32 hash) and coverage from {prefix}00.G
2. Detects the background ID by sampling edges and corners of the image
3. Assigns a 35-color bold palette to foreground materials, ranked by pixel area (largest material gets the most distinct color)
4. Background gets neutral gray (or black with --bg-color black)
5. Zero-coverage pixels are black
Auto-detects channel naming conventions across renderers:
crypto_material00, crypto_object00crypto_mat00, crypto_obj00See ${CLAUDE_SKILL_DIR}/references/cryptomatte.md for format details.
Crypto Options
--type: Force a specific type (crypto_material, crypto_object, crypto_asset). Default: extract all detected.--bg-color: gray (default), black, or auto.--suffix: Custom suffix (default: _materialID, _objectID, _assetID).--no-suffix: Output with same name as input (for dataset prep into separate folders).Arbitrary Channel Extraction
Extract any named channels:
# Normals as RGB
python scripts/exr_extract.py channels render.exr --channels N.X,N.Y,N.ZSingle channel (depth)
python scripts/exr_extract.py channels render.exr --channels depth.Z
When 3 channels are specified, they're composited as RGB. Single channels become grayscale. Other counts produce individual files.
Batch Processing
All subcommands accept a directory path to process every EXR in it:
python scripts/exr_extract.py beauty ./renders/ --output-dir ./target/ --colorspace acescg
python scripts/exr_extract.py crypto ./renders/ --output-dir ./control/ --no-suffix
Existing outputs are skipped unless --force is specified.
Custom Python
For edge cases not covered by the CLI, use the OpenEXR Python API directly:
import OpenEXR, Imath
import numpy as npexr = OpenEXR.InputFile('render.exr')
header = exr.header()
dw = header['dataWindow']
w = dw.max.x - dw.min.x + 1
h = dw.max.y - dw.min.y + 1
pt = Imath.PixelType(Imath.PixelType.FLOAT)
raw = exr.channel('R', pt)
data = np.frombuffer(raw, dtype=np.float32).reshape(h, w)
Always install dependencies first, pin OpenEXR==3.2.4, and use Imath.PixelType.FLOAT.
Related: oiiotool Skill
For tasks beyond what this Python-based EXR skill covers, consider the oiiotool skill (pip install openimageio). It provides:
-i:ch=R,G,B reads only needed channels, critical for large production EXRsWhen to use which
| Task | Use | |------|-----| | Inspect channels, cryptomatte metadata | exr skill | | Extract cryptomatte as colored segmentation | exr skill | | Beauty extraction from ACEScg renders (simple scenes) | exr skill | | HDR review with ACES tone mapping | oiiotool skill | | Exposure adjustment / sweep | oiiotool skill | | EXR sequence to MP4 | oiiotool skill | | Format conversion (EXR to DPX, TIFF, etc.) | oiiotool skill | | Resize, crop, composite | oiiotool skill | | Batch sequence operations | oiiotool skill |
⚙️ Configuration
Install dependencies before first use:
pip install -r requirements.txt
Dependencies: OpenEXR==3.2.4, numpy<2, Pillow.
> Note: OpenEXR 3.2.4 is pinned because later versions (3.4+) can segfault on some platforms. numpy<2 is required for OpenEXR 3.2.x compatibility.