https://github.com/cheind/py-minexr
Minimal, standalone, fast Python OpenEXR reader for single-part, uncompressed scan-line files as produced by Blender.
https://github.com/cheind/py-minexr
Last synced: 12 months ago
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Minimal, standalone, fast Python OpenEXR reader for single-part, uncompressed scan-line files as produced by Blender.
- Host: GitHub
- URL: https://github.com/cheind/py-minexr
- Owner: cheind
- License: mit
- Created: 2020-09-25T05:59:59.000Z (almost 6 years ago)
- Default Branch: develop
- Last Pushed: 2022-06-14T12:04:54.000Z (about 4 years ago)
- Last Synced: 2025-04-14T00:17:08.158Z (about 1 year ago)
- Language: Python
- Size: 637 KB
- Stars: 18
- Watchers: 1
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# minexr
**minexr** is a standalone, fast Python [OpenEXR](https://www.openexr.com/) reader for single-part, uncompressed scan-line files. It is compatible with `.exr` files produced by [Blender](http://blender.org).
## Assumptions
**minexr** makes a couple of assumptions about the `.exr` file to be read:
1. single-part files with arbitrary number of channels,
1. no pixel data compression, and
1. equal channel types (HALF, FLOAT, UINT).
These assumptions allow us to efficiently parse and read the `.exr` file. In particular we gain constant offsets between scan lines which allows us to read the entire image in (H,C,W) format without copying.
## Usage
The following is taken from [example.py](./example.py)
```python
import minexr
with open('file.exr', 'rb') as fp:
reader = minexr.load(fp)
rgba = reader.select(['Color.R','Color.G','Color.B','Color.A'])
# a HxWx4 np.array with dtype based on exr type.
...
```
Full [example.py](./example.py) loads the following images
which were previously rendered using Blender/EEVEE [cube.blend](./etc/cube.blend).
## Runtime
The following timings are produced by [bench.py](./bench.py) by repeatable reading an RGBA image from an `.exr` file. Timings include file and numpy operations.
| Module | [sec/image] | Note |
| :-----------: | :---------: | --------------------------- |
| OpenEXR 1.3.2 | 0.020 | with channel concatenate |
| OpenEXR 1.3.2 | 0.015 | without channel concatenate |
| **minexr** | **0.004** | with channel concatenate |
## Install
Either via pip
```
pip install minexr
```
Or clone this repository and invoke
```
pip install -e .
```
## Tests
To run the tests
```
pytest
```
## Blender support
Use a `FileOutput` node in Blender's compositor to export `.exr` files. Make sure to select `OpenEXR MultiLayer` format and set `CODEC` to None as shown in the following image. `Color Depth` can be chosen as required.
When unsure about which channels are being written, you can inspect the file content as follows
```python
import minexr
with open('file.exr', 'rb') as fp:
reader = minexr.load(fp)
print(reader.channel_names)
# ['Color.R','Color.G','Color.B', ...]
print(reader.attrs)
# Dictionary of all OpenEXR header attributes.
```