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Open .kra and .krz with paint layers (8/16-bit RGBA and gray, any offset), nested and pass-through groups, names, visibility, opacity, locks, blend modes and transparency masks, plus the image's ICC profile and resolution. Vector, filter, fill, file and clone layers and the other mask kinds are left out with a warning; float, CMYK and Lab documents open as Krita's merged image (preview). Import only: Save suggests .ora. Checked against 35 Krita 5.2.9-authored files. Co-authored-by: Scott Campbell <251750033+scottcampbelldata@users.noreply.github.com> Co-authored-by: Brandon Thomas <echelon@gmail.com> Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
70 lines
4.1 KiB
Markdown
70 lines
4.1 KiB
Markdown
# OpenRaster documents
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PhotoCraft opens and saves OpenRaster (`.ora`), the layered format Krita, MyPaint, GIMP, Pinta
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and others share. File › Open, recent files, drops, Save and Save As, the CLI (`convert`, `info`,
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`batch`) and automation (`doc.open`, `doc.save`, MCP) all use the same reader and writer in
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`photocraft-io`. The browser build accepts `.ora` too. A file is recognised by its `mimetype`
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entry, so an OpenRaster file with another extension still opens as one.
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## What is kept
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| | Open | Save |
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|---|---|---|
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| Pixel layers (any size and position, also off-canvas) | yes | yes, cropped to their pixels |
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| Groups, nested | yes | yes |
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| Pass-through groups | `isolation="auto"` without a blend mode | `isolation="auto"` |
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| Names, visibility, opacity | yes | yes |
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| Blend modes | the `svg:*` names, `svg:plus`, and Krita's `krita:*` names | `svg:*` where the spec has the mode, else `krita:*` (read back by Krita, Normal elsewhere) |
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| Locks | `edit-locked`, `alpha-preserve` | the same |
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| 8 and 16-bit | yes (the deepest layer sets the depth) | 8-bit documents as 8-bit PNGs, 16 and 32-bit as 16-bit PNGs |
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| Resolution | `xres` | `xres` and `yres` |
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| Merged image and thumbnail | not read (we render our own) | written (`mergedimage.png`, `Thumbnails/thumbnail.png`) |
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Saving reports what OpenRaster can't hold, layer by layer: pixel masks are applied to the
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layer's pixels, fill opacity is folded into the pixels, text, shape, fill and smart object layers
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are written as their rendered pixels, and adjustment layers, layer styles, vector masks,
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clipping, alpha channels, metadata and the colour profile are left out. Xor and Paint.NET's
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Color Burn and Color Dodge variants have no OpenRaster name and are saved as Normal. CMYK, Lab
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and other modes are refused with a message to convert first; Grayscale saves as RGB.
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OpenRaster elements other than `stack` and `layer` (MyPaint's text, for example), missing
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layer images and unknown composite operations open with a warning instead of failing the file.
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Krita's W3C Soft Light (`svg:soft-light`, `krita:soft_light_svg`) and its own Hard Mix open as
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Photoshop's Soft Light and Hard Mix, which differ slightly, also with a warning.
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## Limits and safety
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The reader takes the archive with the bounded ZIP reader of `photocraft-format` (no ZIP64,
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CRC-checked), parses `stack.xml` with `roxmltree` (16 MiB cap), and decodes each layer image
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through `photocraft-codecs` with size limits. Canvases are at most 300,000 px a side, at most
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8,192 layers and groups, nesting at most `MAX_GROUP_DEPTH` deep, and 1 GiB of decoded pixels in
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total. Malformed archives, XML, numbers and images return errors; truncated and corrupted files
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are covered by tests.
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## Verification
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Unit tests (`crates/io/src/ora/tests.rs`) round-trip layers, groups, pass-through, offsets,
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opacity, visibility, locks and every blend mode at 8 and 16 bit, check masks, rendered layer
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kinds, the archive layout and malformed input. `crates/automation/tests/openraster.rs` saves,
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reopens, edits and saves in place through the agent surface; the CLI test converts both ways.
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Real-file checks use Krita-authored oracles from
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[photocraft-corpus](https://github.com/storytold/photocraft-corpus) (`krita/`, made by
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`tools/krita-oracles/generate.py`). Each Krita file carries Krita's rendering of itself in
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`mergedimage.png`:
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```sh
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KRITA_TEST_DIR=/path/to/photocraft-corpus/krita cargo test -p photocraft-io --test krita_corpus -- --ignored --nocapture
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```
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2026-10-09, Krita 5.2.9: 32 of 35 `.ora` files render within 3/255 of Krita's merged image; the
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other three differ for known reasons listed in `crates/io/tests/krita_corpus.rs` (Krita's
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tie-break in Darker and Lighter Color, and Hard Mix at a channel sum of exactly 1). In the other
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direction, Krita opened every PhotoCraft re-export of the first 34 of those files and rendered 33
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of them identically to its original; the exception is Photoshop's Soft Light, which is written
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as `svg:soft-light`. MyPaint and GIMP files have not been checked yet.
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Format reference: the [OpenRaster specification](https://www.openraster.org/). The reader and
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writer are written from the specification and from files Krita writes; no application code
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was used.
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