# OpenRaster documents

PhotoCraft opens and saves OpenRaster (`.ora`), the layered format Krita, MyPaint, GIMP, Pinta
and others share. File › Open, recent files, drops, Save and Save As, the CLI (`convert`, `info`,
`batch`) and automation (`doc.open`, `doc.save`, MCP) all use the same reader and writer in
`photocraft-io`. The browser build accepts `.ora` too. A file is recognised by its `mimetype`
entry, so an OpenRaster file with another extension still opens as one.

## What is kept

| | Open | Save |
|---|---|---|
| Pixel layers (any size and position, also off-canvas) | yes | yes, cropped to their pixels |
| Groups, nested | yes | yes |
| Pass-through groups | `isolation="auto"` without a blend mode | `isolation="auto"` |
| Names, visibility, opacity | yes | yes |
| 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) |
| Locks | `edit-locked`, `alpha-preserve` | the same |
| 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 |
| Resolution | `xres` | `xres` and `yres` |
| Merged image and thumbnail | not read (we render our own) | written (`mergedimage.png`, `Thumbnails/thumbnail.png`) |

Saving reports what OpenRaster can't hold, layer by layer: pixel masks are applied to the
layer's pixels, fill opacity is folded into the pixels, text, shape, fill and smart object layers
are written as their rendered pixels, and adjustment layers, layer styles, vector masks,
clipping, alpha channels, metadata and the colour profile are left out. Xor and Paint.NET's
Color Burn and Color Dodge variants have no OpenRaster name and are saved as Normal. CMYK, Lab
and other modes are refused with a message to convert first; Grayscale saves as RGB.

OpenRaster elements other than `stack` and `layer` (MyPaint's text, for example), missing
layer images and unknown composite operations open with a warning instead of failing the file.
Krita's W3C Soft Light (`svg:soft-light`, `krita:soft_light_svg`) and its own Hard Mix open as
Photoshop's Soft Light and Hard Mix, which differ slightly, also with a warning.

## Limits and safety

The reader takes the archive with the bounded ZIP reader of `photocraft-format` (no ZIP64,
CRC-checked), parses `stack.xml` with `roxmltree` (16 MiB cap), and decodes each layer image
through `photocraft-codecs` with size limits. Canvases are at most 300,000 px a side, at most
8,192 layers and groups, nesting at most `MAX_GROUP_DEPTH` deep, and 1 GiB of decoded pixels in
total. Malformed archives, XML, numbers and images return errors; truncated and corrupted files
are covered by tests.

## Verification

Unit tests (`crates/io/src/ora/tests.rs`) round-trip layers, groups, pass-through, offsets,
opacity, visibility, locks and every blend mode at 8 and 16 bit, check masks, rendered layer
kinds, the archive layout and malformed input. `crates/automation/tests/openraster.rs` saves,
reopens, edits and saves in place through the agent surface; the CLI test converts both ways.

Real-file checks use Krita-authored oracles from
[photocraft-corpus](https://github.com/storytold/photocraft-corpus) (`krita/`, made by
`tools/krita-oracles/generate.py`). Each Krita file carries Krita's rendering of itself in
`mergedimage.png`:

```sh
KRITA_TEST_DIR=/path/to/photocraft-corpus/krita cargo test -p photocraft-io --test krita_corpus -- --ignored --nocapture
```

2026-10-09, Krita 5.2.9: 30 of 34 `.ora` files render within 3/255 of Krita's merged image; the
other four differ for known reasons listed in `crates/io/tests/krita_corpus.rs` (Krita's
tie-break in Darker and Lighter Color, Hard Mix at a channel sum of exactly 1, and a
linear-light 16-bit document that Krita blends in linear light). In the other direction,
Krita opened every PhotoCraft re-export of those files and rendered 33 of them identically to
its original; the exception is Photoshop's Soft Light, which is written as `svg:soft-light`.
MyPaint and GIMP files have not been checked yet.

Format reference: the [OpenRaster specification](https://www.openraster.org/). The reader and
writer are written from the specification and from files Krita writes; no application code
was used.