OpenRaster documents

Picto 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 picto-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

Files declaring OpenRaster 0.0.6 or newer default to isolated groups; an explicit isolation="auto" passes through regardless of the group's own composite operation. Older files and files without a recognized version keep the legacy inference from the group's blend mode. Pass-through group opacity still uses Picto's interpolation against the backdrop, which can differ from 0.0.6's per-child opacity multiplication for overlapping children.

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 a colour profile other than sRGB 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.

An OpenRaster file is the document's own file only while it holds everything in it (#3806). picto_io::ora_losses lists what a save would leave out, from the same checks the writer warns with, without encoding anything. When that list isn't empty, File › Save doesn't overwrite the .ora: Save As opens on a PSD of the same name, with a notice listing what OpenRaster would drop. A save to an .ora path then writes a copy, as Photoshop does for formats that can't keep everything: the document keeps its file and its unsaved changes. Automation follows the same rule (doc.save and app.save without a path refuse, saying why).

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) is Photoshop's Soft Light and opens as it. Krita's own Soft Light (krita:soft_light, sqrt over dark backdrops) and its own Hard Mix open as Photoshop's Soft Light and Hard Mix, which differ slightly, with a warning.

Limits and safety

The reader takes the archive with the bounded ZIP reader of picto-format (no ZIP64, CRC-checked), parses stack.xml with roxmltree (16 MiB cap), and decodes each layer image through picto-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. Synthetic 8/16-bit pixel fixtures check modern and legacy group-isolation defaults, explicit isolation and pass-through. crates/automation/tests/it/openraster.rs saves, reopens, edits and saves in place through the agent surface, and checks that a document with an adjustment layer never overwrites its .ora; the CLI test converts both ways.

Real-file checks use Krita-authored oracles from picto-corpus (krita/, made by tools/krita-oracles/generate.py). Each Krita file carries Krita's rendering of itself in mergedimage.png:

KRITA_TEST_DIR=/path/to/picto-corpus/krita cargo test -p picto-io --test it -- krita_corpus:: --ignored --nocapture

2026-10-09, Krita 5.2.9: 32 of 35 .ora files render within 3/255 of Krita's merged image; the other three differ for known reasons listed in crates/io/tests/it/krita_corpus.rs (Krita's tie-break in Darker and Lighter Color, and Hard Mix at a channel sum of exactly 1). In the other direction, Krita opened every Picto re-export of the first 34 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. The reader and writer are written from the specification and from files Krita writes; no application code was used.