File Format & Storage

How OpenGPEX handles image import/export across 10+ formats with full color fidelity, and how it stores project data using content-addressable immutable assets.

Storage: Content-Addressable System (CAS)

Every image asset in the editor is stored by its content hash (SHA-256, with a MurmurHash3-128 fallback on insecure HTTP contexts) in IndexedDB:

Import image → SHA-256 hash → Store as {hash: Blob} in IndexedDB
                                    │
                                    ▼
              Layer references hash (metadata only)
              Duplicate imports → same hash → zero extra storage

Design benefits:

Deduplication — Identical images share a single blob regardless of how many layers reference them
Immutability — Original pixels are never modified; edits create new derivative assets
Non-destructive editing — Undo can always restore to any previous asset state
Garbage collection — Unreferenced assets are periodically cleaned by the Asset Sentinel

16-bit Color Fidelity Pipeline

OpenGPEX preserves full color depth from import:

Import 16-bit TIFF/PNG/RAW
    ↓
Store original source via frame.assetId (full precision blob, skipTiling)
    ↓
Generate 8-bit display version for Canvas rendering
    ↓
Edit using 8-bit preview (real-time, native refresh rate)
    ↓
Export: currently 8-bit composited output (16-bit export lane declared via exportBitDepth, not yet wired)

The original high-precision source data is never discarded during editing — it is stored as a regular asset referenced by frame.assetId and preserved through the full project lifecycle (GC-protected, dehydrated into .gpex files, etc.).

Future: When WebGPU enables native float16/float32 compositing, the 16-bit source blob will be consumed directly by the GPU compositor for full-precision export — without the complexity of a separate vips-based composite pipeline.

Format Support

Import (10+ formats)

Category	Formats	Technology
Standard web	JPEG, PNG, WebP, AVIF, BMP, GIF	Browser-native decode
Professional	TIFF (16-bit, CMYK, BigTIFF)	wasm-vips in Worker
Camera RAW	CR2, NEF, ARW, DNG	libraw-wasm in Worker
Vector	SVG, EPS	resvg-wasm / Ghostscript in Worker

Export

Format	Precision	Technology
JPEG, PNG, WebP, BMP	8-bit	Browser-native encode
AVIF	8-bit	@jsquash/avif WASM encoder in dedicated Worker
TIFF	8-bit	wasm-vips in Worker (LZW/ZIP/JPEG compression, BigTIFF option)
GIF	8-bit (animated)	gifenc (NeuQuant + LZW)

Metadata Round-Trip

Full preservation of image metadata across the pipeline:

Data	Supported Formats	Behavior
ICC Color Profiles	JPEG, PNG, TIFF, WebP, HEIC	Extract on import, inject on export
EXIF	JPEG, WebP, TIFF	Preserved through edit cycle
DPI/Resolution	JPEG, PNG, TIFF, BMP	Dual-layer: frame-level + per-layer record
PNG chunks	PNG	9 chunk types parsed (pHYs, iCCP, tEXt, gAMA, etc.)

.gpex Project Format

The native save format is a binary container that bundles:

Project manifest (frames, layers, state)
All referenced image assets (by CAS hash)
Preview thumbnail for cloud file listing

This container is what gets uploaded to GPEX-Cloud for cloud persistence.

GIF Animation

Multi-frame GIF files are decomposed into individual layers on import (linked via gifSequenceId), and reassembled into animated GIF on export — preserving frame timing and loop metadata.

Last updated: 2026-07-30