imazen-26 image corpus

September 10, 2026 · View on GitHub

This repository is the canonical home of the imazen-26 corpus — provenance manifests, the canonical train/validate/test split, the variant-set registry, and generation tooling. Image bytes are not in git on canonical branches: they are served from public R2 (see ACCESS.md); local checkouts may sync them into the class folders (gitignored). Derived render sets live on variant/* branches in Git LFS, with the objects served from R2 rather than GitHub — see Variant branches. Moved out of imazen/codec-corpus on 2026-08-23 so the corpus versions as one unit (git tags cover corpus + splits + registry together). Predecessor record: codec-corpus PR #12.

imazen-26 image corpus

A test corpus for image codecs and processing — 2,160 images, ~5.9 GB across 21 categories. Deliberately diverse: real photographs, stock photography, artwork reproductions, born-digital government documents, document/manuscript scans, synthetic charts and line patterns, UI screenshots, and AI-generated graphics. It spans the hard cases that codecs trip on — photographic noise, hard-edged vector graphics, bilevel scan texture, dense text, and large flat regions.

Every file follows one naming convention (lowercase throughout):

<NNNN>_<category>_<descriptor>[_<keyinfo>...]_<WxH>.<ext>

NNNN is a unique id from the folder's block; descriptor carries the description and attribution; keyinfo holds page/variant/camera/iso (f-stops written f1p8, no dot).

Folders

Folder	n	Size	Format	Dims (MP)	Source	License	Contents
`1000-lilith-photos-general`	72	0.26 GB	jpg/heic	6.9–12.2	lilith (own)	PD-own	Everyday photographs (phones: Note9…S25U, iPhones), mixed subjects
`1200-lilith-interiors`	49	0.20 GB	jpg/heic/png	3.0–12.2	lilith (own)	PD-own	Interior & architecture photos
`1400-lilith-nature`	157	0.75 GB	heic/jpg/png/dng	1.6–124	lilith (own)	PD-own	Landscape/nature; incl. HEIC + 3 DNG raws + panoramas
`1600-lilith-food`	41	0.13 GB	jpg/heic	7.4–24.5	lilith (own)	PD-own	Food & plated dishes
`2000-unsplash-people`	28	0.08 GB	jpg	6.0–32.7	Unsplash	Unsplash-License	Stock portraits / people
`2200-unsplash-renders`	13	0.04 GB	jpg	5.8–99	Unsplash	Unsplash-License	Abstract / 3D renders
`2400-unsplash-textures`	10	0.09 GB	jpg	5.6–102	Unsplash	Unsplash-License	Surfaces / textures
`3000-art-institute-of-chicago-photos`	15	0.04 GB	jpg	1.8–20.9	Art Institute of Chicago	CC0	Open-access artwork reproductions (paintings, prints)
`3300-met-museum-photos`	24	0.06 GB	jpg	0.2–16	The Met	CC0	Open-access artwork reproductions
`5000-national-park-service-brochures`	59	0.56 GB	png	0.5–55.6	NPS	PD-USGov	Park brochures/maps (born-digital PDF→PNG), color + grayscale variants
`5200-epa-climate-impact-2021-report`	25	0.03 GB	png	11.4	EPA	PD-USGov	Report pages — text, tables, charts
`5300-noaa-hurricane-documents`	44	0.06 GB	png	8.4	NOAA/NHC	PD-USGov	Hurricane report pages — text, maps, charts
`6000-lilith-scans-public-patents`	113	0.09 GB	png/jpg	7.9–8.0	USPTO	PD	3 US patents × {1-bit CCITT original, color rescan, gray rescan} — bilevel + scan texture
`6600-ia-scans-manuscript-illustrations`	36	1.04 GB	png	6.0–37	Internet Archive	PD	PD plate scans (Haeckel, Hokusai, Owen Jones, Redouté, Shin-Bijutsukai, Trouvelot)
`6800-ia-scans-manuscript-text`	36	0.32 GB	png	6.0–30	Internet Archive	PD	PD manuscript text-page scans (same works)
`7000-lilith-plots`	126	0.02 GB	png	1.0	lilith (generated)	PD-own	Synthetic charts + line/polygon test patterns (hard-edge graphics)
`8000-lilith-mobile-screenshots`	32	0.04 GB	png/jpg	2.3–5.6	various web/apps	screenshot-unverified	Phone UI/web screenshots — third-party content
`8100-lilith-web-screenshots`	370	0.27 GB	png	0.2–5.2	various web	PD (PD-filtered)	Website viewport crops at multiple resolutions/dpr
`9000-lilith-ai-clipart`	86	0.04 GB	png	1.0–1.6	lilith (AI-gen)	PD-own	AI-generated clipart (flat / transparent)
`9094-lilith-ai-illustrations`	75	0.26 GB	png	1.6	lilith (AI-gen)	PD-own	AI-generated illustrations
`9226-lilith-ai-products`	749	1.53 GB	png/jpg	1.0–17	lilith (AI-gen)	PD-own	AI-generated product images, by product-category subfolders

Licensing status

License	Files	Notes
PD-own	1,360	lilith's own photos, generated plots, AI images — released to public domain
PD	533	US patents + Internet-Archive scans of PD works; per-file `pd_basis` in manifests
PD-USGov	128	NPS/EPA/NOAA federal works (17 USC §105)
Unsplash-License	51	Free to use; attribution appreciated (photographer in filename). Unsplash terms apply
CC0	39	Met + Art Institute open-access (public-domain dedication)
Mailing-list-PD / PD-tool	17	within the web-screenshot set
screenshot-unverified	32	mobile screenshots of third-party sites — not cleared for redistribution

~2,128 of 2,160 files are public-domain or PD-own (freely usable). The 51 Unsplash images follow the Unsplash License; the 32 mobile screenshots are unverified and should be excluded from any redistribution until cleared.

Caveats: license is folder-level best-effort, not per-file legal clearance. Artwork "photos" are reproductions of PD works (CC0 on the reproduction). Document and screenshot renders may embed third-party logos/photos whose rights differ from the page. For redistribution, verify the 8000 set and spot-check embedded media.

Variant branches

Derived render sets are distributed as variant/* branches of this repository, with the bytes in Git LFS, so a consumer can check out exactly one variant without the corpus carrying any of them on main.

Branch	Contents	Pointers	Size
`variant/png-v3`	SDR (+ HDR where present) PNG renders	2,233	15.4 GB
`variant/pristine-8th`	artifact-free 1/8 references, SDR + HDR	581	0.23 GB

git clone --branch variant/png-v3 --single-branch --depth 1 \
  https://github.com/imazen/imazen-26.git

The LFS objects themselves are not on GitHub's LFS store. Each variant branch's .lfsconfig points Git LFS at imazen-lfs.pages.dev, imazen's instance of git-lfs-s3-proxy, which answers a download request with plain https://codec-corpus.r2.imazen.org/lfs/imazen-26/<sha256> URLs. A clone therefore needs no credentials and draws no GitHub LFS bandwidth; the objects are the same bytes as the R2 prefixes in ACCESS.md, stored once more under lfs/imazen-26/ keyed by sha256 (ACCESS.md §7). main carries the same .lfsconfig, so a branch created from it inherits the proxy before its first object is pushed; main itself tracks nothing in LFS.

Pushing a new variant branch needs write access to that prefix: an R2 API token with Object Read & Write on codec-corpus, handed to Git LFS as the username/password for the proxy host — at the credential prompt on the first push, or with git config lfs.url in your own clone set to the .lfsconfig URL with <id>:<secret> as its userinfo. That URL never goes in the repository. scripts/lfs_r2_migrate.py plans, server-side copies, and hash-verifies a branch's objects against its pointers.

Each variant branch carries a VARIANT.md saying what the set is, how it was produced, and where its coverage is incomplete — variant/png-v3 mirrors 2,157 of the 2,160 canonical images and lists the three that have no render in its MISSING.tsv.

corpus-guard enforces the split: canonical branches carry no image bytes, and on a variant/* branch images must be LFS pointers with the filter declared in .gitattributes and a credential-free .lfsconfig naming the proxy. A variant/* branch is never merged into main, and a new render pass gets a new branch rather than rewriting an existing one.

The same bytes stay available over plain HTTPS for consumers who want a handful of files without git or an LFS client — see ACCESS.md.

Manifests

<folder>/MANIFEST.tsv — per-folder, one row per image, with full provenance (original_filename, camera/artist/contributor/pd_basis/url/sha256 where applicable) and license. Source of truth.
CORPUS-MANIFEST.tsv — unified aggregate (regenerate via python3 scripts/build_corpus_manifest.py). Column docs in CORPUS-MANIFEST.README.md.

Excluded from the corpus: nope/ (rejected candidates) and the build-history archive at /mnt/v/output/codec-corpus/imazen-26-archive-2026-06-09/.