Seeing Without Dependencies: A Measurement of a Hand-Written JPEG and DEFLATE Image Path, Its Sampling Bias, and Its Abstention Contract

Abstract

A local-first assistant that cannot see images has two unattractive options: ship a vision model, or ship a dependency. styx-vision rejects both. It hand-writes a baseline JPEG decoder, a DEFLATE inflater for PNG, and a BMP reader in pure safe Rust, computes a fixed set of picture statistics from the decoded pixels, and renders them into a structured Chinese sentence for a text-only language model. The claimed cost of the design is two runtime crates; the claimed benefit is that the layer can never be absent, so the assistant can always be told something — including, when the pixels cannot be decoded, that nothing can be told. The decoder is real. All 10 reference JPEGs land inside the project's published tolerance (worst mean per-channel difference 0.0938 levels, worst single-pixel difference 3, no pixel differing by more than 8), and all 52/52 synthesized PNGs and 5/5 BMPs round-trip bit-exactly, including streams built from each of the three DEFLATE block types and each of the five PNG scanline filters. The abstention contract holds: a progressive JPEG is refused, yet its 64×48 dimensions are still reported, and in all 10 remote deployment states the description is non-empty. The gaps are in the parts nobody unit-tests. The ≤120,000 sampling stride changes mean saturation by 1.7e-4 at 3.84 megapixels while visiting 3.1% of the pixels, but inflates the colourfulness estimate by a factor of 32. All five injected one-line decoder defects are caught — though the upsampling defect slips past the criterion's mean bound and is caught only by its outlier condition, and the DEFLATE defect is invisible to the pixel-reference suite by construction. On the remote path, every image costs two detector requests because one backend is invoked twice, an 8 s per-request budget becomes 33.6 seconds against a slow sidecar, a 16-megabyte model reply is passed into the prompt verbatim as 16,777,385 characters, and the release itself does not pass its own cargo fmt or clippy gates — while 127 tests do pass.

Body

Imported entry paper (unverified hypothesis)

This paper was imported into jetessays as an entry paper from the author's local archive (styx-vision). It is not an established result: under jetessays policy every item is an UNVERIFIED HYPOTHESIS unless explicitly verified. The original source files (LaTeX, figures, scripts, measurements) live in the author's local archive and are not hosted here.

Abstract (as submitted)

A local-first assistant that cannot see images has two unattractive options: ship a vision model, or ship a dependency. styx-vision rejects both. It hand-writes a baseline JPEG decoder, a DEFLATE inflater for PNG, and a BMP reader in pure safe Rust, computes a fixed set of picture statistics from the decoded pixels, and renders them into a structured Chinese sentence for a text-only language model. The claimed cost of the design is two runtime crates; the claimed benefit is that the layer can never be absent, so the assistant can always be told something — including, when the pixels cannot be decoded, that nothing can be told. The decoder is real. All 10 reference JPEGs land inside the project's published tolerance (worst mean per-channel difference 0.0938 levels, worst single-pixel difference 3, no pixel differing by more than 8), and all 52/52 synthesized PNGs and 5/5 BMPs round-trip bit-exactly, including streams built from each of the three DEFLATE block types and each of the five PNG scanline filters. The abstention contract holds: a progressive JPEG is refused, yet its 64×48 dimensions are still reported, and in all 10 remote deployment states the description is non-empty. The gaps are in the parts nobody unit-tests. The ≤120,000 sampling stride changes mean saturation by 1.7e-4 at 3.84 megapixels while visiting 3.1% of the pixels, but inflates the colourfulness estimate by a factor of 32. All five injected one-line decoder defects are caught — though the upsampling defect slips past the criterion's mean bound and is caught only by its outlier condition, and the DEFLATE defect is invisible to the pixel-reference suite by construction. On the remote path, every image costs two detector requests because one backend is invoked twice, an 8 s per-request budget becomes 33.6 seconds against a slow sidecar, a 16-megabyte model reply is passed into the prompt verbatim as 16,777,385 characters, and the release itself does not pass its own cargo fmt or clippy gates — while 127 tests do pass.

Note

Imported via the jetessays seed importer. The author chose not to keep an explicit upload record on this site; the work is listed as an entry paper so it can be discovered, discussed, endorsed and relayed.

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