Crate pith_jpeg 

JPEG decoding for baseline (SOF0/SOF1) and progressive (SOF2) profiles.

Part of the pith zero-dependency hashing suite: this crate depends only on pith-digest, pith-math and pith-image, so the whole suite resolves without a single registry package.

Scope

Decodes JFIF/EXIF-style JPEG streams: 8-bit precision, Huffman entropy coding, 1–3 components, sampling factors up to 2×2 per component (4:4:4, 4:2:2, 4:4:0, 4:2:0 and friends), restart markers, and the full progressive script (spectral selection + successive approximation, interleaved DC scans, EOBRUN). Arithmetic-coded frames (SOF9–SOF11, SOF13–SOF15), lossless frames (SOF3/SOF7/SOF11/SOF15), differential frames (SOF5–SOF7/13–15), 12-bit precision and CMYK output are refused with Error::Unsupported naming the exact coding process.

Fidelity contract

The integer pipeline is a transcription of libjpeg-turbo’s islow IDCT (jidctint.c), fancy chroma upsampling (jdsample.c) and fixed-point YCbCr→RGB (jdcolor.c), so output is byte-exact with libjpeg -dct int -nosmooth (which is what Pillow produces). The only deliberate divergence is arithmetic on adversarially large coefficients: intermediate sums are i64, where libjpeg’s int accumulators would wrap.

pith_math::idct2/idct2_2d is not used on the decode path: it is an orthonormal DCT-III in f64 whose rounding differs from JPEG’s fixed-point islow, so substituting it would break byte-exactness with the reference decoder. It is used in this crate’s test-suite as an independent oracle that the transcription stays inside the documented tolerance (see tests/ and src/idct.rs).

Modules

ffi

The C ABI surface of pith-jpeg: the entry points the Python (ctypes), Node (koffi) and Go (cgo) SDKs bind through.

reference

The committed reference contract of this crate, re-expressed over the crate’s own pipeline.

Enums

Jpeg

A decoded JPEG image: single-component frames yield Image<Gray>, three-component frames yield Image<Rgb>.

Functions

decode

Decodes a JPEG byte stream into pixels.