Crate otf_pixels_codec_jpeg 

Baseline JPEG codec for otf-pixels, implemented from scratch.

“Baseline” here means what the format means by it: 8-bit samples, sequential DCT, Huffman entropy coding. Progressive JPEG is a different enough decoder that ADR-0004 puts it behind a wrapped codec instead; this crate reports it as PixelsError::Unsupported rather than half-decoding it.

Memory

Decode is streaming, at one MCU row. A JPEG’s entropy stream is a single run of bits with no per-row structure, but it is ordered: every block of MCU row n precedes every block of row n + 1. So the decoder keeps one band of component planes — 8 or 16 pixel rows — converts it to interleaved output, serves those rows, and reuses the band. Nothing scales with image height, which is what makes a thumbnail of a 24 MP photograph affordable.

Safety

Every parser here reads attacker-controlled bytes. Malformed input is a value, never a panic: unsafe_code = "forbid" and the workspace’s ban on unwrap/expect/panic! mean the classic decoder failures — a Huffman table indexing past its symbols, an MCU count overflowing, a block written outside its plane — are unrepresentable rather than merely avoided.

Structs

Component

One component of a frame.

Frame

A parsed start-of-frame header.

JpegCodec

The JPEG entry in a sniffing registry.

JpegDecoder

Decodes a JPEG stream.

JpegEncoder

Encodes a baseline JPEG stream.

Scan

A parsed start-of-scan header.

ScanComponent

One component of a scan, naming the entropy tables it is coded with.

Enums

Scale

How much of an image a decode produces, as eighths of full size.

Subsampling

How much the chroma channels are subsampled relative to luma.

Constants

SIGNATURE

The two-byte prefix every JPEG stream starts with, plus the marker that must follow it.

Functions

probe

Whether prefix starts with a JPEG signature.