Module jpeg 

Pure-Rust JPEG coefficient codec (zero external dependencies).

Reads and writes baseline and progressive JPEG files, providing direct access to quantized DCT coefficients without any pixel-domain processing. This is the foundation for steganographic embedding, which operates entirely in the DCT domain.

Supports:

• Baseline sequential DCT (SOF0), 8-bit precision
• Progressive DCT (SOF2) — read-only (always writes baseline)
• YCbCr, grayscale, and arbitrary component counts
• Chroma subsampling: 4:2:0, 4:2:2, 4:4:4
• Restart markers (DRI/RST)
• Byte-for-byte round-trip for unmodified baseline images
• Huffman table rebuild for modified coefficients

Does NOT support:

• Arithmetic coding (SOF9+) – rejected at parse time
• 12-bit precision – rejected at parse time

Modules

bitio

Bit-level I/O for JPEG entropy-coded data.

dct

DCT coefficient storage and quantization tables.

error

Error types for JPEG parsing and encoding.

frame

JPEG frame header (SOF0) parsing.

huffman

Huffman coding tables for JPEG entropy decoding and encoding.

marker

JPEG marker parsing and iteration.

pixels

Pixel-domain conversion for the Y (luminance) channel.

scan

JPEG scan data encoding and decoding.

tables

Quantization and Huffman table parsing/serialization.

zigzag

Zigzag scan order mapping between JPEG coefficient order and natural order.

Structs

JpegImage

A decoded JPEG image providing access to quantized DCT coefficients.