Crate zenpnm 

zenpnm

PNM/PAM/PFM image format decoder and encoder, with optional basic BMP support.

Zero-Copy Decoding

For PNM files with maxval=255 (the common case), decoding returns a borrowed slice into the input buffer — no allocation or copy needed. Formats that require transformation (16-bit downscaling, PFM byte reordering) allocate.

Supported Formats

PNM family (always available)

• P5 (PGM binary) — grayscale, 8-bit and 16-bit
• P6 (PPM binary) — RGB, 8-bit and 16-bit
• P7 (PAM) — arbitrary channels (grayscale, RGB, RGBA), 8-bit and 16-bit
• PFM — floating-point grayscale and RGB (32-bit float per channel)

Basic BMP (basic-bmp feature, opt-in)

• Uncompressed 24-bit (RGB) and 32-bit (RGBA) only
• Not auto-detected — use decode_bmp and encode_bmp explicitly
• No RLE, no indexed color, no advanced headers

Usage

use zenpnm::*;
use enough::Unstoppable;

// Encode pixels to PPM
let pixels = vec![255u8, 0, 0, 0, 255, 0]; // 2 RGB pixels
let encoded = encode_ppm(&pixels, 2, 1, PixelLayout::Rgb8, Unstoppable)?;

// Decode (auto-detects PNM format, zero-copy when possible)
let decoded = decode(&encoded, Unstoppable)?;
assert!(decoded.is_borrowed()); // zero-copy for PPM with maxval=255
assert_eq!(decoded.pixels(), &pixels[..]);

Credits

PNM implementation draws from zune-ppm by Caleb Etemesi (MIT/Apache-2.0/Zlib licensed).

Structs

DecodeOutput

Decoded image output. Pixels may be borrowed (zero-copy) or owned.

Limits

Resource limits for decode/encode operations.

Unstoppable

A Stop implementation that never stops (no cooperative cancellation).

Enums

PixelLayout

Pixel memory layout.

PnmError

Errors from PNM/BMP decoding and encoding.

Traits

Stop

Cooperative cancellation check.

Functions

decode

Decode any PNM format (auto-detected from magic bytes).

decode_with_limits

Decode any PNM format with resource limits.

encode_pam

Encode pixels as PAM (P7, arbitrary channels).

encode_pfm

Encode pixels as PFM (floating-point).

encode_pgm

Encode pixels as PGM (P5, binary grayscale).

encode_ppm

Encode pixels as PPM (P6, binary RGB).