https://github.com/cpg314/png-achunk

Encode and decode custom binary chunks in PNG images
https://github.com/cpg314/png-achunk

encoding-decoding png rust

Last synced: 1 day ago
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Encode and decode custom binary chunks in PNG images

• Host: GitHub
• URL: https://github.com/cpg314/png-achunk
• Owner: cpg314
• License: apache-2.0
• Created: 2023-11-19T11:07:51.000Z (12 months ago)
• Default Branch: main
• Last Pushed: 2024-08-10T16:50:42.000Z (3 months ago)
• Last Synced: 2024-08-10T17:59:12.527Z (3 months ago)
• Topics: encoding-decoding, png, rust
• Language: Rust
• Homepage: https://c.pgdm.ch/code
• Size: 14.6 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
This library allows encoding and decoding custom chunks in PNG images.

These chunks can contain arbitrary binary data (of length at most 2^32-1), placed before or after image data.

If they are properly marked as ancillary (see [PNG specification, section 11.3](https://www.w3.org/TR/png/#11Ancillary-chunks)), good decoders will simply ignore them.

Currently, the encoder always places the custom chunks before the image data, which allows reading them without even decoding the image.

## Usage

### Rust

The [`Encoder`] struct implements the [`image::ImageEncoder`] trait, so that it can be used to encode [`image::DynamicImage`] images:

```rust

// Create custom chunk

// The name implies that this is a private non-critical chunk that is safe to copy

// only when non-critical chuks have not been modified.

let chunk_type = png_achunk::ChunkType::from_ascii(&"teST")?;

let chunk = png_achunk::Chunk::new(chunk_type, vec![4, 5, 6])?;

// Encode an `image::DynamicImage`

image.write_with_encoder(

    png_achunk::Encoder::new_to_file("test.png")?.with_custom_chunk(chunk.clone()),

)?;

```

For decoding:

```rust

// Decode image and ancillary chunks

let (image, chunks) = png_achunk::Decoder::from_file("test.png")?.decode_all()?;

// Decode ancillary chunks without reading the image data

let chunks = png_achunk::Decoder::from_file("test.png")?.decode_ancillary_chunks()?;

```

### Python

Only a primitive interface is implemented at the moment.

First, copy `target/release/libpng_achunk_py.so` to `png_achunk.so`.

```python

import png_achunk

chunk = png_achunk.read_chunk("test.png", "teST")

```

### C

Only a primitive interface is implemented at the moment.

The example in `c/test.c` can be compiled with

```

$ gcc test.c -L. -l:libpng_achunk.a -lm -o test

```

## Implementation

PNG encoding and decoding use the [`png`] crate. For decoding, we need to decode ancillary chunks manually as [`png::Decoder`] does not expose them.