jpeg-decoder

A decoder following the ITU-T.81 Specification. <br />

<p align="center"> <img src="decode/mike.jpg" alt="Original Mike" width="320"/> <img src="decode/gray_mike.png" alt="Grayscale Mike" width="320"/> </p>

use jpeg::prelude::*;

fn main() -> anyhow::Result<()> {
    let mut decoder = Decoder {
        mmap: unsafe { Mmap::map(&File::open("mike.jpg")?)? },
        cursor: 0,
        encoding: CodingProcess::BaselineDCT,
    };

    let ycbcrs: Vec<ColorSpace> = decoder.decode()?;
    let rgbs = ColorSpace::convert_ycbcr_to_rgb(ycbcrs);

    Ok(())
}

Coding Process

The decoder uses baseline sequential as its coding process. For other coding processes, see CODING_PROCESSES.md.

Portable SIMD

jpeg makes use of portable SIMD throughout various steps of the decoding process, as well as color space conversion and grayscaling. For example, consider dequantization:

<img src="decode/dequantization.png" width ="400" align="center"/>

This can be easily vectorized, simply cast the quantization table and coefficients into Simd<u8, 64> and perform a lane-multiplication with each other.

Such trivial cases also exist during coefficient level-shifting and marker segment parsing.