Function decode_linear 

pub fn decode_linear(
    data: &[u8],
    hdr: &LjpegHeader,
    out: &mut [u16],
    parallel: bool,
) -> Result<()>

Decode a lossless JPEG stream as a linear sample stream into out (row-major out.len() samples), decoding restart intervals in parallel when they cover whole rows. Samples beyond out are dropped; missing samples are left untouched.