jxl 0.1.5

High performance Rust implementation of a JPEG XL decoder
Documentation 
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// Copyright (c) the JPEG XL Project Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

use crate::{
    error::{Error, Result},
    frame::{HfMetadata, LfGlobalState},
    headers::frame_header::{Encoding, FrameHeader},
    image::Image,
};

use jxl_transforms::transform_map::*;

pub fn create_sigma_image(
    frame_header: &FrameHeader,
    lf_global: &LfGlobalState,
    hf_meta: &Option<HfMetadata>,
) -> Result<Image<f32>> {
    let size_blocks = frame_header.size_blocks();
    let rf = &frame_header.restoration_filter;
    let sigma_xsize = size_blocks.0;
    let sigma_ysize = size_blocks.1;
    // We might over-read the sigma row slightly when applying EPF, so ensure that there is enough
    // space to avoid having the out-of-bounds read from the row causing a panic (the value does
    // not affect any pixels that are actually visualized, so we don't need to set it to anything
    // special below).
    let mut sigma_image = Image::<f32>::new((sigma_xsize + 2, sigma_ysize))?;
    #[allow(clippy::excessive_precision)]
    const INV_SIGMA_NUM: f32 = -1.1715728752538099024;
    if frame_header.encoding == Encoding::VarDCT {
        let hf_meta = hf_meta.as_ref().unwrap();
        let quant_params = lf_global.quant_params.as_ref().unwrap();
        let quant_scale = 1.0 / quant_params.inv_global_scale();
        for by in 0..size_blocks.1 {
            let raw_quant_row = hf_meta.raw_quant_map.row(by);
            let transform_row = hf_meta.transform_map.row(by);
            for bx in 0..size_blocks.0 {
                let raw_quant = raw_quant_row[bx];
                let raw_transform_id = transform_row[bx];
                let transform_id = raw_transform_id & 127;
                let is_first_block = raw_transform_id >= 128;
                if !is_first_block {
                    continue;
                }
                let transform_type = HfTransformType::from_usize(transform_id as usize)
                    .ok_or(Error::InvalidVarDCTTransform(transform_id as usize))?;
                let cx = covered_blocks_x(transform_type) as usize;
                let cy = covered_blocks_y(transform_type) as usize;
                let sigma_quant =
                    rf.epf_quant_mul / (quant_scale * raw_quant as f32 * INV_SIGMA_NUM);
                for iy in 0..cy {
                    for ix in 0..cx {
                        let sharpness = hf_meta.epf_map.row(by + iy)[bx + ix] as usize;
                        let sigma = (sigma_quant * rf.epf_sharp_lut[sharpness]).min(-1e-4);
                        sigma_image.row_mut(by + iy)[bx + ix] = 1.0 / sigma;
                    }
                }
            }
        }
    } else {
        // TODO(szabadka): Instead of allocating an image, return an enum with image and f32
        // variants.
        let sigma = INV_SIGMA_NUM / rf.epf_sigma_for_modular;
        sigma_image.fill(sigma);
    }
    Ok(sigma_image)
}