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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::{
bit_reader::BitReader,
error::{Error, Result},
frame::quant_weights,
headers::encodings::{Empty, UnconditionalCoder},
};
pub const NUM_QUANT_TABLES: usize = 17;
pub const GLOBAL_SCALE_DENOM: usize = 1 << 16;
#[derive(Debug)]
pub struct LfQuantFactors {
pub quant_factors: [f32; 3],
pub inv_quant_factors: [f32; 3],
}
impl LfQuantFactors {
pub fn new(br: &mut BitReader) -> Result<LfQuantFactors> {
let mut quant_factors = [0.0f32; 3];
if br.read(1)? == 1 {
quant_factors = quant_weights::LF_QUANT;
} else {
for qf in quant_factors.iter_mut() {
*qf = f32::read_unconditional(&(), br, &Empty {})? / 128.0;
if *qf < 1e-8 {
return Err(Error::LfQuantFactorTooSmall(*qf));
}
}
}
let inv_quant_factors = quant_factors.map(f32::recip);
Ok(LfQuantFactors {
quant_factors,
inv_quant_factors,
})
}
}
#[derive(Debug)]
pub struct QuantizerParams {
pub global_scale: u32,
pub quant_lf: u32,
}
impl QuantizerParams {
pub fn read(br: &mut BitReader) -> Result<QuantizerParams> {
let global_scale = match br.read(2)? {
0 => br.read(11)? + 1,
1 => br.read(11)? + 2049,
2 => br.read(12)? + 4097,
_ => br.read(16)? + 8193,
};
let quant_lf = match br.read(2)? {
0 => 16,
1 => br.read(5)? + 1,
2 => br.read(8)? + 1,
_ => br.read(16)? + 1,
};
Ok(QuantizerParams {
global_scale: global_scale as u32,
quant_lf: quant_lf as u32,
})
}
pub fn inv_global_scale(&self) -> f32 {
GLOBAL_SCALE_DENOM as f32 / self.global_scale as f32
}
pub fn inv_quant_lf(&self) -> f32 {
self.inv_global_scale() / self.quant_lf as f32
}
}