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use std::sync::Arc;
use crate::{ColorType, Deadline, Deflater, Options, evaluate::Evaluator, png::PngImage};
pub mod alpha;
use crate::alpha::*;
pub mod bit_depth;
use crate::bit_depth::*;
pub mod color;
use crate::color::*;
pub mod palette;
use crate::palette::*;
pub(crate) fn perform_reductions(
mut png: Arc<PngImage>,
opts: &Options,
deadline: &Deadline,
eval: &Evaluator,
) -> Arc<PngImage> {
let mut evaluation_added = false;
// At low compression levels, skip some transformations which are less likely to be effective
// This currently affects optimization presets 0-2
let cheap = match opts.deflater {
Deflater::Libdeflater { compression } => compression < 12 && opts.fast_evaluation,
_ => false,
};
// Interlacing must be processed first in order to evaluate the rest correctly
if let Some(interlacing) = opts.interlace {
if let Some(reduced) = png.change_interlacing(interlacing) {
png = Arc::new(reduced);
}
}
// If alpha optimization is enabled, clean the alpha channel before continuing
// This can allow some color type reductions which may not have been possible otherwise
if opts.optimize_alpha && !deadline.passed() {
if let Some(reduced) = cleaned_alpha_channel(&png) {
png = Arc::new(reduced);
}
}
// Attempt to reduce 16-bit to 8-bit
// This is just removal of bytes and does not need to be evaluated
if opts.bit_depth_reduction && !deadline.passed() {
if let Some(reduced) = reduced_bit_depth_16_to_8(&png, opts.scale_16) {
png = Arc::new(reduced);
}
}
// Attempt to reduce RGB to grayscale
// This is just removal of bytes and does not need to be evaluated
if opts.color_type_reduction && opts.grayscale_reduction && !deadline.passed() {
if let Some(reduced) = reduced_rgb_to_grayscale(&png) {
png = Arc::new(reduced);
}
}
// Attempt to expand the bit depth to 8
// This does need to be evaluated but will be done so later when it gets reduced again
if opts.bit_depth_reduction && !deadline.passed() {
if let Some(reduced) = expanded_bit_depth_to_8(&png) {
png = Arc::new(reduced);
}
}
// Now retain the current png for the evaluator baseline
// It will only be entered into the evaluator if there are also others to evaluate
let mut baseline = png.clone();
// Attempt to reduce and sort the palette
if opts.palette_reduction && !deadline.passed() {
if let Some(reduced) = reduced_palette(&png, opts.optimize_alpha) {
png = Arc::new(reduced);
// If the palette was reduced but the data is unchanged then this should become the baseline
if png.data == baseline.data {
baseline = png.clone();
}
}
if let Some(reduced) = sorted_palette(&png) {
png = Arc::new(reduced);
}
// If either action changed the data then enter this into the evaluator
if !Arc::ptr_eq(&png, &baseline) {
eval.try_image_with_description(png.clone(), "Indexed (luma sort)");
evaluation_added = true;
}
}
// Attempt alpha removal
if opts.color_type_reduction && !deadline.passed() {
if let Some(reduced) = reduced_alpha_channel(&png, opts.optimize_alpha) {
png = Arc::new(reduced);
// For small differences, if a tRNS chunk is required then enter this into the evaluator
// Otherwise it is mostly just removal of bytes and should become the baseline
if png.ihdr.color_type.has_trns() && baseline.data.len() - png.data.len() <= 1000 {
eval.try_image(png.clone());
evaluation_added = true;
} else {
baseline = png.clone();
}
}
}
// Attempt to convert from indexed to channels
// This may give a better result due to dropping the PLTE chunk
if !cheap && opts.color_type_reduction && !deadline.passed() {
if let Some(reduced) =
indexed_to_channels(&png, opts.grayscale_reduction, opts.optimize_alpha)
{
// This result should not be passed on to subsequent reductions
eval.try_image(Arc::new(reduced));
evaluation_added = true;
}
}
// Attempt to reduce to indexed
// Keep the existing `png` var in case it is grayscale - we can test both for depth reduction later
let mut indexed = None;
if opts.color_type_reduction && opts.palette_reduction && !deadline.passed() {
if let Some(reduced) = reduced_to_indexed(&png, opts.grayscale_reduction) {
// Make sure the palette gets sorted (but don't bother evaluating both results)
let new = Arc::new(sorted_palette(&reduced).unwrap_or(reduced));
// For relatively small differences, enter this into the evaluator
// Otherwise we're confident enough for it to become the baseline
if png.data.len() - new.data.len() <= INDEXED_MAX_DIFF {
eval.try_image_with_description(new.clone(), "Indexed (luma sort)");
evaluation_added = true;
} else {
baseline = new.clone();
}
indexed = Some(new);
}
}
// Attempt additional palette sorting techniques
if !cheap && opts.palette_reduction {
// Collect a list of palettes so we can avoid evaluating the same one twice
let mut palettes = Vec::new();
if let ColorType::Indexed { palette } = &baseline.ihdr.color_type {
palettes.push(palette.clone());
}
// Make sure we use the `indexed` var as input if it exists
// This one doesn't need to be kept in the palette list as the sorters will fail if there's no change
let input = indexed.as_ref().unwrap_or(&png);
// Attempt to sort the palette using the battiato method
if !deadline.passed() {
if let Some(reduced) = sorted_palette_battiato(input) {
if let ColorType::Indexed { palette } = &reduced.ihdr.color_type {
if !palettes.contains(palette) {
palettes.push(palette.clone());
eval.try_image_with_description(
Arc::new(reduced),
"Indexed (battiato sort)",
);
evaluation_added = true;
}
}
}
}
// Attempt to sort the palette using the mzeng method
if !deadline.passed() {
if let Some(reduced) = sorted_palette_mzeng(input) {
if let ColorType::Indexed { palette } = &reduced.ihdr.color_type {
if !palettes.contains(palette) {
palettes.push(palette.clone());
eval.try_image_with_description(Arc::new(reduced), "Indexed (mzeng sort)");
evaluation_added = true;
}
}
}
}
}
// Attempt to reduce to a lower bit depth
if opts.bit_depth_reduction && !deadline.passed() {
// First try the `png` var
let reduced = reduced_bit_depth_8_or_less(&png);
// Then try the `indexed` var, unless we're doing cheap evaluations and already have a reduction
if (!cheap || reduced.is_none()) && !deadline.passed() {
if let Some(indexed) = indexed.and_then(|png| reduced_bit_depth_8_or_less(&png)) {
// Only evaluate this if it's different from the first result (which must be grayscale if it exists)
if reduced.as_ref().is_none_or(|r| r.data != indexed.data) {
eval.try_image(Arc::new(indexed));
evaluation_added = true;
}
}
}
// Enter the first result into the evaluator
if let Some(reduced) = reduced {
eval.try_image(Arc::new(reduced));
evaluation_added = true;
}
}
if evaluation_added {
eval.try_image(baseline.clone());
}
baseline
}