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LibGfx: Implement PNG filtering on write
Is it another great upgrade to our PNG encoder like in 9aafaec259? Well, not really - it's not a 2x or 55x improvement like you saw there, but still it saves something: - a screenshot of a blank Serenity desktop dropped from about 45 KiB to 40 KiB. - re-encoding NASA photo of the Earth to PNG again saves about 25% (16.5 MiB -> 12.3 MiB), compared to not using filters. [1]: https://commons.wikimedia.org/wiki/File:The_Blue_Marble_(remastered).jpg
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Notes:
sideshowbarker
2024-07-17 09:32:11 +09:00
Author: https://github.com/krkk Commit: https://github.com/SerenityOS/serenity/commit/b5420b8a9a Pull-request: https://github.com/SerenityOS/serenity/pull/14537 Reviewed-by: https://github.com/awesomekling
@ -36,6 +36,18 @@ ALWAYS_INLINE static constexpr u32x4 expand4(u32 u)
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// Casting
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template<typename TSrc>
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ALWAYS_INLINE static u8x4 to_u8x4(TSrc v)
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{
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return __builtin_convertvector(v, u8x4);
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}
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template<typename TSrc>
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ALWAYS_INLINE static u16x4 to_u16x4(TSrc v)
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{
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return __builtin_convertvector(v, u16x4);
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}
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template<typename TSrc>
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ALWAYS_INLINE static u32x4 to_u32x4(TSrc v)
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{
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@ -43,4 +43,14 @@ ALWAYS_INLINE u8 paeth_predictor(u8 a, u8 b, u8 c)
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return c;
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}
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ALWAYS_INLINE AK::SIMD::u8x4 paeth_predictor(AK::SIMD::u8x4 a, AK::SIMD::u8x4 b, AK::SIMD::u8x4 c)
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{
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return AK::SIMD::u8x4 {
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paeth_predictor(a[0], b[0], c[0]),
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paeth_predictor(a[1], b[1], c[1]),
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paeth_predictor(a[2], b[2], c[2]),
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paeth_predictor(a[3], b[3], c[3]),
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};
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}
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};
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@ -7,12 +7,15 @@
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*/
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#include <AK/Concepts.h>
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#include <AK/SIMDExtras.h>
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#include <AK/String.h>
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#include <LibCompress/Zlib.h>
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#include <LibCrypto/Checksum/CRC32.h>
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#include <LibGfx/Bitmap.h>
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#include <LibGfx/PNGWriter.h>
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#pragma GCC diagnostic ignored "-Wpsabi"
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namespace Gfx {
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class PNGChunk {
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@ -134,6 +137,24 @@ void PNGWriter::add_IEND_chunk()
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add_chunk(png_chunk);
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}
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union [[gnu::packed]] Pixel {
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ARGB32 rgba { 0 };
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struct {
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u8 red;
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u8 green;
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u8 blue;
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u8 alpha;
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};
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AK::SIMD::u8x4 simd;
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ALWAYS_INLINE static AK::SIMD::u8x4 gfx_to_png(Pixel pixel)
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{
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swap(pixel.red, pixel.blue);
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return pixel.simd;
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}
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};
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static_assert(AssertSize<Pixel, 4>());
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void PNGWriter::add_IDAT_chunk(Gfx::Bitmap const& bitmap)
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{
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PNGChunk png_chunk { "IDAT" };
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@ -142,16 +163,91 @@ void PNGWriter::add_IDAT_chunk(Gfx::Bitmap const& bitmap)
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ByteBuffer uncompressed_block_data;
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uncompressed_block_data.ensure_capacity(bitmap.size_in_bytes() + bitmap.height());
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Pixel const dummy_scanline[bitmap.width()] {};
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auto* scanline_minus_1 = dummy_scanline;
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for (int y = 0; y < bitmap.height(); ++y) {
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uncompressed_block_data.append(0);
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auto* scanline = reinterpret_cast<Pixel const*>(bitmap.scanline(y));
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struct Filter {
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PNG::FilterType type;
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ByteBuffer buffer {};
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int sum = 0;
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void append(u8 byte)
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{
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buffer.append(byte);
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sum += static_cast<i8>(byte);
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}
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void append(AK::SIMD::u8x4 simd)
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{
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append(simd[0]);
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append(simd[1]);
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append(simd[2]);
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append(simd[3]);
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}
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};
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Filter none_filter { .type = PNG::FilterType::None };
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none_filter.buffer.ensure_capacity(sizeof(Pixel) * bitmap.height());
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Filter sub_filter { .type = PNG::FilterType::Sub };
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sub_filter.buffer.ensure_capacity(sizeof(Pixel) * bitmap.height());
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Filter up_filter { .type = PNG::FilterType::Up };
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up_filter.buffer.ensure_capacity(sizeof(Pixel) * bitmap.height());
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Filter average_filter { .type = PNG::FilterType::Average };
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average_filter.buffer.ensure_capacity(sizeof(ARGB32) * bitmap.height());
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Filter paeth_filter { .type = PNG::FilterType::Paeth };
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paeth_filter.buffer.ensure_capacity(sizeof(ARGB32) * bitmap.height());
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auto pixel_x_minus_1 = Pixel::gfx_to_png(*dummy_scanline);
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auto pixel_xy_minus_1 = Pixel::gfx_to_png(*dummy_scanline);
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for (int x = 0; x < bitmap.width(); ++x) {
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auto pixel = bitmap.get_pixel(x, y);
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uncompressed_block_data.append(pixel.red());
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uncompressed_block_data.append(pixel.green());
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uncompressed_block_data.append(pixel.blue());
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uncompressed_block_data.append(pixel.alpha());
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auto pixel = Pixel::gfx_to_png(scanline[x]);
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auto pixel_y_minus_1 = Pixel::gfx_to_png(scanline_minus_1[x]);
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none_filter.append(pixel);
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sub_filter.append(pixel - pixel_x_minus_1);
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up_filter.append(pixel - pixel_y_minus_1);
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// The sum Orig(a) + Orig(b) shall be performed without overflow (using at least nine-bit arithmetic).
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auto sum = AK::SIMD::to_u16x4(pixel_x_minus_1) + AK::SIMD::to_u16x4(pixel_y_minus_1);
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auto average = AK::SIMD::to_u8x4(sum / 2);
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average_filter.append(pixel - average);
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paeth_filter.append(pixel - PNG::paeth_predictor(pixel_x_minus_1, pixel_y_minus_1, pixel_xy_minus_1));
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pixel_x_minus_1 = pixel;
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pixel_xy_minus_1 = pixel_y_minus_1;
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}
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scanline_minus_1 = scanline;
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// 12.8 Filter selection: https://www.w3.org/TR/PNG/#12Filter-selection
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// For best compression of truecolour and greyscale images, the recommended approach
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// is adaptive filtering in which a filter is chosen for each scanline.
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// The following simple heuristic has performed well in early tests:
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// compute the output scanline using all five filters, and select the filter that gives the smallest sum of absolute values of outputs.
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// (Consider the output bytes as signed differences for this test.)
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Filter& best_filter = none_filter;
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if (abs(best_filter.sum) > abs(sub_filter.sum))
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best_filter = sub_filter;
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if (abs(best_filter.sum) > abs(up_filter.sum))
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best_filter = up_filter;
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if (abs(best_filter.sum) > abs(average_filter.sum))
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best_filter = average_filter;
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if (abs(best_filter.sum) > abs(paeth_filter.sum))
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best_filter = paeth_filter;
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uncompressed_block_data.append(to_underlying(best_filter.type));
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uncompressed_block_data.append(best_filter.buffer);
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}
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auto maybe_zlib_buffer = Compress::ZlibCompressor::compress_all(uncompressed_block_data);
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