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Improve quality by only performing partial reductions until the end

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Kovid Goyal 2016-05-09 11:42:51 +05:30
parent e5c47ffb79
commit 9db35f3d7a
1 changed files with 7 additions and 6 deletions
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13
src/calibre/utils/imageops/quantize.cpp
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@ -312,6 +312,8 @@ QImage quantize(const QImage &image, unsigned int maximum_colors, bool dither) {
Node root = Node(); Node root = Node();
QVector<QRgb> color_table = QVector<QRgb>(MAX_COLORS); QVector<QRgb> color_table = QVector<QRgb>(MAX_COLORS);
const QRgb* line = NULL; const QRgb* line = NULL;
// Increasing this number improves quality but also increases running time and memory consumption
static const size_t MAX_LEAVES = 2000;
root.check_compiler(); root.check_compiler();
@ -322,10 +324,8 @@ QImage quantize(const QImage &image, unsigned int maximum_colors, bool dither) {
// by iterating over the color table rather than the pixels // by iterating over the color table rather than the pixels
if (img.format() != QImage::Format_RGB32) img = img.convertToFormat(QImage::Format_RGB32); if (img.format() != QImage::Format_RGB32) img = img.convertToFormat(QImage::Format_RGB32);
if (img.isNull()) throw std::bad_alloc(); if (img.isNull()) throw std::bad_alloc();
// There can be at-most 8*(maximum_colors + 1) nodes, since we reduce the // There can be no more than MAX_LEAVES * 8 nodes. Add 1 in case there is an off by 1 error somewhere.
// tree after each color is added Use an extra eight node just in case Pool<Node> node_pool((MAX_LEAVES + 1) * 8);
// there is an off-by-one error somewhere :)
Pool<Node> node_pool((2 + maximum_colors) * 8);
depth = (size_t)log2(maximum_colors); depth = (size_t)log2(maximum_colors);
depth = MAX(2, MIN(depth, MAX_DEPTH)); depth = MAX(2, MIN(depth, MAX_DEPTH));
@ -335,12 +335,13 @@ QImage quantize(const QImage &image, unsigned int maximum_colors, bool dither) {
for (c = 0; c < iwidth; c++) { for (c = 0; c < iwidth; c++) {
const QRgb pixel = *(line + c); const QRgb pixel = *(line + c);
root.add_color(qRed(pixel), qGreen(pixel), qBlue(pixel), depth, 0, &leaf_count, reducible_nodes, node_pool); root.add_color(qRed(pixel), qGreen(pixel), qBlue(pixel), depth, 0, &leaf_count, reducible_nodes, node_pool);
while (leaf_count > maximum_colors) while (leaf_count > MAX_LEAVES)
root.reduce(depth, &leaf_count, reducible_nodes, node_pool); root.reduce(depth, &leaf_count, reducible_nodes, node_pool);
} }
} }
while (leaf_count > maximum_colors)
root.reduce(depth, &leaf_count, reducible_nodes, node_pool);
if (leaf_count > maximum_colors) throw std::out_of_range("Leaf count > max colors, something bad happened");
color_table.resize(leaf_count); color_table.resize(leaf_count);
root.set_palette_colors(color_table.data(), &index, dither); root.set_palette_colors(color_table.data(), &index, dither);
ans.setColorTable(color_table); ans.setColorTable(color_table);