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Fix error diffusion algorithm

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The error propagation must be limited to 0...255 values, and the new
quantization error must be calculated to that limited value. Also the
1/16 part of the Floyd-Steinberg distribution must be the remaining of
the other parts.
This commit is contained in:
David Capello 2019-04-02 13:54:39 -03:00
parent c2af88343e
commit b6d07d995f
1 changed files with 15 additions and 9 deletions
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24
src/render/error_diffusion.cpp
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@ -64,15 +64,14 @@ doc::color_t ErrorDiffusionDither::ditherRgbToIndex2D(
doc::rgba_getb(color), doc::rgba_getb(color),
doc::rgba_geta(color) doc::rgba_geta(color)
}; };
int u[kChannels];
for (int i=0; i<kChannels; ++i) { for (int i=0; i<kChannels; ++i) {
v[i] += m_err[i][x+1] / 16; v[i] += m_err[i][x+1];
u[i] = MID(0, v[i], 255); v[i] = MID(0, v[i], 255);
} }
const doc::color_t index = const doc::color_t index =
(rgbmap ? rgbmap->mapColor(u[0], u[1], u[2], u[3]): (rgbmap ? rgbmap->mapColor(v[0], v[1], v[2], v[3]):
palette->findBestfit(u[0], u[1], u[2], u[3], m_transparentIndex)); palette->findBestfit(v[0], v[1], v[2], v[3], m_transparentIndex));
doc::color_t palColor = palette->getEntry(index); doc::color_t palColor = palette->getEntry(index);
if (m_transparentIndex == index || doc::rgba_geta(palColor) == 0) { if (m_transparentIndex == index || doc::rgba_geta(palColor) == 0) {
@ -90,10 +89,17 @@ doc::color_t ErrorDiffusionDither::ditherRgbToIndex2D(
// TODO using Floyd-Steinberg matrix here but it should be configurable // TODO using Floyd-Steinberg matrix here but it should be configurable
for (int i=0; i<kChannels; ++i) { for (int i=0; i<kChannels; ++i) {
int* err = &m_err[i][x]; int* err = &m_err[i][x];
err[ +2] += quantError[i] * 7;
err[m_width ] += quantError[i] * 3; const int a = quantError[i] * 7 / 16;
err[m_width+1] += quantError[i] * 5; const int b = quantError[i] * 3 / 16;
err[m_width+2] += quantError[i] * 1; const int c = quantError[i] * 5 / 16;
// Same as d=quantError[i]*1/16 but without rounding errors
const int d = quantError[i] - a - b - c;
err[ +2] += a;
err[m_width ] += b;
err[m_width+1] += c;
err[m_width+2] += d;
} }
return index; return index;