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Make dithering use a serpent scan

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This commit is contained in:
Kovid Goyal 2016-05-08 21:36:58 +05:30
parent e163470978
commit 785da0a1a2
1 changed files with 10 additions and 5 deletions
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15
src/calibre/utils/imageops/quantize.cpp
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@ -221,12 +221,17 @@ static void dither_image(QImage &img, QImage &ans, QVector<QRgb> &color_table, N
QRgb *mline = NULL, *sline = NULL, pixel = 0, new_pixel = 0; QRgb *mline = NULL, *sline = NULL, pixel = 0, new_pixel = 0;
unsigned char *bits = NULL, index = 0; unsigned char *bits = NULL, index = 0;
int red_error = 0, green_error = 0, blue_error = 0, iheight = img.height(), iwidth = img.width(), r = 0, c = 0; int red_error = 0, green_error = 0, blue_error = 0, iheight = img.height(), iwidth = img.width(), r = 0, c = 0;
bool is_odd = false;
int start = 0, delta = 0;
for (r = 0; r < iheight; r++) { for (r = 0; r < iheight; r++) {
mline = reinterpret_cast<QRgb*>(img.scanLine(r)); mline = reinterpret_cast<QRgb*>(img.scanLine(r));
sline = r + 1 < iheight ? reinterpret_cast<QRgb*>(img.scanLine(r+1)) : NULL; sline = r + 1 < iheight ? reinterpret_cast<QRgb*>(img.scanLine(r+1)) : NULL;
bits = ans.scanLine(r); bits = ans.scanLine(r);
for (c = 0; c < iwidth; c++) { is_odd = r & 1;
start = is_odd ? iwidth - 1 : 0;
delta = is_odd ? -1 : 1;
for (c = start; 0 < (is_odd ? c : iwidth - c); c += delta) {
pixel = *(mline + c); pixel = *(mline + c);
index = root.index_for_nearest_color(qRed(pixel), qGreen(pixel), qBlue(pixel), 0); index = root.index_for_nearest_color(qRed(pixel), qGreen(pixel), qBlue(pixel), 0);
*(bits + c) = index; *(bits + c) = index;
@ -234,13 +239,13 @@ static void dither_image(QImage &img, QImage &ans, QVector<QRgb> &color_table, N
red_error = qRed(pixel) - qRed(new_pixel); red_error = qRed(pixel) - qRed(new_pixel);
green_error = qGreen(pixel) - qGreen(new_pixel); green_error = qGreen(pixel) - qGreen(new_pixel);
blue_error = qBlue(pixel) - qBlue(new_pixel); blue_error = qBlue(pixel) - qBlue(new_pixel);
if (c + 1 < iwidth) { if (0 < (is_odd ? c : iwidth - c - 1)) {
propagate_error(mline, c + 1, 7, red_error, green_error, blue_error); propagate_error(mline, c + delta, 7, red_error, green_error, blue_error);
if (sline != NULL) propagate_error(sline, c + 1, 1, red_error, green_error, blue_error); if (sline != NULL) propagate_error(sline, c + delta, 1, red_error, green_error, blue_error);
} }
if (sline != NULL) { if (sline != NULL) {
propagate_error(sline, c, 5, red_error, green_error, blue_error); propagate_error(sline, c, 5, red_error, green_error, blue_error);
if (c > 1) propagate_error(sline, c - 1, 3, red_error, green_error, blue_error); if (0 < (is_odd ? iwidth - c - 1 : c)) propagate_error(sline, c - delta, 3, red_error, green_error, blue_error);
} }
} }
} }