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https://github.com/webmproject/libwebp.git
synced 2025-08-29 23:32:05 +02:00
new segmentation algorithm
fixes the 'blocky sky problem' (saturation problem: when luma was flat, chroma noise was taking over, resulting in random segment id assigned. When just using a common uniform segment was better). + side clean-up and readibility/experimentability MACRO'ization + added '-map 7' option Change-Id: I35982a9e43c0fecbfdd7b05e4813e8ba8c121d71
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@@ -17,31 +17,18 @@
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extern "C" {
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#endif
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static WEBP_INLINE uint8_t clip_8b(int v) {
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return (!(v & ~0xff)) ? v : (v < 0) ? 0 : 255;
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}
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static WEBP_INLINE int clip_max(int v, int max) {
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return (v > max) ? max : v;
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}
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//------------------------------------------------------------------------------
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// Compute susceptibility based on DCT-coeff histograms:
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// the higher, the "easier" the macroblock is to compress.
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static int ClipAlpha(int alpha) {
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return alpha < 0 ? 0 : alpha > 255 ? 255 : alpha;
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}
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int VP8GetAlpha(const int histo[MAX_COEFF_THRESH + 1]) {
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int num = 0, den = 0, val = 0;
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int k;
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int alpha;
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// note: changing this loop to avoid the numerous "k + 1" slows things down.
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for (k = 0; k < MAX_COEFF_THRESH; ++k) {
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if (histo[k + 1]) {
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val += histo[k + 1];
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num += val * (k + 1);
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den += (k + 1) * (k + 1);
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}
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}
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// we scale the value to a usable [0..255] range
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alpha = den ? 10 * num / den - 5 : 0;
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return ClipAlpha(alpha);
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}
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const int VP8DspScan[16 + 4 + 4] = {
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// Luma
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0 + 0 * BPS, 4 + 0 * BPS, 8 + 0 * BPS, 12 + 0 * BPS,
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@@ -53,27 +40,23 @@ const int VP8DspScan[16 + 4 + 4] = {
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8 + 0 * BPS, 12 + 0 * BPS, 8 + 4 * BPS, 12 + 4 * BPS // V
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};
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static int CollectHistogram(const uint8_t* ref, const uint8_t* pred,
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int start_block, int end_block) {
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int histo[MAX_COEFF_THRESH + 1] = { 0 };
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int16_t out[16];
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int j, k;
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static void CollectHistogram(const uint8_t* ref, const uint8_t* pred,
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int start_block, int end_block,
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VP8Histogram* const histo) {
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int j;
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for (j = start_block; j < end_block; ++j) {
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int k;
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int16_t out[16];
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VP8FTransform(ref + VP8DspScan[j], pred + VP8DspScan[j], out);
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// Convert coefficients to bin (within out[]).
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// Convert coefficients to bin.
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for (k = 0; k < 16; ++k) {
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const int v = abs(out[k]) >> 2;
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out[k] = (v > MAX_COEFF_THRESH) ? MAX_COEFF_THRESH : v;
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}
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// Use bin to update histogram.
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for (k = 0; k < 16; ++k) {
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histo[out[k]]++;
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const int v = abs(out[k]) >> 3; // TODO(skal): add rounding?
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const int clipped_value = clip_max(v, MAX_COEFF_THRESH);
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histo->distribution[clipped_value]++;
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}
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}
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return VP8GetAlpha(histo);
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}
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//------------------------------------------------------------------------------
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@@ -89,15 +72,12 @@ static void InitTables(void) {
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if (!tables_ok) {
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int i;
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for (i = -255; i <= 255 + 255; ++i) {
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clip1[255 + i] = (i < 0) ? 0 : (i > 255) ? 255 : i;
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clip1[255 + i] = clip_8b(i);
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}
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tables_ok = 1;
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}
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}
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static WEBP_INLINE uint8_t clip_8b(int v) {
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return (!(v & ~0xff)) ? v : v < 0 ? 0 : 255;
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}
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//------------------------------------------------------------------------------
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// Transforms (Paragraph 14.4)
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