libwebp: update to 0.4.3

This commit imports libwebp 0.4.3, including AUTHORS, COPYING, ChangeLog,
NEWS, PATENTS, README and src directories. In src, only includes header
and source files.

The patches required to build it in Qt will follow in separate
commit(s).

Change-Id: I23ebfd69e47a468c91a9e9b109e9cb8ac63705d4
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: aavit <eirik.aavitsland@theqtcompany.com>

1 files changed, 1114 insertions, 0 deletions

diff --git a/src/3rdparty/libwebp/src/enc/picture_csp.c b/src/3rdparty/libwebp/src/enc/picture_csp.c
new file mode 100644
index 0000000..7875f62
--- /dev/null
+++ b/src/3rdparty/libwebp/src/enc/picture_csp.c
@@ -0,0 +1,1114 @@
+// Copyright 2014 Google Inc. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+// -----------------------------------------------------------------------------
+//
+// WebPPicture utils for colorspace conversion
+//
+// Author: Skal (pascal.massimino@gmail.com)
+
+#include <assert.h>
+#include <stdlib.h>
+#include <math.h>
+
+#include "./vp8enci.h"
+#include "../utils/random.h"
+#include "../utils/utils.h"
+#include "../dsp/yuv.h"
+
+// Uncomment to disable gamma-compression during RGB->U/V averaging
+#define USE_GAMMA_COMPRESSION
+
+// If defined, use table to compute x / alpha.
+#define USE_INVERSE_ALPHA_TABLE
+
+static const union {
+  uint32_t argb;
+  uint8_t  bytes[4];
+} test_endian = { 0xff000000u };
+#define ALPHA_IS_LAST (test_endian.bytes[3] == 0xff)
+
+static WEBP_INLINE uint32_t MakeARGB32(int a, int r, int g, int b) {
+  return (((uint32_t)a << 24) | (r << 16) | (g << 8) | b);
+}
+
+//------------------------------------------------------------------------------
+// Detection of non-trivial transparency
+
+// Returns true if alpha[] has non-0xff values.
+static int CheckNonOpaque(const uint8_t* alpha, int width, int height,
+                          int x_step, int y_step) {
+  if (alpha == NULL) return 0;
+  while (height-- > 0) {
+    int x;
+    for (x = 0; x < width * x_step; x += x_step) {
+      if (alpha[x] != 0xff) return 1;  // TODO(skal): check 4/8 bytes at a time.
+    }
+    alpha += y_step;
+  }
+  return 0;
+}
+
+// Checking for the presence of non-opaque alpha.
+int WebPPictureHasTransparency(const WebPPicture* picture) {
+  if (picture == NULL) return 0;
+  if (!picture->use_argb) {
+    return CheckNonOpaque(picture->a, picture->width, picture->height,
+                          1, picture->a_stride);
+  } else {
+    int x, y;
+    const uint32_t* argb = picture->argb;
+    if (argb == NULL) return 0;
+    for (y = 0; y < picture->height; ++y) {
+      for (x = 0; x < picture->width; ++x) {
+        if (argb[x] < 0xff000000u) return 1;   // test any alpha values != 0xff
+      }
+      argb += picture->argb_stride;
+    }
+  }
+  return 0;
+}
+
+//------------------------------------------------------------------------------
+// Code for gamma correction
+
+#if defined(USE_GAMMA_COMPRESSION)
+
+// gamma-compensates loss of resolution during chroma subsampling
+#define kGamma 0.80      // for now we use a different gamma value than kGammaF
+#define kGammaFix 12     // fixed-point precision for linear values
+#define kGammaScale ((1 << kGammaFix) - 1)
+#define kGammaTabFix 7   // fixed-point fractional bits precision
+#define kGammaTabScale (1 << kGammaTabFix)
+#define kGammaTabRounder (kGammaTabScale >> 1)
+#define kGammaTabSize (1 << (kGammaFix - kGammaTabFix))
+
+static int kLinearToGammaTab[kGammaTabSize + 1];
+static uint16_t kGammaToLinearTab[256];
+static int kGammaTablesOk = 0;
+
+static void InitGammaTables(void) {
+  if (!kGammaTablesOk) {
+    int v;
+    const double scale = (double)(1 << kGammaTabFix) / kGammaScale;
+    const double norm = 1. / 255.;
+    for (v = 0; v <= 255; ++v) {
+      kGammaToLinearTab[v] =
+          (uint16_t)(pow(norm * v, kGamma) * kGammaScale + .5);
+    }
+    for (v = 0; v <= kGammaTabSize; ++v) {
+      kLinearToGammaTab[v] = (int)(255. * pow(scale * v, 1. / kGamma) + .5);
+    }
+    kGammaTablesOk = 1;
+  }
+}
+
+static WEBP_INLINE uint32_t GammaToLinear(uint8_t v) {
+  return kGammaToLinearTab[v];
+}
+
+static WEBP_INLINE int Interpolate(int v) {
+  const int tab_pos = v >> (kGammaTabFix + 2);    // integer part
+  const int x = v & ((kGammaTabScale << 2) - 1);  // fractional part
+  const int v0 = kLinearToGammaTab[tab_pos];
+  const int v1 = kLinearToGammaTab[tab_pos + 1];
+  const int y = v1 * x + v0 * ((kGammaTabScale << 2) - x);   // interpolate
+  assert(tab_pos + 1 < kGammaTabSize + 1);
+  return y;
+}
+
+// Convert a linear value 'v' to YUV_FIX+2 fixed-point precision
+// U/V value, suitable for RGBToU/V calls.
+static WEBP_INLINE int LinearToGamma(uint32_t base_value, int shift) {
+  const int y = Interpolate(base_value << shift);   // final uplifted value
+  return (y + kGammaTabRounder) >> kGammaTabFix;    // descale
+}
+
+#else
+
+static void InitGammaTables(void) {}
+static WEBP_INLINE uint32_t GammaToLinear(uint8_t v) { return v; }
+static WEBP_INLINE int LinearToGamma(uint32_t base_value, int shift) {
+  return (int)(base_value << shift);
+}
+
+#endif    // USE_GAMMA_COMPRESSION
+
+//------------------------------------------------------------------------------
+// RGB -> YUV conversion
+
+static int RGBToY(int r, int g, int b, VP8Random* const rg) {
+  return (rg == NULL) ? VP8RGBToY(r, g, b, YUV_HALF)
+                      : VP8RGBToY(r, g, b, VP8RandomBits(rg, YUV_FIX));
+}
+
+static int RGBToU(int r, int g, int b, VP8Random* const rg) {
+  return (rg == NULL) ? VP8RGBToU(r, g, b, YUV_HALF << 2)
+                      : VP8RGBToU(r, g, b, VP8RandomBits(rg, YUV_FIX + 2));
+}
+
+static int RGBToV(int r, int g, int b, VP8Random* const rg) {
+  return (rg == NULL) ? VP8RGBToV(r, g, b, YUV_HALF << 2)
+                      : VP8RGBToV(r, g, b, VP8RandomBits(rg, YUV_FIX + 2));
+}
+
+//------------------------------------------------------------------------------
+// Smart RGB->YUV conversion
+
+static const int kNumIterations = 6;
+static const int kMinDimensionIterativeConversion = 4;
+
+// We use a-priori a different precision for storing RGB and Y/W components
+// We could use YFIX=0 and only uint8_t for fixed_y_t, but it produces some
+// banding sometimes. Better use extra precision.
+// TODO(skal): cleanup once TFIX/YFIX values are fixed.
+
+typedef int16_t fixed_t;      // signed type with extra TFIX precision for UV
+typedef uint16_t fixed_y_t;   // unsigned type with extra YFIX precision for W
+#define TFIX 6   // fixed-point precision of RGB
+#define YFIX 2   // fixed point precision for Y/W
+
+#define THALF ((1 << TFIX) >> 1)
+#define MAX_Y_T ((256 << YFIX) - 1)
+#define TROUNDER (1 << (YUV_FIX + TFIX - 1))
+
+#if defined(USE_GAMMA_COMPRESSION)
+
+// float variant of gamma-correction
+// We use tables of different size and precision, along with a 'real-world'
+// Gamma value close to ~2.
+#define kGammaF 2.2
+static float kGammaToLinearTabF[MAX_Y_T + 1];   // size scales with Y_FIX
+static float kLinearToGammaTabF[kGammaTabSize + 2];
+static int kGammaTablesFOk = 0;
+
+static void InitGammaTablesF(void) {
+  if (!kGammaTablesFOk) {
+    int v;
+    const double norm = 1. / MAX_Y_T;
+    const double scale = 1. / kGammaTabSize;
+    for (v = 0; v <= MAX_Y_T; ++v) {
+      kGammaToLinearTabF[v] = (float)pow(norm * v, kGammaF);
+    }
+    for (v = 0; v <= kGammaTabSize; ++v) {
+      kLinearToGammaTabF[v] = (float)(MAX_Y_T * pow(scale * v, 1. / kGammaF));
+    }
+    // to prevent small rounding errors to cause read-overflow:
+    kLinearToGammaTabF[kGammaTabSize + 1] = kLinearToGammaTabF[kGammaTabSize];
+    kGammaTablesFOk = 1;
+  }
+}
+
+static WEBP_INLINE float GammaToLinearF(int v) {
+  return kGammaToLinearTabF[v];
+}
+
+static WEBP_INLINE float LinearToGammaF(float value) {
+  const float v = value * kGammaTabSize;
+  const int tab_pos = (int)v;
+  const float x = v - (float)tab_pos;      // fractional part
+  const float v0 = kLinearToGammaTabF[tab_pos + 0];
+  const float v1 = kLinearToGammaTabF[tab_pos + 1];
+  const float y = v1 * x + v0 * (1.f - x);  // interpolate
+  return y;
+}
+
+#else
+
+static void InitGammaTablesF(void) {}
+static WEBP_INLINE float GammaToLinearF(int v) {
+  const float norm = 1.f / MAX_Y_T;
+  return norm * v;
+}
+static WEBP_INLINE float LinearToGammaF(float value) {
+  return MAX_Y_T * value;
+}
+
+#endif    // USE_GAMMA_COMPRESSION
+
+//------------------------------------------------------------------------------
+
+// precision: YFIX -> TFIX
+static WEBP_INLINE int FixedYToW(int v) {
+#if TFIX == YFIX
+  return v;
+#elif TFIX >= YFIX
+  return v << (TFIX - YFIX);
+#else
+  return v >> (YFIX - TFIX);
+#endif
+}
+
+static WEBP_INLINE int FixedWToY(int v) {
+#if TFIX == YFIX
+  return v;
+#elif YFIX >= TFIX
+  return v << (YFIX - TFIX);
+#else
+  return v >> (TFIX - YFIX);
+#endif
+}
+
+static uint8_t clip_8b(fixed_t v) {
+  return (!(v & ~0xff)) ? (uint8_t)v : (v < 0) ? 0u : 255u;
+}
+
+static fixed_y_t clip_y(int y) {
+  return (!(y & ~MAX_Y_T)) ? (fixed_y_t)y : (y < 0) ? 0 : MAX_Y_T;
+}
+
+// precision: TFIX -> YFIX
+static fixed_y_t clip_fixed_t(fixed_t v) {
+  const int y = FixedWToY(v);
+  const fixed_y_t w = clip_y(y);
+  return w;
+}
+
+//------------------------------------------------------------------------------
+
+static int RGBToGray(int r, int g, int b) {
+  const int luma = 19595 * r + 38470 * g + 7471 * b + YUV_HALF;
+  return (luma >> YUV_FIX);
+}
+
+static float RGBToGrayF(float r, float g, float b) {
+  return 0.299f * r + 0.587f * g + 0.114f * b;
+}
+
+static float ScaleDown(int a, int b, int c, int d) {
+  const float A = GammaToLinearF(a);
+  const float B = GammaToLinearF(b);
+  const float C = GammaToLinearF(c);
+  const float D = GammaToLinearF(d);
+  return LinearToGammaF(0.25f * (A + B + C + D));
+}
+
+static WEBP_INLINE void UpdateW(const fixed_y_t* src, fixed_y_t* dst, int len) {
+  while (len-- > 0) {
+    const float R = GammaToLinearF(src[0]);
+    const float G = GammaToLinearF(src[1]);
+    const float B = GammaToLinearF(src[2]);
+    const float Y = RGBToGrayF(R, G, B);
+    *dst++ = (fixed_y_t)(LinearToGammaF(Y) + .5);
+    src += 3;
+  }
+}
+
+static WEBP_INLINE void UpdateChroma(const fixed_y_t* src1,
+                                     const fixed_y_t* src2,
+                                     fixed_t* dst, fixed_y_t* tmp, int len) {
+  while (len--> 0) {
+    const float r = ScaleDown(src1[0], src1[3], src2[0], src2[3]);
+    const float g = ScaleDown(src1[1], src1[4], src2[1], src2[4]);
+    const float b = ScaleDown(src1[2], src1[5], src2[2], src2[5]);
+    const float W = RGBToGrayF(r, g, b);
+    dst[0] = (fixed_t)FixedYToW((int)(r - W));
+    dst[1] = (fixed_t)FixedYToW((int)(g - W));
+    dst[2] = (fixed_t)FixedYToW((int)(b - W));
+    dst += 3;
+    src1 += 6;
+    src2 += 6;
+    if (tmp != NULL) {
+      tmp[0] = tmp[1] = clip_y((int)(W + .5));
+      tmp += 2;
+    }
+  }
+}
+
+//------------------------------------------------------------------------------
+
+static WEBP_INLINE int Filter(const fixed_t* const A, const fixed_t* const B,
+                              int rightwise) {
+  int v;
+  if (!rightwise) {
+    v = (A[0] * 9 + A[-3] * 3 + B[0] * 3 + B[-3]);
+  } else {
+    v = (A[0] * 9 + A[+3] * 3 + B[0] * 3 + B[+3]);
+  }
+  return (v + 8) >> 4;
+}
+
+static WEBP_INLINE int Filter2(int A, int B) { return (A * 3 + B + 2) >> 2; }
+
+//------------------------------------------------------------------------------
+
+// 8bit -> YFIX
+static WEBP_INLINE fixed_y_t UpLift(uint8_t a) {
+  return ((fixed_y_t)a << YFIX) | (1 << (YFIX - 1));
+}
+
+static void ImportOneRow(const uint8_t* const r_ptr,
+                         const uint8_t* const g_ptr,
+                         const uint8_t* const b_ptr,
+                         int step,
+                         int pic_width,
+                         fixed_y_t* const dst) {
+  int i;
+  for (i = 0; i < pic_width; ++i) {
+    const int off = i * step;
+    dst[3 * i + 0] = UpLift(r_ptr[off]);
+    dst[3 * i + 1] = UpLift(g_ptr[off]);
+    dst[3 * i + 2] = UpLift(b_ptr[off]);
+  }
+  if (pic_width & 1) {  // replicate rightmost pixel
+    memcpy(dst + 3 * pic_width, dst + 3 * (pic_width - 1), 3 * sizeof(*dst));
+  }
+}
+
+static void InterpolateTwoRows(const fixed_y_t* const best_y,
+                               const fixed_t* const prev_uv,
+                               const fixed_t* const cur_uv,
+                               const fixed_t* const next_uv,
+                               int w,
+                               fixed_y_t* const out1,
+                               fixed_y_t* const out2) {
+  int i, k;
+  {  // special boundary case for i==0
+    const int W0 = FixedYToW(best_y[0]);
+    const int W1 = FixedYToW(best_y[w]);
+    for (k = 0; k <= 2; ++k) {
+      out1[k] = clip_fixed_t(Filter2(cur_uv[k], prev_uv[k]) + W0);
+      out2[k] = clip_fixed_t(Filter2(cur_uv[k], next_uv[k]) + W1);
+    }
+  }
+  for (i = 1; i < w - 1; ++i) {
+    const int W0 = FixedYToW(best_y[i + 0]);
+    const int W1 = FixedYToW(best_y[i + w]);
+    const int off = 3 * (i >> 1);
+    for (k = 0; k <= 2; ++k) {
+      const int tmp0 = Filter(cur_uv + off + k, prev_uv + off + k, i & 1);
+      const int tmp1 = Filter(cur_uv + off + k, next_uv + off + k, i & 1);
+      out1[3 * i + k] = clip_fixed_t(tmp0 + W0);
+      out2[3 * i + k] = clip_fixed_t(tmp1 + W1);
+    }
+  }
+  {  // special boundary case for i == w - 1
+    const int W0 = FixedYToW(best_y[i + 0]);
+    const int W1 = FixedYToW(best_y[i + w]);
+    const int off = 3 * (i >> 1);
+    for (k = 0; k <= 2; ++k) {
+      out1[3 * i + k] =
+          clip_fixed_t(Filter2(cur_uv[off + k], prev_uv[off + k]) + W0);
+      out2[3 * i + k] =
+          clip_fixed_t(Filter2(cur_uv[off + k], next_uv[off + k]) + W1);
+    }
+  }
+}
+
+static WEBP_INLINE uint8_t ConvertRGBToY(int r, int g, int b) {
+  const int luma = 16839 * r + 33059 * g + 6420 * b + TROUNDER;
+  return clip_8b(16 + (luma >> (YUV_FIX + TFIX)));
+}
+
+static WEBP_INLINE uint8_t ConvertRGBToU(int r, int g, int b) {
+  const int u =  -9719 * r - 19081 * g + 28800 * b + TROUNDER;
+  return clip_8b(128 + (u >> (YUV_FIX + TFIX)));
+}
+
+static WEBP_INLINE uint8_t ConvertRGBToV(int r, int g, int b) {
+  const int v = +28800 * r - 24116 * g -  4684 * b + TROUNDER;
+  return clip_8b(128 + (v >> (YUV_FIX + TFIX)));
+}
+
+static int ConvertWRGBToYUV(const fixed_y_t* const best_y,
+                            const fixed_t* const best_uv,
+                            WebPPicture* const picture) {
+  int i, j;
+  const int w = (picture->width + 1) & ~1;
+  const int h = (picture->height + 1) & ~1;
+  const int uv_w = w >> 1;
+  const int uv_h = h >> 1;
+  for (j = 0; j < picture->height; ++j) {
+    for (i = 0; i < picture->width; ++i) {
+      const int off = 3 * ((i >> 1) + (j >> 1) * uv_w);
+      const int off2 = i + j * picture->y_stride;
+      const int W = FixedYToW(best_y[i + j * w]);
+      const int r = best_uv[off + 0] + W;
+      const int g = best_uv[off + 1] + W;
+      const int b = best_uv[off + 2] + W;
+      picture->y[off2] = ConvertRGBToY(r, g, b);
+    }
+  }
+  for (j = 0; j < uv_h; ++j) {
+    uint8_t* const dst_u = picture->u + j * picture->uv_stride;
+    uint8_t* const dst_v = picture->v + j * picture->uv_stride;
+    for (i = 0; i < uv_w; ++i) {
+      const int off = 3 * (i + j * uv_w);
+      const int r = best_uv[off + 0];
+      const int g = best_uv[off + 1];
+      const int b = best_uv[off + 2];
+      dst_u[i] = ConvertRGBToU(r, g, b);
+      dst_v[i] = ConvertRGBToV(r, g, b);
+    }
+  }
+  return 1;
+}
+
+//------------------------------------------------------------------------------
+// Main function
+
+#define SAFE_ALLOC(W, H, T) ((T*)WebPSafeMalloc((W) * (H), sizeof(T)))
+
+static int PreprocessARGB(const uint8_t* const r_ptr,
+                          const uint8_t* const g_ptr,
+                          const uint8_t* const b_ptr,
+                          int step, int rgb_stride,
+                          WebPPicture* const picture) {
+  // we expand the right/bottom border if needed
+  const int w = (picture->width + 1) & ~1;
+  const int h = (picture->height + 1) & ~1;
+  const int uv_w = w >> 1;
+  const int uv_h = h >> 1;
+  int i, j, iter;
+
+  // TODO(skal): allocate one big memory chunk. But for now, it's easier
+  // for valgrind debugging to have several chunks.
+  fixed_y_t* const tmp_buffer = SAFE_ALLOC(w * 3, 2, fixed_y_t);   // scratch
+  fixed_y_t* const best_y = SAFE_ALLOC(w, h, fixed_y_t);
+  fixed_y_t* const target_y = SAFE_ALLOC(w, h, fixed_y_t);
+  fixed_y_t* const best_rgb_y = SAFE_ALLOC(w, 2, fixed_y_t);
+  fixed_t* const best_uv = SAFE_ALLOC(uv_w * 3, uv_h, fixed_t);
+  fixed_t* const target_uv = SAFE_ALLOC(uv_w * 3, uv_h, fixed_t);
+  fixed_t* const best_rgb_uv = SAFE_ALLOC(uv_w * 3, 1, fixed_t);
+  int ok;
+
+  if (best_y == NULL || best_uv == NULL ||
+      target_y == NULL || target_uv == NULL ||
+      best_rgb_y == NULL || best_rgb_uv == NULL ||
+      tmp_buffer == NULL) {
+    ok = WebPEncodingSetError(picture, VP8_ENC_ERROR_OUT_OF_MEMORY);
+    goto End;
+  }
+  assert(picture->width >= kMinDimensionIterativeConversion);
+  assert(picture->height >= kMinDimensionIterativeConversion);
+
+  // Import RGB samples to W/RGB representation.
+  for (j = 0; j < picture->height; j += 2) {
+    const int is_last_row = (j == picture->height - 1);
+    fixed_y_t* const src1 = tmp_buffer;
+    fixed_y_t* const src2 = tmp_buffer + 3 * w;
+    const int off1 = j * rgb_stride;
+    const int off2 = off1 + rgb_stride;
+    const int uv_off = (j >> 1) * 3 * uv_w;
+    fixed_y_t* const dst_y = best_y + j * w;
+
+    // prepare two rows of input
+    ImportOneRow(r_ptr + off1, g_ptr + off1, b_ptr + off1,
+                 step, picture->width, src1);
+    if (!is_last_row) {
+      ImportOneRow(r_ptr + off2, g_ptr + off2, b_ptr + off2,
+                   step, picture->width, src2);
+    } else {
+      memcpy(src2, src1, 3 * w * sizeof(*src2));
+    }
+    UpdateW(src1, target_y + (j + 0) * w, w);
+    UpdateW(src2, target_y + (j + 1) * w, w);
+    UpdateChroma(src1, src2, target_uv + uv_off, dst_y, uv_w);
+    memcpy(best_uv + uv_off, target_uv + uv_off, 3 * uv_w * sizeof(*best_uv));
+    memcpy(dst_y + w, dst_y, w * sizeof(*dst_y));
+  }
+
+  // Iterate and resolve clipping conflicts.
+  for (iter = 0; iter < kNumIterations; ++iter) {
+    int k;
+    const fixed_t* cur_uv = best_uv;
+    const fixed_t* prev_uv = best_uv;
+    for (j = 0; j < h; j += 2) {
+      fixed_y_t* const src1 = tmp_buffer;
+      fixed_y_t* const src2 = tmp_buffer + 3 * w;
+
+      {
+        const fixed_t* const next_uv = cur_uv + ((j < h - 2) ? 3 * uv_w : 0);
+        InterpolateTwoRows(best_y + j * w, prev_uv, cur_uv, next_uv,
+                           w, src1, src2);
+        prev_uv = cur_uv;
+        cur_uv = next_uv;
+      }
+
+      UpdateW(src1, best_rgb_y + 0 * w, w);
+      UpdateW(src2, best_rgb_y + 1 * w, w);
+      UpdateChroma(src1, src2, best_rgb_uv, NULL, uv_w);
+
+      // update two rows of Y and one row of RGB
+      for (i = 0; i < 2 * w; ++i) {
+        const int off = i + j * w;
+        const int diff_y = target_y[off] - best_rgb_y[i];
+        const int new_y = (int)best_y[off] + diff_y;
+        best_y[off] = clip_y(new_y);
+      }
+      for (i = 0; i < uv_w; ++i) {
+        const int off = 3 * (i + (j >> 1) * uv_w);
+        int W;
+        for (k = 0; k <= 2; ++k) {
+          const int diff_uv = (int)target_uv[off + k] - best_rgb_uv[3 * i + k];
+          best_uv[off + k] += diff_uv;
+        }
+        W = RGBToGray(best_uv[off + 0], best_uv[off + 1], best_uv[off + 2]);
+        for (k = 0; k <= 2; ++k) {
+          best_uv[off + k] -= W;
+        }
+      }
+    }
+    // TODO(skal): add early-termination criterion
+  }
+
+  // final reconstruction
+  ok = ConvertWRGBToYUV(best_y, best_uv, picture);
+
+ End:
+  WebPSafeFree(best_y);
+  WebPSafeFree(best_uv);
+  WebPSafeFree(target_y);
+  WebPSafeFree(target_uv);
+  WebPSafeFree(best_rgb_y);
+  WebPSafeFree(best_rgb_uv);
+  WebPSafeFree(tmp_buffer);
+  return ok;
+}
+#undef SAFE_ALLOC
+
+//------------------------------------------------------------------------------
+// "Fast" regular RGB->YUV
+
+#define SUM4(ptr, step) LinearToGamma(                     \
+    GammaToLinear((ptr)[0]) +                              \
+    GammaToLinear((ptr)[(step)]) +                         \
+    GammaToLinear((ptr)[rgb_stride]) +                     \
+    GammaToLinear((ptr)[rgb_stride + (step)]), 0)          \
+
+#define SUM2(ptr) \
+    LinearToGamma(GammaToLinear((ptr)[0]) + GammaToLinear((ptr)[rgb_stride]), 1)
+
+#define SUM2ALPHA(ptr) ((ptr)[0] + (ptr)[rgb_stride])
+#define SUM4ALPHA(ptr) (SUM2ALPHA(ptr) + SUM2ALPHA((ptr) + 4))
+
+#if defined(USE_INVERSE_ALPHA_TABLE)
+
+static const int kAlphaFix = 19;
+// Following table is (1 << kAlphaFix) / a. The (v * kInvAlpha[a]) >> kAlphaFix
+// formula is then equal to v / a in most (99.6%) cases. Note that this table
+// and constant are adjusted very tightly to fit 32b arithmetic.
+// In particular, they use the fact that the operands for 'v / a' are actually
+// derived as v = (a0.p0 + a1.p1 + a2.p2 + a3.p3) and a = a0 + a1 + a2 + a3
+// with ai in [0..255] and pi in [0..1<<kGammaFix). The constraint to avoid
+// overflow is: kGammaFix + kAlphaFix <= 31.
+static const uint32_t kInvAlpha[4 * 0xff + 1] = {
+  0,  /* alpha = 0 */
+  524288, 262144, 174762, 131072, 104857, 87381, 74898, 65536,
+  58254, 52428, 47662, 43690, 40329, 37449, 34952, 32768,
+  30840, 29127, 27594, 26214, 24966, 23831, 22795, 21845,
+  20971, 20164, 19418, 18724, 18078, 17476, 16912, 16384,
+  15887, 15420, 14979, 14563, 14169, 13797, 13443, 13107,
+  12787, 12483, 12192, 11915, 11650, 11397, 11155, 10922,
+  10699, 10485, 10280, 10082, 9892, 9709, 9532, 9362,
+  9198, 9039, 8886, 8738, 8594, 8456, 8322, 8192,
+  8065, 7943, 7825, 7710, 7598, 7489, 7384, 7281,
+  7182, 7084, 6990, 6898, 6808, 6721, 6636, 6553,
+  6472, 6393, 6316, 6241, 6168, 6096, 6026, 5957,
+  5890, 5825, 5761, 5698, 5637, 5577, 5518, 5461,
+  5405, 5349, 5295, 5242, 5190, 5140, 5090, 5041,
+  4993, 4946, 4899, 4854, 4809, 4766, 4723, 4681,
+  4639, 4599, 4559, 4519, 4481, 4443, 4405, 4369,
+  4332, 4297, 4262, 4228, 4194, 4161, 4128, 4096,
+  4064, 4032, 4002, 3971, 3942, 3912, 3883, 3855,
+  3826, 3799, 3771, 3744, 3718, 3692, 3666, 3640,
+  3615, 3591, 3566, 3542, 3518, 3495, 3472, 3449,
+  3426, 3404, 3382, 3360, 3339, 3318, 3297, 3276,
+  3256, 3236, 3216, 3196, 3177, 3158, 3139, 3120,
+  3102, 3084, 3066, 3048, 3030, 3013, 2995, 2978,
+  2962, 2945, 2928, 2912, 2896, 2880, 2864, 2849,
+  2833, 2818, 2803, 2788, 2774, 2759, 2744, 2730,
+  2716, 2702, 2688, 2674, 2661, 2647, 2634, 2621,
+  2608, 2595, 2582, 2570, 2557, 2545, 2532, 2520,
+  2508, 2496, 2484, 2473, 2461, 2449, 2438, 2427,
+  2416, 2404, 2394, 2383, 2372, 2361, 2351, 2340,
+  2330, 2319, 2309, 2299, 2289, 2279, 2269, 2259,
+  2250, 2240, 2231, 2221, 2212, 2202, 2193, 2184,
+  2175, 2166, 2157, 2148, 2139, 2131, 2122, 2114,
+  2105, 2097, 2088, 2080, 2072, 2064, 2056, 2048,
+  2040, 2032, 2024, 2016, 2008, 2001, 1993, 1985,
+  1978, 1971, 1963, 1956, 1949, 1941, 1934, 1927,
+  1920, 1913, 1906, 1899, 1892, 1885, 1879, 1872,
+  1865, 1859, 1852, 1846, 1839, 1833, 1826, 1820,
+  1814, 1807, 1801, 1795, 1789, 1783, 1777, 1771,
+  1765, 1759, 1753, 1747, 1741, 1736, 1730, 1724,
+  1718, 1713, 1707, 1702, 1696, 1691, 1685, 1680,
+  1675, 1669, 1664, 1659, 1653, 1648, 1643, 1638,
+  1633, 1628, 1623, 1618, 1613, 1608, 1603, 1598,
+  1593, 1588, 1583, 1579, 1574, 1569, 1565, 1560,
+  1555, 1551, 1546, 1542, 1537, 1533, 1528, 1524,
+  1519, 1515, 1510, 1506, 1502, 1497, 1493, 1489,
+  1485, 1481, 1476, 1472, 1468, 1464, 1460, 1456,
+  1452, 1448, 1444, 1440, 1436, 1432, 1428, 1424,
+  1420, 1416, 1413, 1409, 1405, 1401, 1398, 1394,
+  1390, 1387, 1383, 1379, 1376, 1372, 1368, 1365,
+  1361, 1358, 1354, 1351, 1347, 1344, 1340, 1337,
+  1334, 1330, 1327, 1323, 1320, 1317, 1314, 1310,
+  1307, 1304, 1300, 1297, 1294, 1291, 1288, 1285,
+  1281, 1278, 1275, 1272, 1269, 1266, 1263, 1260,
+  1257, 1254, 1251, 1248, 1245, 1242, 1239, 1236,
+  1233, 1230, 1227, 1224, 1222, 1219, 1216, 1213,
+  1210, 1208, 1205, 1202, 1199, 1197, 1194, 1191,
+  1188, 1186, 1183, 1180, 1178, 1175, 1172, 1170,
+  1167, 1165, 1162, 1159, 1157, 1154, 1152, 1149,
+  1147, 1144, 1142, 1139, 1137, 1134, 1132, 1129,
+  1127, 1125, 1122, 1120, 1117, 1115, 1113, 1110,
+  1108, 1106, 1103, 1101, 1099, 1096, 1094, 1092,
+  1089, 1087, 1085, 1083, 1081, 1078, 1076, 1074,
+  1072, 1069, 1067, 1065, 1063, 1061, 1059, 1057,
+  1054, 1052, 1050, 1048, 1046, 1044, 1042, 1040,
+  1038, 1036, 1034, 1032, 1030, 1028, 1026, 1024,
+  1022, 1020, 1018, 1016, 1014, 1012, 1010, 1008,
+  1006, 1004, 1002, 1000, 998, 996, 994, 992,
+  991, 989, 987, 985, 983, 981, 979, 978,
+  976, 974, 972, 970, 969, 967, 965, 963,
+  961, 960, 958, 956, 954, 953, 951, 949,
+  948, 946, 944, 942, 941, 939, 937, 936,
+  934, 932, 931, 929, 927, 926, 924, 923,
+  921, 919, 918, 916, 914, 913, 911, 910,
+  908, 907, 905, 903, 902, 900, 899, 897,
+  896, 894, 893, 891, 890, 888, 887, 885,
+  884, 882, 881, 879, 878, 876, 875, 873,
+  872, 870, 869, 868, 866, 865, 863, 862,
+  860, 859, 858, 856, 855, 853, 852, 851,
+  849, 848, 846, 845, 844, 842, 841, 840,
+  838, 837, 836, 834, 833, 832, 830, 829,
+  828, 826, 825, 824, 823, 821, 820, 819,
+  817, 816, 815, 814, 812, 811, 810, 809,
+  807, 806, 805, 804, 802, 801, 800, 799,
+  798, 796, 795, 794, 793, 791, 790, 789,
+  788, 787, 786, 784, 783, 782, 781, 780,
+  779, 777, 776, 775, 774, 773, 772, 771,
+  769, 768, 767, 766, 765, 764, 763, 762,
+  760, 759, 758, 757, 756, 755, 754, 753,
+  752, 751, 750, 748, 747, 746, 745, 744,
+  743, 742, 741, 740, 739, 738, 737, 736,
+  735, 734, 733, 732, 731, 730, 729, 728,
+  727, 726, 725, 724, 723, 722, 721, 720,
+  719, 718, 717, 716, 715, 714, 713, 712,
+  711, 710, 709, 708, 707, 706, 705, 704,
+  703, 702, 701, 700, 699, 699, 698, 697,
+  696, 695, 694, 693, 692, 691, 690, 689,
+  688, 688, 687, 686, 685, 684, 683, 682,
+  681, 680, 680, 679, 678, 677, 676, 675,
+  674, 673, 673, 672, 671, 670, 669, 668,
+  667, 667, 666, 665, 664, 663, 662, 661,
+  661, 660, 659, 658, 657, 657, 656, 655,
+  654, 653, 652, 652, 651, 650, 649, 648,
+  648, 647, 646, 645, 644, 644, 643, 642,
+  641, 640, 640, 639, 638, 637, 637, 636,
+  635, 634, 633, 633, 632, 631, 630, 630,
+  629, 628, 627, 627, 626, 625, 624, 624,
+  623, 622, 621, 621, 620, 619, 618, 618,
+  617, 616, 616, 615, 614, 613, 613, 612,
+  611, 611, 610, 609, 608, 608, 607, 606,
+  606, 605, 604, 604, 603, 602, 601, 601,
+  600, 599, 599, 598, 597, 597, 596, 595,
+  595, 594, 593, 593, 592, 591, 591, 590,
+  589, 589, 588, 587, 587, 586, 585, 585,
+  584, 583, 583, 582, 581, 581, 580, 579,
+  579, 578, 578, 577, 576, 576, 575, 574,
+  574, 573, 572, 572, 571, 571, 570, 569,
+  569, 568, 568, 567, 566, 566, 565, 564,
+  564, 563, 563, 562, 561, 561, 560, 560,
+  559, 558, 558, 557, 557, 556, 555, 555,
+  554, 554, 553, 553, 552, 551, 551, 550,
+  550, 549, 548, 548, 547, 547, 546, 546,
+  545, 544, 544, 543, 543, 542, 542, 541,
+  541, 540, 539, 539, 538, 538, 537, 537,
+  536, 536, 535, 534, 534, 533, 533, 532,
+  532, 531, 531, 530, 530, 529, 529, 528,
+  527, 527, 526, 526, 525, 525, 524, 524,
+  523, 523, 522, 522, 521, 521, 520, 520,
+  519, 519, 518, 518, 517, 517, 516, 516,
+  515, 515, 514, 514
+};
+
+// Note that LinearToGamma() expects the values to be premultiplied by 4,
+// so we incorporate this factor 4 inside the DIVIDE_BY_ALPHA macro directly.
+#define DIVIDE_BY_ALPHA(sum, a)  (((sum) * kInvAlpha[(a)]) >> (kAlphaFix - 2))
+
+#else
+
+#define DIVIDE_BY_ALPHA(sum, a) (4 * (sum) / (a))
+
+#endif  // USE_INVERSE_ALPHA_TABLE
+
+static WEBP_INLINE int LinearToGammaWeighted(const uint8_t* src,
+                                             const uint8_t* a_ptr,
+                                             uint32_t total_a, int step,
+                                             int rgb_stride) {
+  const uint32_t sum =
+      a_ptr[0] * GammaToLinear(src[0]) +
+      a_ptr[step] * GammaToLinear(src[step]) +
+      a_ptr[rgb_stride] * GammaToLinear(src[rgb_stride]) +
+      a_ptr[rgb_stride + step] * GammaToLinear(src[rgb_stride + step]);
+  assert(total_a > 0 && total_a <= 4 * 0xff);
+#if defined(USE_INVERSE_ALPHA_TABLE)
+  assert((uint64_t)sum * kInvAlpha[total_a] < ((uint64_t)1 << 32));
+#endif
+  return LinearToGamma(DIVIDE_BY_ALPHA(sum, total_a), 0);
+}
+
+static WEBP_INLINE void ConvertRowToY(const uint8_t* const r_ptr,
+                                      const uint8_t* const g_ptr,
+                                      const uint8_t* const b_ptr,
+                                      int step,
+                                      uint8_t* const dst_y,
+                                      int width,
+                                      VP8Random* const rg) {
+  int i, j;
+  for (i = 0, j = 0; i < width; ++i, j += step) {
+    dst_y[i] = RGBToY(r_ptr[j], g_ptr[j], b_ptr[j], rg);
+  }
+}
+
+static WEBP_INLINE void ConvertRowsToUVWithAlpha(const uint8_t* const r_ptr,
+                                                 const uint8_t* const g_ptr,
+                                                 const uint8_t* const b_ptr,
+                                                 const uint8_t* const a_ptr,
+                                                 int rgb_stride,
+                                                 uint8_t* const dst_u,
+                                                 uint8_t* const dst_v,
+                                                 int width,
+                                                 VP8Random* const rg) {
+  int i, j;
+  // we loop over 2x2 blocks and produce one U/V value for each.
+  for (i = 0, j = 0; i < (width >> 1); ++i, j += 2 * sizeof(uint32_t)) {
+    const uint32_t a = SUM4ALPHA(a_ptr + j);
+    int r, g, b;
+    if (a == 4 * 0xff || a == 0) {
+      r = SUM4(r_ptr + j, 4);
+      g = SUM4(g_ptr + j, 4);
+      b = SUM4(b_ptr + j, 4);
+    } else {
+      r = LinearToGammaWeighted(r_ptr + j, a_ptr + j, a, 4, rgb_stride);
+      g = LinearToGammaWeighted(g_ptr + j, a_ptr + j, a, 4, rgb_stride);
+      b = LinearToGammaWeighted(b_ptr + j, a_ptr + j, a, 4, rgb_stride);
+    }
+    dst_u[i] = RGBToU(r, g, b, rg);
+    dst_v[i] = RGBToV(r, g, b, rg);
+  }
+  if (width & 1) {
+    const uint32_t a = 2u * SUM2ALPHA(a_ptr + j);
+    int r, g, b;
+    if (a == 4 * 0xff || a == 0) {
+      r = SUM2(r_ptr + j);
+      g = SUM2(g_ptr + j);
+      b = SUM2(b_ptr + j);
+    } else {
+      r = LinearToGammaWeighted(r_ptr + j, a_ptr + j, a, 0, rgb_stride);
+      g = LinearToGammaWeighted(g_ptr + j, a_ptr + j, a, 0, rgb_stride);
+      b = LinearToGammaWeighted(b_ptr + j, a_ptr + j, a, 0, rgb_stride);
+    }
+    dst_u[i] = RGBToU(r, g, b, rg);
+    dst_v[i] = RGBToV(r, g, b, rg);
+  }
+}
+
+static WEBP_INLINE void ConvertRowsToUV(const uint8_t* const r_ptr,
+                                        const uint8_t* const g_ptr,
+                                        const uint8_t* const b_ptr,
+                                        int step, int rgb_stride,
+                                        uint8_t* const dst_u,
+                                        uint8_t* const dst_v,
+                                        int width,
+                                        VP8Random* const rg) {
+  int i, j;
+  for (i = 0, j = 0; i < (width >> 1); ++i, j += 2 * step) {
+    const int r = SUM4(r_ptr + j, step);
+    const int g = SUM4(g_ptr + j, step);
+    const int b = SUM4(b_ptr + j, step);
+    dst_u[i] = RGBToU(r, g, b, rg);
+    dst_v[i] = RGBToV(r, g, b, rg);
+  }
+  if (width & 1) {
+    const int r = SUM2(r_ptr + j);
+    const int g = SUM2(g_ptr + j);
+    const int b = SUM2(b_ptr + j);
+    dst_u[i] = RGBToU(r, g, b, rg);
+    dst_v[i] = RGBToV(r, g, b, rg);
+  }
+}
+
+static int ImportYUVAFromRGBA(const uint8_t* const r_ptr,
+                              const uint8_t* const g_ptr,
+                              const uint8_t* const b_ptr,
+                              const uint8_t* const a_ptr,
+                              int step,         // bytes per pixel
+                              int rgb_stride,   // bytes per scanline
+                              float dithering,
+                              int use_iterative_conversion,
+                              WebPPicture* const picture) {
+  int y;
+  const int width = picture->width;
+  const int height = picture->height;
+  const int has_alpha = CheckNonOpaque(a_ptr, width, height, step, rgb_stride);
+
+  picture->colorspace = has_alpha ? WEBP_YUV420A : WEBP_YUV420;
+  picture->use_argb = 0;
+
+  // disable smart conversion if source is too small (overkill).
+  if (width < kMinDimensionIterativeConversion ||
+      height < kMinDimensionIterativeConversion) {
+    use_iterative_conversion = 0;
+  }
+
+  if (!WebPPictureAllocYUVA(picture, width, height)) {
+    return 0;
+  }
+  if (has_alpha) {
+    WebPInitAlphaProcessing();
+    assert(step == 4);
+#if defined(USE_INVERSE_ALPHA_TABLE)
+    assert(kAlphaFix + kGammaFix <= 31);
+#endif
+  }
+
+  if (use_iterative_conversion) {
+    InitGammaTablesF();
+    if (!PreprocessARGB(r_ptr, g_ptr, b_ptr, step, rgb_stride, picture)) {
+      return 0;
+    }
+    if (has_alpha) {
+      WebPExtractAlpha(a_ptr, rgb_stride, width, height,
+                       picture->a, picture->a_stride);
+    }
+  } else {
+    uint8_t* dst_y = picture->y;
+    uint8_t* dst_u = picture->u;
+    uint8_t* dst_v = picture->v;
+    uint8_t* dst_a = picture->a;
+
+    VP8Random base_rg;
+    VP8Random* rg = NULL;
+    if (dithering > 0.) {
+      VP8InitRandom(&base_rg, dithering);
+      rg = &base_rg;
+    }
+
+    InitGammaTables();
+
+    // Downsample Y/U/V planes, two rows at a time
+    for (y = 0; y < (height >> 1); ++y) {
+      int rows_have_alpha = has_alpha;
+      const int off1 = (2 * y + 0) * rgb_stride;
+      const int off2 = (2 * y + 1) * rgb_stride;
+      ConvertRowToY(r_ptr + off1, g_ptr + off1, b_ptr + off1, step,
+                    dst_y, width, rg);
+      ConvertRowToY(r_ptr + off2, g_ptr + off2, b_ptr + off2, step,
+                    dst_y + picture->y_stride, width, rg);
+      dst_y += 2 * picture->y_stride;
+      if (has_alpha) {
+        rows_have_alpha &= !WebPExtractAlpha(a_ptr + off1, rgb_stride,
+                                             width, 2,
+                                             dst_a, picture->a_stride);
+        dst_a += 2 * picture->a_stride;
+      }
+      if (!rows_have_alpha) {
+        ConvertRowsToUV(r_ptr + off1, g_ptr + off1, b_ptr + off1,
+                        step, rgb_stride, dst_u, dst_v, width, rg);
+      } else {
+        ConvertRowsToUVWithAlpha(r_ptr + off1, g_ptr + off1, b_ptr + off1,
+                                 a_ptr + off1, rgb_stride,
+                                 dst_u, dst_v, width, rg);
+      }
+      dst_u += picture->uv_stride;
+      dst_v += picture->uv_stride;
+    }
+    if (height & 1) {    // extra last row
+      const int off = 2 * y * rgb_stride;
+      int row_has_alpha = has_alpha;
+      ConvertRowToY(r_ptr + off, g_ptr + off, b_ptr + off, step,
+                    dst_y, width, rg);
+      if (row_has_alpha) {
+        row_has_alpha &= !WebPExtractAlpha(a_ptr + off, 0, width, 1, dst_a, 0);
+      }
+      if (!row_has_alpha) {
+        ConvertRowsToUV(r_ptr + off, g_ptr + off, b_ptr + off,
+                        step, 0, dst_u, dst_v, width, rg);
+      } else {
+        ConvertRowsToUVWithAlpha(r_ptr + off, g_ptr + off, b_ptr + off,
+                                 a_ptr + off, 0,
+                                 dst_u, dst_v, width, rg);
+      }
+    }
+  }
+  return 1;
+}
+
+#undef SUM4
+#undef SUM2
+#undef SUM4ALPHA
+#undef SUM2ALPHA
+
+//------------------------------------------------------------------------------
+// call for ARGB->YUVA conversion
+
+static int PictureARGBToYUVA(WebPPicture* picture, WebPEncCSP colorspace,
+                             float dithering, int use_iterative_conversion) {
+  if (picture == NULL) return 0;
+  if (picture->argb == NULL) {
+    return WebPEncodingSetError(picture, VP8_ENC_ERROR_NULL_PARAMETER);
+  } else if ((colorspace & WEBP_CSP_UV_MASK) != WEBP_YUV420) {
+    return WebPEncodingSetError(picture, VP8_ENC_ERROR_INVALID_CONFIGURATION);
+  } else {
+    const uint8_t* const argb = (const uint8_t*)picture->argb;
+    const uint8_t* const r = ALPHA_IS_LAST ? argb + 2 : argb + 1;
+    const uint8_t* const g = ALPHA_IS_LAST ? argb + 1 : argb + 2;
+    const uint8_t* const b = ALPHA_IS_LAST ? argb + 0 : argb + 3;
+    const uint8_t* const a = ALPHA_IS_LAST ? argb + 3 : argb + 0;
+
+    picture->colorspace = WEBP_YUV420;
+    return ImportYUVAFromRGBA(r, g, b, a, 4, 4 * picture->argb_stride,
+                              dithering, use_iterative_conversion, picture);
+  }
+}
+
+int WebPPictureARGBToYUVADithered(WebPPicture* picture, WebPEncCSP colorspace,
+                                  float dithering) {
+  return PictureARGBToYUVA(picture, colorspace, dithering, 0);
+}
+
+int WebPPictureARGBToYUVA(WebPPicture* picture, WebPEncCSP colorspace) {
+  return PictureARGBToYUVA(picture, colorspace, 0.f, 0);
+}
+
+#if WEBP_ENCODER_ABI_VERSION > 0x0204
+int WebPPictureSmartARGBToYUVA(WebPPicture* picture) {
+  return PictureARGBToYUVA(picture, WEBP_YUV420, 0.f, 1);
+}
+#endif
+
+//------------------------------------------------------------------------------
+// call for YUVA -> ARGB conversion
+
+int WebPPictureYUVAToARGB(WebPPicture* picture) {
+  if (picture == NULL) return 0;
+  if (picture->y == NULL || picture->u == NULL || picture->v == NULL) {
+    return WebPEncodingSetError(picture, VP8_ENC_ERROR_NULL_PARAMETER);
+  }
+  if ((picture->colorspace & WEBP_CSP_ALPHA_BIT) && picture->a == NULL) {
+    return WebPEncodingSetError(picture, VP8_ENC_ERROR_NULL_PARAMETER);
+  }
+  if ((picture->colorspace & WEBP_CSP_UV_MASK) != WEBP_YUV420) {
+    return WebPEncodingSetError(picture, VP8_ENC_ERROR_INVALID_CONFIGURATION);
+  }
+  // Allocate a new argb buffer (discarding the previous one).
+  if (!WebPPictureAllocARGB(picture, picture->width, picture->height)) return 0;
+  picture->use_argb = 1;
+
+  // Convert
+  {
+    int y;
+    const int width = picture->width;
+    const int height = picture->height;
+    const int argb_stride = 4 * picture->argb_stride;
+    uint8_t* dst = (uint8_t*)picture->argb;
+    const uint8_t *cur_u = picture->u, *cur_v = picture->v, *cur_y = picture->y;
+    WebPUpsampleLinePairFunc upsample = WebPGetLinePairConverter(ALPHA_IS_LAST);
+
+    // First row, with replicated top samples.
+    upsample(cur_y, NULL, cur_u, cur_v, cur_u, cur_v, dst, NULL, width);
+    cur_y += picture->y_stride;
+    dst += argb_stride;
+    // Center rows.
+    for (y = 1; y + 1 < height; y += 2) {
+      const uint8_t* const top_u = cur_u;
+      const uint8_t* const top_v = cur_v;
+      cur_u += picture->uv_stride;
+      cur_v += picture->uv_stride;
+      upsample(cur_y, cur_y + picture->y_stride, top_u, top_v, cur_u, cur_v,
+               dst, dst + argb_stride, width);
+      cur_y += 2 * picture->y_stride;
+      dst += 2 * argb_stride;
+    }
+    // Last row (if needed), with replicated bottom samples.
+    if (height > 1 && !(height & 1)) {
+      upsample(cur_y, NULL, cur_u, cur_v, cur_u, cur_v, dst, NULL, width);
+    }
+    // Insert alpha values if needed, in replacement for the default 0xff ones.
+    if (picture->colorspace & WEBP_CSP_ALPHA_BIT) {
+      for (y = 0; y < height; ++y) {
+        uint32_t* const argb_dst = picture->argb + y * picture->argb_stride;
+        const uint8_t* const src = picture->a + y * picture->a_stride;
+        int x;
+        for (x = 0; x < width; ++x) {
+          argb_dst[x] = (argb_dst[x] & 0x00ffffffu) | ((uint32_t)src[x] << 24);
+        }
+      }
+    }
+  }
+  return 1;
+}
+
+//------------------------------------------------------------------------------
+// automatic import / conversion
+
+static int Import(WebPPicture* const picture,
+                  const uint8_t* const rgb, int rgb_stride,
+                  int step, int swap_rb, int import_alpha) {
+  int y;
+  const uint8_t* const r_ptr = rgb + (swap_rb ? 2 : 0);
+  const uint8_t* const g_ptr = rgb + 1;
+  const uint8_t* const b_ptr = rgb + (swap_rb ? 0 : 2);
+  const uint8_t* const a_ptr = import_alpha ? rgb + 3 : NULL;
+  const int width = picture->width;
+  const int height = picture->height;
+
+  if (!picture->use_argb) {
+    return ImportYUVAFromRGBA(r_ptr, g_ptr, b_ptr, a_ptr, step, rgb_stride,
+                              0.f /* no dithering */, 0, picture);
+  }
+  if (!WebPPictureAlloc(picture)) return 0;
+
+  assert(step >= (import_alpha ? 4 : 3));
+  for (y = 0; y < height; ++y) {
+    uint32_t* const dst = &picture->argb[y * picture->argb_stride];
+    int x;
+    for (x = 0; x < width; ++x) {
+      const int offset = step * x + y * rgb_stride;
+      dst[x] = MakeARGB32(import_alpha ? a_ptr[offset] : 0xff,
+                          r_ptr[offset], g_ptr[offset], b_ptr[offset]);
+    }
+  }
+  return 1;
+}
+
+// Public API
+
+int WebPPictureImportRGB(WebPPicture* picture,
+                         const uint8_t* rgb, int rgb_stride) {
+  return (picture != NULL) ? Import(picture, rgb, rgb_stride, 3, 0, 0) : 0;
+}
+
+int WebPPictureImportBGR(WebPPicture* picture,
+                         const uint8_t* rgb, int rgb_stride) {
+  return (picture != NULL) ? Import(picture, rgb, rgb_stride, 3, 1, 0) : 0;
+}
+
+int WebPPictureImportRGBA(WebPPicture* picture,
+                          const uint8_t* rgba, int rgba_stride) {
+  return (picture != NULL) ? Import(picture, rgba, rgba_stride, 4, 0, 1) : 0;
+}
+
+int WebPPictureImportBGRA(WebPPicture* picture,
+                          const uint8_t* rgba, int rgba_stride) {
+  return (picture != NULL) ? Import(picture, rgba, rgba_stride, 4, 1, 1) : 0;
+}
+
+int WebPPictureImportRGBX(WebPPicture* picture,
+                          const uint8_t* rgba, int rgba_stride) {
+  return (picture != NULL) ? Import(picture, rgba, rgba_stride, 4, 0, 0) : 0;
+}
+
+int WebPPictureImportBGRX(WebPPicture* picture,
+                          const uint8_t* rgba, int rgba_stride) {
+  return (picture != NULL) ? Import(picture, rgba, rgba_stride, 4, 1, 0) : 0;
+}
+
+//------------------------------------------------------------------------------