go-libwebp

near_lossless_enc.c (5396B)

---

 // 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.
 // -----------------------------------------------------------------------------
 //
 // Near-lossless image preprocessing adjusts pixel values to help
 // compressibility with a guarantee of maximum deviation between original and
 // resulting pixel values.
 //
 // Author: Jyrki Alakuijala (jyrki@google.com)
 // Converted to C by Aleksander Kramarz (akramarz@google.com)
 
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include "src/dsp/lossless_common.h"
 #include "src/webp/types.h"
 #include "src/enc/vp8li_enc.h"
 #include "src/utils/utils.h"
 #include "src/webp/encode.h"
 
 #if (WEBP_NEAR_LOSSLESS == 1)
 
 #define MIN_DIM_FOR_NEAR_LOSSLESS 64
 #define MAX_LIMIT_BITS             5
 
 // Quantizes the value up or down to a multiple of 1<<bits (or to 255),
 // choosing the closer one, resolving ties using bankers' rounding.
 static uint32_t FindClosestDiscretized(uint32_t a, int bits) {
   const uint32_t mask = (1u << bits) - 1;
   const uint32_t biased = a + (mask >> 1) + ((a >> bits) & 1);
   assert(bits > 0);
   if (biased > 0xff) return 0xff;
   return biased & ~mask;
 }
 
 // Applies FindClosestDiscretized to all channels of pixel.
 static uint32_t ClosestDiscretizedArgb(uint32_t a, int bits) {
   return
       (FindClosestDiscretized(a >> 24, bits) << 24) |
       (FindClosestDiscretized((a >> 16) & 0xff, bits) << 16) |
       (FindClosestDiscretized((a >> 8) & 0xff, bits) << 8) |
       (FindClosestDiscretized(a & 0xff, bits));
 }
 
 // Checks if distance between corresponding channel values of pixels a and b
 // is within the given limit.
 static int IsNear(uint32_t a, uint32_t b, int limit) {
   int k;
   for (k = 0; k < 4; ++k) {
     const int delta =
         (int)((a >> (k * 8)) & 0xff) - (int)((b >> (k * 8)) & 0xff);
     if (delta >= limit || delta <= -limit) {
       return 0;
     }
   }
   return 1;
 }
 
 static int IsSmooth(const uint32_t* const prev_row,
                     const uint32_t* const curr_row,
                     const uint32_t* const next_row,
                     int ix, int limit) {
   // Check that all pixels in 4-connected neighborhood are smooth.
   return (IsNear(curr_row[ix], curr_row[ix - 1], limit) &&
           IsNear(curr_row[ix], curr_row[ix + 1], limit) &&
           IsNear(curr_row[ix], prev_row[ix], limit) &&
           IsNear(curr_row[ix], next_row[ix], limit));
 }
 
 // Adjusts pixel values of image with given maximum error.
 static void NearLossless(int xsize, int ysize, const uint32_t* argb_src,
                          int stride, int limit_bits, uint32_t* copy_buffer,
                          uint32_t* argb_dst) {
   int x, y;
   const int limit = 1 << limit_bits;
   uint32_t* prev_row = copy_buffer;
   uint32_t* curr_row = prev_row + xsize;
   uint32_t* next_row = curr_row + xsize;
   memcpy(curr_row, argb_src, xsize * sizeof(argb_src[0]));
   memcpy(next_row, argb_src + stride, xsize * sizeof(argb_src[0]));
 
   for (y = 0; y < ysize; ++y, argb_src += stride, argb_dst += xsize) {
     if (y == 0 || y == ysize - 1) {
       memcpy(argb_dst, argb_src, xsize * sizeof(argb_src[0]));
     } else {
       memcpy(next_row, argb_src + stride, xsize * sizeof(argb_src[0]));
       argb_dst[0] = argb_src[0];
       argb_dst[xsize - 1] = argb_src[xsize - 1];
       for (x = 1; x < xsize - 1; ++x) {
         if (IsSmooth(prev_row, curr_row, next_row, x, limit)) {
           argb_dst[x] = curr_row[x];
         } else {
           argb_dst[x] = ClosestDiscretizedArgb(curr_row[x], limit_bits);
         }
       }
     }
     {
       // Three-way swap.
       uint32_t* const temp = prev_row;
       prev_row = curr_row;
       curr_row = next_row;
       next_row = temp;
     }
   }
 }
 
 int VP8ApplyNearLossless(const WebPPicture* const picture, int quality,
                          uint32_t* const argb_dst) {
   int i;
   const int xsize = picture->width;
   const int ysize = picture->height;
   const int stride = picture->argb_stride;
   uint32_t* const copy_buffer =
       (uint32_t*)WebPSafeMalloc(xsize * 3, sizeof(*copy_buffer));
   const int limit_bits = VP8LNearLosslessBits(quality);
   assert(argb_dst != NULL);
   assert(limit_bits > 0);
   assert(limit_bits <= MAX_LIMIT_BITS);
   if (copy_buffer == NULL) {
     return 0;
   }
   // For small icon images, don't attempt to apply near-lossless compression.
   if ((xsize < MIN_DIM_FOR_NEAR_LOSSLESS &&
        ysize < MIN_DIM_FOR_NEAR_LOSSLESS) ||
       ysize < 3) {
     for (i = 0; i < ysize; ++i) {
       memcpy(argb_dst + i * xsize, picture->argb + i * picture->argb_stride,
              xsize * sizeof(*argb_dst));
     }
     WebPSafeFree(copy_buffer);
     return 1;
   }
 
   NearLossless(xsize, ysize, picture->argb, stride, limit_bits, copy_buffer,
                argb_dst);
   for (i = limit_bits - 1; i != 0; --i) {
     NearLossless(xsize, ysize, argb_dst, xsize, i, copy_buffer, argb_dst);
   }
   WebPSafeFree(copy_buffer);
   return 1;
 }
 #else  // (WEBP_NEAR_LOSSLESS == 1)
 
 // Define a stub to suppress compiler warnings.
 extern void VP8LNearLosslessStub(void);
 void VP8LNearLosslessStub(void) {}
 
 #endif  // (WEBP_NEAR_LOSSLESS == 1)