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Diffstat (limited to 'media/libwebp/enc/near_lossless_enc.c')
| -rw-r--r-- | media/libwebp/enc/near_lossless_enc.c | 151 |
1 files changed, 151 insertions, 0 deletions
diff --git a/media/libwebp/enc/near_lossless_enc.c b/media/libwebp/enc/near_lossless_enc.c new file mode 100644 index 0000000000..1fd12a4364 --- /dev/null +++ b/media/libwebp/enc/near_lossless_enc.c @@ -0,0 +1,151 @@ +// 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 "../dsp/lossless_common.h" +#include "../utils/utils.h" +#include "../enc/vp8li_enc.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) |