// 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 "src/dsp/lossless_common.h"

#include "src/utils/utils.h"

#include "src/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)