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Cleaup Near-lossless code.

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Cleaup Near-lossless code
- Simplified and refactored the code.
- Removed the requirement (TODO) to allocate the buffer of size WxH and work
  with buffer of size 3xW.
- Disabled the Near-lossless prr-processing for small icon images (W < 64 and H < 64).

Change-Id: Id7ee90c90622368d5528de4dd14fd5ead593bb1b
This commit is contained in:
Vikas Arora 2015-01-26 14:55:54 -08:00
parent 9814ddb601
commit ec0d1be577
1 changed files with 67 additions and 53 deletions
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118
src/enc/near_lossless.c
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@ -21,6 +21,10 @@
#include "./vp8enci.h"
#ifdef WEBP_EXPERIMENTAL_FEATURES
#define MIN_DIM_FOR_NEAR_LOSSLESS 64
#define MAX_LIMIT_BITS 5
// Computes quantized pixel value and distance from original value.
static void GetValAndDistance(int a, int initial, int bits,
int* const val, int* const distance) {
@ -29,20 +33,21 @@ static void GetValAndDistance(int a, int initial, int bits,
*distance = 2 * abs(a - *val);
}
// Quantizes values {a, a+(1<<bits), a-(1<<bits)}, checks if in [min, max] range
// and returns the nearest one.
static int FindClosestDiscretized(int a, int bits, int min, int max) {
// Clamps the value to range [0, 255].
static int Clamp8b(int val) {
const int min_val = 0;
const int max_val = 0xff;
return (val < min_val) ? min_val : (val > max_val) ? max_val : val;
}
// Quantizes values {a, a+(1<<bits), a-(1<<bits)} and returns the nearest one.
static int FindClosestDiscretized(int a, int bits) {
int best_val = a, i;
int min_distance = 256;
for (i = -1; i <= 1; ++i) {
int val = a + i * (1 << bits);
int candidate, distance;
if (val < 0) {
val = 0;
} else if (val > 255) {
val = 255;
}
const int val = Clamp8b(a + i * (1 << bits));
GetValAndDistance(a, val, bits, &candidate, &distance);
if (i != 0) {
++distance;
@ -50,7 +55,7 @@ static int FindClosestDiscretized(int a, int bits, int min, int max) {
// Smallest distance but favor i == 0 over i == -1 and i == 1
// since that keeps the overall intensity more constant in the
// images.
if (distance < min_distance && candidate >= min && candidate <= max) {
if (distance < min_distance) {
min_distance = distance;
best_val = candidate;
}
@ -59,30 +64,37 @@ static int FindClosestDiscretized(int a, int bits, int min, int max) {
}
// Applies FindClosestDiscretized to all channels of pixel.
static uint32_t ClosestDiscretizedArgb(uint32_t a, int bits,
uint32_t min, uint32_t max) {
return (FindClosestDiscretized(a >> 24, bits, min >> 24, max >> 24) << 24) |
(FindClosestDiscretized((a >> 16) & 0xff, bits,
(min >> 16) & 0xff,
(max >> 16) & 0xff) << 16) |
(FindClosestDiscretized((a >> 8) & 0xff, bits,
(min >> 8) & 0xff,
(max >> 8) & 0xff) << 8) |
(FindClosestDiscretized(a & 0xff, bits, min & 0xff, max & 0xff));
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
// exceeds given limit.
static int IsFar(uint32_t a, uint32_t b, int limit) {
// 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);
const int delta =
(int)((a >> (k * 8)) & 0xff) - (int)((b >> (k * 8)) & 0xff);
if (delta >= limit || delta <= -limit) {
return 0;
}
}
return 1;
}
}
return 0;
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.
@ -90,39 +102,37 @@ static void NearLossless(int xsize, int ysize, uint32_t* argb,
int limit_bits, uint32_t* copy_buffer) {
int x, y;
const int limit = 1 << limit_bits;
memcpy(copy_buffer, argb, xsize * ysize * sizeof(argb[0]));
uint32_t* prev_row = copy_buffer;
uint32_t* curr_row = prev_row + xsize;
uint32_t* next_row = curr_row + xsize;
memcpy(copy_buffer, argb, xsize * 2 * sizeof(argb[0]));
for (y = 0; y < ysize; ++y) {
const int offset = y * xsize;
for (x = 0; x < xsize; ++x) {
const int ix = offset + x;
// Check that all pixels in 4-connected neighborhood are smooth.
int smooth_area = 1;
if (x != 0 && IsFar(copy_buffer[ix], copy_buffer[ix - 1], limit)) {
smooth_area = 0;
} else if (y != 0 &&
IsFar(copy_buffer[ix], copy_buffer[ix - xsize], limit)) {
smooth_area = 0;
} else if (x != xsize - 1 &&
IsFar(copy_buffer[ix], copy_buffer[ix + 1], limit)) {
smooth_area = 0;
} else if (y != ysize - 1 &&
IsFar(copy_buffer[ix], copy_buffer[ix + xsize], limit)) {
smooth_area = 0;
for (y = 1; y < ysize - 1; ++y) {
uint32_t* const curr_argb_row = argb + y * xsize;
uint32_t* const next_argb_row = curr_argb_row + xsize;
memcpy(next_row, next_argb_row, xsize * sizeof(argb[0]));
for (x = 1; x < xsize - 1; ++x) {
if (!IsSmooth(prev_row, curr_row, next_row, x, limit)) {
curr_argb_row[x] = ClosestDiscretizedArgb(curr_row[x], limit_bits);
}
if (!smooth_area) {
argb[ix] = ClosestDiscretizedArgb(argb[ix], limit_bits, 0, 0xffffffff);
}
{
// Three-way swap.
uint32_t* const temp = prev_row;
prev_row = curr_row;
curr_row = next_row;
next_row = temp;
}
}
}
static int QualityToLimitBits(int quality) {
return 5 - (quality + 12) / 25;
// quality mapping 0..12 -> 5
// 13..100 -> 4..1
return MAX_LIMIT_BITS - (quality + 12) / 25;
}
#endif // WEBP_EXPERIMENTAL_FEATURES
// TODO(vikasa): optimize memory to O(xsize)
int VP8ApplyNearLossless(int xsize, int ysize, uint32_t* argb, int quality) {
#ifndef WEBP_EXPERIMENTAL_FEATURES
(void)xsize;
@ -132,16 +142,20 @@ int VP8ApplyNearLossless(int xsize, int ysize, uint32_t* argb, int quality) {
#else
int i;
uint32_t* const copy_buffer =
(uint32_t *)WebPSafeMalloc(xsize * ysize, sizeof(*copy_buffer));
// quality mapping 0..12 -> 5
// 13..100 -> 4..1
(uint32_t*)WebPSafeMalloc(xsize * 3, sizeof(*copy_buffer));
const int limit_bits = QualityToLimitBits(quality);
assert(argb != NULL);
assert(limit_bits >= 0);
assert(limit_bits < 31);
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) {
WebPSafeFree(copy_buffer);
return 1;
}
for (i = limit_bits; i != 0; --i) {
NearLossless(xsize, ysize, argb, i, copy_buffer);
}