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Fix a compression regression for images with long uniform regions.

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Change-Id: Id87a4ac2a22daaa71e8f3132e69703b9b3ddd752
This commit is contained in:
Vincent Rabaud 2016-06-14 21:51:10 +02:00
parent 8190374c2b
commit 059aab4fa1
1 changed files with 40 additions and 44 deletions
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84
src/enc/backward_references.c
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@ -648,9 +648,7 @@ typedef struct {
CostCacheInterval* cache_intervals_;
size_t cache_intervals_size_;
double cost_cache_[MAX_LENGTH]; // Contains the GetLengthCost(cost_model, k).
// cost_cache_min_dist_[i] contains the index of the minimum in
// cost_cache_[1:i]. cost_cache_min_dist_[0] is unused.
uint16_t cost_cache_min_dist_[MAX_LENGTH];
double min_cost_cache_; // The minimum value in cost_cache_[1:].
float* costs_;
uint16_t* dist_array_;
// Most of the time, we only need few intervals -> use a free-list, to avoid
@ -720,22 +718,6 @@ static void CostManagerClear(CostManager* const manager) {
CostManagerInitFreeList(manager);
}
static void CostManagerMinDistCacheInit(CostManager* const manager) {
int min_idx = 1;
double min = manager->cost_cache_[1];
int i;
// cost_cache_min_dist_[i] contains the index of the minimum in
// cost_cache_[1:i].
for (i = 1; i < MAX_LENGTH; ++i) {
manager->cost_cache_min_dist_[i] = min_idx;
if (manager->cost_cache_[i] < min) {
min_idx = i;
min = manager->cost_cache_[i];
}
}
}
static int CostManagerInit(CostManager* const manager,
uint16_t* const dist_array, int pix_count,
const CostModel* const cost_model) {
@ -761,10 +743,14 @@ static int CostManagerInit(CostManager* const manager,
min_cost_diff) {
++manager->cache_intervals_size_;
}
// Compute the minimum of cost_cache_.
if (i == 1) {
manager->min_cost_cache_ = manager->cost_cache_[1];
} else if (manager->cost_cache_[i] < manager->min_cost_cache_) {
manager->min_cost_cache_ = manager->cost_cache_[i];
}
}
CostManagerMinDistCacheInit(manager);
// With the current cost models, we have 15 intervals, so we are safe by
// setting a maximum of COST_CACHE_INTERVAL_SIZE_MAX.
if (manager->cache_intervals_size_ > COST_CACHE_INTERVAL_SIZE_MAX) {
@ -841,17 +827,10 @@ static int CostManagerInit(CostManager* const manager,
// Given the distance_cost for pixel 'index', update the cost at pixel 'i' if it
// is smaller than the previously computed value.
// If index is negative, the distance is computed using
// manager->cost_cache_min_dist_[-index] instead.
static WEBP_INLINE void UpdateCost(CostManager* const manager, int i, int index,
double distance_cost) {
int k;
int k = i - index;
double cost_tmp;
if (index < 0) {
k = manager->cost_cache_min_dist_[-index];
} else {
k = i - index;
}
cost_tmp = distance_cost + manager->cost_cache_[k];
if (manager->costs_[i] > cost_tmp) {
@ -1173,10 +1152,18 @@ static int BackwardReferencesHashChainDistanceOnly(
if (len >= MIN_LENGTH) {
const int code = DistanceToPlaneCode(xsize, offset);
const double offset_cost = GetDistanceCost(cost_model, code);
double distance_cost = prev_cost + offset_cost;
const int first_i = i;
int j_max;
PushInterval(cost_manager, distance_cost, i, len);
if (offset_cost == 0.) {
j_max = 1;
} else {
j_max = ceil(cost_manager->min_cost_cache_ / offset_cost);
}
// With the values we currently use for the model, offset_cost is
// between 10 and 20 and j_max ends up at 2 or 3.
if (j_max > MAX_LENGTH - 1) j_max = MAX_LENGTH - 1;
// The cost to get to pixel i+k is:
// prev_cost + best weight of path going from i to l.
@ -1188,26 +1175,36 @@ static int BackwardReferencesHashChainDistanceOnly(
// As the offset_cost is close to the values in cost_cache_ (both are the
// cost to store a number, whether it's an offset or a length), the best
// paths are therefore the ones involving one hop.
for (; i + 1 < pix_count - 1; ++i) {
int offset_next, len_next, diff;
for (; i < pix_count - 1; ++i) {
int offset_next, len_next;
double distance_cost;
prev_cost = cost_manager->costs_[i - 1];
distance_cost = prev_cost + offset_cost;
if (len != MAX_LENGTH || i == first_i) {
PushInterval(cost_manager, distance_cost, i, len);
} else {
int j;
// The pixel at i + MAX_LENGTH - 1 is influenced by all the pixels
// before at i + MAX_LENGTH - j. Then again, the distance cost
// provided by those is increased by offset_cost*j. Therefore, only
// the pixels providing a length cost inferior to offset_cost*j can be
// considered.
// As we know this cost is at least cost_manager->min_cost_cache_:
// therefore only the first j_max pixels from i influence
// i + MAX_LENGTH - 1.
// Reciprocally, pixel i only influences the last j_max pixels.
for (j = 1; j <= j_max; ++j) {
UpdateCost(cost_manager, i + MAX_LENGTH - j, i, distance_cost);
}
}
// Check whether i is the last pixel to consider, as it is handled
// differently.
if (i + 1 >= pix_count - 1) break;
HashChainFindCopy(hash_chain, i + 1, &offset_next, &len_next);
if (offset_next != offset) break;
diff = i - first_i;
if (diff > 0) {
assert(len > 1);
if (diff >= len) diff = len - 1;
// The best path going to pixel i is the one starting in a pixel
// within diff hence at the pixel:
// i - manager->cost_cache_min_dist_[diff].
UpdateCost(cost_manager, i, -diff, distance_cost);
}
len = len_next;
UpdateCostPerIndex(cost_manager, i);
AddSingleLiteralWithCostModel(argb + i, &hashers, cost_model, i,
@ -1215,7 +1212,6 @@ static int BackwardReferencesHashChainDistanceOnly(
cost_manager->costs_, dist_array);
}
// Submit the last pixel.
if (first_i != i) PushInterval(cost_manager, distance_cost, i, len);
UpdateCostPerIndex(cost_manager, i + 1);
// This if is for speedup only. It roughly doubles the speed, and