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Generate ordering histogram for endpoint indexes based on the prediction order

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This change improves compression ratio.

Explanation:
The original histogram has been generated based on the linear order of encoded endpoint indexes. In the modified version of the algorithm, endpoint indexes are predicted using the nearest left block on the image, which is not necessarily the preceding block in the encoded sequence. Using the same block ordering both for prediction and Zeng optimization normally improves the compression ratio.

Testing:
The modified algorithm has been tested on the Kodak test set using 64-bit build with default settings (running on Windows 10, i7-4790, 3.6GHz). All the decompressed test images are identical to the images being compressed and decompressed using original version of Crunch.

[Compressing Kodak set without mipmaps]
Original: 1582222 bytes / 28.905 sec
Modified: 1566133 bytes / 28.457 sec
Improvement: 1.02% (compression ratio) / 1.55% (compression time)

[Compressing Kodak set with mipmaps]
Original: 2065243 bytes / 37.021 sec
Modified: 2040086 bytes / 36.300 sec
Improvement: 1.22% (compression ratio) / 1.95% (compression time)
This commit is contained in:
Alexander Suvorov
2017-04-28 13:49:47 +02:00
parent 19f05aadbc
commit a4ab9fedee
2 changed files with 33 additions and 12 deletions
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bin/crunch_x64.exe
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crnlib/crn_comp.cpp
+33 -12
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@@ -1364,12 +1364,21 @@ bool crn_comp::optimize_color_endpoint_codebook(crnlib::vector<uint>& remapping)
uint n = m_hvq.get_color_endpoint_codebook_size();
hist_type xhist(n * n);
for (uint i = 0; i < m_endpoint_indices[cColor].size(); i++) {
const int prev_val = (i > 0) ? m_endpoint_indices[cColor][i - 1] : -1;
const int cur_val = m_endpoint_indices[cColor][i];
const int next_val = (i < (m_endpoint_indices[cColor].size() - 1)) ? m_endpoint_indices[cColor][i + 1] : -1;
update_hist(xhist, cur_val, prev_val, n);
update_hist(xhist, cur_val, next_val, n);
uint endpoint_index[2][2] = {};
for (uint chunk_index = 0; chunk_index < m_chunks.size(); chunk_index++) {
const chunk_detail& details = m_chunk_details[chunk_index];
for (uint y = 0; y < 2; y++) {
for (uint x = 0; x < 2; x++) {
uint8 endpoint_reference = details.m_endpoint_references[cColor][y][x];
if (!endpoint_reference) {
endpoint_index[y][x] = details.m_endpoint_indices[cColor][y][x];
update_hist(xhist, endpoint_index[y][x], endpoint_index[y][x ^ 1], n);
update_hist(xhist, endpoint_index[y][x ^ 1], endpoint_index[y][x], n);
} else {
endpoint_index[y][x] = endpoint_reference == 1 ? endpoint_index[y][x ^ 1] : endpoint_index[y ^ 1][x];
}
}
}
}
for (uint i = 0; i <= cMaxEndpointRemapIters; i++) {
@@ -1610,12 +1619,24 @@ bool crn_comp::optimize_alpha_endpoint_codebook(crnlib::vector<uint>& remapping)
uint n = m_hvq.get_alpha_endpoint_codebook_size();
hist_type xhist(n * n);
for (uint i = 0; i < alpha_indices.size(); i++) {
const int prev_val = (i > 0) ? alpha_indices[i - 1] : -1;
const int cur_val = alpha_indices[i];
const int next_val = (i < (alpha_indices.size() - 1)) ? alpha_indices[i + 1] : -1;
update_hist(xhist, cur_val, prev_val, n);
update_hist(xhist, cur_val, next_val, n);
uint endpoint_index[cNumComps][2][2] = {};
uint min_comp_index = m_has_comp[cAlpha0] ? cAlpha0 : cAlpha1, max_comp_index = m_has_comp[cAlpha1] ? cAlpha1 : cAlpha0;
for (uint chunk_index = 0; chunk_index < m_chunks.size(); chunk_index++) {
const chunk_detail& details = m_chunk_details[chunk_index];
for (uint comp_index = min_comp_index; comp_index <= max_comp_index; comp_index++) {
for (uint y = 0; y < 2; y++) {
for (uint x = 0; x < 2; x++) {
uint8 endpoint_reference = details.m_endpoint_references[comp_index][y][x];
if (!endpoint_reference) {
endpoint_index[comp_index][y][x] = details.m_endpoint_indices[comp_index][y][x];
update_hist(xhist, endpoint_index[comp_index][y][x], endpoint_index[comp_index][y][x ^ 1], n);
update_hist(xhist, endpoint_index[comp_index][y][x ^ 1], endpoint_index[comp_index][y][x], n);
} else {
endpoint_index[comp_index][y][x] = endpoint_reference == 1 ? endpoint_index[comp_index][y][x ^ 1] : endpoint_index[comp_index][y ^ 1][x];
}
}
}
}
}
for (uint i = 0; i <= cMaxEndpointRemapIters; i++) {