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d69e36ec59
histogram.c: - Verified (earlier) that there's low correlation between Red & Blue colors (particularly after applying Cross-color transform). The Bin based histogram merge, bins on three entropies viz literal, red & blue symbols. Removing either of blue or red increases the compression density. So keeping the bins for red & blue sybmols. - Keeping the compact bins method as-is. This way it's simpler to read. huffman_encode.h: Added field comments for struct HuffmanTree and removed the TODO. Change-Id: Ia76f7bc730079d1b3b644038c5d9931db3797f0e
61 lines
2.1 KiB
C
61 lines
2.1 KiB
C
// Copyright 2011 Google Inc. All Rights Reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the COPYING file in the root of the source
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// tree. An additional intellectual property rights grant can be found
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// in the file PATENTS. All contributing project authors may
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// be found in the AUTHORS file in the root of the source tree.
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// -----------------------------------------------------------------------------
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//
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// Author: Jyrki Alakuijala (jyrki@google.com)
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//
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// Entropy encoding (Huffman) for webp lossless
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#ifndef WEBP_UTILS_HUFFMAN_ENCODE_H_
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#define WEBP_UTILS_HUFFMAN_ENCODE_H_
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#include "../webp/types.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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// Struct for holding the tree header in coded form.
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typedef struct {
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uint8_t code; // value (0..15) or escape code (16,17,18)
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uint8_t extra_bits; // extra bits for escape codes
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} HuffmanTreeToken;
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// Struct to represent the tree codes (depth and bits array).
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typedef struct {
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int num_symbols; // Number of symbols.
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uint8_t* code_lengths; // Code lengths of the symbols.
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uint16_t* codes; // Symbol Codes.
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} HuffmanTreeCode;
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// Struct to represent the Huffman tree.
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typedef struct {
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uint32_t total_count_; // Symbol frequency.
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int value_; // Symbol value.
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int pool_index_left_; // Index for the left sub-tree.
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int pool_index_right_; // Index for the right sub-tree.
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} HuffmanTree;
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// Turn the Huffman tree into a token sequence.
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// Returns the number of tokens used.
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int VP8LCreateCompressedHuffmanTree(const HuffmanTreeCode* const tree,
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HuffmanTreeToken* tokens, int max_tokens);
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// Create an optimized tree, and tokenize it.
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// 'buf_rle' and 'huff_tree' are pre-allocated and the 'tree' is the constructed
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// huffman code tree.
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void VP8LCreateHuffmanTree(uint32_t* const histogram, int tree_depth_limit,
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uint8_t* const buf_rle, HuffmanTree* const huff_tree,
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HuffmanTreeCode* const tree);
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#ifdef __cplusplus
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}
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#endif
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#endif // WEBP_UTILS_HUFFMAN_ENCODE_H_
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