lz77 huffman matlab
时间: 2023-10-16 19:12:20 浏览: 47
以下是使用LZ77和Huffman编码实现数据压缩的Matlab代码示例:
```matlab
function compressed = lz77_huffman_encode(data)
% LZ77编码
window_size = 256;
lookahead_size = 64;
len_bits = ceil(log2(window_size));
offset_bits = ceil(log2(lookahead_size));
compressed = [];
i = 1;
while i <= length(data)
j = max(i - window_size, 1);
match_length = 0;
match_offset = 0;
for k = j:i-1
n = 0;
while n < lookahead_size && k+n <= length(data) && data(k+n) == data(i+n)
n = n + 1;
end
if n > match_length
match_length = n;
match_offset = i - k;
end
end
if match_length > 2
compressed = [compressed; match_length-2 match_offset-1];
i = i + match_length;
else
compressed = [compressed; 0 data(i)];
i = i + 1;
end
end
% Huffman编码
symbol_counts = zeros(1, 256);
for i = 1:length(compressed)
if compressed(i, 1) == 0
symbol_counts(compressed(i, 2)+1) = symbol_counts(compressed(i, 2)+1) + 1;
else
symbol_counts(256+ceil(log2(compressed(i, 1)+1))) = symbol_counts(256+ceil(log2(compressed(i, 1)+1))) + 1;
symbol_counts(256+len_bits+ceil(log2(compressed(i, 2)+1))) = symbol_counts(256+len_bits+ceil(log2(compressed(i, 2)+1))) + 1;
end
end
tree = huffmantree(symbol_counts);
codes = huffmancodes(tree);
% 生成压缩数据
compressed_data = [];
for i = 1:length(compressed)
if compressed(i, 1) == 0
compressed_data = [compressed_data codes{compressed(i, 2)+1}];
else
len_code = codes{256+ceil(log2(compressed(i, 1)+1))};
offset_code = codes{256+len_bits+ceil(log2(compressed(i, 2)+1))};
compressed_data = [compressed_data len_code offset_code];
compressed_data = [compressed_data dec2bin(compressed(i, 1), ceil(log2(compressed(i, 1)+1)))];
compressed_data = [compressed_data dec2bin(compressed(i, 2), ceil(log2(lookahead_size)))];
end
end
compressed_data = bin2dec(compressed_data);
compressed = [length(data) length(compressed_data) compressed_data];
end
function tree = huffmantree(symbol_counts)
% 构建Huffman树
n = length(symbol_counts);
tree = cell(2*n-1, 3);
for i = 1:n
tree{i, 1} = i;
tree{i, 2} = symbol_counts(i);
end
for i = n+1:2*n-1
min1 = inf;
min2 = inf;
for j = 1:i-1
if isempty(tree{j, 3})
if tree{j, 2} < min1
min2 = min1;
min1 = tree{j, 2};
min1_index = j;
elseif tree{j, 2} < min2
min2 = tree{j, 2};
min2_index = j;
end
end
end
tree{i, 1} = i;
tree{i, 2} = min1 + min2;
tree{min1_index, 3} = i;
tree{min2_index, 3} = i;
end
end
function codes = huffmancodes(tree)
% 生成Huffman编码
n = size(tree, 1);
codes = cell(1, n);
for i = 1:n
code = '';
index = i;
while index ~= n
parent = tree{index, 3};
if tree{parent, 1} > index
code = ['0' code];
else
code = ['1' code];
end
index = parent;
end
codes{i} = code;
end
end
```
使用示例:
```matlab
data = 'hello world';
compressed = lz77_huffman_encode(data);
```
输出为一个长度为3的向量,第一个元素表示原始数据长度,第二个元素表示压缩数据长度,第三个元素为压缩数据。
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