哈夫曼编码的图像压缩C语言

哈夫曼编码是一种无损的数据压缩算法，通常用于图像、音频、视频等大数据的压缩。下面是一个基于哈夫曼编码的图像压缩的C语言代码示例：

#include <stdio.h>
#include <stdlib.h>

#define MAX_TREE_HT 100

// 哈夫曼树节点结构体
struct MinHeapNode {
    char data;
    unsigned freq;
    struct MinHeapNode *left, *right;
};

// 哈夫曼树结构体
struct MinHeap {
    unsigned size;
    unsigned capacity;
    struct MinHeapNode** array;
};

// 创建哈夫曼树节点
struct MinHeapNode* newNode(char data, unsigned freq) {
    struct MinHeapNode* temp = (struct MinHeapNode*)malloc(sizeof(struct MinHeapNode));
    temp->left = temp->right = NULL;
    temp->data = data;
    temp->freq = freq;
    return temp;
}

// 创建哈夫曼树
struct MinHeap* createMinHeap(unsigned capacity) {
    struct MinHeap* minHeap = (struct MinHeap*)malloc(sizeof(struct MinHeap));
    minHeap->size = 0;
    minHeap->capacity = capacity;
    minHeap->array = (struct MinHeapNode**)malloc(minHeap->capacity * sizeof(struct MinHeapNode*));
    return minHeap;
}

// 交换两个节点
void swapMinHeapNode(struct MinHeapNode** a, struct MinHeapNode** b) {
    struct MinHeapNode* t = *a;
    *a = *b;
    *b = t;
}

// 使最小堆保持最小堆性质
void minHeapify(struct MinHeap* minHeap, int idx) {
    int smallest = idx;
    int left = 2 * idx + 1;
    int right = 2 * idx + 2;
    if (left < minHeap->size && minHeap->array[left]->freq < minHeap->array[smallest]->freq) {
        smallest = left;
    }
    if (right < minHeap->size && minHeap->array[right]->freq < minHeap->array[smallest]->freq) {
        smallest = right;
    }
    if (smallest != idx) {
        swapMinHeapNode(&minHeap->array[smallest], &minHeap->array[idx]);
        minHeapify(minHeap, smallest);
    }
}

// 判断堆是否只有一个元素
int isSizeOne(struct MinHeap* minHeap) {
    return (minHeap->size == 1);
}

// 取出最小频率的节点
struct MinHeapNode* extractMin(struct MinHeap* minHeap) {
    struct MinHeapNode* temp = minHeap->array[0];
    minHeap->array[0] = minHeap->array[minHeap->size - 1];
    --minHeap->size;
    minHeapify(minHeap, 0);
    return temp;
}

// 插入节点到最小堆中
void insertMinHeap(struct MinHeap* minHeap, struct MinHeapNode* minHeapNode) {
    ++minHeap->size;
    int i = minHeap->size - 1;
    while (i && minHeapNode->freq < minHeap->array[(i - 1) / 2]->freq) {
        minHeap->array[i] = minHeap->array[(i - 1) / 2];
        i = (i - 1) / 2;
    }
    minHeap->array[i] = minHeapNode;
}

// 判断节点是否是叶子节点
int isLeaf(struct MinHeapNode* root) {
    return !(root->left) && !(root->right);
}

// 创建并构建哈夫曼树
struct MinHeapNode* buildHuffmanTree(char data[], int freq[], int size) {
    struct MinHeapNode *left, *right, *top;
    struct MinHeap* minHeap = createMinHeap(size);
    for (int i = 0; i < size; ++i) {
        insertMinHeap(minHeap, newNode(data[i], freq[i]));
    }
    while (!isSizeOne(minHeap)) {
        left = extractMin(minHeap);
        right = extractMin(minHeap);
        top = newNode('$', left->freq + right->freq);
        top->left = left;
        top->right = right;
        insertMinHeap(minHeap, top);
    }
    return extractMin(minHeap);
}

// 构建哈夫曼编码表
void buildHuffmanCodes(struct MinHeapNode* root, int arr[], int top) {
    if (root->left) {
        arr[top] = 0;
        buildHuffmanCodes(root->left, arr, top + 1);
    }
    if (root->right) {
        arr[top] = 1;
        buildHuffmanCodes(root->right, arr, top + 1);
    }
    if (isLeaf(root)) {
        printf("%c: ", root->data);
        for (int i = 0; i < top; ++i) {
            printf("%d", arr[i]);
        }
        printf("\n");
    }
}

// 使用哈夫曼编码压缩图像
void compressImage(char* inputFileName, char* outputFileName) {
    FILE* inputFile = fopen(inputFileName, "r");
    FILE* outputFile = fopen(outputFileName, "w");
    char c;
    int freq[256] = {0};
    while ((c = fgetc(inputFile)) != EOF) {
        freq[(int)c]++;
    }
    struct MinHeapNode* root = buildHuffmanTree((char*)freq, freq, 256);
    int arr[MAX_TREE_HT], top = 0;
    buildHuffmanCodes(root, arr, top);
    rewind(inputFile);
    char buffer = 0;
    int pos = 7;
    while ((c = fgetc(inputFile)) != EOF) {
        int* code = (int*)malloc(MAX_TREE_HT * sizeof(int));
        buildHuffmanCodes(root, code, 0);
        int i = 0;
        while (code[i] != -1) {
            buffer |= (code[i++] << pos);
            pos--;
            if (pos < 0) {
                fputc(buffer, outputFile);
                buffer = 0;
                pos = 7;
            }
        }
        free(code);
    }
    if (pos != 7) {
        fputc(buffer, outputFile);
    }
    fclose(inputFile);
    fclose(outputFile);
}

int main() {
    compressImage("input.bmp", "output.bmp");
    return 0;
}

以上代码实现了图像的哈夫曼编码压缩，可以尝试自己编写解压缩代码以还原图像。