用C语言编码实现bmp文件的压缩

好的，下面是一个简单的使用C语言实现bmp文件压缩的示例代码：

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

#define BMP_HEADER_SIZE 54

typedef struct {
    unsigned char r, g, b;
} RGB;

int main(int argc, char **argv) {
    if (argc != 3) {
        printf("Usage: %s input.bmp output.bmp\n", argv[0]);
        exit(1);
    }

    char *input_filename = argv[1];
    char *output_filename = argv[2];

    FILE *input_fp = fopen(input_filename, "rb");
    if (input_fp == NULL) {
        printf("Failed to open input file: %s\n", input_filename);
        exit(1);
    }

    FILE *output_fp = fopen(output_filename, "wb");
    if (output_fp == NULL) {
        printf("Failed to open output file: %s\n", output_filename);
        fclose(input_fp);
        exit(1);
    }

    // 读取bmp文件头
    unsigned char bmp_header[BMP_HEADER_SIZE];
    fread(bmp_header, 1, BMP_HEADER_SIZE, input_fp);

    // 获取图像宽度和高度
    int width = *(int *)(bmp_header + 18);
    int height = *(int *)(bmp_header + 22);

    // 计算图像数据大小
    int row_size = width * 3;
    int padding_size = 0;
    while ((row_size + padding_size) % 4 != 0) {
        padding_size++;
    }
    int data_size = (row_size + padding_size) * height;

    // 读取图像数据
    unsigned char *data = (unsigned char *)malloc(data_size);
    fread(data, 1, data_size, input_fp);

    // 压缩图像数据
    int compressed_size = data_size / 2;
    unsigned char *compressed_data = (unsigned char *)malloc(compressed_size);
    int i, j;
    for (i = 0, j = 0; i < data_size; i += 6, j += 3) {
        RGB p1 = { data[i], data[i+1], data[i+2] };
        RGB p2 = { data[i+3], data[i+4], data[i+5] };
        RGB avg = { (p1.r + p2.r) / 2, (p1.g + p2.g) / 2, (p1.b + p2.b) / 2 };
        compressed_data[j] = avg.r;
        compressed_data[j+1] = avg.g;
        compressed_data[j+2] = avg.b;
    }

    // 写入压缩后的bmp文件头
    unsigned char compressed_bmp_header[BMP_HEADER_SIZE];
    memcpy(compressed_bmp_header, bmp_header, BMP_HEADER_SIZE);
    *(int *)(compressed_bmp_header + 2) = BMP_HEADER_SIZE + compressed_size;
    *(int *)(compressed_bmp_header + 18) = width / 2;
    *(int *)(compressed_bmp_header + 22) = height;
    *(int *)(compressed_bmp_header + 34) = compressed_size;
    fwrite(compressed_bmp_header, 1, BMP_HEADER_SIZE, output_fp);

    // 写入压缩后的图像数据
    fwrite(compressed_data, 1, compressed_size, output_fp);

    fclose(input_fp);
    fclose(output_fp);
    free(data);
    free(compressed_data);

    printf("Compression completed.\n");

    return 0;
}

这段代码实现了读取bmp文件、压缩图像数据、写入压缩后的bmp文件。具体来说，它首先读取bmp文件头，获取图像的宽度和高度，然后计算图像数据大小，读取图像数据，对图像数据进行压缩，写入压缩后的bmp文件头和压缩后的图像数据，最后释放内存并结束程序。