使用C语言 图像缩放 双线性插值算法

双线性插值算法是一种常用的图像缩放方法，可以在缩放过程中保持图像的平滑性和细节信息。下面是使用C语言实现双线性插值算法的代码示例：

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

#define CHANNELS 3 // 图像通道数
#define SCALE 2 // 缩放倍数

// 双线性插值算法
void bilinear_interpolation(unsigned char *input, unsigned char *output, int width, int height, int channels, float scale) {
    int new_width = (int)(width * scale);
    int new_height = (int)(height * scale);
    float x_ratio = (float)(width - 1) / (float)(new_width - 1);
    float y_ratio = (float)(height - 1) / (float)(new_height - 1);

    for (int i = 0; i < new_height; i++) {
        for (int j = 0; j < new_width; j++) {
            float x = j * x_ratio;
            float y = i * y_ratio;
            int x1 = (int)x;
            int y1 = (int)y;
            int x2 = x1 + 1;
            int y2 = y1 + 1;
            float fx = x - x1;
            float fy = y - y1;

            for (int k = 0; k < channels; k++) {
                float p1 = input[(y1 * width + x1) * channels + k];
                float p2 = input[(y1 * width + x2) * channels + k];
                float p3 = input[(y2 * width + x1) * channels + k];
                float p4 = input[(y2 * width + x2) * channels + k];

                float value = (1 - fx) * (1 - fy) * p1 + fx * (1 - fy) * p2 + (1 - fx) * fy * p3 + fx * fy * p4;
                output[(i * new_width + j) * channels + k] = (unsigned char)value;
            }
        }
    }
}

int main() {
    FILE *fp_in, *fp_out;
    unsigned char *input, *output;
    int width, height;

    fp_in = fopen("input.bmp", "rb");
    if (fp_in == NULL) {
        printf("Error: cannot open input file!\n");
        return -1;
    }

    // 读取BMP文件头
    fseek(fp_in, 18, SEEK_SET);
    fread(&width, sizeof(int), 1, fp_in);
    fread(&height, sizeof(int), 1, fp_in);

    // 计算图像数据大小
    int size = width * height * CHANNELS;

    // 分配内存并读取图像数据
    input = (unsigned char*)malloc(size);
    fread(input, sizeof(unsigned char), size, fp_in);

    // 缩放图像
    int new_width = (int)(width * SCALE);
    int new_height = (int)(height * SCALE);
    output = (unsigned char*)malloc(new_width * new_height * CHANNELS);
    bilinear_interpolation(input, output, width, height, CHANNELS, SCALE);

    // 写入输出文件
    fp_out = fopen("output.bmp", "wb");
    if (fp_out == NULL) {
        printf("Error: cannot open output file!\n");
        return -1;
    }
    fwrite(input, sizeof(unsigned char), size, fp_out);
    fclose(fp_out);

    // 释放内存
    free(input);
    free(output);

    return 0;
}

上面的代码使用双线性插值算法实现了图像缩放，输入图像为BMP格式，输出图像也是BMP格式。在实际应用中，还需要考虑图像的边缘处理、颜色空间转换等问题。