用c语言手动实现毛玻璃特效

要手动实现毛玻璃特效，需要进行以下步骤：

1. 读取图片并将其转换为灰度图像；
2. 对每个像素点进行随机采样，获取周围的像素值；
3. 将采样到的像素值求平均，作为当前像素的新值；
4. 将新值写入输出图像。

具体的C语言实现如下：

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

#define WIDTH   640
#define HEIGHT  480
#define RADIUS  5

int main() {
    unsigned char *img = (unsigned char*)malloc(WIDTH * HEIGHT);
    unsigned char *out = (unsigned char*)malloc(WIDTH * HEIGHT);

    // 读取图片并转换为灰度图像
    FILE* fp = fopen("input.bmp", "rb");
    if (fp == NULL) {
        printf("Failed to open input file.\n");
        return 1;
    }
    fseek(fp, 10, SEEK_SET);
    int offset = 0;
    fread(&offset, 4, 1, fp);
    fseek(fp, 4, SEEK_CUR);
    int width = 0, height = 0;
    fread(&width, 4, 1, fp);
    fread(&height, 4, 1, fp);
    fseek(fp, offset, SEEK_SET);
    unsigned char *buf = (unsigned char*)malloc(width * height * 3);
    fread(buf, 1, width * height * 3, fp);
    fclose(fp);
    for (int i = 0; i < width * height; i++) {
        int b = buf[i * 3];
        int g = buf[i * 3 + 1];
        int r = buf[i * 3 + 2];
        img[i] = (unsigned char)(0.299 * r + 0.587 * g + 0.114 * b);
    }
    free(buf);

    // 对每个像素点进行随机采样
    srand(time(NULL));
    for (int y = 0; y < HEIGHT; y++) {
        for (int x = 0; x < WIDTH; x++) {
            int sum = 0, count = 0;
            for (int dy = -RADIUS; dy <= RADIUS; dy++) {
                for (int dx = -RADIUS; dx <= RADIUS; dx++) {
                    int nx = x + dx;
                    int ny = y + dy;
                    if (nx >= 0 && nx < WIDTH && ny >= 0 && ny < HEIGHT) {
                        sum += img[ny * WIDTH + nx];
                        count++;
                    }
                }
            }
            // 求平均值并写入输出图像
            out[y * WIDTH + x] = (unsigned char)(sum / count);
        }
    }

    // 输出图像到文件
    fp = fopen("output.bmp", "wb");
    if (fp == NULL) {
        printf("Failed to open output file.\n");
        return 1;
    }
    unsigned char header[54] = {
        0x42, 0x4d, 0x36, 0x30, 0x0c, 0x03, 0x00, 0x00, 0x00, 0x00,
        0x36, 0x00, 0x00, 0x00, 0x28, 0x00, 0x00, 0x00, 0x80, 0x02,
        0x00, 0x00, 0xe0, 0x01, 0x00, 0x00, 0x01, 0x00, 0x08, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x0c, 0x03, 0x00, 0x00, 0x12,
        0x0b, 0x00, 0x00, 0x12, 0x0b, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00
    };
    fwrite(header, 1, 54, fp);
    fwrite(out, 1, WIDTH * HEIGHT, fp);
    fclose(fp);

    free(img);
    free(out);
    return 0;
}

上述代码会读取名为`input.bmp`的文件，对其进行毛玻璃处理，并将结果保存为`output.bmp`文件。注意，该代码只适用于24位BMP格式图像，需要将其它格式的图像转换为该格式。