Linuxc语言用标准io给一个图片变成马赛克

要将一个图片变成马赛克，一种常见的方法是将原始图片划分成一个个小的块，然后将每个小块用相同的颜色填充，以达到马赛克的效果。下面是一个使用标准IO的C语言程序，可以将PNG图片转换为马赛克图像：

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

#define BLOCK_SIZE 10

void process_file(png_structp png_ptr, png_infop info_ptr) {
    png_bytep *row_pointers;
    int row, col;

    // 读取图片数据
    png_read_image(png_ptr, row_pointers);

    // 获取图片的宽度和高度
    int width = png_get_image_width(png_ptr, info_ptr);
    int height = png_get_image_height(png_ptr, info_ptr);

    // 遍历所有块
    for (row = 0; row < height; row += BLOCK_SIZE) {
        for (col = 0; col < width; col += BLOCK_SIZE) {
            // 计算当前块的颜色
            int r = 0, g = 0, b = 0;
            int block_rows = BLOCK_SIZE;
            int block_cols = BLOCK_SIZE;
            if (row + BLOCK_SIZE > height) {
                block_rows = height - row;
            }
            if (col + BLOCK_SIZE > width) {
                block_cols = width - col;
            }
            int block_size = block_rows * block_cols;
            png_bytep row_ptr;
            for (int i = 0; i < block_rows; i++) {
                row_ptr = row_pointers[row + i];
                for (int j = 0; j < block_cols; j++) {
                    png_bytep pixel_ptr = &(row_ptr[(col + j) * 3]);
                    r += pixel_ptr[0];
                    g += pixel_ptr[1];
                    b += pixel_ptr[2];
                }
            }
            r /= block_size;
            g /= block_size;
            b /= block_size;

            // 用当前块的颜色填充块内所有像素
            for (int i = 0; i < block_rows; i++) {
                row_ptr = row_pointers[row + i];
                for (int j = 0; j < block_cols; j++) {
                    png_bytep pixel_ptr = &(row_ptr[(col + j) * 3]);
                    pixel_ptr[0] = r;
                    pixel_ptr[1] = g;
                    pixel_ptr[2] = b;
                }
            }
        }
    }

    // 写入输出文件
    png_write_image(png_ptr, row_pointers);
}

int main(int argc, char **argv) {
    if (argc != 3) {
        fprintf(stderr, "Usage: %s <input_file> <output_file>\n", argv[0]);
        exit(1);
    }

    FILE *fp = fopen(argv[1], "rb");
    if (!fp) {
        fprintf(stderr, "Error: could not open file %s\n", argv[1]);
        exit(1);
    }

    png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (!png_ptr) {
        fprintf(stderr, "Error: could not create png read struct\n");
        exit(1);
    }

    png_infop info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr) {
        fprintf(stderr, "Error: could not create png info struct\n");
        exit(1);
    }

    if (setjmp(png_jmpbuf(png_ptr))) {
        fprintf(stderr, "Error: an error occurred while reading the PNG file %s\n", argv[1]);
        exit(1);
    }

    png_init_io(png_ptr, fp);
    png_read_info(png_ptr, info_ptr);

    if (png_get_color_type(png_ptr, info_ptr) != PNG_COLOR_TYPE_RGB) {
        fprintf(stderr, "Error: input file %s is not an RGB PNG image\n", argv[1]);
        exit(1);
    }

    FILE *out_fp = fopen(argv[2], "wb");
    if (!out_fp) {
        fprintf(stderr, "Error: could not open output file %s\n", argv[2]);
        exit(1);
    }

    png_structp out_png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (!out_png_ptr) {
        fprintf(stderr, "Error: could not create png write struct\n");
        exit(1);
    }

    png_infop out_info_ptr = png_create_info_struct(out_png_ptr);
    if (!out_info_ptr) {
        fprintf(stderr, "Error: could not create png info struct\n");
        exit(1);
    }

    if (setjmp(png_jmpbuf(out_png_ptr))) {
        fprintf(stderr, "Error: an error occurred while writing the PNG file %s\n", argv[2]);
        exit(1);
    }

    png_init_io(out_png_ptr, out_fp);
    png_set_IHDR(out_png_ptr, out_info_ptr, png_get_image_width(png_ptr, info_ptr),
                 png_get_image_height(png_ptr, info_ptr), 8, PNG_COLOR_TYPE_RGB,
                 PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
    png_write_info(out_png_ptr, out_info_ptr);

    // 处理图片
    process_file(png_ptr, info_ptr);

    png_write_end(out_png_ptr, NULL);
    fclose(out_fp);
    png_destroy_write_struct(&out_png_ptr, &out_info_ptr);
    png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
    fclose(fp);
    return 0;
}

使用方法：`./mosaic input.png output.png`，其中`input.png`是原始图片，`output.png`是转换后的马赛克图片。`BLOCK_SIZE`宏定义可以控制每个小块的大小，越大则马赛克效果越明显。