使用vs2019，不引用库函数生成三层影像金字塔且可以输出图片的c语言代码

以下是一个简单的三层影像金字塔生成代码，使用C语言编写，不需要引用任何库函数。在Windows下使用VS2019进行编译运行。

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

#define WIDTH 256
#define HEIGHT 256

void generate_pyramid(unsigned char* image, unsigned char* pyramid)
{
    int i, j, k;
    int width = WIDTH, height = HEIGHT;

    // 第一层
    for (i = 0; i < height; i += 2)
    {
        for (j = 0; j < width; j += 2)
        {
            int idx = i * width + j;
            pyramid[idx / 4] = image[idx];
        }
    }

    // 第二层
    width /= 2;
    height /= 2;
    for (k = 1; k < 3; k++)
    {
        for (i = 0; i < height; i++)
        {
            for (j = 0; j < width; j++)
            {
                int idx = i * width * 2 + j * 2;
                int idx1 = i * width + j;
                int idx2 = (i + height) * width + j;
                int idx3 = i * width + j + width;
                int idx4 = (i + height) * width + j + width;

                int sum = image[idx] + image[idx1] + image[idx2] + image[idx3] + image[idx4];
                pyramid[(k * height * width + idx1) / 4] = sum / 5;
            }
        }

        width /= 2;
        height /= 2;
    }
}

void write_image(const char* filename, unsigned char* image, int width, int height)
{
    FILE* fp;
    int i, j;

    fp = fopen(filename, "wb");
    if (!fp)
    {
        printf("Error: Couldn't open %s for writing!\n", filename);
        return;
    }

    fprintf(fp, "P5\n%d %d\n255\n", width, height);

    for (i = 0; i < height; i++)
    {
        for (j = 0; j < width; j++)
        {
            fputc(image[i * width + j], fp);
        }
    }

    fclose(fp);
}

int main()
{
    unsigned char* image = (unsigned char*)malloc(WIDTH * HEIGHT * sizeof(unsigned char));
    unsigned char* pyramid = (unsigned char*)malloc(WIDTH * HEIGHT / 4 * sizeof(unsigned char));
    int i, j;

    // 生成一张随机的灰度图像
    for (i = 0; i < HEIGHT; i++)
    {
        for (j = 0; j < WIDTH; j++)
        {
            image[i * WIDTH + j] = rand() % 256;
        }
    }

    // 生成三层影像金字塔
    generate_pyramid(image, pyramid);

    // 输出三层影像金字塔
    write_image("pyramid0.pgm", image, WIDTH, HEIGHT);
    write_image("pyramid1.pgm", pyramid + WIDTH * HEIGHT / 16, WIDTH / 2, HEIGHT / 2);
    write_image("pyramid2.pgm", pyramid + WIDTH * HEIGHT / 16 + WIDTH * HEIGHT / 64, WIDTH / 4, HEIGHT / 4);

    free(image);
    free(pyramid);

    return 0;
}

这个代码生成一张随机的灰度图像，然后生成三层影像金字塔，并输出三层金字塔的图片。可以通过修改WIDTH和HEIGHT来调整图像的大小，也可以通过修改generate_pyramid函数来生成不同层数的金字塔。