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

以下是使用C语言生成三层影像金字塔的简单示例代码：

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

#define STB_IMAGE_IMPLEMENTATION
#define STB_IMAGE_WRITE_IMPLEMENTATION
#include "stb_image.h"
#include "stb_image_write.h"

int main(int argc, char *argv[])
{
    if (argc != 2)
    {
        printf("Usage: %s <input_image>\n", argv[0]);
        return 1;
    }

    int width, height, channels;
    unsigned char *image_data = stbi_load(argv[1], &width, &height, &channels, 0);
    if (!image_data)
    {
        printf("Failed to load image %s\n", argv[1]);
        return 1;
    }

    // Allocate memory for pyramid levels
    unsigned char *level1_data = malloc(width / 2 * height / 2 * channels);
    unsigned char *level2_data = malloc(width / 4 * height / 4 * channels);

    // Downsample first level
    int level1_width = width / 2;
    int level1_height = height / 2;
    for (int y = 0; y < level1_height; y++)
    {
        for (int x = 0; x < level1_width; x++)
        {
            for (int c = 0; c < channels; c++)
            {
                int index = (y * 2 * width + x * 2) * channels + c;
                int sum = image_data[index] + image_data[index + 1] + image_data[index + width * 2] + image_data[index + width * 2 + 1];
                level1_data[(y * level1_width + x) * channels + c] = sum / 4;
            }
        }
    }

    // Downsample second level
    int level2_width = width / 4;
    int level2_height = height / 4;
    for (int y = 0; y < level2_height; y++)
    {
        for (int x = 0; x < level2_width; x++)
        {
            for (int c = 0; c < channels; c++)
            {
                int index = (y * 2 * level1_width + x * 2) * channels + c;
                int sum = level1_data[index] + level1_data[index + 1] + level1_data[index + level1_width * 2] + level1_data[index + level1_width * 2 + 1];
                level2_data[(y * level2_width + x) * channels + c] = sum / 4;
            }
        }
    }

    // Save pyramid levels to files
    char *filename = malloc(strlen(argv[1]) + 10);
    strcpy(filename, argv[1]);
    char *dot = strrchr(filename, '.');
    if (dot)
    {
        *dot = '\0';
    }
    stbi_write_png(strcat(filename, "_level0.png"), width, height, channels, image_data, width * channels);
    stbi_write_png(strcat(filename, "_level1.png"), level1_width, level1_height, channels, level1_data, level1_width * channels);
    stbi_write_png(strcat(filename, "_level2.png"), level2_width, level2_height, channels, level2_data, level2_width * channels);

    // Free memory
    stbi_image_free(image_data);
    free(level1_data);
    free(level2_data);
    free(filename);

    return 0;
}

这个示例代码使用了STB库来加载和保存PNG图像。要使用这个库，只需要在代码中包含 `"stb_image.h"` 和 `"stb_image_write.h"` 文件，并定义 `STB_IMAGE_IMPLEMENTATION` 和 `STB_IMAGE_WRITE_IMPLEMENTATION` 宏。这些宏告诉编译器在编译时包含库的实现代码。

请注意，这个示例代码中的金字塔级别是硬编码的。如果您想生成不同数量或不同大小的级别，请相应地修改代码。