使用libpng将图片转换为RGB数组的代码

下面是使用libpng将一张PNG图片转换为RGB数组的代码示例：

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

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

    const char *filename = argv[1];
    FILE *fp = fopen(filename, "rb");
    if (!fp) {
        fprintf(stderr, "Failed to open file: %s\n", filename);
        return 1;
    }

    png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (!png_ptr) {
        fprintf(stderr, "Failed to create PNG read structure\n");
        fclose(fp);
        return 1;
    }

    png_infop info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr) {
        fprintf(stderr, "Failed to create PNG info structure\n");
        png_destroy_read_struct(&png_ptr, NULL, NULL);
        fclose(fp);
        return 1;
    }

    if (setjmp(png_jmpbuf(png_ptr))) {
        fprintf(stderr, "Failed to set PNG error handling\n");
        png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
        fclose(fp);
        return 1;
    }

    png_init_io(png_ptr, fp);
    png_read_info(png_ptr, info_ptr);
    png_uint_32 width = png_get_image_width(png_ptr, info_ptr);
    png_uint_32 height = png_get_image_height(png_ptr, info_ptr);
    png_byte color_type = png_get_color_type(png_ptr, info_ptr);
    png_byte bit_depth = png_get_bit_depth(png_ptr, info_ptr);

    if (color_type != PNG_COLOR_TYPE_RGB_ALPHA) {
        fprintf(stderr, "Only RGB with alpha channel PNG images are supported\n");
        png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
        fclose(fp);
        return 1;
    }

    if (bit_depth != 8) {
        fprintf(stderr, "Only 8-bit per channel PNG images are supported\n");
        png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
        fclose(fp);
        return 1;
    }

    png_bytepp rows = png_malloc(png_ptr, height * sizeof(png_bytep));
    for (png_uint_32 y = 0; y < height; y++) {
        rows[y] = png_malloc(png_ptr, png_get_rowbytes(png_ptr, info_ptr));
    }
    png_read_image(png_ptr, rows);

    png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
    fclose(fp);

    // Convert the image to an RGBA array
    size_t num_pixels = width * height;
    unsigned char *rgba_data = malloc(num_pixels * 4);
    for (size_t i = 0; i < num_pixels; i++) {
        rgba_data[i * 4 + 0] = rows[i / width][i % width * 4 + 0];
        rgba_data[i * 4 + 1] = rows[i / width][i % width * 4 + 1];
        rgba_data[i * 4 + 2] = rows[i / width][i % width * 4 + 2];
        rgba_data[i * 4 + 3] = rows[i / width][i % width * 4 + 3];
    }

    // Convert the RGBA array to an RGB array
    unsigned char *rgb_data = malloc(num_pixels * 3);
    for (size_t i = 0; i < num_pixels; i++) {
        rgb_data[i * 3 + 0] = rgba_data[i * 4 + 0];
        rgb_data[i * 3 + 1] = rgba_data[i * 4 + 1];
        rgb_data[i * 3 + 2] = rgba_data[i * 4 + 2];
    }

    // Free memory
    for (png_uint_32 y = 0; y < height; y++) {
        png_free(png_ptr, rows[y]);
    }
    png_free(png_ptr, rows);
    free(rgba_data);

    // Do something with the RGB data here...

    free(rgb_data);
    return 0;
}

注意，这个示例只支持RGB格式的PNG图片，并且要求每个通道都是8位精度。如果你需要处理其他格式的图片，需要修改相应的代码。