为什么 libjpeg 不正确地存储我的图像数组？答案

【问题标题】：Why does libjpeg store my image array incorrectly?为什么 libjpeg 不正确地存储我的图像数组？
【发布时间】：2020-07-30 01:45:26
【问题描述】：

我使用libjpg 将图像保存到磁盘。我有一个像素数组，但生成的图像看起来不像我想的那样。

数组是 8x8 像素，每个像素有 3 个分量。谁能解释我可能做错了什么？

uint32 data[] = {255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0,
    255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0,
    255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0,
    255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0,
    255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0,
    255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0,
    255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0,
    255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0, 255, 0, 0,
};
write_JPEG_file("foo.jpg", 100, width, height, (JSAMPROW)data);

这是原始输出：

放大到 128x128：

我使用示例中的default write function：

int write_JPEG_file (const char * filename, int quality, int width, int height, JSAMPROW raw_image)
{
    struct jpeg_compress_struct cinfo;
    struct jpeg_error_mgr jerr;
    
    JSAMPROW row_pointer[1];
    FILE *outfile = fopen( filename, "wb" );
    
    if ( !outfile )
    {
        printf("Error opening output jpeg file %s\n!", filename );
        return -1;
    }
    cinfo.err = jpeg_std_error( &jerr );
    jpeg_create_compress(&cinfo);
    jpeg_stdio_dest(&cinfo, outfile);


    cinfo.image_width = width;
    cinfo.image_height = height;
    cinfo.input_components = 3;
    cinfo.in_color_space = JCS_RGB;

    jpeg_set_defaults( &cinfo );

    jpeg_start_compress( &cinfo, TRUE );

    while( cinfo.next_scanline < cinfo.image_height )
    {
        row_pointer[0] = &raw_image[ cinfo.next_scanline * cinfo.image_width *  cinfo.input_components];
        jpeg_write_scanlines( &cinfo, row_pointer, 1 );
    }

    jpeg_finish_compress( &cinfo );
    jpeg_destroy_compress( &cinfo );
    fclose( outfile );

    return 1;
}

【问题讨论】：

标签： jpeg libjpeg

【解决方案1】：

我不小心在每个组件中使用了uint32，而不是unsigned char。

【讨论】：