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phpgdthumbnailsmime-typesexif

Is there any way to determine an image's type from its GD handle?

I am writing a thumbnailing script, and from what I've seen thumbnails tend to look best in the same format as their source. However, the script may be fetching images from the web, so I can't access the file twice. So is there any way to get the file type other than exif_imagetype and other functions that have to re-open the image? I don't want to rely on the extension as that can obviously be wrong.

I'm doing the thumbnail processing with GD, so something that uses the handle would be perfect, but I could also use the file's contents. And yes, I'm aware that GD handles reference uncompressed data, but I'm not sure that they don't remember what they decompressed from.

Solution 
  • function getImageExt($bytes)
{
    $hex_bytes = '';
    for ($i = 0; $i < strlen($bytes); $i++)
    {
        $hex_bytes .=  dechex(ord($bytes[$i]));
    }
    if (strncasecmp($hex_bytes,'FFD8',4) === 0) return 'jpg';
    if (strncasecmp($hex_bytes,'474946',6) === 0) return 'gif';
    if (strncasecmp($hex_bytes,'89504e47',8) === 0) return 'png';
    if (strncasecmp($hex_bytes,'424d',4) === 0) return 'bmp';
    return false;
}