Get DPI value of an image using PHP

February 19, 2008 | PHP

This is a simple function I wrote to get a DPI (dot per inch) value from an image using PHP only, without the need of ImageMagick nor GD library. The script was inspired from denisb post (the third post). At the forum, he described how to get the DPI value stored within the file.

< ?php
function get_dpi($filename){

    // open the file and read first 20 bytes.
    $a = fopen($filename,'r');
    $string = fread($a,20);
    fclose($a);

    // get the value of byte 14th up to 18th
    $data = bin2hex(substr($string,14,4));
    $x = substr($data,0,4);
    $y = substr($data,4,4);
    return array(hexdec($x),hexdec($y));

}

// output the result:
print_r(get_dpi2('filename.jpg'));
?>

I have tried this function to get DPI value of an image that I generated using Photoshop and worked as expected but failed to get DPI value from an image from any digital camera. It returned weird value instead.

Any idea why this function failed to retrieve DPI value from image that generated by digital camera? Please share your opinion.

13 comments

This post has 13 comments, wow!

  1. tom 08/04/2008 at 11:12

    hi,
    this is an excellent little script that i found from the forum you mention! for some reason though i am getting the values 100, 100 returned from both a 72dpi file and a 300 dpi file…?
    Would you know why this is at all? I have resized both images in photoshop and saved out at the DPI’s mentioned.

    Any help would be greatly appreciated!

    Thanks,

    Tom

  2. moe 10/04/2008 at 09:32

    hi,
    i know this is way offfff topic, but you think you know how to get a Snap shot of a website in different sizes? if so, could you post it on as a blog or maybe give some ideas and point us to few tutorials that maybe helpful?

    thanks a bunch!

  3. PHP ile resim dosyas?n?n DPI bilgisini alal?m – Günlük Haftal?k Ayl?k 15/05/2008 at 20:34

    [...] Kaynak: Get DPI value of an image using PHP [...]

  4. john 23/07/2008 at 08:40

    Man, this is a great function that works really well. However, it seems it can’t read DPI information of a JPEG created on a MAC. I guess encoding methods differ. Do you know where the DPI information is located on a MAC-created JPEG?

  5. MS 19/10/2009 at 21:21

    This doesn’t work at all, and I like the author writing:
    print_r(get_dpi2(‘filename.jpg’));

    when he calls the function “get_dpi” and then call “get_dpi2″ for some reason that I can’t seem to understand.

    Lovely function, beside the non-working part.

  6. Sindre 30/10/2009 at 05:56

    For some reason i get a DPI value: 17490
    Isnt this to high? Its just a png-logo..

  7. Rosario Rojas 27/11/2009 at 15:22

    This is a very good code. Saved me a lot of work to modify more than 1,000 JPG images.

    Thank you very much!!!.

  8. Mohammad 04/03/2010 at 23:31

    Nice work!
    This works well with JPEG images but not for PNG images.

  9. Sebastian 01/06/2011 at 22:43

    Sure this would be much easier to do using the imageMagick library. Imagemagick::getImageResolution

    That should save a lot of hacking.

  10. Sartaj 19/07/2011 at 13:55

    The above code is not working for uploaded image please tell me how to get DPI of uploaded image using php.

  11. Damy 18/10/2011 at 17:47

    I was strugeling with this, and since I found it, her you go.

    function get_dpi($filename){
    $a = fopen($filename,’r');
    $string = fread($a,20);
    fclose($a);

    $data = bin2hex(substr($string,14,4));
    $x = substr($data,0,4);
    $y = substr($data,0,4);
    return array(hexdec($x),hexdec($y));
    }

    and then print the array or do with it what you want.

    Cheers

  12. asd 23/02/2014 at 07:47

    hahahaha

  13. asd 23/02/2014 at 07:49

    testing

 

Leave a comment

Allowed tags are: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>