[Image-SIG] DPI

[Fredrik Lundh]

Resolution info is optional in JPEG files (it's a part of the JFIF
standard, not JPEG itself) and even if present, it may not be
expressed in dots per inch.  PIL only sets the "dpi" field if the
information is there, leaving it to your code to provide a suitable
default value (or behaviour) for your application.  You can do e.g.

    dpi = im.info.get("dpi", (72, 72))

If the JFIF header is present, but the resolution isn't specified as
DPI, you can check if the "jfif_unit" and "jfif_density" fields
contain information useful for your application; their contents are
described here:

http://en.wikipedia.org/wiki/JPEG_File_Interchange_Format#JFIF_segment_format

</F>

On Fri, Apr 16, 2010 at 2:48 PM, Samuel Moore <blindlemonsam at gmail.com> wrote:
> I am trying to determine DPI from images. Can anyone help?
>
> I tried:
>
>
>
> img = Image.open(“Hamerkop.jpg”)
>
> img.info[“dpi”]
>
>
>
> but it doesn’t work for all jpegs.
>
>
>
> Python 2.5.1
>
> PIL 1.1.7
>
>
>
> Regards,
>
> Sam
>
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