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I was recently reading a wikipedia article on what is the difference between the DPI (dots per inch) and PPI (pixels per inch). I've came up to the point that the DPI value is relevant for the printer and the PPI value is relevant for the monitor.

As I'm not even a hobbyist photographer, I wonder, if a single image can store both DPI and PPI in the image's metadata? (so i.e. the picture would have different physical dimensions (in inches) on a monitor and when printed). Is this a common practice with pictures?

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Metadata is arbitrary, and the exif data used for cameras seems to have fields for both resolution (in pixels) and resolution in dpi.

I'll use photome, which while old , shows a lot of useful data and the example photo provided with it to point out the exif fields.

enter image description here Image resolution in DPI

Camera resolution in PPI - under 'camera'

enter image description here

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thank you. This is actually interesting. Should I interpret your answer like this?: the picture's exif data contains two values: a DPI of the picture (how many inches should the picture be ~in length if printed) and a PPI of the CCD sensor inside the camera (how many points (pixels) the CCD sensor can catch on 1 inch of sensor's surface). Only the DPI value describes the picture, so a picture exif data cannot store both DPI and PPI values (or, rather, both DPI and PPI are always the same thing in the picture exif data context - the DPI of the picture) (~DPI == PPI). This makes sense ;) –  colemik Mar 18 '12 at 3:17
    
focal plane picture: personalpages.manchester.ac.uk/staff/p.dudek/projects/scamp/… –  colemik Mar 18 '12 at 3:27
    
yup - and in the context of PPI on displays its probably based on your resolution/size rather than the original photo –  Journeyman Geek Mar 18 '12 at 5:00

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