How to find pixels per inch (PPI) using ImageMagick

Question

I can get PPI for a JPEG image using the following command:

$ identify -format \"%w x %h %x x %y\" mypic.jpg 
1600 x 1200 72 PixelsPerInch x 72 PixelsPerInch
         


        

Answer 1

You can use the fx operator and some smart formatting in the output of identify like this:

identify -format "%[fx:int(resolution.x*2.54)]" image.png
299

Of course, the true joy of this is that it is platform-independent, so you don't have to shell out to dc on OS X and Linux, or do whatever muppetry is required on Windows to do the maths.