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I'm writing a python script to get the dpi of a pdf page. To get the DPI of scanned PDF I am using pdfimages command.

$ pdfimages -list test.pdf
page   num  type   width height color comp bpc  enc interp  object ID x-ppi y-ppi size ratio
--------------------------------------------------------------------------------------------
1       0  image    1096  2074  gray    1   8  image  yes        9  0   500   500  536K  24%

and I get the DPI in x-ppi and y-ppi fields. I'm using the above command in the program with subprocess module But when I try this with a machine-generated PDF it gives me the below output.

page   num  type   width height color comp bpc  enc interp  object ID x-ppi y-ppi size ratio
--------------------------------------------------------------------------------------------

Can someone please help how can I get the DPI of a Machine-generated PDF from the ubuntu command line or python.

Anand Joshi
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  • could you clarify/modify your question to include what you mean by "fails" with "machine generated" PDFs. do you get empty fields, crazy answers, no output at all, something else? – Sam Mason Aug 21 '19 at 13:17

2 Answers2

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PDFs don't have a "DPI", they're mostly about encoding vector images which can be rasterized at arbitrary resolutions. the images you're extracting are also just arbitrary 2d arrays of pixels, what determines their "DPI" is are the PDF commands in the file that specify what size the image is going to be rendered into the page

an image stored in a PDF can be displayed multiple times at different sizes (though mostly it's just once) and hence the same image can appear multiple times in the output of -list, and the source code does seem to reference the transform matrix, so it's probably doing the right thing

the code also doesn't seem to have any way of not doing this, so I'm not sure what you mean by it failing with a "machine-generated PDF"

Sam Mason
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The machine generated PDF is probably a vector PDF whereas your scanned PDF is a raster PDF. DPI has no meaning in a vector PDF hence it does not report it.

noslenkwah
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