When converting the first PDF page to an image using Ghostscript, I sometimes get "extra" space. What for?
I am creating a simple script that converts the first PDF page to an image using Ghostscript. Here is the command I'm using:
gs -q -o output.png -sDEVICE=pngalpha -dLastPage=1 input.pdf
This works great with some PDFs, for example. if I convert the first PDF page that looks like this:
I actually get this first page as an image and no problem.
But I noticed that with some first pages of other PDFs, like the following:
With the same command gs
after conversion, the .png image looks like this:
The problem is I am getting this extra free space on the left inside the image when I convert this page, why is GhostsScript doing this? Where does this extra white space come from?
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Chances are your PDFs don't use the same values for /MediaBox
and for /CropBox
. For more on these technical terms associated with the page, see this illustration from the German Wikipedia :
In other words: the values /CropBox
(if given) for the PDF page determine which (smaller) piece of general information about the page (which is inside /MediaBox
) the PDF viewer should be visible to the user (or to the printer).
Decision
To determine what the different values are for all pages in your book, run the following command:
pdfinfo -f 1 -l 1000 -box my.pdf
To see these values for the first page only, run
pdfinfo -l 1 -box my.pdf
To get Ghostscript to produce the results you want, add -dUseCropBox
to your command line:
gs -q -o output.png -sDEVICE=pngalpha -dLastPage=1 -dUseCropBox input.pdf
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