[Image-SIG] PIL - problem with crop()

Guy K. Kloss g.kloss at massey.ac.nz
Mon Apr 27 21:24:40 CEST 2009

On Mon, 27 Apr 2009 08:53:40 Eduardo Ismael wrote:
> Now, if I use the method above to convert to PDF, the PDF will open at
> 21,9% - the image got much bigger! - and if I zoom up to 100%, it gets
> awful. I understand PIl is not only cropping the image, but also affecting
> its quality.

As far as I'm assuming it is *not* tinkering with its quality. I'm assuming 
that it is changing the resolution (in dpi == dots per inch) inside the JPEG 
header. Adobe Acrobat is a programme that has its history in the graphic arts 
industry, and there resolution is *not* just X pixels by Y pixels, but also 
towards absolute sizes of the image in output. So setting the display to 100% 
will try to yield the image's representation in terms of absolute size on your 
screen together with the (estimated) screen resolution (again in dpi). So this 
did not change the physical number of pixels, but just the attached meta 
information of the resolution in the image's header.

Hope that helps to understand the effect,


Guy K. Kloss
Institute of Information and Mathematical Sciences
Te Kura Pūtaiao o Mōhiohio me Pāngarau
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Massey University, Auckland, Albany
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voice: +64 9 414-0800 ext. 9585   fax: +64 9 441-8181
eMail: G.Kloss at massey.ac.nz  http://iims.massey.ac.nz

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