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From "Kirk, Kenneth" <Kk...@ILSOS.NET>
Subject RE: Rendering PDImageXObject
Date Tue, 11 Aug 2015 15:19:53 GMT

How would I know what DPI the image was drawn with?  Some of the PDF pages come from source
outside of my control but I have to extract them just the same.

-----Original Message-----
From: John Hewson [mailto:john@jahewson.com] 
Sent: Monday, August 10, 2015 1:38 PM
To: users@pdfbox.apache.org
Subject: Re: Rendering PDImageXObject

> On 10 Aug 2015, at 05:58, Kirk, Kenneth <Kkirk@ILSOS.NET> wrote:
> I have a situation that maybe someone has already solved in a more efficient manner.
 When converting a tiff image to PDF I use the drawImage method of the PDPageContentStream.
 The tiff image has a resolution of 200 DPI which is 1700x2200.  When PDFRenderer renders
this image from the resulting PDF page  it does so at the PDF default of 72 DPI which logically
translates to page 23 inches by 30 inches when applied to the original iamge size of 1700x2200.
 Since I don't know after the fact what DPI a image object on PDF page was drawn at I came
up with down scaling the image at PDF creation time to 72 DPI.  I'm sure there must a better
way one of you computer science PHDs have come up with.

You can draw the image with a scale of 72 / 200, in other words:

double dpi = 200; // you’ll want to fetch this from the tiff content.drawImage(image, x,
y, image.getWidth() * 72 / dpi, image.getHeight() * 72 / dpi;

— John
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