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From John Hewson <j...@jahewson.com>
Subject Re: image Resolution
Date Mon, 29 Jun 2015 16:12:27 GMT

> On 29 Jun 2015, at 07:00, Kirk, Kenneth <Kkirk@ILSOS.NET> wrote:
> 
> Well after checking further I found that the problem was in the scaling after the image
was created.  I wanting to scale it to 200 dpi using ImageIO and that is where the size discrepancy
came about.  If I leave it at 72 dpi it's okay.  One other problem I having is generating
a image from a PDF page with lines that are light gray.  When rendering the page as ImageType.BINARY
the lines drops them out completely when the image rendered.  I have to render it as RBG first
and make an extra call to convert to black and white which slow the process way down.  It
seems the threshold value need to be manipulated but I'm not sure where one changes that at.

If grayscale would do, then use that instead. If you really do need a binary image then you'll
get a better result by rendering in color or grayscale and then thresholding the image yourself.


You'll also get better results if you render at a higher DPI (4x, 8x, 16x) and scale down
the image with a high-quality algorithm such as Lanczos.

-- John

> -----Original Message-----
> From: Tilman Hausherr [mailto:THausherr@t-online.de] 
> Sent: Friday, June 26, 2015 3:51 PM
> To: users@pdfbox.apache.org
> Subject: Re: image Resolution
> 
> Why not just use the dpi parameter when rendering?
> 
> Tilman
> 
>> Am 26.06.2015 um 21:43 schrieb Kirk, Kenneth:
>> I'm sure this question has been asked before but I wasn't on the list when it was.
 I have PDFs that I need to convert to images.  Most are 8.5x11.  Some are 8.5 x 3.5.  My
problem is figuring out the resolution when I save them as 200dpi tiff images.  I made some
assumptions that held true until I encountered PDFs that deviated from the those assumptions.
 Although I can assume all PDFs are 8.5 inch wide and therefore I can deduce the resolution
based of the width of the actually page I don't want to assume anything but calculate the
resolution base on what I can get from the PDF structure itself.
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
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