[gs-devel] Default resolution not properly calculated for raster pdf files

[Ralph Giles]

On Fri, Oct 19, 2007 at 02:14:48PM -0400, Barry wrote:

> gswin32c -sOutputFile=PCIE-Report-%03d.tif -r150 -sDEVICE=tiff32nc -dBATCH
> -dNOPAUSE "document.pdf"
> 
> But the 150 resolution that's specified in the command is arbitrary. I
> don't know if it's lower or higher than necessary for the best quality
> conversion.

Ghostscript is rasterizing the document, as if you were going to print
it, which isn't really "conversion" in the sense you mean it. It's a
nice idea, but how should it behave if the document has embedded images
with different resolutions? What if there's a low-resolution scan
annotated with vector graphics that are illegible at that resolution?

I'm not trying to be unhelpful, just explaining why it doesn't work
that way. Usually people pick some resolution they'll eventually
target and leave it at that. 72 or 100 dpi for screen display, 
300 or 600 dpi for print. I'd use 300 dpi for OCR input unless 
there's fine print and live with the overhead if there's stuff
at fax resolution.

There are image extraction tools which can pull the scanner images
out of the original PDF, doing a lossless transcode to a standard
format if necessary. That's a more efficient approach for scanned
documents, but not something Ghostscript does.

Hope that helps,
 -r