[sane-devel] Re: XSane's PDF output disliked by macosx's Preview

[Oliver Rauch]

On Monday 19 March 2007 17:20, Stefan Monnier wrote:
> > What xsane version did you use?
>
> It was 0.991.
>
> > Please test xsane-0.994 and please test with and without zlib compression
> > for   PDF (Preferences/setup/filetype)
>
> I've just tried it with zlib compressed (I always use this option) and the
> problem is indeed fixed, so the PDF generated is now viewable with
> macosx's preview.
>
> While testing it I noticed that for the picture I tried (a scan of
> a mostly blank letter-size yellow sheet in 150dpi and greyscale) I get the
> following file sizes in bytes:
>
> 0.991: 1551241
> 0.994: 1211006
> 0.991 through pdf2ps|ps2pdf: 127159
> 0.994 through pdf2ps|ps2pdf: 127163
>
> So the 0.994 version also generates smaller files (at least for this one
> test).  Oddly enough pdf2ps|ps2pdf generates much smaller files still (my
> experience has indeed been that it generates smaller files, but usually
> just by maybe 10-20%, kind of like what we see between the 0.991 and 0.994
> files, so it seems this here test is not representative of my more usual
> scans ;-)

xsane-0.994 uses 8 bit encoding while older versions used a special 7 bit 
encoding that has to be used for several posctscript printers.
This is the reason why xsane-0.994 produces smaller pdf files.

when you do pdf2ps | ps2pdf then there is possibly a resampling of the image 
data so that you get a lower resolution than you used while scanning the 
image. It also is possible that you get jpeg coded images this way, xsane 
stores the images in a lossless way.

Best regards
Oliver