Re: downsampling images

Path	csiph.com!usenet.pasdenom.info!weretis.net!feeder4.news.weretis.net!storethat.news.telefonica.de!telefonica.de!news-1.dfn.de!news.dfn.de!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From	Helge Blischke <h.blischke@acm.org>
Newsgroups	comp.lang.postscript
Subject	Re: downsampling images
Followup-To	comp.lang.postscript
Date	Tue, 04 Dec 2012 22:32:39 +0100
Lines	51
Message-ID	<ai78foFrmihU1@mid.individual.net> (permalink)
References	<ai6v4lFolknU1@mid.individual.net>
Mime-Version	1.0
Content-Type	text/plain; charset="us-ascii"
Content-Transfer-Encoding	7Bit
X-Trace	individual.net OqCEJSI7hjr3OjI3OKm7IwKDK+HnmYMh/HQ+gwx4lfeTd+nrNm8AjXV4YnNAX9N/x2
Cancel-Lock	sha1:CDj0WTeODkivKuuk5RxkyD1uTKU=
User-Agent	KNode/0.99.01
Xref	csiph.com comp.lang.postscript:1146

Followups directed to: comp.lang.postscript

Show key headers only | View raw

Michael Unger wrote:

> I want to control the downsampling parameters of (JPEG) images from
> within each PostScript program individually instead of modifying the
> Distiller parameters ("joboptions" file) globally. The following lines
> from the "joboptions" file seem to be relevant here:
> 
> |  << /DownsampleColorImages true
> |     /ColorImageDownsampleType /Bicubic
> |     /ColorImageResolution 300
>                             ^^^ (1)
> |     /ColorImageDepth -1
> |     /ColorImageDownsampleThreshold 2.00000
>                                      ^^^^^^^ (2)
> |     /EncodeColorImages true
> |     /ColorImageFilter /DCTEncode
> |     /AutoFilterColorImages true
> |     /ColorImageAutoFilterStrategy /JPEG
> |  >> setdistillerparams
> 
> Am I correct assuming the "Resolution" (1) is the desired final image
> resolution (dpi) to be embedded into the final PDF document and
> "Threshold" (2) is a multiplier indicationg a resolution ratio above
> which the downsampling will take place? (The JPEG iamges are converted
> to EPS using the freeware utility "jpeg2ps" [1] and included via the
> "run" command into the PostScript program.)
> 
> Michael
> 
> 
> [1] <http://www.pdflib.com/download/free-software/jpeg2ps/>
> 


Ad (1):
---------
The resolution is the lower bound for the downsampling procedure; the actual 
resolution achieved is dependent on the downsampling algorithm (subsampling, 
average downsampling, or bicubid downsampling).

Ad (2):
---------
If the original image resolution is already below the "destination" 
resolution times this factor, no downsampling/subsampling takes place

For details see the documents on distiller parameters (or the "Adobe PDF 
Creation Settings).

Helge

Back to comp.lang.postscript | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

downsampling images Michael Unger <spam.to.unger@spamgourmet.com> - 2012-12-04 19:48 +0100
  Re: downsampling images Helge Blischke <h.blischke@acm.org> - 2012-12-04 22:32 +0100

csiph-web