[NTG-context] shrink JPGs to some resolution (dpi) ?

Alan BRASLAU alan.braslau at cea.fr
Mon Mar 9 22:50:29 CET 2015


I use ImageMagick/GraphicsMagick to resample HUGE high resolution tiff
images to something more manageable to work with. Using a script, I
converted hundreds of images to lower resolution copies. Then it was
simply a question of pointing ConTeXt to use the appropriate directory
to find the right figures.

The basic comand is

convert -resample 300x300

(or 100x100) and you can play with "-quality 75%"

This can be done once and is much better than getting ConTeXt to
convert every time on the fly.


On Mon, 9 Mar 2015 22:12:24 +0100
Harald Koenig <koenig at tat.physik.uni-tuebingen.de> wrote:

> Hi,
> so here's my very generic question #1 for my India book:
> is it possible that context (lua?) will "shrink" all \externalfigure
> jpegs automatically to some specified dpi resolution and quality
> (e.g. 300 dpi with 95% jpeg 'quality' for print and
> 100 dpi and 75% for screen quality) ?
> since I'm only using Linux, using Acrobat unfortueately is not an
> option (thanks, Adobe:-(
> that book will be ~100 A4 pages with ~50% and 50% pictures, 
> trying to have 2 pictures per page with text flowing around.
> the pictures are JPG photos with quite high resolution, upto 24
> Mpixel. so those picutres are HUGE and horrible overkill for a final
> print on A4 with typical images withs around 0.5\textwith.
> I know about ghostscript being able to convert/shrink PDFs,
> but first the "original" PDF with full size JPGs with be really huge,
> and ghostscript takes ages to shrink them.  so that's not real fun 
> doing this too often...
> right now I write the real typeset size of all images to the log file
> and use some external script to calculate the current resolution
> and then create a new set of images which e.g. 300 dpi.
> but that's still an ugly hack still has some issues with EXIF data,
> rotation, clipping, ... and right now leads to strage problems (see
> mext mail;)
> any hints to read the original large JPGs, but only write "print
> quality" 300dpi images, or low quaity 75dpi images for speed (and
> saving net bandwidth when mailing PDFs to co-workers of the group)?
> thanks,
> Harald

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