Image compression/resizing in PDFs

Image compression/resizing in PDFs

[John Devereux]

Hi all,

Is there a way to have context automatically compress or resample
included images to a given output resolution? I have not been following
recent developments...

I can obviously "pre-reduce" all images to the desired dpi. But:

1) This is a bit of work (and hard to get non-technical people to do)

2) In 5 years time we might want the images to be higher resolution and
not be as concerned about PDF size. But the information will be lost (or
be elsewhere).

So a command line or document setting would be ideal, is there such a
thing? \setpdfimageresolution[300dpi].

Thanks,

-- 

John Devereux
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Re: Image compression/resizing in PDFs

[Peter Münster]

On Fri, Oct 21 2011, John Devereux wrote:

> Is there a way to have context automatically compress or resample
> included images to a given output resolution?

Hello,

See also
http://archive.contextgarden.net/thread/20110629.173015.6dcd7b3e.en.html

t-degrade.tex is broken with latest context. If you fix it (should be
easy), please send me the patch! :-)
(Sorry, too busy now for fixing it myself...)

-- 
           Peter
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Re: Image compression/resizing in PDFs

[Hans Hagen]

On 21-10-2011 11:54, John Devereux wrote:
>
> Hi all,
>
> Is there a way to have context automatically compress or resample
> included images to a given output resolution? I have not been following
> recent developments...
>
> I can obviously "pre-reduce" all images to the desired dpi. But:
>
> 1) This is a bit of work (and hard to get non-technical people to do)
>
> 2) In 5 years time we might want the images to be higher resolution and
> not be as concerned about PDF size. But the information will be lost (or
> be elsewhere).
>
> So a command line or document setting would be ideal, is there such a
> thing? \setpdfimageresolution[300dpi].

You can plug in a converter:

\startluacode

figures.converters["png"] = {
     ["lowres.png"] = function(oldname,newname,resolution)
         os.execute(string.format('gm convert -depth 1 "%s" 
"%s"',oldname,newname))
     end,
}

-- the following is automatic in next beta

figures.suffixes["lowres.png"] = figures.suffixes.png

\stopluacode

And then use:

\starttext
     \externalfigure[mill.png][conversion=lowres.png]
\stoptext

downsamples images are cached so the overhead is minimal

Hans



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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
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                                              | www.pragma-pod.nl
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Re: Image compression/resizing in PDFs

[Aditya Mahajan]

> downsamples images are cached so the overhead is minimal

Is caching based only on the figure name? If I change the original figure, 
will the cached figure be updated?

Aditya
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Re: Image compression/resizing in PDFs

[Hans Hagen]

On 24-10-2011 16:29, Aditya Mahajan wrote:
>> downsamples images are cached so the overhead is minimal
>
> Is caching based only on the figure name? If I change the original
> figure, will the cached figure be updated?

Sure,

                     local oldtime = 
lfs.attributes(oldname,'modification') or 0
                     local newtime = 
lfs.attributes(newname,'modification') or 0
                     if newtime == 0 or oldtime > newtime then

In fact it's just integration of old resource library code (ruby stuff 
that happened between runs).

Hans

-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
     tel: 038 477 53 69 | voip: 087 875 68 74 | www.pragma-ade.com
                                              | www.pragma-pod.nl
-----------------------------------------------------------------
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