Re: shrink JPGs to some resolution (dpi) ?

From: Hans Hagen <pragma@wxs.nl>
To: Harald Koenig <koenig@tat.physik.uni-tuebingen.de>
Cc: mailing list for ConTeXt users <ntg-context@ntg.nl>
Subject: Re: shrink JPGs to some resolution (dpi) ?
Date: Tue, 10 Mar 2015 12:12:21 +0100	[thread overview]
Message-ID: <54FED195.60005@wxs.nl> (raw)
In-Reply-To: <20150310013315.GA8706@hl.fritz.box>

On 3/10/2015 2:33 AM, Harald Koenig wrote:
> On Mar 10, Hans Hagen wrote:
>
>> anyway, i need to think a bit about it but we do have all the info
>> available, like
>>
>> - needed width/height
>> - original width/height
>>
>> and from that we can calculate some conversion parameters
>
> if you start thinking/working on this, some data from EXIF
> might be interesting and helpful too, esp. the "Orientation".
> using that data, automatic rotation to the "correct" orientation
> would be possible.
>
> maybe there are more interesting information in the exif data?!
> what about color space infos ?
> or time stamps or GPS data which might be used to be typeset...
>
>
>> if it would help you i can provide a tracker that will save info
>> like this (per image):
>
> that would be great as my current \message{} stuff is far from being perfect...

Luigi and I looked into the engine bit and decided that it makes no 
sense to intercept it there as it would mean obscuring possible errors.

But, I can intercept it in context so that is what happens now. You will 
get something:

LuaTeX warning: arithmetic: number too big
graphics        > inclusion > image './IMG_9712c1_bad.jpg' has bad 
dimensions (-32768pt,23849.10001pt), discarding

I also added a tracker:

\starttext

% \pdfimageresolution300

\enabletrackers[graphics.lognames,graphics.usage]

\externalfigure[IMG_9712c1_ok]

\externalfigure[IMG_9712c1_bad]

\stoptext

btw, you can simulate some of the issues with setting 
\pdfimageresolution to 1-10

The tracker makes a file <jobname>-figures-usage.lya that has two 
subtables, one with found images, and another with how they are used, 
including an error flag.

I'll upload a beta.

Now who will wikify this ...

Hans

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