New subject: [Multimedia] Hashing Wikimedia Commons

5 Sep 2014

Thanks to everyone who took time to contribute here!

Let me try to sum up, from my understanding. For metadata information
about an image, using the imageinfo/extmetadata API is sensible for
the moment. We're aware and followed the talks on the structured data
project during Wikimania, and we're quite keen to see the results of
that when and if it starts being useful.

For thumbnails, there's no way to know if a thumbnail size has already
been rendered or not, but given that the MediaViewer has a default
list of widths that correspond to popular screen size resolutions[1],
it's a fair bet that for instance 640x and 800x would work, except for
situations when the image file is smaller than the requested thumbnail
size.

It's possible to use Special:Redirect or thumb.php to get the
thumbnail/URL, but both are actually PHP scripts that need running. So
while perhaps not ideal, it seems to make the most sense here to
generate the thumbnail URLs ourselves and hit the web server directly.

Sincerely,
Jonas

[1]
https://git.wikimedia.org/blob/mediawiki%2Fextensions%2FMultimediaViewer/e7…

On 4 September 2014 21:47, Derk-Jan Hartman &lt;hartman.wiki(a)gmail.com&gt; wrote:
...
  Correct, better not rely on thumb.php, the servers
will just generate
 the thumb if it is not yet present on the canonical address yet, that
 Special:Redirect can point you at.

 Also, almost all this info can be retrieved in one go from the api.php
 of course:

http://commons.wikimedia.org/w/api.php?action=query&titles=File:30C3_Co…

 Lists almost all the info of the latest revision of the file.

 DJ

 On Thu, Sep 4, 2014 at 3:04 PM, Daniel Schwen &lt;daniel(a)schwen.de&gt; wrote:
  I was told thumb.php is evil (for lack of
caching).
 I'm using special:redirect with the width=640 parameter.
 Daniel

 On Sep 4, 2014 5:49 AM, "Jean-Frédéric" &lt;jeanfrederic.wiki(a)gmail.com&gt;
wrote:

 > > The first three we can get from pretty
much either API, or extract
> > directly from
> > a dump file. The latter is eluding us though, for two reasons. One is
> > that a
> > file, like 30C3_Commons_Machinery_2.jpg, is actually in the /b/ba/
> > directory -
> > but where this /b/ba/ comes from (a hash?) is unclear to us now, and
> > it's not
> > something we find in the dumps - though we can get it from one of the
> > APIs.

 Yes, /b/ba ist based on the first two digits of the MD5 hash of the
 title:

 md5( "30C3_Commons_Machinery_2.jpg" ) -> ba253c78d894a80788940a3ca765debb

 But this is "arcane knowledge" which nobody should really rely on. The
 canonical
 way would be to use

 https://commons.wikimedia.org/wiki/Special:Redirect/file/30C3_Commons_Machi…

 Which generates a redirect to

 https://upload.wikimedia.org/wikipedia/commons/b/ba/30C3_Commons_Machinery_…

 To get a thumbnail, you can directly manipulate that URL, by inserting
 "thumb/"
 and the desired size in the correct location (maybe Special:Redirect can
 do that
 for you, but I do not know how):

https://upload.wikimedia.org/wikipedia/commons/thumb/b/ba/30C3_Commons_Mach…

 If I am not mistaken you can use thumb.php to get the needed thumb?
 <https://commons.wikimedia.org/w/thumb.php?f=Example.jpg&width=100>

 (That’s what I used in my CommonsDownloader [1])

 [1]

<https://github.com/Commonists/CommonsDownloader/blob/master/commonsdownloader/thumbnaildownload.py>

 Hope that helps,
 --
 Jean-Frédéric

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Re: [Commons-l] [Multimedia] Hashing Wikimedia Commons