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List:       kde-devel
Subject:    Re: [Bug 154698] Won't open some TIFF files
From:       Thiago Macieira <thiago () kde ! org>
Date:       2007-12-28 23:10:52
Message-ID: 200712282110.52695.thiago () kde ! org
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James Richard Tyrer wrote:
>> According to that spec
>> (http://standards.freedesktop.org/shared-mime-info-spec/shared-mime-in
>>fo-spec-latest.html#id2447161) the globbing should be preferred for
>> magics with priority below 80. Both image/jpeg and image/tiff are at
>> level 50 in the latest database I have.
>
>IIUC, an image file contains a "magic number".  This would seem to
>indicate that there would be very little chance for a misidentification
>from using magic.  So, I wonder why image/jpeg and image/tiff are at
>level 50.

Because your assumption is wrong.

You said there would be very little chance for misidentification. That's 
not true. The database says that those entries whose priority is over 80 
are those for which the false positives are very few. Which means those 
for which the priority is less are actually creating false positives.

Maybe it's not misidentifying JPEG as something else, but making something 
else be identified mistakenly as JPEG.

In any case, your beef is with the MIME Spec and with the database. Please 
take the discussion to the appropriate mailing lists.

> IAC, in KDE3, a JPEG file called *.tif is correctly identified as JPEG 
> and in KDE4 it is incorrectly identified as image/tiff.  Should we 
> consider this to be a regression?

Only if that was and is the intended behaviour. Given the MIME DB right 
now, it looks like it isn't. I can be wrong, though.

> And as I said, GwenView has no problem determining the correct image
> type. 

And as you've been told over and over again, GwenView is not using the 
MIME-Type detection mechanism.

Now try this use-case, please. It's using the same architectural 
components as the Okular case and uses GwenView:

rename your JPEG file to *.txt and click on it on Dolphin/Konqueror. Does 
GwenView correctly detect the file type? No! GwenView won't even be 
loaded!

This is the situation we're talking about in Okular. It has to decide 
which backend to load given the MIME type. If the file has been 
misidentified, it can only be shown if, by chance, the backend that was 
loaded can also understand that file format.

GwenView, on the other hand, does not have to decide which backend to 
load. It has no backends -- or, should we say, it has only one backend. 
And that backend *does* support both formats.

-- 
  Thiago Macieira  -  thiago (AT) macieira.info - thiago (AT) kde.org
    PGP/GPG: 0x6EF45358; fingerprint:
    E067 918B B660 DBD1 105C  966C 33F5 F005 6EF4 5358

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