[Digikam-users] digikam and JPEG thumbs rendering : need JPEG files vertically oriented...

Gilles Caulier caulier.gilles at kdemail.net
Mon Mar 27 17:04:58 BST 2006

Hi all, 

I'm currently working to remove libKExif depency in digiKam core and use Exiv2 
library instead. libKExif is used to get JPEG image thumbnails and get or set 
thumbs orientation using Exif informations.

A digiKam part witch use libKExif is for example cameragui to render JPEG 
thumbnails. I have fixed this part using Exiv2 and during this task, i have 
found an indeep bug in libkexif (:=)))

Let's me explain how to work libKexif :

This library parse all raw Exif data to provides JPEG thumbs, using Qt 
internaly. All RAW Exif data are passed and decrypted by Qt. But during 
thumbnail extraction, QT change the thumb orientation. This change is wrong 
and do not respect the Exif orientation tag available with the RAW data. I 
don't know why and i suspect a bug in Qt.

After that, digiKam fix thumbs orientation in a second time using Exif 
orientation tag... and finally the JPEG thumb is completly dummy.

A solution about libkexif problem is to parse only thumb image data by Qt 
without others Exif informations... But this subject is out since digiKam 
will remove libKexif depency... (In others words, i have no more time to hack 

When i have ported cameragui code to Exiv2, i have used an Exiv2 method to get 
only the thumbs image data without any orientation correction. In this way i 
can fix orientation without problems into digikam.

To finalize my implementation i need to use some JPEG files comming from 
others camera (without any corrections please !). These images must be 
_VERTICALLY_ oriented with the camera turned to the _LEFT_, and to the 
_RIGHT_ (typically i need 2 images from one camera to complete my tests).

Some digikam users can take and send me some JPEG pictures like this ? Thanks 
in advance.

Gilles Caulier

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