[Digikam-devel] Experimental : image preview on main interface

Gilles Caulier caulier.gilles at kdemail.net
Fri Jun 16 06:56:30 BST 2006

On Thursday 15 June 2006 22:37, Mikolaj Machowski wrote:
> Dnia czwartek, 15 czerwca 2006 00:19, Caulier Gilles napisaƂ:
> > The patch is here :
> >
> > http://digikam3rdparty.free.fr/misc.tarballs/preview.patch
> Great!
> > - don't use the embedded preview from JPEG/TIFF/PNG files available in
> > Makernote metadata. Canon, Nikon, Minolta, etc, record a small preview
> > image in Camera Settings. This is must be used instead to load the whole
> > image. In fact, Exiv2 need to be improved for that. i'm currently
> > working with Andreas about this subject.
> Rather not. Preview for JPEG is very small image, useless for purpose of
> this functionality (cannot say about other formats).

No !!! Preview is not the embedded Exif thumb (160x120 pixels). It come from 
Makernote and it's not standardized. It used to render image to TV screen by 
camera. For example, Preview in Minolta makernote tag "PreviewImage" :


...is always a 640x480 pixels image, in Nikon and Canon makernotes :


...is an image size depending of camera model and camera settings (640x480, 
1024x768, etc.).

These tags are completly differents than standard Exif thumb tag...

There is also a preview image available into IPTC tag :


Look the tags named ObjectPreviewFileFormat and ObjectPreviewData. There just 
a lenght limitation of preview image data (256Kb), not the image size. Theses 
tags can be used for example to record a 800x600 JPEG preview into large 
JPEG, TIFF, PNG pictures saved by image editor ! 

> This functionality already speeds up loading of single
> image comparing to ImageEditor, and moving between images (JPEGs) is
> slightly faster than in image editor.

And this is can be improved to use Makernote preview with JPEG, TIFF, and PNG.

> However quality of zooming(?) is 
> lower in this preview, for me this is acceptable.

This is depending of preview image size.

> > Please don't ask me to create a very advanced new feature for 0.9.0. I
> > have not commited this code in svn because i'm not sure if this is the
> > right way to implement an image previewing. Also to finalize properlly
> > this code, we need more time, and i would delay this implementation
> > later 0.9.0.
> Few comments:
> - images smaller than preview area are forcibly scaled up to fill it

Yes. I have use a scale method. This can be fixed easily.

> - some kind of context menu would be useful, proposed actions:
>   - Album view (F3)
>   - Edit       (F4)
>   - Open in    >
>   - Assign tag >
>   - Remove tag >
>   - Rating     >
>   - Change name...

You talking about RMB menu or Main interface menu ?

> - some kind of background (important especially for horizontal images)?

Well, Theme rule must be used to render background.

> - with this functionality navigation in main window is more important,
>   please make navigation panel with bigger icons (file name can be moved
>   to new line) and/or allow for key navigation through images in main 
>   window.

Yes keyboard shortcuts must be added here. TODO


More information about the Digikam-devel mailing list