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

Marcel Wiesweg marcel.wiesweg at gmx.de
Thu Jun 15 21:10:48 BST 2006

> Hi all,
> Following some reports from B.K.O and discussions by IRC/mails, some users
> would to have a preview mode of current album item, directly in main
> interface, without to start an instance of image editor. Image editor take
> a while with old computer to just previewing a RAW picture.
> I have search a simple solution to do it.... and this is my proposal :
> http://digikam3rdparty.free.fr/Screenshots/image_preview_on_main_interface.
> I have make an experimental patch using QWidgetStack to embed into album
> collection area a new image preview. You toogle between preview and album
> view using F3.
> The patch is here :
> http://digikam3rdparty.free.fr/misc.tarballs/preview.patch
> The RAW preview use the -e dcraw option to load the embedded JPEG image in
> RAW file (used to display a RAW picture on TV screen)
> This patch separate Preview mode (F3) and the Edit mode (F4) on Image menu
> entries. If you enable the ImageProperties sidebar, use the navigate button
> to change the current image to preview.
> This code is simple and not finalized. For example the code :
> - don't use a cache to speed up rendering.
> - 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.
> - use QImage, not Dimg.
> - don't load the preview using a separate thread to unfreeze ther GUI
> (Image Editor do it). We can use a new KIO slave for that but not sure
> (Marcel, your viewpoint ?)

I am wondering if the following is true:

The image histogram can use (if found in cache)
1. The dcraw loaded image
2. The dcraw loaded image with halfSizeColor
3. The preview image??

The preview can use (if found in cache)
1. The dcraw loaded image
2. The embedded preview image

The image editor can use (if found in cache)
1. The dcraw loaded image

The image histogram will load
the dcraw loaded image with halfSizeColor

The preview will load
the embedded preview image

The image editor will load
the dcraw loaded image

I'm not familiar with some important facts here, so please correct me.
If we can create a hierarchy like the one above, we can implement this in the 
LoadingCache. I just yesterday began to write something similar to integrate 
the halfSizeColor images (I know I wrote I'd fix it "till tomorrow", but it's 
football world cup)

> 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.

If I had enough time I'd anyway love to write a really cool grandma-compatible 
highly integrated presentation mode (tm), think of KPDF, optimized for 
viewing. Talking about advanced features.

If your current solution works, i.e. it shows images properly and nothing 
else, that's IMO a good and pragmatic solution for 0.9.[0,1].

> To patch your local source repository, use these command lines :
> # cd digikam
> # patch -p0 < preview.patch
> Note : You need to re-install digiKam before to use this version because a
> new menu item have been added in main interface (digikamrc file changed)
> Please, give me a feedback. Thanks in advance
> Gilles
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