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

[Caulier Gilles]

Le Jeudi 15 Juin 2006 20:34, Andreas Huggel a écrit :
> On Thursday 15 June 2006 22:48, Gilles Caulier wrote:
> > On Thursday 15 June 2006 16:37, Laurent Rathle wrote:
> > > Le Jeudi 15 Juin 2006 00:19, Caulier Gilles a écrit :
> > > > Please, give me a feedback. Thanks in advance
> > >
> > > Previewing raw is effectively much faster with this than with the
> > > editor on my Athlon XP 3200 / 1 Gb Ram. In the editor, it stops at 10 %
> > > and wait for at least 30 s to load the rest. New preview is less than
> > > one second
> > >
> > > :-)
> >
> > Yes, but take a care that preview isn't the RAW image data. It's a JPEG
> > or TIFF or PPM file embedded into Camera Settings - Exif Makernotes
> > metadata area. It's used by camera to display image on TV screen (it's
> > more faster to render a small JPEG than the RAW file).
> >
> > Note this preview image is also available into JPEG, TIFF and PNG files
> > if Makernote is available. Preview image extraction will be possible
> > using Exiv2 when :
> >
> > - Exif data size limitation will be removed into Exiv2 about this
> > metadata. - MakerNotes will be updated, especially CANON, NIKON, OLYMPUS,
> > etc. Actually, only my Minolta makernote implementation include preview
> > tags. This is not very complicated to do using Exiftools tags reference.
> >
> > Andreas, we have already talking about Exiv2 preview extraction in the
> > past. Can you give me your viewpoint in this room ?
> >
> > Gilles
>
> The Exif data of JPEGs usually contains a small thumbnail (typically only
> 120x160 px), in JPEG or TIFF format. I guess that's pretty useless.

yes, it can be used to give a thumbnail, not a large preview like that :

http://digikam3rdparty.free.fr/Screenshots/image_preview_on_main_interface.png

> Besides, some Makernotes point to a larger preview image somewhere in the
> JPEG (but possibly outside of the Exif data). In RAW files I have seen up
> to 4 images, including the RAW image. There is no standard for these
> preview images, they come in different sizes and image formats (but mostly
> JPEG).
>
> I was first of all wondering if it is desireable/a good idea if these could
> be accessed through Exiv2.
>
> If so, two options come to mind:
> 1) extract the relevant metadata tags into ExifData and let the application
> do the work.
> + Exiv2 interface remains the same
> - apps need to know for each format which tags to look at
> - these tags may need to be treated specially by Exiv2

Yes, i have started to work into this way (in my DMetadata interface), using 
Minolta makernote preview image. But it can work duing the limitation of size 
data from Exif tags.

>
> 2) extend the Exiv2::Image interface to access preview images
> + apps just need to decide which preview image to use if there are several
> - a bit weird: the library would then give access to metadata and preview
> images, but not to the actual image
>
> For the moment I like option 2 better, although I don't know how the new
> interface should look like, ideas welcome.

And me the first one, because the choose of the preview to use (in the case to 
multiple previews available) is just a makernote tag selection. It can be 
done easily by the host application. I think it's not necessary to make a new 
interface into Exiv2 for that. 

Gilles