I think relying on Qt to read and resize the image is probably not the right
approach. After all, OIIO is an image reading package! We probably already
have the images in memory (or will need them in memory), so the last thing we
want is a redundant read and copy by Qt.
Some of the images formats we support can contain thumbnail images in the
files. In those cases, we should use the pre-computed thumbnails. By
convention, we store those in the metadata as "thumbnail_width",
"thumbnail_height", "thumbnail_nchannels", and "thumbnail_image". Look
through the code in src/targa.imageio to see an example of how those are used.
If those aren't present, we'll have to read the image and downsize it. Also,
for files that are already MIP-maps, you can pull a thumbnail out by just
grabbing one of the low res MIPmap levels.
What do we do if no thumbnail is present in the file and it's not a MIPmap?
Well, you could pre-read all the files and generate thumbnails. But you don't
want to hold everything up for that to happen, so you probably want a second
thread that is reading ahead and filling in the thumbnail images as it goes.
Is it a big cost every time you start up? Should there be a cache of
thumbnails on disk (say, in $HOME/.ivthumb/*)? Which would need to be careful
to check for updates, delete old ones, and not let cruft accumulate too much
space there.
-- lg
On Mar 27, 2012, at 4:23 PM, Panks wrote:
> Hello!
> I would like to put proposal for iv viewer thumbnail view.
> I just have a small idea of how we can put it all together, we can put a bar
> at the bottom of the iv with slider if required with a toggle button in the
> menu bar which shows and hide the thumbnail bar at the bottom.
> If the images have thumbnails embedded and they are of acceptable ratio then
> we can use them directly else we can use QImage Scale() to scale them to the
> required resolution.
> And in case big images when we don't have thumbnails at all, we can make the
> thumbnails in a separate thread using QImageReader class as this article
> describes:
> http://olliwang.com/2010/01/30/creating-thumbnail-images-in-qt/
> so that it will not affect the performance of iv viewer. We can implement
> multiple selection on thumbnails and implement 'delete', 'shuffle by drag and
> drop' and few more functions.
>
> Please Comment or put suggestion.
>
> Thank you
>
> --
> Pankaj
> UG Student | Dept. of Computer Science and Engineering
> IIT Madras, Chennai, India
>
--
Larry Gritz
[email protected]
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