Re: thumbs.el and transparency

[Juri Linkov <juri@jurta.org>]

> I think both "dired style" and "photo album" style could be useful in
> difference circumstances, depending on what I want to do with the
> pics:  if I'm re-arranging the files, deleting etc., dired would be
> useful; if I just want to look at pictures, a photo-album style layout
> [with slightly larger thumbnails] would be useful...

This is what I expect from a thumbnail package too.  In dired style
I wish small thumbnails to be displayed in dired buffers, and in
photo-album style - larger thumbnails together with captions containing
image attributes like image dimension, size, etc.

Currently neither of Emacs thumbnail packages does this.  A simple way to
imitate photo-album style is to generate a Emacs buffer with a table
with cells like:

  ~/.thumbnails/normal/072fe850fe7459ff797873891fbeb9ab.png
  imgp2017.jpg
  1.9MB  1600x1200

and to invoke `iimage-mode' on it (with making thumbnail file names
invisible).

>> Personally, I do not like the larger size of the thumbnail files used
>> by the Thumbnail Managing Standard although I like standards.
>
> It seems like it should be user-configurable, and configurable
> separately for the different cases (you're right the, in the dired
> case, they should be a bit smaller).
>
> Does the "standard" allow for saving thumbs with multiple sizes?  Is
> the thumb size encoded in the filename somehow?

The Thumbnail Managing Standard defines two sizes for thumbnails: 128x128
and 256x256, and two corresponding directories with the following meaning:

~/.thumbnails/normal/
  The default place for storing thumbnails.  The image size must not exceed
  128x128 pixel.  Programs which need smaller resolutions should read and
  write the 128x128 thumbnails and downscale them afterwards to the desired
  dimension.

~/.thumbnails/large/
  The previous notes apply to this directory too, except that the thumbnail
  size must be 256x256 pixel.

There are also more suggestions in http://jens.triq.net/thumbnail-spec/creation.html:

  If a program uses another size for it's previews it loads one of the
  two versions and scales them down to the desired size.

  However, these are suggestions.  Implementations should cope also with
  images that are smaller than the suggested size for the normal and large
  subdirectories.  Depending on the difference between the actual and the
  desired size, they can either use the smaller one found in the cache and
  scale it down or recreate a thumbnail with the proposed size for
  this directory.

Since Emacs can't scale down images itself, it could create (with the help
of external programs) and use smaller thumbnails in ~/.thumbnails/normal/.
But writing smaller thumbnails to this directory is not a good thing.
I definitely wouldn't like if Gimp (which uses the same directory)
displayed thumbnails smaller than 128x128.

Perhaps we should use third directory ~/.thumbnails/small/ even though
it is not defined by the Thumbnail Managing Standard.

-- 
Juri Linkov
http://www.jurta.org/emacs/