Why a png, why not a thumbnail, why a control.

[Michael Meeks <michael ximian com>]

Hi Jens,

        Firstly libthumb fills a different niche than a preview. I am
fairly convinced that you're not going to get a sensible amount of preview
information into a 64x64 pixmap - and if you interpolate it up you'll just
get rubbish. My feeling is that a relatively large (but compressed) png
would be ideal. Many document views have a very regular - compressible
layout and thus it seems reasonable to pick a largish sort of size;
perhaps 320x200 or somesuch - interpolated to a sensible size on display.

        Of course - a thumbnailing library could operate on a compound
doc. file to further shrink the thumbnail to 64x64 if that is what was
required. Personaly I would do this sparingly - a preview of a word
document is going to look just like any other word document at that sort
of size - better to have a pretty TigerT icon [1].

        So - yes libthumb is useful, but I feel not for previews.

On Mon, 10 Dec 2001, Jens Finke wrote:
> Well, your point is to use a BonoboControl for displaying all this.
> Let's assume you have a dir with 30 different files in it. I don't
> believe it's very efficient to start multiple controls to create a
> preview for all the different file types.

        Quite - and that's why the control use is only suggested for a
single pane to the left of a file selector window. I think we're talking
at cross purposes here. No-one would suggest using BonoboControl as a
generic thumbnailing abstraction - for a start it wouldn't anti-alias
nicely, it'd kill the XServer etc. etc.

> My idea is to define a standard way of storing such previews on the
> filesystem level.

        Indeed - best inside some sort of standard compound doc. format -
which apparently, is going to be pkzip [ according to rumours ]. Of course
- libthumb will have a different standard for caching thumbnails - since
it's operating on an entirely different set of constraints and performance
requirements.

        Regards,

                Michael.

[1] - if you were feeling particularly cunning - you could write some sort
of edge detection / count code and get some metric of whether there was in
fact useful / visible data in the file. Or whether to have a stock icon
type [ inside libthumb ]

-- 
 mmeeks gnu org  <><, Pseudo Engineer, itinerant idiot