[Digikam-devel] Re: face detection process...

[Gilles Caulier]

2011/1/6 Marcel Wiesweg <marcel.wiesweg at gmx.de>

>
> > - 133 unknown items found.
> > - 5 items are not faces. All others are fine.
>
> Judging this result of course depends on the "true positive" number: How
> many
> pictures truly have a face?
>

Not too many. there is a lots of nature photo. some from my son and familly
events. Judging visually, this sound correct for me.

i can test with my huge collection at home where a lots of picture have
face. I can select alum where i know that all photo have at least a face and
see the result.


The important part here, for use in digikam, is to run real-world tests: A
> collection where only 10-20% have faces at all.
> The initial implementation gave me lots of false positives. And this gave a
> bad first impression: almost all found entries were not faces. Users will
> see
> and judge that it doesnt work at all. We must have most entries correct
> there.
> Why the difference? The Positive Predictive Value of a test depends on the
> prevalence!
>
> The current implementation is a two step approach:
> 1) With a single cascade, faces are scanned
> 2) With a larger number of cascades, faces are verified.
>
> Step 1 determines the upper limit of sensitivity. Step 2 improves
> specificity
> and decreases sensitivity (but in my experience, not much)
>
>
> >
> > Bugs :
> > - when scan is complete, progress bar continue to move...
>
> Does it display a percentage number?
>

No percentage. In fact progress bar use moving mode indication (when minimum
and maximum values are set to 0)

Gilles


>
> > - There is an album displayed as Unknown where there is no item. Why ?
> Look
> > screenshot for details. in fact, it's an icon view problem at scrolling.
> > Moving contents with mouse wheel change icon view.
> >
> > http://www.flickr.com/photos/digikam/5322873069
> > http://www.flickr.com/photos/digikam/5322873101
> > http://www.flickr.com/photos/digikam/5323478176
>
> This is a model-view problem. I have seen it in a few cases, usually a
> problem
> with sorting. No idea atm, did never seen that with faces.
>
> Marcel
>
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