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Subject: Re: Algorithm to set Face image background to transparent



Harris,

about Blue Screen / Chroma-Key:
http://www.seanet.com/users/bradford/bluscrn.html

This is used for replacing the uniformly blue background
by something else.

IMO, in your case the photo should be taken in front of a
white background.
A typical scene illumination:
Soft strong light from top right (in camera viewing direc-
tion), less strong light from the left in order to lighten
the otherwise dark part of the face, and an auxiliary lamp
for making the background lighter.

For a passport photo one has to follow some rules which
I don't know. Perhaps only front light, which will cause a
geometrically flat appearance, 'politically correct'.

It shouldn't be necessary to replace the background in
the image by paper white. It's mostly possible to make
light gray somewhat lighter by gradation curves.
Nevertheless, if you want plain paper white as back-
ground, then you should use a white background instead
of transparency.
For a transparent background it's impossible to inter-
polate edges - the contours will look fuzzy.

Making a selection for a face with haires is even by
Photoshop very difficult.
You'll find more advice in the Adobe Forum Photoshop:
http://www.adobeforums.com/

The suggestions for lighting are based on books by
Ren=E9 Bouillot (www.amazon.fr) and experiments, following
his recommendations.

An example is here:
http://www.fho-emden.de/~hoffmann/francine28082003.pdf

Best regards --Gernot Hoffmann


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