in news:ce0r1v$7l8$1@chho.imagico.de Christoph Hormann wrote:

> No, that's because they are physically impossible.  No photographic 
> technique can generate a photo where a brightness difference of the 
> scene in reality is inverted on the photo (i.e. a part brighter than a 
> second one in reality is darker than the second one on the photo).
> 

Actually, the guys at kodak etc. put a lot of effort in making film behave 
decently. Old, unbuffered film and also old TV camera's do exactly that. 
The gamma curve of a film doesn't stop at the shoulder. After it reached 
the top it goes down again. You can see the result in old photographs, 
where the sun is black instead of white. Also in old TV recordings it can 
be seen, the black highlights on trumpets for example.

For what Severi means, check out the "zone system", if you don't know it 
already. Every photograph has manipulated contrast.

Ingo

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