Re: [Openexr-devel] magic numbers

[Peter Kümmel]

Florian Kainz wrote:
 > Mapping pixel value 0.18, or middle gray, to 0.883 times the
> monitor's maximum brightness means that diffuse white objects
> do not map to the monitor's maximum brightness; there's some
> headroom left for specular highlights, which are often much
> brighter than diffuse white objects.  As I mentioned in my
> earlier mail, the decision to display images this way is
> pretty arbitrary.

It was 0. 0 882: sqrt(x)/x=middle with x=128.

I've figured it out, where 0.18 comes from:

sqrt(x)/x = x^(-1/2) = middle
x^(1/2) = 1/middle
x = (1/middle)^2

Because of this using 0.18 as middle value is
equivalent to assume a contrast of only 1:31.

Seems this is a more realistic contrast of
current monitors. Or I am completely wrong?

Peter