Bart_van_der_Wolf
pro member
These are of course the reason why major standard color spaces contemplate a certain surround ambiance for viewing (although there are a number of paradoxes in those specifications).
In any case, by way of general reference, the sRGB standard contemplates a delivered white point illuminance of 80 cd/m^2 with a surround of reflectance 0.20 illuminated at 200 lx.
If we work through the photometric equations, that comes out to a surround luminance of 12.7 cd/m^2, or about 16% of the white point luminance.
That would be a surround at about RGB 112,112,112, about like so:
<disrespectful snip of Carla's image, just for brevity>
But the overall environment illuminance is also a factor - not just the luminance of the immediate surround.
Indeed, but there is some mix of physics and psychology (= Human visual system) involved as well:
http://www.michaelbach.de/ot/lum_dynsimcontrast/index.html
and
http://web.mit.edu/persci/gaz/gaz-teaching/flash/koffka-movie.swf
These effects already take place at small areas of an image.
Another thing is that it's hard to make a nice looking page based on an RGB 112, 112, 112 background, because text will always be low contrast unless done in screaming colors, and viewing conditions (ambient light level) vary.
Cheers,
Bart