Chrome Erazor is a very special chroma key plug in. Normal chroma key
as know from film and TV removes a specified color range (e.g. a blue screen)
and replaces it with a new background. So far so good.
But this plug in can much more. At first it is a photoshop
plugin. And in photoshop we are usually work with layers. We do not want to
combine a foreground and a background. We want to cut out the blue screen parts
from the foreground and apply this foreground layer on top of all background layers.
This seems to be simply at a first thought but need a special handling of the
foreground image. Cheep solutions perform a simple blend, so the color we want to
remove remains still in the foreground image. That's why better solutions subtractively
remove the key color. This works fine when combining it with a background image.
But not with photoshop where we want to have a transparency instead of an added background.
The transparancy itself is quite simply to archive, it's only a kind of mask. But when
we subtract the key color from the foreground we will have black borders instead of blue or green
Want we want is a processed foreground image as it would be if the foreground was
never combined (and therefore actually blended) with any kind of background. We want to
have the effect that the blonde person in front of a blue screen looks like
she never stand before a blue screen. No blue border, nor a black border should suround
her blonde hair. Only transparancy.
That's why Chrome Erazor has a special kind of algorithm: "color restoring".
Color restoring guesses what foreground color there would be if it were no blending.