18442Re: White (Neutral) Balance in Panoramas
- Mar 4, 2008--- In PanoToolsNG@yahoogroups.com, "William Donelson" <wd@...> wrote:
>Using black velvet this way is a very clever trick. What happens, I
> --- In PanoToolsNG@yahoogroups.com, Snowy Aldon <lists@> wrote:
> > It seems strange that the velvet gives a neutral value when
> > illuminated to be in the mid-tone. I would have have supposed
> > that the colour bias of the dyes would become apparent
> > and introduce a cast.
> You have to be careful which patch of velvet you use.
> Some are not black.
> > Do you colour balance/correct/neutralise to the velvet
> > and adjust the images to give an equal RGB value grey?
> > And how does achieving a truly "black" black give any
> > information regarding the colour balance
> > of the image?
> We do not use the box-of-velvet anymore, as our
> "4 patches of velvet" at different orientations
> works very well. Some of the patches look blacker
> than others, and some can be used as gray-level samples.
believe, is that the "gray" appearance is caused by a myriad of
specular reflections from the surfaces of the fibers. Specular
reflections are always non-colored, so indeed this method should
produce a very neutral gray as long as the body of the fibers is very
dark in comparison.
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