Am 23.11.2015 um 23:12 schrieb Cousin Ricky:

> When I try to render the data directly, the greens from G5 up look very cyan to
> me.  Munsell is supposed to visually space out the hues evenly, but the swath
> from G5 to BP5 transitions very slowly to my eyes.
> 
> What weirds me out is that Munsell uses the very purplish illuminant C instead
> of the normal D65 or D50.  Whether it is used as the color system white point or
> the reference white point I have been unable to find out.  (That information is
> probably available for purchase.)  Worse, I have been unable to understand what
> "reference white point" even means, which certainly hampers my understanding of
> color.

In contrast to colour systems typically used in computer graphics (like
sRGB, CIE RGB, CIE XY etc.), which reference light colours, Munsell is a
system to reference pigment colours. Within the boundaries of such a
system, referencing an illuminant /per se/ doesn't make any sense.

Likewise, giving xyY coordinates for such a system doesn't make sense
either -- unless you also mention the lighting conditions under which
the pigments are viewed, i.e. the illuminant.


I would therefore conclude that the Munsell white point you dug up
refers to the illuminant that was used to measure the pigments' xyY
coordinates.

Thus -- assuming I got the colour physics right on this one -- for
proper representation of the actual Munsell pigments you'd need to
divide the pigment colours by the colour of illuminant C, in order to
undo the presumed white point bias. (Theoretically you'd need to to this
in continuous spectrum space; in practice, you should do this in either
XYZ or sRGB space, but whatever you choose it will be imprecise.)

You also need to make sure that the colour of all light emitters
(light_source, background, ambient_light and emission parameter) is
uniform, but as Munsell at its core only describes pigments, you can
choose any illuminant you like -- I'd recommend D65, i.e. <1,1,1>, to
make the image's overall hue harmonize with the surroundings the image
may be presented in, which will typically be web pages. (The W3C has
standardized sRGB as the colour space for the web, so any "pure" white
or grey on the web corresponds to D65).


As for the term "reference white point", this is the light colour that,
in any given context, corresponds to some "official" white. When talking
about colour systems, the term is synonymous to "system white point"
from all I know.

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