Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@y..., "Robert Rex" 
<chameleon@i...> wrote:
> --- In DigitalBlackandWhiteThePrint@y..., "Antonis Ricos" 
> <antonisphoto@y...> wrote:
> > --- In DigitalBlackandWhiteThePrint@y..., chameleon@i... wrote:
> > >  Brightness is not the same as 
> > > whiteness in paper tech talk.  Whiteness is measured on the "L" 
> > > scale 
> > > of LAB, whereas brightness is a measure of reflectivity (how 
much 
> > > light is reflected off the paper). 
> 
> > But Robert, isn't the L reading the "grayscale" component and not 
> > the color? 
> > Hence it is expressing the same thing as brightness in different 
> > terms (% light 
> > reflectance vs position on a grayscale). I would imagine that
> > "whiteness" 
> > would need to take into account _color_ info not just light-to-
> > dark. Color info is 
> > only contained in the "a" and "b" of Lab.???
> > Antonis
> 
> Antonis,
> sorry for the delayed response.
> you are right that "whiteness" needs to take into account ALL color 
> info.  I really should have denoted L, A, and B numbers for the 
> various papers i listed.  this is because "color" is a point on the 
> grid, and the L reference is not helpful without the other two. i 
was 
> just trying to be quick, but also sloppy.
> i'll probably email you a little matrix/excel file that you could 
> upload on the files portion of this list for future reference.
> 
> However, L is not a function of grayscale. L and Brightness are NOT 
> the same thing.  L, with a and b as discussed above, describe the 
> color in the 3d grid, whereas brightness is a function of 
> reflectivity, and as previously mentioned is dependent on light 
> source.
> 
> hope this answers your question,
> RObert Rex

Antonis, Robert

Just to tag on an additional note. If there are optical brighteners 
present that are fluorescing, the amount of visible light coming off 
the surface is the reflected light plus the fluoresced light. You 
have UV falling on the print, which is not visible, and a portion of 
that energy is consumed by the brighteners and emitted in the visible 
spectrum. This should be detected by densitometers and spectrometers 
but will be dependent upon the UV content and intensity of the 
instruments' light sources.

Martin