Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Austin 


> Once again, RGB values from a CCD imaging device
> encompass the entire spectral range that Tri-X encompasses,
> and therefore you DO have the original complete spectrum
> to work from, with the "original" spectrum being
> defined as the spectrum that Tri-X can record.  Good
> grief.

He MAY have a point but he hasn't provided any empirical evidence of 
it.  He's also doing a lousy job explaining his argument so I'll try 
to paraphrase.
   
Say you have a CCD with RGB sensors whose PEAK response is 610nm, 
500 nm and 430 nm.  They all overlap but those are their peaks.  Say 
you have two "yellow" objects - X comprised of a mix of red (610 nm) 
and green (500 nm) and Y - true yellow - 560 nm. 

X will produce a strong signal in the R and G channels, so when 
converted to B+W it will be "bright".   Y will still produce a 
signal in the R and G channels but it will be down the skirts of 
both filters so that signal will be weaker.  Thus when converted to 
grayscale the two yellows will have different intensities. 

But since b+w film has more-or-less uniform spectral response the 
two yellows would look the same on Tri-X.  

Did I explain that right, Anthony? 

Here's the flaw, as I see it.  For X to have the same intensity in 
the original scene as pure yellow the R and G components would each 
have to be half as bright as the pure yellow.  Think of it this way -
 suppose you have a 10mW yellow LED.   What wattage would an R and  
G LED have to be to produce the same brightness of yellow?  5mW 
each.  (pretending linear response, equal efficiency, etc)  So in 
the X and Y example, above the R and G would each have to be dimmer 
to start with, so it all evens out.

So I agree with you - I think Anthony has to come up with real-world 
evidence that what he's saying is true.