Re: [APML] Wondering about histograms

[Wei-Hao Wang <astrophoto@gmail.com>]

Hi Carlos and Ray,

In some part I would like to confirm what Carlos said.  It is true that 
negatives have larger dynamic range.  Ray, perhaps you can go to 
Kodak's website and randomly look at the HD curves of some color 
negatives and color reversals.  You will find that color negatives 
usually have curves spanning considerably more than 3 units in 
X-axis.  (3 units in log10 scale means 10 stops in log2 scale.)  This 
translates into a dynamic range of more than 1000.  On the other 
hand, color reversals usually have steep HD curves that have 
narrower X-axis range.  Usually their dynamical range is 10x 
smaller than negatives.

And it is true that color negatives have very low contrast, which is 
the key to its large dynamical range.  Because the film has low 
contrast, the photo paper for negatives has to have high contrast.  
This is indeed the case. 

On the other hand, I am not 100% sure if what Carlos said about 
histogram is correct.  Although color negatives have larger dynamical
ranges, they translate this large brightness range into a small density
range.  This is exactly what "low contrast" means.  If we shoot a fixed
dynamical range target with a color negative and a color reversal and 
both with correct exposures, the negative one should have a smaller 
density range.  In other words, the negative should have a narrower 
histogram, if both are scanned with identical settings.  

Cheers,
Wei-Hao

-- 
________________________________________________________________
Wei-Hao Wang  :)

Institute for Astronomy at University of Hawaii

Address:                       
2680 Woodlawn Drive         Personal Website:
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