- Sep 5, 2007
- Saint Paul,
I believe that's because it's already factored into his developmental model. It's the same tweak that Adams basically does. The development model in WBM is shown on page 128 fig 2. It appears to use a LER / NDR of 1.20.
View attachment 332440
Interestingly, these numbers are very close to the ones I've obtained using my practical flare model. Flare reduces the effective luminance, but if you don't use flare to reduce the luminance range variable, then you need to increase the LER / DR variable to compensate. A constant if you will. Working backwards from a normal negative of 0.58, each stop of the luminance range would average 0.30 * 0.58 = slightly over 0.17 units of density per stop of luminance. To keep it simple, a 7 stop luminance range would result in a negative density range of 7 * 0.17 = 1.19. Approximately what WBM uses. As we know in reality, average flare reduces the seven stop luminance range to six stops so the resulting negative density range should be more like 6 * 0.17 = 1.02.
On page 62 fig. 6, WBM has grade 2 as ranging from 0.95 to 1.15 with the average as 1.05. 1.20 falls outside the range of a grade 2 paper. For the math to work when determining a CI, you need to add an extra 0.15 density range to the grade 2 aim density range of 1.05 in the equation or subtract flare from the luminance range. The end result is the same. Only one reflects reality.
Thank you for pointing it out! It's been a while since I read that chapter, and I am glad you brought it up because it made me go back and re-read it. Yes, the NDR of 1.2 is kind of their thing, as well as the speed point at 0.17 over B+F, if I remember correctly. It turns out I had put some of these calculations in my code, I just forgot I did it. It's not the first time. My memory is not what it used to be.
I have a question, if you don't mind. I have been reviewing my code for paper testing, and I came across a function I wrote that calculates ISO paper grades. I just don't remember where I got the formula from. My notes say "1992 ISO standard" so I am wondering if it's this one:
"ISO 6846:1992 Photography — Black-and-white continuous-tone papers — Determination of ISO speed and ISO range for printing"
Do you happen to know if this is the current standard? Thanks! I am grateful for your input. I always learn something new.