On May 26, 2013, at 3:47 PM, José Ángel Bueno García <jbueno61@gmail.com> wrote:
I'm sure that my old Minolta IV with its accuracy of 1/10 will stay with me for years, but what kind of instrument you make use of to obtain 1/100?
I'm getting those numbers by shooting a chart, developing it as a linear 1.0 gamma UNIWB TIFF, building a profile from that, doing a reverse lookup of L*=100 a*=0 b*=0, and comparing the resulting RGB values across multiple frames. This is all wrapped up in a Perl script, of course. It generates numbers (in EV units, or stops) that I then feed to Raw Photo Processor to simultaneously normalize exposure and set white balance. This is typical: _06C3301: R = 1.20476442084827 G = 0.112331028392598 B = 0.72696339739706 _06C3302: R = 1.20242543114168 G = 0.109944528198645 B = 0.722810030669048 _06C3303: R = 1.20551595895193 G = 0.111145831718312 B = 0.723527251434194 I think most will agree that a difference of 0.003 EV is entirely academic -- at least, in this context....
And what about 2dE asociated to a difference of 1/10 stop?.
Open an image in Adobe Camera Raw (or the like). Find something neutral -- use it as the white balance reference if need be. Adjust the exposure slider until it's a midtone. Now, change the exposure slider by 1/10 stop. You'll see a difference of about 4 RGB units, which works out to about 2 L* units (check with the color picker) -- or, roughly, 2 DE. You could calculate it more precisely, I'm sure, but we're discussing rough approximations in the first place. Cheers, b&