Lighting math help needed

[feppe]

I'm building my own diffusion panels, and picked up three cloth samples from a local store. I'd like to know which one gives the most neutral white to avoid color casts, and how much diffusion there is in stops.

Below results of tests of bare bulb and three cloths.
- Each RGB row is an average of three flashes taken from neutral grey on Colorchecker Passport, 51x51 sample size, same location, camera on tripod on manual. They were quite consistent across flashes, within 2 units of each other
- Average is average of those averages, perhaps useful in calculating the diffusion level
- STDEV is standard deviation across all measurements (3 for each color for 9 total for each cloth). I'd imagine this is useful in calculating the neutrality?

To me "Cloth 4.95 (EUR per meter)" seems most neutral, with lowest standard deviation. Is that the case, and how much diffusion does that have?

          R G B Average STDEV
Bare bulb 202 204 220 209 8,8
Cloth 4.00 131 132 154 139 11,4
Cloth 4.95 129 130 152 137 11,0
Cloth 6.95 120 121 144 128 11,8

I haven't bothered to do a t-test to see if the measurements are statistically valid - I think that would be overkill, as I already think I'm overdoing this I have the full dataset as an Open Office doc if anyone is interested.

[langier]

Unless your math is more important than the photo simply test and base your choice on the photo. To go simlpy by the numbers and mediocre result for some mathematical equation will have you polishing a turd to justify the numbers.

Simply take a cloth, shoot with it and just the photo for yourself. There's nothing better than hands' on to knowing what's the best!

[anwarp]

Perhaps looking at the data using the HSV (Hue, Saturation and Value) model would simplify the problem, making it more intutive.  The Value will provide you with the brightness, or an estimate on the light loss.  The hue will show you the colour shift.  The saturation will show you how strong the shift is.

Regards,

Anwar.