Am 06.04.2016 um 14:06 schrieb And:
> clipka <ano### [at] anonymousorg> wrote:
>> Am 06.04.2016 um 09:52 schrieb And:
>>
>>> I derived a solution on what I said the albedo value getting dark when sigma
>>> increase.
>>> I study the formula from the wikipedia. It said A=1-0.5*..., B=0.45*...(Both
>>> rely on the sigma)
>>>
>>> And the result albedo seems rho*A + rho*B*(2/3-64/45/pi) instead rho
>>> itself. So maybe you can divide it when apply the diffuse albedo feature.
>>
>> Thanks! That correction factor appears to make a lot more sense than the
>> hack I had come up with :)
>>
>> Not too surprisingly, experiments indicate that it does indeed fit like
>> a glove.
> 
> Ok ok! cheers.
> 
> If I don't make mistake. but it should correct because I calculate formula
> carefully.

Actually, once I thought about your result, I realized that the
bihemispherical albedo /must/ be

    rho*( A*a + B*b )

with the terms A and B depending on sigma as specified in the Oren-Nayar
description, and a,b being constant.

From the fact that Oren-Nayar includes the Lambertian model as a special
case with A=1,B=0 it follows that a /must/ be 1.

The value 2/3+(64/45)*(1/pi) for b looks a bit complicated, but
experiments with high sigma clearly indicate that it indeed at least
approximates the proper value very closely, and it looks plausible
enough as an exact value, so I'm pretty sure you did indeed get the
hemispherical integral right.

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