Am 06.04.2016 um 11:42 schrieb And:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> On 5-4-2016 15:19, And wrote:
>>> Thomas de Groot <tho### [at] degrootorg> wrote:
>>>> OK. One final example: a pot with albedo added as well as some specular
>>>> value.
>>>>
>>>> I don't know how to interpret or make sense of all this, so some
>>>> feedback is appreciated.
>>>>
>>>> --
>>>> Thomas
>>>
>>> The texture is fun. It has some contrast to the before.
>>>
>>
>> I confess that I am confused. The textures appear darker and somehow
>> with less "contrast". So, my question really is: /when/ to use these
>> alternatives instead of pure Lambertian? To me, at this stage and
>> totally instinctively, pure Lambertian has my preference.

The darker appearance is inherent in the mathematical models: At the
same nominal brightness, the alternative models result in a lower
effective bihemispherical albedo (ratio of total reflected light vs.
total incoming light); a similar effect happens with the conventional
model when you use a high "brilliance" parameter. I'll need to implement
correction factors for that, just as I did for the "brilliance"
mechanism, when the "albedo" keyword is used.

As for having less "contrast", that is also to be expected, and is
actually the feature making them more realistic for some materials.

> Lambertian diffuse is very well truly. I think the others can be used when you
> feel the pure diffuse is plodding, or sometimes Oren-Nayar can be used in an
> ....powdery object like chalk.

Chalk, plaster, sandstone, unglazed clay, Shapeways' 3d-printed
"unpolished strong & flexible plastic", textiles, eggshells, even paper
-- there's plenty of stuff in our world that is seriously non-lambertian.

Granted, smooth plastic, glossy cardboard, finished wood and painted
surfaces are quite dominant in our world, and Lambertian does quite a
good job for those. But as soon as you have something in your scene that
in real life exhibits non-Lambertian reflection, using one of the
alternative models may give your scene that little extra realism.

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