[req] Change exponent (0-???) to roughness (0-100) OR....

[Whaat]

.....OR at least provide a method to correlate the Indigo exponent setting to the Maxwell roughness setting. I have never used Maxwell but many SkIndigo users have and would have no clue how to convert their Maxwell roughness setting to Indigo's exponent setting. Choosing the appropriate exponent value is not very intuitive for me. Is there a formula to convert "roughness" to "exponent"? Obviously, they are directly related so there must be....

Whaat

[Kram1032]

A tiny simple scene with two light sources, a sphere and a floor in both indigo and maxwell...
start with equal values and look, which one is weaker...

... close up, close up....

until you have an about simmilar setting...

look at the difference between roughness and exponent...

then, there could be a couple of solutions:
linear - just add/substract a number...
exponetial - you have to do more tests, to find this out... seach for quadratic, cubic..... numbers... much harder to find out the exact value

...
there are some more, I thinck, but they don't want to cross my mind...

(deus? )

[Kram1032]

Ah, there should be some things, that can reflect

[StompinTom]

well the way it works now, you cant get a perfectly sharp mirror because the 'specular' tag can go on infinitely, you can only approximate it. so why not make "specularity = 100/roughness" and make it impossible for roughness to be 0 (like make sure the minimum value is something like 0.000001 or something). thats just off the top of my head, prolly a better way too.

[Kram1032]

Uhm...

Why should indigo use a Maxwell-value (or 100/Maxwell-roughness)?

Why shouldn't maxwell change it (<- I know, they wont, but why should Indigo?)

[StompinTom]

Maxwell didnt invent the term 'roughness', nor is the term Maxwell specific. itd be easier to use a roughness value from 1 to 100 because then you know that setting it at 1 will guarantee you a near-perfectly sharp reflection (as near as you can get) and 100 will get you a diffuse material, instead of taking a stab at the values (like 100000000 to get sharp reflections). right now its hard to tweak yano? like you have to take a guess at what value will give you the effect you want. with a limited roughness value, you at least have a set scale/range to work with.

but i tihnk implementing something like that would be better in the actual exporter. all itd take is simply adding in the equation above, instead of directly transferring the exponent value, and calling it 'roughness'.

i think itd be pretty useful, as it is more intuitive than the unlimited exponent range.

[CTZn]

As long as Indigo can deal with big numbers, for me it's ok if a value going toward infinity means going closer of a perfect mirror. Also maybe clamping the value would bias your perception of physical correctness. I mean most physically based values in Indigo are not clamped, there may be a good reason why...

[StompinTom]

right, but you could still potentially get an infinite exponent value by entering a value like 10^-100 as long as the float can handle such precision. basically what it means is 100/divided by really really really small number which equals really really really big number. i think its just how you look at it really. i just think itd be more intuitive if it was a logarithmic scale of some sort for quick set up.

[Kram1032]

Maybe, Ono can use both...
You know, a Maxwelllike Roughness and an Indigolike Exponent, with a little formula, which calculates the correct other value...

'Cause I'm quite happy with Exponent and I don't think it's that hard, to find the correct Exponent...