Unlocked RGB Exponent.

[grantwarwick]

http://www.vizpark.com/color-combine-reference-guide/

going to look into using this over the composite map for simplicity's sake

[joconnell]

Why not. I'll fire over a copy of the script and a preset gradient for you to have a look at and see if you get similar results.

[grantwarwick]

Why not. I'll fire over a copy of the script and a preset gradient for you to have a look at and see if you get similar results.

Thanks heaps,
I'll share the results here!

[joconnell]

Sent a pm - I don't think it'll make a massive difference right now or let you get that nice chroma spread on the spec - you can make a bit of a fringe on one side but not on the other alas. (unless you want to do some evil shadow / light falloff map stuff and sacrifice the reflections purely to get that highlight)

[grantwarwick]

After taking a look at the script and scene setup, is it not possible to control the gradient by simply matching the bezier curves in the output rollout set to RGB mode?

[grantwarwick]

[joconnell]

Yep it probably is - I didn't get a chance to check it and do a quick a / b comparison between the two but this should work fine!

[grantwarwick]

Would be really handy to pop out that gradient dialogue, pain in the ass having it so small :/

I made some decent progress today, that red shader you saw in the other thread is using a modified gradient you supplied!
I got it to match the Iron Man Mark 3 suit very closely.

While we are on the subject of metal. Does anybody know how to get the physical diffuse information? And does it also have an IOR Value?
I've seen others experiment with polarised textures to get the values but Vlado used a different approach on his leaf tutorial.

For my shaders sometimes I use fresnel in the diffuse and other times not, always by eye though as I don't understand the physics.

[joconnell]

Ah yes. This is a very handy thing that a poster called rens on the forum explained to me. Metal has no diffuse at all and the scan data you have in those curves is the total amount of light reflected from the surface - diffuse, spec and reflection all at the same time - so if the curve is 60% reflective at the front facing parts, then only 60% of the light that hits the metal bounces back full stop - the rest is likely absorbed. What happens to differentiate between diffuse and mirrored metals is nothing but surface glossiness / polish / focus. If you were to have a really, really rough metal like a material you set the glossiness to 0 for, it'd end up looking like a simple diffuse shader, albeit at incredibly wasteful sampling times.

Metal has no IOR at all - I think the distinction might come with the difference between conductors and dielectric materials - dielectrics are pretty much all non conductive materials, or all non metals. They've got a very strong fresnel effect as we understand it in vray terms, metals on the other hand use a complex ior which is the equation I sent over which we can't simulate with the current material settings. Here's a comparison - http://www.graphics.cornell.edu/~wes...c/fresnel.html

So pretty much ignore fresnel when you're doing metals - there is a tiny bit of a curve in most metals but again we don't have separate ior values for red, green and blue and with the current settings in the material you wouldn't be able to make the correct curve anyway - putting in high numbers in the ior causes the reflections to be quite strong for most of the facing angles, and then they take a huge dive down as they go toward the edge before shooting up again to 100% reflective. What'd be more useful in terms of a fake is having a 0 degree reflectance %, a 90 degree reflectance % and then a mid point curve control to allow you to bias how the curve changes between the two values which is what mental ray's brdf thingy does I believe.

[grantwarwick]

So much to learn still, thanks for sharing your information. I kind of hate myself a little for building wrong shaders for so long but thanks!

Sorry, I should note, I was aware that most metals "diffuse" look comes from larger than expected glossiness values however I wasn't aware it had zero at all and often the diffuse component to my shaders is wayyyyy too high now that I think about it

[joconnell]

If it looks right then it is right

[grantwarwick]

I'm trying to push more towards physicality though due to the nature of what I'm trying to do (Keep things as simple as possible and workable in different lighting environments)

If I go and ad 90% white values to a metal shader in a scene lit by a very dark HDR it can be tweaked to still look right but go put it in the sun and it turns to shit. I just want to make sure I'm going in the right direction

[joconnell]

True true, last bit of info that rens gave me is if you want to add some diffuse to your metal or different levels of glossy on it, then you're into slow land. If you have a yellow diffuse and a yellow reflection colour, of course it means that the reflection filters out all the yellow light from hitting your diffuse and it'll swing to a green colour instead. Since with metals it's all the one medium and thus the shiny parts don't filter the less shiny parts that means you can't have diffuse and reflection in one shader. What you have to do is use the blend material and have one for your diffuse only part (zero reflections - same gradient as your reflection curve i the diffuse slot) and then a shader with only glossy reflections using the same curve blended on top. The key is to only use grey values to blend the two together. What'll happen is you avoid the tinting problem for one thing, and the grey values also prevent you from adding more reflectivity to the material than is possible - remember that the graph you've made for reflectance is the total light reflective, diffuse and reflection combined so if you're increasing your glossy shader, your diffuse shader must come down by the same amount so that the curve data is respected.

[grantwarwick]

This is what I currently do, maybe a little bit different

Most shaders have the base layer (with diffuse and glossy reflections) then I put a clear coat layer on top and blend it with a fresnel falloff.
This should still preserve light laws.

On a re-read this makes sense. I will share with you a base metal shader tomorrow to see your opinion on it.

[joconnell]

Mine isn't all that important - it's people like Brett Simms, Bertrand and Peter Guthrie who count! Will be interested to see it from a sampling point of view though. As I say, great work.