I’m not claiming that the reflections in all opaque materials are necessarily “correctly” fresnel, but they certainly do have a falloff. With almost all reflective materials, reflection is stronger on surfaces closer to parallel to the viewing angle than they are on surfaces perpendicular. I suppose you could get similar results with a perpendicular/parallel falloff map in the reflection slot, but I prefer the fresnel falloff instead. I think it looks better and I can control it numerically with IOR values.
Cos it isn’t. The light can be either transmitted or refracted. Transmitted eg the light energy becomes absorbed into the medium that the light hits and thus dies off from visibility, or refeacted as we know. Either of these two contribute to the deadening of the light that is reflected back.
ditto!
As far as I know Fresnel is only applicable to dielectric materilas.
Dielectric definition:
noun
a material such as glass or porcelain with negligible electrical or thermal conductivity
Therefore chrom and other metals shouldn’t use IOR. Setting IOR for chrom to 12 or more is so unrealistic that practicaly cancels the influence of IOR on that material.
Z.
Exactly, i doubt that 12 is noticeable at all.
an IO Reflectance of 12 on chrome is noticeable by the fact that it is then not mirror-like shiny
(as a result I persoanlly set chrome and stainless steels to IOR OFF and then use the reflect level to tune it to a little below full reflection)
but but but I still think there is confusion..
I have a brass door knob at home - getting right up close to it I can clearly see more reflection in the glancing angles than straight on - ergo a non-dielectric material is showing fresnel reflectance!
I think Vlado needs to visit this post and comment - now where’s the call-for-Vlado button?
Ultimately its about what looks right… if it looks good, then it is. I personally find that glossy fresnel reflections on most surfaces look good…
There was a thread about that if i recall right. And what you notice on the doorknobs is not necessarily MORE or LESS reflection but more or less GLOSSINESS. As vlado discussed in that other thread, materials tend to be sharper on the sides then when looked straight on.
Regards,
Thorsten
I’m not sure if it’s the same thread -- but I remember a discussion about glossiness changing in a frensel way.
Essentially, the flatter (or more glancing) the reflective angle, the less glossy a reflection would appear… or to say it another way, surfaces that ran parallel (or nearly parallel to the camera’s view would look sharper than those that were perpendicular.)
The example that Vlado showed was a plane with a fine noise bump on it. As it rotated from perpendicular (from camera view) to parallel the glossiness went from blurry to sharp. I assume it’s sort of like taking a blurry photograph and shrinking it in one dimension… as it gets compressed it will appear sharper. When you rotate a plane from perpendicular to parallel -- it’s the same type of effect.
In the case of the doorknob -- I would agree with Thorsten -- I think it’s the apparent glossiness is changing and not it’s amount of reflectivity. I would think the curvature of the doorknob would cause the reflections of nearby objects to appear more “compressed” and therfore sharper (which could be mistaken for increased reflectivity). But who knows, I guess I’d have to see the doorknob.
Exactly - the bumps in the surface that cause the roughness move closer together making a more smooth mirror like surface.
Right --- the part that really confuses me though is… I asked Vlado whether vray reproduced that parallel-view “compression” in ordinary glossy materials (i.e., not ones made glossy by adding a bump map). He said ‘no’ even though I thought it was almost an automatic byproduct.
Therefore, if vray doesn’t account for that, I suppose it means we should be adding fresnel maps to our glossiness map slot too? I guess?
:?:
I was playing with just this after reading Thorsten’s post, works great after adjusting the curve a bit in the fresnel falloff map. Great for rough paint or plastics too. Just uncheck “overide material ior” and it adjusts along with the reflection ior.
Mind posting an image as an example? I’m a bit lost.
But why just these materials? -- rough paint or plastics -- Shouldn’t this fresnel function apply to anything with a degree of glossiness? Isn’t that what makes something ‘glossy’ -- an inherent roughness in the surface. Whether it’s slightly rough or very rough -- it seems the ‘parallel compression effect’ would still occur to some extent.
I did not mean just those, as I look around the room here I see the reflections behaving like this all around, even my waxy drink cup…
Pailhead, I’ll see if I can get the time to show something.
have been looking again at the doorknob in the reflectivity lab..
- still not sure about the glossiness changing, it is a smooth highly shiny surface, but one thing that adds to the illusion is that, head on, all I can see is my face - which is stretched out - but at the sides of the knob I can see the room walls, a window, another door, very like a fisheye lens, and
these are compressed into a small area and as a result appear pin sharp
as I said I mostly do without fresnel for chrome /stainless - full reflection gives a more ‘bling’ look which suits the design style on those projects