Fresnel reflection to dark?

[Micha_cg]

Hi,

often I have the serious problem, that I have the feeling, the fresnel reflection is to dark. It is not possible to increase the reflection intensity per standard multiplier. Changing the IOR makes no sense, because the material get a light metalic look.

I ask me, how could we test the current fresnel? Is it realy working right?

I have found a way to increase the fresnel intensity and to keep the plastic look - take two reflection layers with IOR 1.55. It help to get the look I want to get.

Should a plastic material with IOR 1.55 give us a total reflection at the "edges" of a sphere?

Here an example: left double reflection layer - right single layer. Two spheres in a white environment and a big ring around.

[joe_b]

Fresnel reflection to dark?

I don't know that a multiplier truly makes sense in the case of using a Fresnel texture on a reflection map. The reflection color and map is essentially used like transparency. If the reflection color is white then no light gets through ( so its equivalent to a black color for other transparencys ). To get this equivalency I use the white complement on whatever value is in the reflection color / map slot. So when you apply a multiplier to your texture, for simplicity lets say its just an AColor texture with a a white color and a multiplier of 2, the final color applied will be ( 1.0f - 2.0f, 1.0f - 2.0f, 1.0f - 2.0f ). As you can see this yields a negative color. The error in my way of evaluating is I suppose I should be clamping to 0,0,0. This probably explains your problems with multipliers on fresnel. For now I would suggest not using them because they aren't doing what you are expecting them to do. The "transparency", or amount of light the reflection allows to go to layers beneath, only really makes sense between Black and White. The total of light going through this layer is limited to the range of None -> All. You can't have less than none, you can't have more than all. I hope this make sense.

Again, I blame this on my UI. However, I can't assume its only being used in one map slot so disabling the texture multiplier outright for fresnel textures may not make sense. I'm up for suggestions though.

If after this explanation you still feel something is not right - I can ask Vlado to look into your example as he would have a better eye for technical issues on his end.

[Micha_cg]

Fresnel reflection to dark?

Thank you Joe for the background infos.

I will devide my question in smaller ones. A part of my problem could be, that the Fresnel dosn't show anywhere 100% of reflection. The maximum looks to less intensiv. I'm not sure that fresnel will reflect 100% of the environment in flat view angle, but maybe we find here an evidence for my "bad feeling" about the fresnel reflection. Can fresnel produce a 100% total reflection?

My current project is a yacht. The dark colored windows on the top has not reflect the environment like I have expected. So I have test my new double fresnel layer trick and it looks better. I suppose so, this trick dosn't ignore the 100% rule.

[joe_b]

Fresnel reflection to dark?

The fresnel texture blends the reflection color and refraction color based on the fresnel coefficient calculated. This is meant to calculate the reflected/refracted intensity ratio. In our UI the one that defaults to white is the reflection color and the one that defaults to black is the refraction color. So the final color at any point can be written as...

final_color = fresnel * reflect_color + (1.0f - fresnel ) * refract_color

The fresnel coefficient will be 0 when there is pure refraction. It will be 1 when there is total internal reflection. Based on this information, a "100% reflection" would be when there was 100% of the reflect_color, which would be when the fresnel coefficient was 1 (total internal reflection).

I will look into this further to see if I'm overlooking anything.

[edit]
As an afterthought - you also will never reach that 100% reflectivity if your reflection color is not white.

[Micha_cg]

Fresnel reflection to dark?

Will be the fresnel coefficient 1 at the "edge" of a sphere? Here a new example. Open the image in photoshop and look at the sample values: environment 245 - left sphere max 238 - right sphere max 201. If fresnel would be 1and we would get total reflection than we should get a reflected value of 245 or?

[joe_b]

Fresnel reflection to dark?

I'll have Vlado look at this thread - perhaps he can weigh in more on the subject.

[Micha_cg]

Fresnel reflection to dark?

Here an example: both HDRI environments are set at the same intensity and the materials are using double reflection layers. Is it wrong looking? I like it.

[joe_b]

Fresnel reflection to dark?

Are both your reflection layers the exact same? If you don't mind - could you send me that scene( along with hdrs, etc ). If its large you can upload it to ftp://asgvis.com/incoming . Thanks

[Micha_cg]

Fresnel reflection to dark?

You can find all at the current material user tutorial. Yes, both layers per material are the same - fresnel and glossiness.

[vlado]

Re: Fresnel reflection to dark?

It is not possible to increase the reflection intensity per standard multiplier.

It is possible in general, in the same way that you have a "multiplier" for the glass fog value. It is actually a power value, not a multiplier, but it may do what you need. In your case, adding two reflection layers with the same fresnel value is the same as using the square of the fresnel function.

Best regards,
Vlado

[Micha_cg]

Fresnel reflection to dark?

Vlado, I'm confused now. My question is: does the fresnel work right now or not? My experience says me, it could be show more reflection. If you say it works well so, than I must live with it and would wish from Joe a "doublicate layer" for the reflection layer.

What did you think about my last test? If I use Fresnel 1.55 and full reflection, should I get more reflection on the "edges" of the sphere or not? What says the theory? Is it not a total reflection what I can expect?

[joe_b]

Fresnel reflection to dark?

...would wish from Joe a "doublicate layer" for the reflection layer.

I could also just change how the multiplier is applied to the Fresnel texture - as Vlado said I should be applying it as a power.

[Micha_cg]

Fresnel reflection to dark?

So if I need more intensity, than I could set the multiplier at 2. This would help me a lot.

[vlado]

Fresnel reflection to dark?

Vlado, I'm confused now. My question is: does the fresnel work right now or not?

I followed the formula in a physics book, which I hope was correct Other than that, everything is more or less subjective. The formula is mainly for things like glass. Plastics probably do not follow the same Fresnel law exactly.

Best regards,
Vlado

[Micha_cg]

Fresnel reflection to dark?

Good, so it would be nice to leave the phsical correctness and to boost values.

I suppose so, that the color mapping of the human eye has a big influence to the visibility of light fresnel reflections. If I look around, I see very light fresnel reflections often, but if I close my eyes a little, than the reflections are gone. Could be good to have the artistic freedom to leave the physic and for example to get 120% reflection.