Dispersion without dispersion

[robcat2075]

Dispersion is how refraction bends the different colors of white light differently causing the color fringing you see in prisms, cheap camera lenses and other irregularly shaped transparent objects.

 

This is an attempt to simulate it by changing the Index of refraction of the glass material as the color of the light is swept across the spectrum during a multipass render. I also moved the light to fringe the shadow a bit.

 

 

 

This is not a fast process, but if you need dispersion, it can be done.

[John Bigboote]

This is not a fast process, but if you need dispersion, it can be done.

 

Truth be told...before today I had never even HEARD the word 'dispersion'! But now I know what it is, and I appreciate the example. I wonder where you learned this one? LOVE to see it under a moving camera circumstance, but that's me...motion is my bag.

[photoman]

Certain shaders from some other programs have ways of doing physically accurate aberation from refraction. I wonder if it would be possible to have a shader in A:M do that without a multipass setup?

 

Photoman

[robcat2075]

I wonder if it would be possible to have a shader in A:M do that without a multipass setup?

 

Short answer... yes, a shader could do that, i think, but someone would have to write it. I don't know that it would be any faster.

 

A long time ago Marcel Bricman put for the this technique, but its also a muti-pass technique and requires his gradient plugin which may not be available now.

 

 

My experiment is based on Jeremy Birn's suggestion of changing the IOR of the glass while the renderer did the R, G and B channels. A:M doesn't actually do the R G and B at separate times so you can't key IOR for them. Using multipass and keying the light to change color is about the same thing in practice.

[dblhelix]

but, how is this done?

when rendering, a:m goes mute. you can't operate the program not even to just scroll a window.

there's something i'm not getting, right?

[Fuchur]

but, how is this done?

when rendering, a:m goes mute. you can't operate the program not even to just scroll a window.

there's something i'm not getting, right?

 

I'd say, he is changing the lightcolor that fast, that it doesn't take one frame. (you can scale the color-animation to less than a frame.

It is the same method that is used to create softshadows with a very fast light and multipass.

 

But this is a very nice found... will have to see how well it works.

Thank you very much robert!

 

See you

*Fuchur*

[robcat2075]

If you have multi pass on and motion blur set to 20% then you need to key your light change to happen from 0:00 to 0:00.2

 

Yes that's less than a frame and yes, you can type in fractional time values like 0.2 to set to cursor to 0:00.2

 

 

Does that clear it up?

[dblhelix]

you can type in fractional time values like 0.2 to set to cursor to 0:00.2

 

1) wow.

 

2) now you're telling me!

 

3) this is operating the timeline in time not by frame?

 

4) if i set start frame to fractional value in an animation, will this "push" step count so that the fraction is maintained throughout? (nope, testing on my own sounds scary! how'd you ever think of doing something like this?)

[robcat2075]

3) this is operating the timeline in time not by frame?

 

It's going to a time that is not an exact frame. But Next frame /Prev frame will still go to whole frames.

 

4) how'd you ever think of doing something like this?)

I saw that scaled keyframes would get fractional values in their properties, so i tried typing one in directly.

[robcat2075]

Thinking about the light sweeping some more, I had trouble getting the R G and B correctly balanced, because I was continuously sweeping them.

 

Perhaps a more accurate way would be to step them . do the full R value for one third, the full green value for one third and then the blue for one third

[jason1025]

Dispersion is how refraction bends the different colors of white light differently causing the color fringing you see in prisms, cheap camera lenses and other irregularly shaped transparent objects.

 

This is an attempt to simulate it by changing the Index of refraction of the glass material as the color of the light is swept across the spectrum during a multipass render. I also moved the light to fringe the shadow a bit.

 

 

 

This is not a fast process, but if you need dispersion, it can be done.

 

 

I could be wrong but in the SPFX / film world I have always here'd this revered to as chromatic aberration. This is a sought after look in a trend where lens flares and shaky cameras are all the rage.

 

 

Can you post the settings to make this happen?

[robcat2075]

Here's an example that steps the light. A bit on the red side.

 

glass04_Dispersion.prj

 

 

 

The light is set to step from Red to Green to Blue at

 

0:00.0

0:00.7

0:00.14

 

and motion blur was set to 21% (easily divisible by 3), multi pass ON

 

 

Chromatic aberration and Dispersion are different names for the same thing , I think. One for lenses, one for non-lenses.

[agep]

Here's an example that steps the light. A bit on the red side.

 

This looks absolutely wonderful!

[NancyGormezano]

Have to agree - looks terrific!

[zandoriastudios]

Nice! I recently read Goethe's "Theory of Colors", and even bought a glass prism--but I never thought of trying to do it with a rendering!

[robcat2075]

It's a slight effect, but interesting.

 

For more accuracy one will likely want to study some reference photos of real glass to see where the effect should and shouldn't be. But it looks like the basic elements are there for the using.