Thin plastic chair - Ghost = How?

[ecximer]

scene

[Ondra]

ok, the scene is fine, no bug there. There is slight color shift after the colored refraction, because Corona uses internally different color space than RGB, so you get something like 0.59 -0.01 0.01. Multiply it by 100 (because the light is very strong), you get 59, -1, 1. Clamp it, and you get 1, 0, 1.

[ecximer]

And what You Ondra suggest to do in such cases?
And it will be used very often - a color plafond of lamps.
How to set up?

vray: no problem.....

[Ondra]

best would be to use better colormapping/lower intensity of the light. If that is not possible, try tweaking the shade color, smallest changes could make significant differences

[ecximer]

It is called "crutches"
It isn't convenient for work - to guess in 0,000001 without knowing will help or not... It is a pity. :(

[vicnaum]

Why is it negative? The -0.01

The source glass colour is 255 30 30. There is green there. Why there is no green when it's lit up? (there's even negative green)

[Ondra]

Because Corona internally does not work in RGB. See here: http://forum.corona-renderer.com/index.php/topic,60.msg207.html#msg207

[ecximer]

I ask me to forgive, for my stupidity, but it isn't normal:

[Ondra]

I dont exactly know what are the two setups, but I would suggest starting by turning diffuse color off (unless you actually want it there)

[ecximer]

At the left from below - diffusion color 0 0 0 - you see, as there is any imbalance?
Why I shall set up color at random?
In an example what to receive RED, I shall set color of refraction by the ORANGE. ?

[vicnaum]

The setup is simple:
1) A plane Emitting light (Multiplier: 1500) with a gradient (from RGB(1 0 1) to RGB(254 254 253)
2) A thin red film (made with a Plane), and a thin red box (made with a Box), with Material like this one: http://www.naumik.com/temp/scr4/20130620-552-65kb.jpg (Red color is: 172 2 1)
3) Several Refraction modes (onesided, twosided, hybrid), and different Exposure compensation.

Here is what is expected in reality:

And here's what Corona renders:

Plane, Onesided (solid):
+1EV: http://www.naumik.com/temp/scr4/20130620-1k4-164kb.jpg
+8EV: http://www.naumik.com/temp/scr4/20130620-haw-162kb.jpg

Plane, Twosided (thin):
+1EV: http://www.naumik.com/temp/scr4/20130620-7ul-320kb.jpg
+8EV: http://www.naumik.com/temp/scr4/20130620-t02-138kb.jpg

Plane, Hybrid (Solid w/o shadows):
+1EV: http://www.naumik.com/temp/scr4/20130620-h80-313kb.jpg
+8EV: http://www.naumik.com/temp/scr4/20130620-3as-151kb.jpg

---

Box, Onesided (solid):
+1EV: http://www.naumik.com/temp/scr4/20130620-41a-288kb.jpg
+ManyEV: http://www.naumik.com/temp/scr4/20130620-7u0-168kb.jpg

Box, Twosided (thin):
+1EV: http://www.naumik.com/temp/scr4/20130620-pml-307kb.jpg
+ManyEV: http://www.naumik.com/temp/scr4/20130620-5f3-195kb.jpg

Box, Hybrid (Solid w/o shadows):
+1EV: http://www.naumik.com/temp/scr4/20130620-w97-316kb.jpg
+ManyEV: http://www.naumik.com/temp/scr4/20130620-h91-180kb.jpg

As you can see - when using a simple one-sided Plane - everything works like in reality.

But if you use something solid, like a box - then Green is running deeply in negative numbers, and you NEVER get white, even if you make a 1000000 multiplier and +1000000 Exposure compensation, cause when you make it brighter - green channel becomes even darker (?!).

To me - this is absolutely WRONG, no matter what color space is used internally - XYZ, Lab, HSB, etc. It shouldn't act like that.
I think there is some tricky little error somewhere in volume refractions calculations...


--------

Also repeated the test using ordinary CoronaLights, and a simple Plane, Onesided (solid):

6500K: http://www.naumik.com/temp/scr4/20130620-264-115kb.jpg
5000K: http://www.naumik.com/temp/scr4/20130620-172-312kb.jpg
4500K: http://www.naumik.com/temp/scr4/20130620-x8q-131kb.jpg

As you can see - if the light temperature is 5000K or lower - it also cannot give white overexposure no matter what, even with a Plane.

Tricky...

Btw, in the video test above there are all kinds of lamps (in order of appearance):
 1) Circular = 6800K
 2) Piramydal = 4000K
 3) Simple tubeal on a wire = 2600K
 4) Spherical = 4000K
 5) Flashlight = 6000K

But each and every one of them gave me Red/Purple/Yellow/White transition on over-exposure through Red film.

If I make the red film less red (by rising the G/B colors to 10-15, and lowering the red to 150) - then transitions work to white with Plane, but not with a Box.
To get white overexposure on Box - I need to make it something like (100, 39, 25), but this is no longer a Red...

------

Taking this a bit further:

Set the Refraction map like this:


The gradient goes from 255 full-Red on the left, to 0 Red on the right.
Also G/B channels are added from 0/0 in the top to 255/255 G/B in the bottom.

And no matter of the Light color temp, we have a clear line, where green goes negative:



Taking this to Photoshop, we can see where the "non-overexposure" border exactly goes:


This test is made with a Box, Onesided (solid). The color temp of CoronaLight doesn't shift this border anyhow, so it doesn't matter.

So, if you make the Refraction color above the line - it will give you violet when overexposure. If below - then it will give you normal overexposure.
So the most red glass you can have passing the light normally is (255, 75, 75). Making G/B lower will lead to violet.

Here's the (255, 75, 75) Box:


As you can see - there is still negative green on the sides (resulting in violet color). So the problem is not completely solved.

Also, two boxes one on top of another give the same violet, so color works only if the object is one:

[Polymax]

Keymaster, what do you think about this research?