A version of this has been floating around on the web (google image search
"same color illusion") and I felt like making a raytraced version. (This
might have already been shown here, or even already raytraced by someone
else.)

I used a parallel light source to ensure exact uniform lighting.

I'm not sure mine is as baffling as the original, but maybe that's just
because I've been staring at it too long...

 - Slime
 [ http://www.slimeland.com/ ]

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And to help see it...

 - Slime
 [ http://www.slimeland.com/ ]

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Wow, that's pretty cool.  I would have bet they were different colors,
even though I understand why our eyes see the shades differently.  I
actually had to open it in Gimp to see if you were trying to fool us!
;-)  The colors are definitely the same, though.  I like it.


Kyle

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"Slime" <fak### [at] emailaddress> wrote:
> A version of this has been floating around on the web (google image search
> "same color illusion") and I felt like making a raytraced version. (This
> might have already been shown here, or even already raytraced by someone
> else.)
>
> I used a parallel light source to ensure exact uniform lighting.
>
> I'm not sure mine is as baffling as the original, but maybe that's just
> because I've been staring at it too long...
>
>  - Slime
>  [ http://www.slimeland.com/ ]

The illusion is not new to me. But the thing is, that how did you do it with
pov-ray?!?
By trial and error (I hope not)? :)


My civ3-units - modelled and animated with pov-ray:
http://forums.civfanatics.com/showpost.php?p=2036938&postcount=4

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> The illusion is not new to me. But the thing is, that how did you do it
with
> pov-ray?!?
> By trial and error (I hope not)? :)

I just had to make sure that POV-Ray's lighting calculations would create
the same colors. So I wanted

dark square color * (light source color * cos(angle to light) * surface
diffuse + surface ambient) = light square color * surface ambient

To simplify this, I made the light source color 1/cos(angle to light):

dark square color * (surface diffuse + surface ambient) = light square color
* surface ambient

I also required that the diffuse + ambient = 1:

dark square color = light square color * surface ambient

So then I was able to choose any diffuse/ambient values as long as they
summed to 1, and as long as the dark square color was the same as the light
square color times the ambient value.

I guess I made this seem pretty complicated. in my head it was a lot
simpler, like "If I make sure the amount of light hitting the surface is
exactly 1, and the color of the dark square is the same as the ambient
light, it will work."

 - Slime
 [ http://www.slimeland.com/ ]

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> I guess I made this seem pretty complicated. in my head it was a lot
> simpler, like "If I make sure the amount of light hitting the surface is
> exactly 1, and the color of the dark square is the same as the ambient
> light, it will work."

To a genius, everything is simple. :)

This is one of the most powerful optical illusions I've ever seen. I first
saw it on Pickover's "Reality Carnival" page.

>
>  - Slime
>  [ http://www.slimeland.com/ ]

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Slime wrote:
> A version of this has been floating around on the web (google image
> search "same color illusion") and I felt like making a raytraced
> version. (This might have already been shown here, or even already
> raytraced by someone else.)
>
> I used a parallel light source to ensure exact uniform lighting.
>
> I'm not sure mine is as baffling as the original, but maybe that's
> just because I've been staring at it too long...

It certainly looks pretty good to me.

FYI I have this page bookmarked:

http://www.michaelbach.de/ot/index.html

Has a lot of illusions with good explanations.

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Among other things, Slime saw fit to write:

> A version of this has been floating around on the web (google image search
> "same color illusion") and I felt like making a raytraced version. (This
> might have already been shown here, or even already raytraced by someone
> else.)

Brilliant! I've seen a coloured version of this illusion somewhere. It had
two Rubik-like cubes under coloured light, it showed we perceive equal
colours when they're not and vice-versa. Could you do that? ;-)

-- 
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby

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"Slime" <fak### [at] emailaddress> wrote:
> I just had to make sure that POV-Ray's lighting calculations would create
> the same colors. So I wanted
>
> dark square color * (light source color * cos(angle to light) * surface
> diffuse + surface ambient) = light square color * surface ambient
>
> To simplify this, I made the light source color 1/cos(angle to light):
>
> dark square color * (surface diffuse + surface ambient) = light square color
> * surface ambient
>
> I also required that the diffuse + ambient = 1:
>
> dark square color = light square color * surface ambient
>
> So then I was able to choose any diffuse/ambient values as long as they
> summed to 1, and as long as the dark square color was the same as the light
> square color times the ambient value.
>
> I guess I made this seem pretty complicated. in my head it was a lot
> simpler, like "If I make sure the amount of light hitting the surface is
> exactly 1, and the color of the dark square is the same as the ambient
> light, it will work."
>
>  - Slime
>  [ http://www.slimeland.com/ ]

That is really excellent, and it's given me a few other ideas....don't know
if they'll work.

Thanks for the picture and the analysis.

Dave Matthews

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