Inspired by some images posted in this group lately, I decided to make my
own reflection image,
I had a lot fun, rendering in 100x120 etc. This is reflective spheres in a
reflectiv sphere...
Is this the "trick" behind the images posted by mr. Nospam and the rest of
you ?

Anyway, Im pretty pleased by the image, it looks kind of interesting..
Especially near the bottom
left and bottom right, where there are some non sphere shapes for sure! too
bad the renering
time is so horrbile, I also did nothing to the "max trace levels", should I
do that ?

Tech, details : Render time: 1:47:51 (AMD K6-II 64MB Ram.)
Peak memory: 8MB
Reflected rays: 98,400,000 :-) Don excactly know what this number is, but It
looks impresive.
Jpeg compression: 20 (PSP, looks okay!)


Technical question, might be a stupid one, but Ill fire anyway (I have NO
pride to lose! Never had..)

Q1) I suspect the answer is YES from observation, but I wonder why.... Why
does pigments affect
100% reflecting surfaces ? If I had a red texture, with 100% reflection, it
would look different
than a blue texture with 100% reflection, or ??? Are there any use at all to
have a pigment for example
when using 100% reflective surfaces ?


Q2) In Real life, reflection increases when the viewers angle with with a
plane decreases, right ? (My physics might
be a little rusty, long time ago..) Does povray or other raytracers support
this ?

How's the Horror images coming along for people ?~

Have fun!

Glenn.

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Attachments:
Download 'reflect-20.jpg' (74 KB)

Preview of image 'reflect-20.jpg'

>Why does pigments affect 100% reflecting surfaces?<
Not really sure...but I have a modified version of POV that I am working
on that allows you to use a separate pigment for calculating reflection.

>In Real life, reflection increases when the viewers angle with with a
plane decreases, right ?<
This happens with many substances, water, for example. There is an
unofficial version called WyzPov that does have it, along with things
like blurred reflection. WyzPov is included in the Superpatch version of
POV-Ray, which has a lot of additional features, and is available here:
http://www2.fwi.com/~parkerr/superpatch/
WyzPov, and a good tutorial for making water, is here:
http://www.worldaxes.com/paul_fam/wyzpov/INDEX.HTM

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Glenn Bech wrote:
> 
> Q1)

The pigment of the surface is added to the reflected colour. So rgb
<1,0,0> reflection 1 is not a pure red mirror. A pure red mirror would
be rgb <0,0,0> reflection <1,0,0>
> 
> Q2) In Real life, reflection increases when the viewers angle with with a
> plane decreases, right ? (My physics might
> be a little rusty, long time ago..) Does povray or other raytracers support
> this ?
> 

The variable reflection patch (also included in the superpatch) does
this. It has two models. In the first one, where you simply specify the
minimum and maximum reflection and an optional falloff rate. The second
one uses the Fresnel reflectance function, which calculates reflection
based on ior. It is more accurate, but only works correctly with
transparent materials.
I've seen an implementation of the Fresnel model that works for both
dielectrics and metals, but that too required an ior value (copper was
something like 0.83). The result was extremely realistic metal surfaces.

Margus

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----- Original Message -----
From: Glenn Bech <130### [at] swineduau>

> Q1) I suspect the answer is YES from observation, but I wonder why.... Why
> does pigments affect
> 100% reflecting surfaces ? If I had a red texture, with 100% reflection,
it
> would look different
> than a blue texture with 100% reflection, or ??? Are there any use at all
to
> have a pigment for example
> when using 100% reflective surfaces ?

    How it works (I think this is all correct): "Reflection 1" is not "100%
of what you see is reflection" but "Adds 100% of the reflected image into
the mix".

    So "Reflection 1 diffuse 1"  [you get diffuse 1 or close to it by
default, if you don't specify it to be less] means

    Light from object is 100% of reflected image + 100% of (diffuse lighting
* color)

    "Reflection 1 diffuse 1 ambient 1" means

    Light from object is 100% of reflected image + 100% of (diffuse lighting
* color) + 100% of color

    This means that such an object will typically give off more light than
hits it, which is why "hall-of-mirrors" scenes tend to get so bright. The
objects are, as it were, "lasing"! A ray bouncing off four "diffuse 1
reflection 1" mirrors will consist of:


    After first object (assumed lit but not reflecting): diffuse light1 *
color1

    After second mirror: (diffuse light 1 * color 1 ) * 100% reflection +
diffuse light 2*color 2

    After final mirror:

(((diffuse light 1 * color 1 ) * 100% reflection + diffuse light 2*color
2)*100% reflection + diffuse light 3 * color 3) * 100% reflection + diffuse
light 4 * color 4.  This is the same as "color1 + color2 + color3 + color
4", usually white!


    As a real mirror does not emit energy, it follows that whoever would
create a realistic raytraced mirror should always ensure that
ambient+diffuse+reflection <= 1.0.  If you don't want realism, do what you
like!

    -Robert Dawson

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>The pigment of the surface is added to the reflected colour. So rgb
><1,0,0> reflection 1 is not a pure red mirror. A pure red mirror would
>be rgb <0,0,0> reflection <1,0,0>


I thought it was the fact that the surface absorbs all other frequencies
than red, and all red incoming light is reflected. I believe that it is the
color model that makes the topic a bit fuzzy. If one could model the light
as a collection of frequencies rather than only <r, g, b>, we could get
simpler modelling. But I am not sure.

As for the secont question: Yes, light is reflected more perfectly at acute
incoming angles. I believe it is very difficult to model accurately. You
would have to supply several parameters, like the reflection rate when the
incoming ray is perpendicular to the surface normal (this would never
happen, though...), the rate of reflection when the incoming ray is
parallell to the surface normal, and so forth. That is, if it is not a clear
relation between the values that are "universal." I have thinked of it,
myself, but I haven't come across any papers on the phenomena. Anyone?

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Simen Kvaal wrote:
> 
> >The pigment of the surface is added to the reflected colour. So rgb
> ><1,0,0> reflection 1 is not a pure red mirror. A pure red mirror would
> >be rgb <0,0,0> reflection <1,0,0>
> 
> I thought it was the fact that the surface absorbs all other frequencies
> than red, and all red incoming light is reflected. I believe that it is the
> color model that makes the topic a bit fuzzy. If one could model the light
> as a collection of frequencies rather than only <r, g, b>, we could get
> simpler modelling. But I am not sure.

The person doing the light model would have to have considerable knowlege
of light and light frequencies and I doubt the "average" Pov user would
want to go to the trouble of learning it for simple color operations.
 
> As for the secont question: Yes, light is reflected more perfectly at acute
> incoming angles. I believe it is very difficult to model accurately. You
> would have to supply several parameters, like the reflection rate when the
> incoming ray is perpendicular to the surface normal (this would never
> happen, though...), the rate of reflection when the incoming ray is
> parallell to the surface normal, and so forth. That is, if it is not a clear
> relation between the values that are "universal." I have thinked of it,
> myself, but I haven't come across any papers on the phenomena. Anyone?

You will find more information on incident angles of reflection in
photography texts. It has been well researched and documented. You
might try a search of online siggraph papers at:

http://w3imagis.imag.fr/Membres/Fredo.Durand/Book/sig98.html


-- 
Ken Tyler
1100+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html

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>
>You will find more information on incident angles of reflection in
>photography texts. It has been well researched and documented. You
>might try a search of online siggraph papers at:
>
>http://w3imagis.imag.fr/Membres/Fredo.Durand/Book/sig98.html
>


Cheez. Thanks. :) *drool*

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I usually follow the rule that
ambient + diffuse + reflection = albedo of the surface

The logic is simple: all these model some form of reflection, with
'specular' simulating a near-specular reflection of the light source and
should therefore be roughly equal to 'reflection'.
If the equation falls short of 1 it means some of the light is absorbed
(which is true for most surfaces).

Margus

Robert Dawson wrote:
> 
>     This means that such an object will typically give off more light than
> hits it, which is why "hall-of-mirrors" scenes tend to get so bright. The
> objects are, as it were, "lasing"! A ray bouncing off four "diffuse 1
> reflection 1" mirrors will consist of:
>

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Glenn

This is a beautiful image, and will be my wallpaper very
soon.

The image has a hand painted feel to it in some areas, I
think that this is quite hard to come by especially for this
type of image. 


-- 
Cheers
Steve              email mailto:sjl### [at] ndirectcouk

%HAV-A-NICEDAY Error not enough coffee  0 pps. 

web http://www.ndirect.co.uk/~sjeln/

or  http://start.at/zero-pps

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>This is a beautiful image, and will be my wallpaper very
>soon.


Wow, Milestone for me .-) Nobody EVER said that they wanted to put
one of my images on their desktop, thanks! (smile)

Regards,

Glenn.

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