I wanted to get smoother transisions (no "banding")
between the different colours in a pigment color_map.

A macro I made generates the different colour entries
for the color_map.

Here's two images rendered with the code below.

Any comments ?

Are there other ways to get smooth transitions 
between colours in a color_map ?


Tor Olav
--
mailto:tor### [at] hotmailcom
http://www.crosswinds.net/~tok/tokrays.html


// ===== 1 ======= 2 ======= 3 ======= 4 ======= 5 ======= 6 ======= 7

#version 3.1;

// ===== 1 ======= 2 ======= 3 ======= 4 ======= 5 ======= 6 ======= 7

#macro Bezier(TT, StartPoint, StartVector, EndPoint, EndVector)

  #local aa =  2*StartPoint - 2*EndPoint + 3*StartVector - 3*EndVector;
  #local bb = -3*StartPoint + 3*EndPoint - 6*StartVector + 3*EndVector;
  #local cc =  3*StartVector;
  #local dd =  StartPoint;

  (((aa*TT + bb)*TT + cc)*TT + dd)
  
#end // macro Bezier

// ===== 1 ======= 2 ======= 3 ======= 4 ======= 5 ======= 6 ======= 7

#declare FirstColour    = <0.5, 0.0, 0.0>;
#declare FirstDirection = <4.0, 1.0, 0.0>;
#declare LastDirection  = <0.0, 1.0, 1.0>;
#declare LastColour     = <0.0, 0.0, 0.5>;
#declare Bright = 0.3;

/* // Also try this
#declare FirstColour    = <  2,  0,   0>;
#declare FirstDirection = <  0,  2,   0>;
#declare LastDirection  = <  0, -1,   1>;
#declare LastColour     = <  0,  0,   1>;
#declare Bright = 0.5;
*/

#declare NrOfEntries = 100; // min 2, max 256
 
#declare BezierMap = 
color_map {
  #declare TT = 0;
  #while (TT < 1)
    [ TT rgb Bright*Bezier(TT, 
                           FirstColour, FirstDirection, 
                           LastDirection, LastColour) ]
    #declare TT = TT + 1/NrOfEntries;
  #end // while
}

#declare BezierPigment =
pigment {
//  bozo
  gradient y
  turbulence 0.3
  color_map { BezierMap }
}

sky_sphere { pigment { BezierPigment } }

light_source { <0, 0, 0> color 1.5*<1, 1, 1> }

camera {
  location <1, 0, 0>
  look_at <0, 0, 0>
  angle 120
}                                                    

// ===== 1 ======= 2 ======= 3 ======= 4 ======= 5 ======= 6 ======= 7

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Attachments:
Download 'bezierpigment02.jpg' (11 KB) Download 'bezierpigment03.jpg' (9 KB)

Preview of image 'bezierpigment02.jpg'

Preview of image 'bezierpigment03.jpg'

"Tor Olav Kristensen" <tor### [at] hotmailcom> wrote in message
news:3937D74E.8B3772EB@hotmail.com...
|
| I wanted to get smoother transisions (no "banding")
| between the different colours in a pigment color_map.
|
| Are there other ways to get smooth transitions
| between colours in a color_map ?

By using 'sine_wave' in it, if I understand right.

Bob

Post a reply to this message

"Bob Hughes" wrote:
> "Tor Olav Kristensen" wrote:
> | I wanted to get smoother transisions (no "banding")
> | between the different colours in a pigment color_map.
> |
> | Are there other ways to get smooth transitions
> | between colours in a color_map ?
>
> By using 'sine_wave' in it, if I understand right.

That only works if you have 2 colors in the color_map only.
One color at 0.0 and the other at 1.0

Currently the linear interpolation between colors are the only one available
as far as I know. (The different wave-types does not change this.)

Greetings,

Rune

---
Updated April 25: http://rsj.mobilixnet.dk
Containing 3D images, stereograms, tutorials,
The POV Desktop Theme, 350+ raytracing jokes,
miscellaneous other things, and a lot of fun!

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Tor Olav Kristensen wrote:
> 
> Any comments ?
>

I'd like to see some way to specify color_map indices in the macro call.
Perhaps have the macro take an array as a parameter. Something like:

array[6][Number of indices]
{
{Position, StartP, StartV, EndP, EndV, Nr_of_entries},
{Position, StartP, StartV, EndP, EndV, Nr_of_entries},
...
}

> Are there other ways to get smooth transitions
> between colours in a color_map ?
> 

MegaPOV has built-in spline functions. They work very much like your
macro, but IIRC only linear and cubic splines are supported. The basic
method would still have to be the same, though.

Margus

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"Rune" <run### [at] inamecom> wrote in message
news:39384b26@news.povray.org...
| "Bob Hughes" wrote:
| > "Tor Olav Kristensen" wrote:
| > | I wanted to get smoother transisions (no "banding")
| > | between the different colours in a pigment color_map.
| > |
| > | Are there other ways to get smooth transitions
| > | between colours in a color_map ?
| >
| > By using 'sine_wave' in it, if I understand right.
|
| That only works if you have 2 colors in the color_map only.
| One color at 0.0 and the other at 1.0
|
| Currently the linear interpolation between colors are the only one available
| as far as I know. (The different wave-types does not change this.)

Good point.  A 'blend' keyword would be great.

Post a reply to this message

"Bob Hughes" wrote:
> "Rune" wrote:
> | "Bob Hughes" wrote:
> | > "Tor Olav Kristensen" wrote:
> | > | I wanted to get smoother transisions (no "banding")
> | > | between the different colours in a pigment color_map.
> | > |
> | > | Are there other ways to get smooth transitions
> | > | between colours in a color_map ?
> | >
> | > By using 'sine_wave' in it, if I understand right.
> |
> | That only works if you have 2 colors in the color_map only.
> | One color at 0.0 and the other at 1.0
> |
> | Currently the linear interpolation between colors are the
> | only one available as far as I know. (The different
> | wave-types does not change this.)
>
> Good point.  A 'blend' keyword would be great.

I agree, that would be a very nice feature.

Greetings,

Rune

---
Updated April 25: http://rsj.mobilixnet.dk
Containing 3D images, stereograms, tutorials,
The POV Desktop Theme, 350+ raytracing jokes,
miscellaneous other things, and a lot of fun!

Post a reply to this message

Margus Ramst wrote:
> 
> I'd like to see some way to specify color_map indices in the macro call.
> Perhaps have the macro take an array as a parameter. Something like:
> 
> array[6][Number of indices]
> {
> {Position, StartP, StartV, EndP, EndV, Nr_of_entries},
> {Position, StartP, StartV, EndP, EndV, Nr_of_entries},
> ...
> }

Would this be for assembling the color_map from several 
Bezier coloured "bands" ?


> > Are there other ways to get smooth transitions
> > between colours in a color_map ?
> 
> MegaPOV has built-in spline functions. They work very much like your
> macro, but IIRC only linear and cubic splines are supported. The basic
> method would still have to be the same, though.

Useful feature !


Thank you for answering.

Tor Olav
--
mailto:tor### [at] hotmailcom
http://www.crosswinds.net/~tok/tokrays.html

Post a reply to this message

Tor Olav Kristensen wrote:
> 
> Would this be for assembling the color_map from several
> Bezier coloured "bands" ?
> 

Yes. To go, let's say, from blue to red to green in your colour map.

-- 
Margus Ramst

Personal e-mail: mar### [at] peakeduee
TAG (Team Assistance Group) e-mail: mar### [at] tagpovrayorg

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