I'm trying to find a website:  it had an excellent tutorial on turning flat
bitmaps of rocks into heightfields.  The guy also had an image gallery
with pictures of an indoor swimming pool (POV-Ray generated).
Sorry, that's really all I have to go on... anybody know this site?

- Doug Eichenberg
  http://www.getinfo.net/douge
  dou### [at] nlsnet

Post a reply to this message

Doug Eichenberg wrote:
>
> with pictures of an indoor swimming pool (POV-Ray generated).
> Sorry, that's really all I have to go on... anybody know this site?

I know this site. There is also that teapot picture from pov Hall of Fame.
http://www.kivisalo.net

K.K.

Post a reply to this message

Kari Kivisalo wrote:

>Doug Eichenberg wrote:
>>
>> with pictures of an indoor swimming pool (POV-Ray generated).
>> Sorry, that's really all I have to go on... anybody know this site?
>
>I know this site. There is also that teapot picture from pov Hall of
>Fame. http://www.kivisalo.net

I like your Level Connector. 
It makes me wonder, would something like this also be possible in 3d-
space? A level_connect warp? It would be nice in combination with Chris' 
object pattern and other colour list pigments.

Ingo

-- 
Photography: http://members.home.nl/ingoogni/
Pov-Ray    : http://members.home.nl/seed7/

Post a reply to this message

ingo wrote:
>
> I like your Level Connector.
> It makes me wonder, would something like this also be possible in 3d-
> space?

I like to think this as a simple electrical potential, so it can
be extented to 3d. Time and memory consumption would be too high
with the iterative method currently used. FFT would be more efficient
way to solve the potential field. I have to think about this :)

Just as in 2d the input and solution would be discrete. In 3d
that would be discrete volumes of densities. I can see this
had media applications but not sure if it can be used for surface
generation, maybe with isosurface functions.

Can someone lend me a Cray for the 3D FFT calculations :)

K.K.

Post a reply to this message

That's the one Kari!  (Nice site, BTW).  Thanks!

- Doug Eichenberg
  http://www.getinfo.net/douge
  dou### [at] nlsnet

Post a reply to this message

In article <39954523.5752D334@kivisalo.net>, Kari Kivisalo 
<kar### [at] kivisalonet> wrote:

> I like to think this as a simple electrical potential, so it can
> be extented to 3d. Time and memory consumption would be too high
> with the iterative method currently used. FFT would be more efficient
> way to solve the potential field. I have to think about this :)
> 
> Just as in 2d the input and solution would be discrete. In 3d
> that would be discrete volumes of densities. I can see this
> had media applications but not sure if it can be used for surface
> generation, maybe with isosurface functions.

This looks like it could be a useful enhancement for the proximity 
pattern(it could solve the grainyness problem)...or something to be 
applied to any pattern. Could you give more details on how you calculate 
it? I didn't see an in-depth explanation on the site.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

Post a reply to this message

Chris Huff wrote:
>
> Could you give more details on how you calculate
> it? I didn't see an in-depth explanation on the site.

Here is the theory on 2d electrical potential and how to obtain numerical
approximation using difference equations and iterations. This can be solved
with FFT also but I don't yet know how. Should be easy enough to find:
"solving poisson with fft". Numerical Recipes has nice code for 3D FFT
which calculates the solution in-place saving memory.

Laplace: u(xx) + u(yy) = 0
u(xx) = 2nd derivative of u over variable x

Here u is potential (hf height). x and y are hf coordinates.
Resulting difference formula in free areas (x,y) + 1 pixel boundary:

u(x+1,y) + u(x,y+1) + u(x-1,y) + u(x,y-1) = 4*u(x,y)

So basically the procedure is: Take surrounding 4 pixels and put
the average in the middle. Repeat for all free pixels (x,y). If
there are n free pixels the resulting linear system is n*5. I solve
this with Gauss-Seidel iteration.

More on this method in Advanced Engineering Mathematics by Kreyszig
in section Numerical methods for differential equations.


I sent this uncleaned code to the Terragen guy and he made it a new filter.

------------------------------------------------------------------
LevelConnector uses these pseudo functions to communicate with the
rest of the app.

  SetHeight(x, y, hv);      
  hv=GetHeight(x, y);
  Sel=GetSelValue(x, y); // is pixel selected
  PixV=HVToFloat(hv);    // convert from internal type to float
  hv=FloatToHV(PixV);    // convert to internal type


//def for the compare func used by bsearch
typedef int (*fptr)(const void*, const void*);

int compare(const int *a,const int *b)
{
  return(*a - *b);
}


// The main calculations. Processes data in u[].
// Solves this Laplace's 2nd order differential
// equation using Gauss-Seidel iteration.
//
//   d2u   d2u
//   --- + --- = 0 + (force, not used)  
//   dx2   dy2
//
// Can be solved by FFT also but this iterative method lets user control
// the accuracy of the solution. If all pixels are selected then this works
// like smooth with variable radius. Basically it just averages 4 adjacent
// pixels into the middle pixel :) Note however that one iteration pass uses
// uses 2 values per pixel already computed in that pass so it's a kind of
// cumulative smooth.

void SolveEquations(int **s, float *h, float *u, int Nodes, int maxiter)
{
  int i,c,dir=1,Node;
  float sum;

  for(i=0;i<maxiter;i++)
    {for(Node=(Nodes-1)*(1-dir)/2;dir*Node<=(Nodes-1)*(1+dir)/2;Node=Node+dir)
        { sum=h[Node];
          for(c=1;c<=s[Node][0];c++)
            sum=sum+u[s[Node][c]];
          u[Node]=0.25*sum;
        }
      dir=-dir;  // toggle direction
    }
}


// Prepares data for SolveEquations

void LevelConnector(int width,int height, int maxiter)
{
  int xo[4]={1,-1,0,0},yo[4]={0,0,1,-1};
  int c,Nodes=0,*NodeP,Node,PixN;
  int x,y,xt,yt,i,j,*Pos,**s;
  float *h,*u,Sel,PixV,k;

  // Count selected pixels
  for(y=0;y<height;y++)
    {for(x=0;x<width;x++)
       {if(GetSelValue(x, y) == SELECTED)
          Nodes++;
       }
    } 

  u=(float *)malloc(Nodes*sizeof(float)); // This is the actual height data
  h=(float *)malloc(Nodes*sizeof(float)); // aux data for equations
  Pos=(int *)malloc(Nodes*sizeof(int));   // Stores pixel positions of nodes
  s=(int **)malloc(Nodes*sizeof(int *));  // aux data for equations


  // clear arrays
  for(Node=0;Node<Nodes;Node++)
  { 
    s[Node]=(int *)malloc(5*sizeof(int));
    if (s[Node] == NULL) {perror("memory error");exit(1);}
    for(j=0;j<5;j++)
      s[Node][j]=0;
    u[Node]=0;
    h[Node]=0;
    Pos[Node]=0;
  }


  // Fill position table
  Node=0;PixN=0;
  for(y=0;y<height;y++)
    {for(x=0;x<width;x++)
       {Sel=GetSelValue(x, y);
        if(Sel == SELECTED)
          {Pos[Node]=PixN;
           Node++;
          }
        PixN++;
       }
    }


  // Make equations
  Node=0;PixN=0;
  for(y=0;y<height;y++)
    {for(x=0;x<width;x++)
       {if(GetSelValue(x, y) == SELECTED)
          {k=0;c=0;
	   for(i=0;i<4;i++)
             {yt=y+yo[i];
              xt=x+xo[i];
              if (yt == -1)      yt=height-1;
	      if (yt == height) yt=0;
	      if (xt == -1)      xt=width-1;
	      if (xt == width)   xt=0;
              hv=GetHeight(xt, yt);
              PixV=HVToFloat(hv);
              if(GetSelValue(xt, yt) != SELECTED)
                k=k+PixV;
              else
                {c++;
                 PixN=yt*width+xt;
	         NodeP=(int *)bsearch(&PixN,Pos,Nodes,sizeof(int),(fptr)compare);
                 if(NodeP == NULL)
                   {perror("error in bserch");
                    exit(1);
                   }
                 s[Node][c]=(int)(NodeP-Pos);
                }
	     }
           hv=GetHeight(x, y);
           u[Node]=HVToFloat(hv);
	   h[Node]=k;
	   // h[Node]=k-force;  past experiment
	   s[Node][0]=c;
	   Node++;
	  }
       }
    }

  SolveEquations(s,h,u,Nodes,maxiter);
  free(h);
  
  // Write data in u[] back to hf
  for(Node=0;Node<Nodes;Node++)
    { 
      free(s[Node]);
      hv=FloatToHV(u[Node]);
      x=Pos[Node]%width;
      y=Pos[Node]/width;
      SetHeight(x, y, hv);
    }
  
  free(s);
  free(Pos);
  free(u);
}

K.K.

Post a reply to this message

In article <3995801A.AC206C81@kivisalo.net>, Kari Kivisalo 
<kar### [at] kivisalonet> wrote:

> Here is the theory on 2d electrical potential and how to obtain 
> numerical approximation using difference equations and iterations. 
> This can be solved with FFT also but I don't yet know how. Should be 
> easy enough to find: "solving poisson with fft". Numerical Recipes 
> has nice code for 3D FFT which calculates the solution in-place 
> saving memory.

Thanks...it looks like it will take a while to analyze this and convert 
it to 3d, though. I guess it would help if I had some calculus...and 
don't expect a FFT solving method from me. :-)

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

Post a reply to this message

"Kari Kivisalo" <kar### [at] kivisalonet> wrote in message
news:3995801A.AC206C81@kivisalo.net...
> Chris Huff wrote:
> >
> > Could you give more details on how you calculate
> > it? I didn't see an in-depth explanation on the site.
>
> Here is the theory on 2d electrical potential and how to obtain numerical
> approximation using difference equations and iterations. This can be
solved
> with FFT also but I don't yet know how. Should be easy enough to find:
> "solving poisson with fft". Numerical Recipes has nice code for 3D FFT
> which calculates the solution in-place saving memory.
>
> Laplace: u(xx) + u(yy) = 0
> u(xx) = 2nd derivative of u over variable x
>
> Here u is potential (hf height). x and y are hf coordinates.
> Resulting difference formula in free areas (x,y) + 1 pixel boundary:
>
> u(x+1,y) + u(x,y+1) + u(x-1,y) + u(x,y-1) = 4*u(x,y)
>
> So basically the procedure is: Take surrounding 4 pixels and put
> the average in the middle. Repeat for all free pixels (x,y). If
> there are n free pixels the resulting linear system is n*5. I solve
> this with Gauss-Seidel iteration.
>
> More on this method in Advanced Engineering Mathematics by Kreyszig
> in section Numerical methods for differential equations.
>
>
> I sent this uncleaned code to the Terragen guy and he made it a new
filter.
>
> ------------------------------------------------------------------
> LevelConnector uses these pseudo functions to communicate with the
> rest of the app.
>
>   SetHeight(x, y, hv);
>   hv=GetHeight(x, y);
>   Sel=GetSelValue(x, y); // is pixel selected
>   PixV=HVToFloat(hv);    // convert from internal type to float
>   hv=FloatToHV(PixV);    // convert to internal type
>
>
> file://def for the compare func used by bsearch
> typedef int (*fptr)(const void*, const void*);
>
> int compare(const int *a,const int *b)
> {
>   return(*a - *b);
> }
>
>
> // The main calculations. Processes data in u[].
> // Solves this Laplace's 2nd order differential
> // equation using Gauss-Seidel iteration.
> //
> //   d2u   d2u
> //   --- + --- = 0 + (force, not used)
> //   dx2   dy2
> //
> // Can be solved by FFT also but this iterative method lets user control
> // the accuracy of the solution. If all pixels are selected then this
works
> // like smooth with variable radius. Basically it just averages 4 adjacent
> // pixels into the middle pixel :) Note however that one iteration pass
uses
> // uses 2 values per pixel already computed in that pass so it's a kind of
> // cumulative smooth.
>
> void SolveEquations(int **s, float *h, float *u, int Nodes, int maxiter)
> {
>   int i,c,dir=1,Node;
>   float sum;
>
>   for(i=0;i<maxiter;i++)
>
{for(Node=(Nodes-1)*(1-dir)/2;dir*Node<=(Nodes-1)*(1+dir)/2;Node=Node+dir)
>         { sum=h[Node];
>           for(c=1;c<=s[Node][0];c++)
>             sum=sum+u[s[Node][c]];
>           u[Node]=0.25*sum;
>         }
>       dir=-dir;  // toggle direction
>     }
> }
>
>
> // Prepares data for SolveEquations
>
> void LevelConnector(int width,int height, int maxiter)
> {
>   int xo[4]={1,-1,0,0},yo[4]={0,0,1,-1};
>   int c,Nodes=0,*NodeP,Node,PixN;
>   int x,y,xt,yt,i,j,*Pos,**s;
>   float *h,*u,Sel,PixV,k;
>
>   // Count selected pixels
>   for(y=0;y<height;y++)
>     {for(x=0;x<width;x++)
>        {if(GetSelValue(x, y) == SELECTED)
>           Nodes++;
>        }
>     }
>
>   u=(float *)malloc(Nodes*sizeof(float)); // This is the actual height
data
>   h=(float *)malloc(Nodes*sizeof(float)); // aux data for equations
>   Pos=(int *)malloc(Nodes*sizeof(int));   // Stores pixel positions of
nodes
>   s=(int **)malloc(Nodes*sizeof(int *));  // aux data for equations
>
>
>   // clear arrays
>   for(Node=0;Node<Nodes;Node++)
>

>     s[Node]=(int *)malloc(5*sizeof(int));
>     if (s[Node] == NULL) {perror("memory error");exit(1);}
>     for(j=0;j<5;j++)
>       s[Node][j]=0;
>     u[Node]=0;
>     h[Node]=0;
>     Pos[Node]=0;
>   }
>
>
>   // Fill position table
>   Node=0;PixN=0;
>   for(y=0;y<height;y++)
>     {for(x=0;x<width;x++)
>        {Sel=GetSelValue(x, y);
>         if(Sel == SELECTED)
>           {Pos[Node]=PixN;
>            Node++;
>           }
>         PixN++;
>        }
>     }
>
>
>   // Make equations
>   Node=0;PixN=0;
>   for(y=0;y<height;y++)
>     {for(x=0;x<width;x++)
>        {if(GetSelValue(x, y) == SELECTED)
>           {k=0;c=0;
>    for(i=0;i<4;i++)
>              {yt=y+yo[i];
>               xt=x+xo[i];
>               if (yt == -1)      yt=height-1;
>       if (yt == height) yt=0;
>       if (xt == -1)      xt=width-1;
>       if (xt == width)   xt=0;
>               hv=GetHeight(xt, yt);
>               PixV=HVToFloat(hv);
>               if(GetSelValue(xt, yt) != SELECTED)
>                 k=k+PixV;
>               else
>                 {c++;
>                  PixN=yt*width+xt;
>          NodeP=(int *)bsearch(&PixN,Pos,Nodes,sizeof(int),(fptr)compare);
>                  if(NodeP == NULL)
>                    {perror("error in bserch");
>                     exit(1);
>                    }
>                  s[Node][c]=(int)(NodeP-Pos);
>                 }
>      }
>            hv=GetHeight(x, y);
>            u[Node]=HVToFloat(hv);
>    h[Node]=k;
>    // h[Node]=k-force;  past experiment
>    s[Node][0]=c;
>    Node++;
>   }
>        }
>     }
>
>   SolveEquations(s,h,u,Nodes,maxiter);
>   free(h);
>
>   // Write data in u[] back to hf
>   for(Node=0;Node<Nodes;Node++)
>

>       free(s[Node]);
>       hv=FloatToHV(u[Node]);
>       x=Pos[Node]%width;
>       y=Pos[Node]/width;
>       SetHeight(x, y, hv);
>     }
>
>   free(s);
>   free(Pos);
>   free(u);
> }
>
> K.K.


   Aaaaaaaargh!!!  You've frightened the s**t out of me now
  Kari!!  Whats a man to do?? (Need new specs after that! Me 'eads gone all
dizzy!! ;o)

                                ~Steve~

    PS, how do I save an image as .jpg, *in POV-Ray*, to 'send' to you very
'NICE' people to perooooose over? Simple question, I know, but I'M sure that
you can handle it, Kari............thanx.

Post a reply to this message

In article <3995c067@news.povray.org>, "25ct" <25c### [at] lineonenet> wrote:

>     PS, how do I save an image as .jpg, *in POV-Ray*, to 'send' to you 
> very 'NICE' people to perooooose over? Simple question, I know, but 
> I'M sure that you can handle it, Kari............thanx.

You don't. You have to use an external program to convert an image 
generated by POV(in PNG or TGA format, for example) to JPEG. The next 
version may include JPEG *input*, but JPEG, as a "lossy" format, won't 
be available for output.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

Post a reply to this message

So what do I *do* If I haven't got PNG? or TGA?
  I've got Photo deluxe 2.0,(Hahaha!!) and PS 5 (LE, nice!). Deluxe can
convert an image to .jpeg, but it won't do it, with Pov.
   I am at a loss, so far!

                   ~Steve~     (What? Where? When? ;o)




"Chris Huff" <chr### [at] maccom> wrote in message
news:chrishuff-CC5169.16461612082000@news.povray.org...
> In article <3995c067@news.povray.org>, "25ct" <25c### [at] lineonenet> wrote:
>
> >     PS, how do I save an image as .jpg, *in POV-Ray*, to 'send' to you
> > very 'NICE' people to perooooose over? Simple question, I know, but
> > I'M sure that you can handle it, Kari............thanx.
>
> You don't. You have to use an external program to convert an image
> generated by POV(in PNG or TGA format, for example) to JPEG. The next
> version may include JPEG *input*, but JPEG, as a "lossy" format, won't
> be available for output.
>
> --
> Christopher James Huff - Personal e-mail: chr### [at] maccom
> TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
> Personal Web page: http://homepage.mac.com/chrishuff/
> TAG Web page: http://tag.povray.org/

Post a reply to this message

In article <3995ce72@news.povray.org>, "25ct" <25c### [at] lineonenet> wrote:

>     So what do I *do* If I haven't got PNG? or TGA?
>   I've got Photo deluxe 2.0,(Hahaha!!) and PS 5 (LE, nice!). Deluxe can
> convert an image to .jpeg, but it won't do it, with Pov.
>    I am at a loss, so far!

What do you mean?
Are you trying to convert a .pov file? That won't work, you have to 
render it with POV and convert the resulting image. POV-Ray can output 
to many file formats, including TGA and PNG. The default settings place 
the rendered image in the same folder the .pov file is in.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

Post a reply to this message

"Chris Huff" <chr### [at] maccom> wrote in message
news:chrishuff-73B1CD.17435312082000@news.povray.org...
| In article <3995ce72@news.povray.org>, "25ct" <25c### [at] lineonenet> wrote:
|
| >     So what do I *do* If I haven't got PNG? or TGA?
| >   I've got Photo deluxe 2.0,(Hahaha!!) and PS 5 (LE, nice!). Deluxe can
| > convert an image to .jpeg, but it won't do it, with Pov.
| >    I am at a loss, so far!
|
| What do you mean?
| Are you trying to convert a .pov file? That won't work, you have to
| render it with POV and convert the resulting image. POV-Ray can output
| to many file formats, including TGA and PNG. The default settings place
| the rendered image in the same folder the .pov file is in.

My guess is that (s)he is saying that nothing there is capable of opening a
Targa or Portable Network Graphics image.  But only because I'm not sure
about what either of those programs can open.  Somehow I'd bet Photoshop
could do it, just a hunch.

Bob

Post a reply to this message

Chris Huff wrote:
>
> > Here is the theory on 2d electrical potential
> > u(xx) + u(yy) = 0
> > u(x+1,y) + u(x,y+1) + u(x-1,y) + u(x,y-1) = 4*u(x,y)
>
> Thanks...it looks like it will take a while to analyze this and convert
> it to 3d, though.

I think the equations  would just be

u(xx) + u(yy) + u(zz) = 0 and

u(x+1,y,z) + u(x,y+1,z) + u(x-1,y,z) + u(x,y-1,z) + u(x,y,z+1) + u(x,y,z-1) =
6*u(x,y,z)

I could convert my code quite easy to 3D for testing purposes but it would
require lots of RAM to run. Then I would write a macro that outputs an object/volume
as voxel image slice by slice as animation. What's the format of the pov
voxel image type (for input to pov)?

This setup would be enough to determine how useful Volume Connector :) vould be.


K.K.

Post a reply to this message

Kari Kivisalo wrote:

>What's the format of the pov
>voxel image type (for input to pov)?

The density_file.

from the doc: "The df3 format consists of a 6 byte header of three 16-bit 
integers with high order byte first. These three values give the x,y,z 
size of the data in pixels (or more appropriately called voxels). This is 
followed by x*y*z unsigned integer bytes of data. The data in the range of 
0 to 255 is scaled into a float value in the range 0.0 to 1.0. It remains 
at 0.0 for all areas beyond the unit cube. The pattern occupies the unit 
cube regardless of the dimensions in voxels."

Ingo

-- 
Photography: http://members.home.nl/ingoogni/
Pov-Ray    : http://members.home.nl/seed7/

Post a reply to this message

Chris Huff wrote:
>
> This looks like it could be a useful enhancement for the proximity
> pattern(it could solve the grainyness problem)

Yes. If the volume contains just the object with potential 1 and the
remaining space is set free then every iteration pass would diffuse
the objects "electrical field" very smoothly around the object.

K.K.

Post a reply to this message

"Chris Huff" <chr### [at] maccom> wrote in message
news:chrishuff-73B1CD.17435312082000@news.povray.org...
> In article <3995ce72@news.povray.org>, "25ct" <25c### [at] lineonenet> wrote:
>
> >     So what do I *do* If I haven't got PNG? or TGA?
> >   I've got Photo deluxe 2.0,(Hahaha!!) and PS 5 (LE, nice!). Deluxe can
> > convert an image to .jpeg, but it won't do it, with Pov.
> >    I am at a loss, so far!
>
> What do you mean?
> Are you trying to convert a .pov file? That won't work, you have to
> render it with POV and convert the resulting image. POV-Ray can output
> to many file formats, including TGA and PNG. The default settings place
> the rendered image in the same folder the .pov file is in.
>
> --
> Christopher James Huff - Personal e-mail: chr### [at] maccom
> TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
> Personal Web page: http://homepage.mac.com/chrishuff/
> TAG Web page: http://tag.povray.org/


Hi Chris, apologies, that was the beer talking last night ;o)

   In Pov, I can't see any clear option to turn an image into a JPEG image,
like you can in Photo Deluxe 2 or Photoshop 5.   However, I have now found
my image saved as a .bmp, in MS Paint??!! (how'd it get there?)
   After rendering, do the images save as .bmp's by default? And is it ok to
send to pov.images in this format?
    As i've said in .newusers, i'm 'puter illit. So finding my way around
mine is a nightmare sometimes. I've only had it 6 months :o(  but i'm
getting there :o)

                                  ~Steve~

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25ct wrote:
>
>    After rendering, do the images save as .bmp's by default?

In the winpov, yes.

> And is it ok to send to pov.images in this format?

jpg is the best format because you can choose between file size
and image quality. In photoshop open bmp, file/save a copy, choose jpg,
check preview, move the slider left until the image starts to look bad,
now save an post :)

K.K.

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That's brilliant!!  Thanks very much Kari.....  :o) :o) :o)

                                  ~Steve~


"Kari Kivisalo" <kar### [at] kivisalonet> wrote in message
news:3996698C.FBA075CE@kivisalo.net...
> 25ct wrote:
> >
> >    After rendering, do the images save as .bmp's by default?
>
> In the winpov, yes.
>
> > And is it ok to send to pov.images in this format?
>
> jpg is the best format because you can choose between file size
> and image quality. In photoshop open bmp, file/save a copy, choose jpg,
> check preview, move the slider left until the image starts to look bad,
> now save an post :)
>
> K.K.

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On Sun, 13 Aug 2000 10:01:47 +0100 "25ct" <25c### [at] lineonenet> wrote:

>   After rendering, do the images save as .bmp's by default? And is it ok to
>send to pov.images in this format?

  Hi, Steve. I suggest reading all of the messages in the
povray.announce.frequently-asked-questions group, specifically "Where
can I post my binary or text file?"

-- 
Alan - ako### [at] povrayorg - a k o n g <at> p o v r a y <dot> o r g
http://www.povray.org - Home of the Persistence of Vision Ray Tracer

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"Alan Kong" <ako### [at] povrayNO-SPAMorg> wrote in message
news:9j9dpskbadaq99b7j75a7ilngf83t6f3e0@4ax.com...
> On Sun, 13 Aug 2000 10:01:47 +0100 "25ct" <25c### [at] lineonenet> wrote:
>
> >   After rendering, do the images save as .bmp's by default? And is it ok
to
> >send to pov.images in this format?


>
>   Hi, Steve. I suggest reading all of the messages in the
> povray.announce.frequently-asked-questions group, specifically "Where
> can I post my binary or text file?"


>
> --
> Alan - ako### [at] povrayorg - a k o n g <at> p o v r a y <dot> o r g
> http://www.povray.org - Home of the Persistence of Vision Ray Tracer

       Thanks Alan. I have subscribed to it, but haven't got around to
reading the messages yet. Been busy with an image! (ref; pov.images)  ;o)
It's next on my list though.

                 ~Steve~

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In article <3996558A.CDAA55FF@kivisalo.net>, Kari Kivisalo 
<kar### [at] kivisalonet> wrote:

> I think the equations  would just be
> 
> u(xx) + u(yy) + u(zz) = 0 and
> 
> u(x+1,y,z) + u(x,y+1,z) + u(x-1,y,z) + u(x,y-1,z) + u(x,y,z+1) + 
> u(x,y,z-1) = 6*u(x,y,z)

Yeah, but the problem is figuring out what that means. :-)
It looks simple, but I can't translate it into an algorithm, and I have 
only a slight idea what u() is supposed to do.


> I could convert my code quite easy to 3D for testing purposes but it 
> would require lots of RAM to run. Then I would write a macro that 
> outputs an object/volume as voxel image slice by slice as animation. 
> What's the format of the pov voxel image type (for input to pov)?

Does it require that the density field be converted to a voxel image? I 
hope not...but if it requires multiple passes that can't be done at 
once, I don't see a way around it.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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Chris Huff wrote:
> > u(xx) + u(yy) + u(zz) = 0 and
> >
> > u(x+1,y,z) + u(x,y+1,z) + u(x-1,y,z) + u(x,y-1,z) + u(x,y,z+1) +
> > u(x,y,z-1) = 6*u(x,y,z)
>
> only a slight idea what u() is supposed to do.

u is the density/potential at (x,y,z).

> Does it require that the density field be converted to a voxel image? 

As I said before this algrithm is a numerical discrete approximation,
not analythical. The input and output are are voxel images just like
the 2d case works with 2d images. Only certain special cases of potential
fields can be solved analythically at any point. The whole volume must
be solved at once so it's impossible solve just one point at a time.

In povray terms this requires a pre-rendering pass to sample the volume
of interest at specified resolution and then solving the potential field
within that volume.

K.K.

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In article <399### [at] kivisalonet>, Kari Kivisalo 
<kar### [at] kivisalonet> wrote:

> u is the density/potential at (x,y,z).

Simply the field value? Then this is nothing more than a kind of 3D 
convolution matrix...right? Basically a blurring operation.


> > Does it require that the density field be converted to a voxel image? 
> 
> As I said before this algrithm is a numerical discrete approximation,
> not analythical. The input and output are are voxel images just like
> the 2d case works with 2d images. Only certain special cases of potential
> fields can be solved analythically at any point. The whole volume must
> be solved at once so it's impossible solve just one point at a time.

Are you sure about this? It seems like some kind of recursive algorithm 
could be used to do a similar effect, sampling at one distance, 
subdividing and interpolating, sampling again, etc. I am going to have 
to experiment with this...
It wouldn't be the same algorithm, but it should be similar in results.


> In povray terms this requires a pre-rendering pass to sample the volume
> of interest at specified resolution and then solving the potential field
> within that volume.

This could most easily be done in the parsing stage, and would probably 
be a density_file pattern internally. However, you would have to specify 
a resolution large enough, and it would consume a lot of memory. :-(
If this absolutely requires a voxel image, then might as well implement 
it as a density_file feature, and add the ability to create a 
density_file pattern from another pattern(like object). You could 
already do so with a macro and eval_pattern() or eval_pigment(), but the 
parse time would be long.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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Chris Huff wrote:
>
> > u is the density/potential at (x,y,z).
> 
> Simply the field value? Then this is nothing more than a kind of 3D
> convolution matrix...right? Basically a blurring operation.

One iteration of the linear system is just a blur which can be seen
from the bevel mode example pictures. When the change between iterations
drops below tolerance that's the solution for the Laplace equation.

> > The whole volume must
> > be solved at once so it's impossible solve just one point at a time.
> 
> Are you sure about this?

That math book I mentioned only spoke about methods using linear systems
of equations and iteration. There may be other numerical methods geared
towards applications other than electrical engineering. Look for them using
laplace, poisson , differential, numerical.



K.K.

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