"Kenneth" <kdw### [at] gmailcom> wrote:
> "Leroy" <whe### [at] gmailcom> wrote:
> > "Leroy" <whe### [at] gmailcom> wrote:
> > I found a big difference in using a image pigment in the height_field function
> > and that pigment in the height_field alone.
> >
> > that is
> >  #declare PigM=function{pigment{image_map{ tga "FinalB.tga"}}}
> >  #declare Dirt =
> > function(x,z){select(PigM(x,1-z,0).blue,0,0,PigM(x,1-z,0).blue)}
> >  height_field {function 400,400{ Dirt(x,y) }...
> > and
> >
> >  height_field {tga "FinalB.tga"
> >
> > they don't match! The function has a lower height and seems to be shifted both
> > in the +z and +x directions
> >
>
> Out of curiosity, I used your code examples but with my own .png image_map (not
> ..tga), and I see some interesting things:
>
> First, I was surprised that your constructed DIRT function works at all. Z's
> instead of y's there? But it does work! Substituting y for z *also* works:
>        function(x,y){select(PigM(x,1-y,0).blue,0,0,PigM(x,1-y,0).blue)}
>
> But moving on...
> My test image_map includes 3 primary colors, plus a linear white-to-black ramp.
> The resulting height_fields have a gradient-y color_map applied, from black to
> reddish. (I shouldn't have used black; it makes the results difficult to see.)
>
> I don't see any x or z reversal between the two HF examples. We're both using
> the (1-z) trick for the function version, so that should solve it. It does for
> me.
>
> But *most* interestingly, the two HF-creation methods show some different
> results for the height values. The 'direct' approach uses only the RED color
> channel, AND shows the linear white-to-black 'ramp' correctly; the function
> approach uses only the BLUE channel...but shows an unexpected gamma-value(?)
> bending of the 'ramp' (and some other shapes there too.) I wasn't expecting
> that!

First, I like your image base documentation!

 function(x,z){select(PigM(x,1-z,0).blue,0,0,PigM(x,1-z,0).blue)} was made to
take care of some funky HF,s made with tga palette images. It seem that the HF
function produce negative value that showed up as spikes.
 function(x,z){PigM(x,1-z,0).hf} works for all of the other image formats I've
tried.( gif | jpeg | pgm | png | ppm | tga )

 Things I think I've learned:

 function(a,b) will work as long as those variables are used in the function.

 function(x,y,z){pigment{...} won't work

 height_field{will take function(x) I guess it sends 3 variables x,y,z float
types that have nothing to do with the x,y,z vectors.

The image_map goes on forever in the +z direction so
  function(x,z){PigM(x,1-z,.5).hf}
 still works, it might do so in the -z direction, I haven't tried it.

I'm still testing image formats. I've done at lease one test of these gif , jpeg
, pgm , png , ppm , tga(256 mapped, 24 bit compressed,24 bit NOT compressed)

I plan to do all the image formats that POV can Make and Read.

Have fun!

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