"Kenneth" <kdw### [at] gmailcom> wrote:

> 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)}

You can of course put anything you want in those "slots".   It's a function.
When you render an image and you are evaluating a pigment pattern, then you have
the ability to sample the x, y, and z values at the place where the ray-object
intersection takes place.  But there sure isn't a requirement to invoke any
function in that order, or even using those values at all.
Using z instead of y just switches the plane in which that function is
evaluated.

> 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!

I'd like to see if the function approach using the red channel gives the same
result as either of these experiments.

Also, you should look into all of the input_gamma for gamma pre-corrected file
formats stuff, to see if that's what's going on.   Maybe if the image file gets
loaded with an input gamma specifying 1.0 or 2.2 (srgb) then they will be the
same.   Just to check that it's the heightfied creation method vs the image
input method that supplies the data to the heighfield.

- BW

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