"Robert McGregor" <rob### [at] mcgregorfineartcom> wrote:

That's a wonderful scene, very mysterious and evocative. And thanks for sharing
the details of your techniques, plus the image of the various assets you used.
>
> As a post-processing step I also wrote a simple brightness mask scene file that
> reads in an existing image and masks off (as black) areas that are below a
> specified brightness threshold.

That idea gave me some thoughts about my recent post regarding AA problems with
very bright objects, where AA fails for those bright pixels (Thanks!) So I put
together something similar(?) to your idea: Rendering a scene the normal way,
then bringing the image back into POV-ray and doing an
image-to-function-to-pigments conversion on it (all 3 color channels). Then
re-combining (using 'average') those 3 pigment functions-- with simple but
proper r-g-b color_maps-- to re-create the image as before. At this point, I
discovered that I could change the color_maps' index values to effectively
mask-off (as black) any pixels over a certain 0-1 brightness threshold... like
your idea. Great, so far!

> A simple 5x5 Gaussian convolution matrix is then
> iterated across the resulting masked image to blur the remaining pixels for a
> simple glow effect...

This is the 2nd part of my task. I looked up 'gaussian blur', and I see that it
involves matrix use in some way. I'm still a rank beginner when it comes to
manipulating matrices, but aside from that small problem (ha), I can't even get
a *basic* experiment with a matrix to work in v3.8xx for Windows:

#declare MY_MATRIX =
transform{
              matrix
              <1,1,1,
              1,1,1,
              1,1,1,
              0,0,1>
              }

.... with or without a semi-colon at the end. "Fatal error in parser:
uncategorized error"

So I must be doing something basically wrong-- or else my syntax is incorrect,
although I don't see where.

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