Yep, I knew about the color interactions.
Did a B&W render for the AOL 3D Render Challenge long time ago, but I
converted to grayscale jpg because post-processing isn't as much a
concern there. I was actually working by way of getting an appropriate
enough color image that would look right in all grays.
Think Ken wants a purely artistic manipulation approach.
The hf_gray_16 method needs a orthographic camera.
256 grays is never going to be very good.
Anyone try Spiders idea yet? Sounds interesting, but I'm not sure of how
the color interactions would take place if all are converted to monotone
first then used as the light(s)/texture(s). Same thing as Kens way,
except no manipulation upon them.
Post-conversion is different than pre-conversion no matter I would
think.
Oh, and yes, you can multiply color vectors by -1, i.e.
rgb<.5,.6,.7>*-1, however getting the neutral gray by combining the
positive with negative I don't see happening right.
I tried a simple test, a red object with white light, multiplied both
color vectors by -1 (the only way to see the negative red object). This
makes a similar red object once again. Then I used the result as a
image_map filtered in front of the original object positive red object
and left the negative light.
Well, long story short here, I failed to see a way to get a grayscale
from this sort of thing. Either you get color or you get black only
apparently. Maybe there's still a way, but like I said this was a
"simple test".


Lance Birch wrote:
> 
> Um, yes... but you won't get the same result...
> 
> OK, I think I should stop bothering everyone after this... But I just want
> to prove a little point first:
> 
> You CANNOT get the same effect of converting and image to greyscale later by
> colouring the objects in your scene with greyscale equivalents.  It doesn't
> work.
> 
> The reason is simple and I won't go on about it after this :)
> 
> If you plan to have only white lights in your scene, fine, it doesn't make
> ANY difference (except for reflections) if you convert a colour image to
> greyscale, or if you build your scene with the greyscale equivalents.
> However, if you are going to use coloured lights, things get tricky.  The
> reason it won't work properly is because different colours react in
> different ways on other colours.  For example, the highlight or specular on
> an object will look like it has a different exposure.  A good example is to
> place a yellow sphere with a red light on one side and a blue light on the
> other.  If you examine the highlights you'll find that the one produced by
> the red light will be exposed more than the one from the blue light.  Now if
> you were to convert your scene's colours to greyscale before rendering, this
> effect isn't produced because you now only have intensities, so all the
> highlights will have a linear progression of magnitude.  This means that you
> can no longer produce scenes with realistic lighting (or reflections), and
> that's why it is VERY hard to get the right contrast in a B&W scene if
> you're going to make it by using intensities.  See?  So, ultimately, Peter's
> solutions is the ONLY REAL solution to the problem, because that way you are
> ACTUALLY rendering the colour, but it is being converted to greyscale later
> (well, not later, still in POV-Ray) using the HF16G option, and then
> converted to RGB still using POV-Ray by making a height_field from the
> resulting PNG image and then colouring the height_field with a gradient from
> black to white.
> 
> (Did anyone understand my point?)
> OK, I'll shut up now...
> 
> --
> Lance.
> 
> ---
> For the latest 3D Studio MAX plug-ins, images and much more, go to:
> The Zone - http://come.to/the.zone

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