On 10/06/2021 2:25 am, Bald Eagle wrote:
> Hi Matt,
> 
>>> "m@b" <sai### [at] googlemailcom> wrote:
>>>> Trying to emulate mechanical shading.
> 
> This is clever!  I like it.  :)
> 

Thanks.


................ snip

>> (I am not sure where this function came from - I used it many years ago
>> in another project.)
> 
> I see in your posted code that you comment that "map_type 0" is required - but
> the docs say that this is the default planar mapping, so maybe it's not actually
> a requirement?
.
You are right - it is the default, perhaps it was a requirement 20 years 
ago when I last played with POV-Ray


> 
> I had this bouncing around in my head today,  and maybe it would be faster to
> make some pigment patterns and use a pigment map instead of sphere primitives.

But I would need some primitives to put the pattern on?

> 
>
http://news.povray.org/povray.binaries.images/thread/%3Cweb.5a7774f01a0c102c5cafe28e0%40news.povray.org%3E/
> 
> You could even just make a single linear pattern and the others would just be
> rotations or scales of it. (have the line thickness be dependent on the color
> channel value)
> 
> The other thing I was thinking was that you might also be able to get an outline
> or shape-following effect if you calculated not only the value of any given
> pixel, but the gradient of the function there as well.  Then you could make the
> lines perpendicular to the gradient / tangent to the curve.
> 
> I know TOK wrote the gradient functions in the distributed include files, and
> there are edge-finding algorithms that give you the gradient of the image as a
> bonus.

Hmm - I need to think about these things. Interesting suggestions.

> 
> This looks like something super fun to play with, with a lot of potential for
> future development!  Good work  :)
> 
>

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On 08/06/2021 11:21 am, m@b wrote:
> Trying to emulate mechanical shading.
> 
> m@

An example with cylinders instead of spheres, I like the maze effect at 
the boundaries.

And a first attempt at edge detection.

m@

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Attachments:
Download 'test cylinders 01.png' (128 KB) Download 'image cross hatch 03.png' (181 KB)

Preview of image 'test cylinders 01.png'

Preview of image 'image cross hatch 03.png'

"m@b" <sai### [at] googlemailcom> wrote:

> But I would need some primitives to put the pattern on?

Of course.  A thin box or the union of 2 triangles works well.  A plane if you
just want to have the largest possible palette.

But the idea is that you have a lot of stuff going on after you "extract" the
colors.  Rather than do that, you use the color values directly to select a
pigment, by using a pigment_map.

I am curious about
#declare GreyTest = 0.001 + abs(TestK(X,Y,0) -
abs((TestR(X,Y,0) + TestG(X,Y,0) - TestB(X,Y,0))));

What is the underlying logic/reasoning behind this "greyness test"?

> > there are edge-finding algorithms that give you the gradient of the image as a
> > bonus.
>
> Hmm - I need to think about these things. Interesting suggestions.

https://www.youtube.com/watch?v=uihBwtPIBxM
skip to 3:30 if you want.

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"Tor Olav Kristensen" <tor### [at] TOBEREMOVEDgmailcom> wrote:

> Hi Bill
>
> Please note that most of the credit for the Vector analysis macros should go to
> Christoph Hormann, which did the heavy lifting. I just suggested some
> corrections.

So noted!  He did an excellent job, especially that clever bit about employing
f_r - which took me a bit of time to wrap my head around.

http://www.povray.org/documentation/view/3.6.1/448/
f_r(x,y,z) = sqrt( x*x + y*y + z*z )
When used alone, the "R" function gives a surface that consists of all the
points that are a specific distance (threshold value) from the origin, i.e. a
sphere.



> Btw.:
> I agree with you; it may be that experimenting with pigment maps will be
> rewarding here.

Indeed.  I think he could get some interesting half-tone effects as well.

rgbf would look great if unmodified spheres of all 3 colors were used.

There's also the potential for using different shapes - boxes, triangles,
hexagons, etc.  I'm also thinking that using cones would give a Voronoi effect.

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"Bald Eagle" <cre### [at] netscapenet> wrote:

> I'm also thinking that using cones would give a Voronoi effect.

I just did this one because it was quick.

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=?UTF-8?Q?J=c3=b6rg_=22Yadgar=22_Bleimann?= <yaz### [at] gmxde> wrote:

> Yadgar

I really just have to say that if you got some dark sunglasses and a leather
biker vest, you could totally pull off that "bouncer at a biker bar" look.

:D

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"Bald Eagle" <cre### [at] netscapenet> wrote:
> "Bald Eagle" <cre### [at] netscapenet> wrote:
>
> > I'm also thinking that using cones would give a Voronoi effect.
>
> I just did this one because it was quick.

They make a nice texture that reminds me of mashed paper.

--
Tor Olav
http://subcube.com
https://github.com/t-o-k

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On 11/06/2021 2:27 am, Bald Eagle wrote:
> I am curious about
> #declare GreyTest = 0.001 + abs(TestK(X,Y,0) -
> abs((TestR(X,Y,0) + TestG(X,Y,0) - TestB(X,Y,0))));
> 
> What is the underlying logic/reasoning behind this "greyness test"?

I wish to represent 4 colours - R, G, B and Grey.

The 0.001 is now redundant, I put it in to prevent a divide by zero 
error in a previous version.

TestK(X,Y,0) returns the mean value of R, G, B. (1)

R+G-B will also return the mean if R, G and B are all the same, i.e. 
colour is Grey. (Black and White are just shades of Grey :-))  (2)

So the GreyTest (1)-(2) returns zero if R, G and B are equal and a small 
value if they are close.

BUT --------------------------------------------------------

You got me thinking, are there any cases where the test returns zero but 
R, G, B are not equal?

Answer - yes, the test sometimes falls down when the 3 numbers are 
equally spaced. e.g  0.1, 0.2, 0.3    or 0.3, 0.6, 0.9

I was over thinking, maybe this will work:

#declare GreyTest = abs(TestR(X,Y,0)-TestG(X,Y,0)) + 
abs(TestR(X,Y,0)-TestB(X,Y,0)) + abs(TestB(X,Y,0)-TestG(X,Y,0));

m@

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Hi(gh)!

On 10.06.21 23:55, Bald Eagle wrote:
> =?UTF-8?Q?J=c3=b6rg_=22Yadgar=22_Bleimann?= <yaz### [at] gmxde> wrote:
> 
>> Yadgar
> 
> I really just have to say that if you got some dark sunglasses and a leather
> biker vest, you could totally pull off that "bouncer at a biker bar" look.

Yes, and I'm about as heavyweight as the typical biker bar bouncer - but 
unfortunately, it's more fat than muscle... but nevertheless, I prefer 
muscle-powered cycling over motorbiking!

Now playing: Nobody Home (Pink Floyd)

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