POV-Ray : Newsgroups : povray.binaries.images : An experiment in monochrome Server Time
22 Sep 2021 05:30:39 EDT (-0400)
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From: m@b
Subject: Re: An experiment in monochrome
Date: 10 Jun 2021 08:28:04
Message: <60c20554@news.povray.org>
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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From: m@b
Subject: Re: An experiment in monochrome
Date: 10 Jun 2021 08:31:42
Message: <60c2062e@news.povray.org>
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'
test cylinders 01.png

Preview of image 'image cross hatch 03.png'
image cross hatch 03.png


 

From: Bald Eagle
Subject: Re: An experiment in monochrome
Date: 10 Jun 2021 14:30:00
Message: <web.60c2599b23b82ed51f9dae3025979125@news.povray.org>
"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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From: Bald Eagle
Subject: Re: An experiment in monochrome
Date: 10 Jun 2021 14:40:00
Message: <web.60c25b8c23b82ed51f9dae3025979125@news.povray.org>
"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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From: Bald Eagle
Subject: Re: An experiment in monochrome
Date: 10 Jun 2021 17:55:00
Message: <web.60c2896123b82ed51f9dae3025979125@news.povray.org>
"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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Attachments:
Download 'monochrome_be.png' (567 KB)

Preview of image 'monochrome_be.png'
monochrome_be.png


 

From: Bald Eagle
Subject: Re: An experiment in monochrome
Date: 10 Jun 2021 18:00:00
Message: <web.60c28a6b23b82ed51f9dae3025979125@news.povray.org>
=?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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From: Tor Olav Kristensen
Subject: Re: An experiment in monochrome
Date: 10 Jun 2021 20:40:00
Message: <web.60c2afe723b82ed58e52cc8789db30a9@news.povray.org>
"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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From: Bald Eagle
Subject: Re: An experiment in monochrome
Date: 10 Jun 2021 20:40:00
Message: <web.60c2b06d23b82ed51f9dae3025979125@news.povray.org>
This is a multi-part message in MIME format.


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Attachments:
Download 'monochrome_be.png' (615 KB)

Preview of image 'monochrome_be.png'
monochrome_be.png


 

From: m@b
Subject: Re: An experiment in monochrome
Date: 11 Jun 2021 06:16:35
Message: <60c33803$1@news.povray.org>
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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From: Jörg "Yadgar" Bleimann
Subject: Re: An experiment in monochrome
Date: 11 Jun 2021 12:12:32
Message: <60c38b70$1@news.povray.org>
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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