POV-Ray : Newsgroups : povray.general : Abrupt color changes in blobs Server Time
7 Aug 2024 13:17:11 EDT (-0400)
  Abrupt color changes in blobs (Message 1 to 7 of 7)  
From: Greg M  Johnson
Subject: Abrupt color changes in blobs
Date: 2 Oct 2001 21:40:06
Message: <3bba6c76@news.povray.org>
I have a human figure that's a blob of perhaps 100 or so components.  I
want to make it look like it's wearing clothes, with for example, an
abrupt color change at the wrist between the "hand skin color" and
"shirt sleeve color."

i)  In general, with blobs, if you declare the pigments individually
inside the components, you'll get a nice smooth blending of the colors
between the two components.   I suppose I could just go ahead and do
this but  I'm worried it will look tacky close up.

ii)  I could OTOH use CSG.  It would make the scene code more
complicated, but hey it's just a computer doing the thinkin' right?

iii) I suppose I could make another blob slightly bigger with the hands
and head cut off, and make this the "clothing."

Any other pointers?


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From: Bob H 
Subject: Re: Abrupt color changes in blobs
Date: 3 Oct 2001 00:23:44
Message: <3bba92d0@news.povray.org>
"Greg M. Johnson" <"gregj;-)56590\""@aol.c;-)om> wrote in message
news:3bba6c76@news.povray.org...
> I have a human figure that's a blob of perhaps 100 or so components.  I
> want to make it look like it's wearing clothes, with for example, an
> abrupt color change at the wrist between the "hand skin color" and
> "shirt sleeve color."
>
> i)  In general, with blobs, if you declare the pigments individually
> inside the components, you'll get a nice smooth blending of the colors
> between the two components.   I suppose I could just go ahead and do
> this but  I'm worried it will look tacky close up.
>
> ii)  I could OTOH use CSG.  It would make the scene code more
> complicated, but hey it's just a computer doing the thinkin' right?
>
> iii) I suppose I could make another blob slightly bigger with the hands
> and head cut off, and make this the "clothing."
>
> Any other pointers?

I did #3 before, since it seemed the only quick and easy way.  I only used a
copy of the body and CSG differenced parts from it and scaled up slightly,
exactly what you are thinking.  Turned out that scaling a blob is like
scaling a sphere that has already been placed in a location, which is to say
it all moves as well as resizes.  I ended up compromising scale and an added
translation to sort of fit the shirt to the body.
If you intend to animate the thing, and I know you are, it'll be heck to
deal with because I also did that too.

Bob H.


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From: Nekar Xenos
Subject: Re: Abrupt color changes in blobs
Date: 3 Oct 2001 02:11:07
Message: <3bbaabfb@news.povray.org>
"Bob H." <omn### [at] msncom> wrote in message news:3bba92d0@news.povray.org...
> "Greg M. Johnson" <"gregj;-)56590\""@aol.c;-)om> wrote in message
> news:3bba6c76@news.povray.org...
> > I have a human figure that's a blob of perhaps 100 or so components.  I
> > want to make it look like it's wearing clothes, with for example, an
> > abrupt color change at the wrist between the "hand skin color" and
> > "shirt sleeve color."
> >
> > i)  In general, with blobs, if you declare the pigments individually
> > inside the components, you'll get a nice smooth blending of the colors
> > between the two components.   I suppose I could just go ahead and do
> > this but  I'm worried it will look tacky close up.
> >
> > ii)  I could OTOH use CSG.  It would make the scene code more
> > complicated, but hey it's just a computer doing the thinkin' right?
> >
> > iii) I suppose I could make another blob slightly bigger with the hands
> > and head cut off, and make this the "clothing."
> >
> > Any other pointers?
>
> I did #3 before, since it seemed the only quick and easy way.  I only used a
> copy of the body and CSG differenced parts from it and scaled up slightly,
> exactly what you are thinking.  Turned out that scaling a blob is like
> scaling a sphere that has already been placed in a location, which is to say
> it all moves as well as resizes.

If you have your blob-spheres like this:

sphere{0,Radius,1 Strength scale <a,b,c> translate <X,Y,Z>}

Then you shouldn't have that problem. I did the rubber lining for my car windows
in a similar way.

- Nekar


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From: Dave Dunn
Subject: Re: Abrupt color changes in blobs
Date: 3 Oct 2001 10:18:33
Message: <3BBB1E4C.AEE16D1E@aol.com>
"Bob H." wrote:

>   I ended up compromising scale and an added
> translation to sort of fit the shirt to the body.

It might be a pain, but I would suggest, instead of scaling the whole blob,
which must be centered (you could use min and max extents to do this) in order
to be scaled in place, to create a second blob and go into the radii, and bump
them up a little. You could also, using this method, create nice sleeves by
converting the spheres at the ends to ones with negative strength.


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From: Rune
Subject: Re: Abrupt color changes in blobs
Date: 3 Oct 2001 10:48:25
Message: <3bbb2539$1@news.povray.org>
"Greg M. Johnson" wrote:
> I want to make it look like it's wearing clothes,
> with for example, an abrupt color change at the wrist
> between the "hand skin color" and "shirt sleeve color."

I probably haven't understood the problem correctly, but what prevents you
from just using a pigment with an abrupt color change?

Rune
--
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Rune's World:    http://rsj.mobilixnet.dk (updated June 26)
POV-Ray Users:   http://rsj.mobilixnet.dk/povrayusers/
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From: Dave Dunn
Subject: Re: Abrupt color changes in blobs
Date: 3 Oct 2001 11:32:43
Message: <3BBB2FAF.E7D4F5AA@aol.com>
Rune wrote:

>>I probably haven't understood the problem correctly, but what prevents you

It has to do with the fact that, when using different pigments on different
adjacent blob components, the pigments blend in a smooth gradient centered at
the equipotential mean. There is no way around this. (unless a POV 4.0 keyword
called preserve_blob_pigment = true is created heh heh).


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From: Bill DeWitt
Subject: Re: Abrupt color changes in blobs
Date: 3 Oct 2001 11:51:06
Message: <3bbb33ea$1@news.povray.org>
"Rune" <run### [at] mobilixnetdk> wrote :
>
> I probably haven't understood the problem correctly, but what prevents you
> from just using a pigment with an abrupt color change?

    Depending on the blob component placement, that should work.


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