POV-Ray : Newsgroups : povray.binaries.images : Atari Logo Server Time: 19 Jan 2019 03:49:29 GMT
  Atari Logo (Message 1 to 6 of 6)  
From: Dave Blandston
Subject: Atari Logo
Date: 24 Jan 2011 17:20:00
Message: <web.4d3db445d3c96cb11df6284f0@news.povray.org>
Hello,

This is an old scene with some slight improvements. Getting the rainbow gradient
right is tricky. Making a mathematically linear gradient doesn't seem to give
visually linear results. The primary colors appear to dominate the secondary
colors, causing uneven transitions. This scene uses a partial fix but it's still
not perfect. I have seen what appear to be perfectly balanced rainbow gradients
before - does anybody know the trick to getting it just right?

Regards,
Dave Blandston


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From: clipka
Subject: Re: Atari Logo
Date: 24 Jan 2011 17:37:22
Message: <4d3db8d2@news.povray.org>
Am 24.01.2011 18:17, schrieb Dave Blandston:

> This is an old scene with some slight improvements. Getting the rainbow gradient
> right is tricky. Making a mathematically linear gradient doesn't seem to give
> visually linear results. The primary colors appear to dominate the secondary
> colors, causing uneven transitions. This scene uses a partial fix but it's still
> not perfect. I have seen what appear to be perfectly balanced rainbow gradients
> before - does anybody know the trick to getting it just right?

What assumed_gamma are you using?

While assumed_gamma 2.2 gives visually more pleasing dark-to-bright 
gradients, assumed_gamma 1.0 generally seems to give more pleasing 
color-to-color gradients.


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From: Samuel Benge
Subject: Re: Atari Logo
Date: 24 Jan 2011 19:00:00
Message: <web.4d3dcb584cc34acfe32b58850@news.povray.org>
"Dave Blandston" <nomail@nomail> wrote:
> Hello,
>
> This is an old scene with some slight improvements. Getting the rainbow gradient
> right is tricky. Making a mathematically linear gradient doesn't seem to give
> visually linear results. The primary colors appear to dominate the secondary
> colors, causing uneven transitions. This scene uses a partial fix but it's still
> not perfect. I have seen what appear to be perfectly balanced rainbow gradients
> before - does anybody know the trick to getting it just right?

Somewhere (in the POV docs or elsewhere) you can find the relative intensities
for RGB values. I have no idea where to find that information anymore. I know
for a fact that green overpowers the other two.

Another thing you can try is to find an image of the gradient you want, and fill
up a color_map with the colors from it. You can use eval_pigment (slow), or you
can make a function from the image and test it directly. You might still have
gamma issues, but the result should be close to what you want.

~Sam


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From: Samuel Benge
Subject: Re: Atari Logo
Date: 24 Jan 2011 19:20:01
Message: <web.4d3dd0184cc34acfe32b58850@news.povray.org>
"Samuel Benge" <stb### [at] hotmailcom> wrote:
> "Dave Blandston" <nomail@nomail> wrote:
> > - does anybody know the trick to getting it just right?
>
> Somewhere (in the POV docs or elsewhere) you can find the relative intensities
> for RGB values. I have no idea where to find that information anymore. I know
> for a fact that green overpowers the other two.

....It seems that I was remembering a method for converting a color image to
grayscale, though it might still be applicable here since we're talking about
the visual influence of colors...

From the POV docs, in reference to grayscale output:

  "The brightness of a pixel is calculated in the same way that color images are
converted to grayscale images: height = 0.3 * red + 0.59 * green + 0.11 * blue."

Maybe this helps, maybe it doesn't :/


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From: Alain
Subject: Re: Atari Logo
Date: 25 Jan 2011 02:40:15
Message: <4d3e380f$1@news.povray.org>
Le 2011/01/24 12:17, Dave Blandston a écrit :
> Hello,
>
> This is an old scene with some slight improvements. Getting the rainbow gradient
> right is tricky. Making a mathematically linear gradient doesn't seem to give
> visually linear results. The primary colors appear to dominate the secondary
> colors, causing uneven transitions. This scene uses a partial fix but it's still
> not perfect. I have seen what appear to be perfectly balanced rainbow gradients
> before - does anybody know the trick to getting it just right?
>
> Regards,
> Dave Blandston

A simple way: Add some more intermediate tints to your colour_map.

If you need, say, the green to be visualy narower, shift the neiboring 
entries closer a bit.



Alain


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From: Dave Blandston
Subject: Re: Atari Logo
Date: 25 Jan 2011 16:30:01
Message: <web.4d3efa474cc34acf1df6284f0@news.povray.org>
Thanks for the suggestions. Using more intermediate values is an effective fix.
I may tinker around with some of the other ideas too - this is an interesting
topic to me.

Regards,
Dave Blandston


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