I'm not sure where this problem lies.

I have a number of glass objects in a scene, all with identical interior 
statements using media.

For some reason, the blue one is much darker than the others.
Where could I look for non-obvious reasons why?

The colors are all simple, rgbf values like 1,0,1,0.5
In particular, the blue is <0,0,1,0.5>

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"dave vanhorn" <mic### [at] gmailcom> wrote:
> I'm not sure where this problem lies.
>
> I have a number of glass objects in a scene, all with identical interior
> statements using media.
>
> For some reason, the blue one is much darker than the others.
> Where could I look for non-obvious reasons why?
>
> The colors are all simple, rgbf values like 1,0,1,0.5
> In particular, the blue is <0,0,1,0.5>

Hello Dave.

Perhaps I am wrong, but I can see 2 reasons why color rgb <0,0,1> looks
darker than <1,0,1>:

    -) <0,0,1> carries half the 'energy' of <1,0,1>. To be comparable in
brightness, the 2 colors you mentionned should be of equal energy (use
vnormalize)

    -) the human eye does not perceive the whole spectrum with the same
intensity: with the same magnitude, a green color looks brighter than red
and even brighter than blue.

I think these reasons apply as well to plain colors for surfaces, to
fade_color for interiors, and to scattering color for medias.

Hope that helps.

    Bruno

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"Bruno Cabasson" <bru### [at] alcatelaleniaspacefr> wrote:
> > The colors are all simple, rgbf values like 1,0,1,0.5
> > In particular, the blue is <0,0,1,0.5>
>
> Hello Dave.
>
> Perhaps I am wrong, but I can see 2 reasons why color rgb <0,0,1> looks
> darker than <1,0,1>:
>
>     -) <0,0,1> carries half the 'energy' of <1,0,1>. To be comparable in
> brightness, the 2 colors you mentionned should be of equal energy (use
> vnormalize)
>
>     -) the human eye does not perceive the whole spectrum with the same
> intensity: with the same magnitude, a green color looks brighter than red
> and even brighter than blue.

It's even more so then that. POV uses the standard for grayscale conversion,
which is based on real light energies

GRAY = 0.3*R + 0.59*G + 0.11*B

RGB<0,0,1>=0.11
RGB<1,0,1>=0.41
almost 4 times the apparent brightness


-tgq

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>
> Perhaps I am wrong, but I can see 2 reasons why color rgb <0,0,1> looks
> darker than <1,0,1>:
>
>    -) <0,0,1> carries half the 'energy' of <1,0,1>. To be comparable in
> brightness, the 2 colors you mentionned should be of equal energy (use
> vnormalize)

How is that done, I've never heard of Vnormalize before.
I looked in the docs, but I don't see how to apply it to a color.

>    -) the human eye does not perceive the whole spectrum with the same
> intensity: with the same magnitude, a green color looks brighter than red
> and even brighter than blue.

I knew that.

> I think these reasons apply as well to plain colors for surfaces, to
> fade_color for interiors, and to scattering color for medias.

Probably so.

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> It's even more so then that. POV uses the standard for grayscale 
> conversion,
> which is based on real light energies
>
> GRAY = 0.3*R + 0.59*G + 0.11*B
>
> RGB<0,0,1>=0.11
> RGB<1,0,1>=0.41
> almost 4 times the apparent brightness

Given that the eye does that already, wouldn't applying this make it worse?
I see what you're saying, but now I'm confused.

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"dave vanhorn" <mic### [at] gmailcom> wrote:
> > It's even more so then that. POV uses the standard for grayscale
> > conversion,
> > which is based on real light energies
> >
> > GRAY = 0.3*R + 0.59*G + 0.11*B
> >
> > RGB<0,0,1>=0.11
> > RGB<1,0,1>=0.41
> > almost 4 times the apparent brightness
>
> Given that the eye does that already, wouldn't applying this make it worse?
> I see what you're saying, but now I'm confused.

Perhaps I explained incorrectly.  POV doesn't scale the blue down, (except
when converting to grayscale), but this was merely to demonstrate the real
perception of blue relative to the other colours.

Maybe if you post your image and some code, it would be easier to see if
there is something odd, or make it easier to explain the phenomenon you are
seeing.

-tgq

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>> Given that the eye does that already, wouldn't applying this make it 
>> worse?
>> I see what you're saying, but now I'm confused.
>
> Perhaps I explained incorrectly.  POV doesn't scale the blue down, (except
> when converting to grayscale), but this was merely to demonstrate the real
> perception of blue relative to the other colours.

OK! I think I see it.. So instead of using 0,1,1 for cyan, I should use 0, 
0.5, 0.5
I know about the eye sensitivity curve, that's not an issue here.
I just thought maybe I was hosing something up that wasn't obvious.
Like how media dosen't work unless the object is hollow.

THANKS!,  I'm rolling now.

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