Warp wrote:
> Warp <war### [at] tagpovrayorg> wrote:
>>   Now the lower half of the rendered images is a checkerboard pattern of
>> alternating black and white pixels.
> 
>   There was a warning somewhere that a checkerboard patter should *not* be
> used for this kind of test because it doesn't work properly with CRT
> monitors. Instead, alternating horizontal lines should be used instead.

I have an LCD monitor, and the checkerboard looked *green*. Quite strange.

Now with the horizontal stripes. POV3.6 looks too dark and POV3.7 looks too
light.

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Nicolas Alvarez <nic### [at] gmailcom> wrote:
> Now with the horizontal stripes. POV3.6 looks too dark and POV3.7 looks too
> light.

  As I already wrote, now that I'm using the proper test (at least for CRT
monitors, which is what I have), I must admit that the 3.7 image background
looks very even with my monitor. I suppose that my monitor does indeed
require a gamma correction of almost exactly 2.2 for proper brightness,
and that my system settings were correct to begin with.

  On the other hand, I'm wondering how precise this test really is.
Bright white lines stand out a lot more than black lines, and the brighter
the white lines are, the more they tend to glow to the human eye. A bit
like color bleeding. This would mean that if your monitor is set very
bright, then the white lines will overwhelm the black ones, requiring
a different gamma correction value than if your monitor was set to a
very dim setting, in which case the white lines won't stand out that much
compared to the black lines.

-- 
                                                          - Warp

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Warp wrote:
> This would mean that if your monitor is set very
> bright, then the white lines will overwhelm the black ones, requiring
> a different gamma correction value 

Isn't this kind of the point, tho? Unless you turn up both the black level 
and the white level in a controlled way, I'd think increasing the brightness 
of one or the other is going to mean you have to correct your images 
differently for them to "look right".

-- 
   Darren New, San Diego CA, USA (PST)
   Understanding the structure of the universe
    via religion is like understanding the
     structure of computers via Tron.

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Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> > This would mean that if your monitor is set very
> > bright, then the white lines will overwhelm the black ones, requiring
> > a different gamma correction value 

> Isn't this kind of the point, tho? Unless you turn up both the black level 
> and the white level in a controlled way, I'd think increasing the brightness 
> of one or the other is going to mean you have to correct your images 
> differently for them to "look right".

  What I meant is that, at least it seems to me, this phenomenon would be
exclusive to this precise test (in other words, alternating black/white
horizontal lines) and might not correspond to what is intended to be a
"50% gray" in an image would really look like on your monitor.

  Or if I try to express myself more clearly: Could it be that this
precise test (the horizontal lines) gives you the wrong impression of
what the proper gamma setting for your monitor would really be, this
visual impression being biased by the brightness setting of the monitor?

  If you used a completely different test, eg. physical pieces of paper
colored appropriately, would you end up with the same gamma setting?

-- 
                                                          - Warp

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Warp wrote:
>   What I meant is that, at least it seems to me, this phenomenon would be
> exclusive to this precise test 

I see. That makes more sense, yes.

-- 
   Darren New, San Diego CA, USA (PST)
   Understanding the structure of the universe
    via religion is like understanding the
     structure of computers via Tron.

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Warp schrieb:
>   I find it a bit hypocritical for you to criticize me and tell me to shut
> the fuck up when even you can't get the math right.

That's what happens when one gets annoyed by the other one not 
listening, alleging that one is "explaining nothing at all", and being 
extraordinarily demanding: It drastically reduces the motivation to 
invest time into it.

Besides it would be more humiliating for me if I didn't know already 
that I keep getting the exponent wrong way round.

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Warp schrieb:
>   (Btw, IMO there still should be a way of telling POV-Ray to not gamma
> correct anything if that's what the user wishes. Currently it seems to
> be difficult, as POV-Ray seems to be writing a gamma value of 2.2 to the
> output PNG file regardless of what File_Gamma is. I don't even understand
> where it's getting that 2.2 value from.)

That's not POV-Ray, it's the display software. Encoded pixel data and 
the embedded gamma information together allow the viewing software to 
reconstruct the linear values, and it will then convert this to whatever 
it assumes the actual display hardware gamma to be.

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Warp schrieb:
>   It was not, after all, a problem with my monitor gamma. It was a problem
> with the test being skewed by how CRT works.

That does explain the whole smash then. I didn't expect it to make that 
much of a difference (I'm using an LCD myself).

>   There's still the problem of the image map incorrectly brightening, though.

Input file gamma issues. POV-Ray, as mentioned already, is currently 
pretty poor about this (and has always been, by the way).

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Nicolas Alvarez schrieb:
> I have an LCD monitor, and the checkerboard looked *green*. Quite strange.

Do you use an analog or digital connection?

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Warp schrieb:
>   On the other hand, I'm wondering how precise this test really is.
> Bright white lines stand out a lot more than black lines, and the brighter
> the white lines are, the more they tend to glow to the human eye. A bit
> like color bleeding. This would mean that if your monitor is set very
> bright, then the white lines will overwhelm the black ones, requiring
> a different gamma correction value than if your monitor was set to a
> very dim setting, in which case the white lines won't stand out that much
> compared to the black lines.

You can do the same test with a 0.0 / 0.5 checkerboard and 0.25 
background, for instance.

Indeed lighting conditions (of your room, not your scene ;-)) do 
influence the perception of brightness and mess with the gamma, so I'd 
assume display brightness possibly does as well.

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