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29 Mar 2024 02:41:26 EDT (-0400)
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From: Thomas de Groot
Subject: Re: Media density
Date: 25 Jul 2016 02:57:38
Message: <5795b862$1@news.povray.org>
On 24-7-2016 18:09, clipka wrote:
> Am 24.07.2016 um 12:50 schrieb Thomas de Groot:
>
>> Also be aware that in a density pattern colours are
>> interpreted as grey tints.
>
> Actually, no, they're not. They do modify the media's effective colour.
>

Yes, but are the 'colours' used /inside/ the density statements not read 
as grey tints? That is what I have understood (which doesn't mean 
anything of course). ;-)

-- 
Thomas


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From: Thomas de Groot
Subject: Re: Media density
Date: 25 Jul 2016 03:21:08
Message: <5795bde4$1@news.povray.org>
On 25-7-2016 8:57, Thomas de Groot wrote:
> On 24-7-2016 18:09, clipka wrote:
>> Am 24.07.2016 um 12:50 schrieb Thomas de Groot:
>>
>>> Also be aware that in a density pattern colours are
>>> interpreted as grey tints.
>>
>> Actually, no, they're not. They do modify the media's effective colour.
>>
>
> Yes, but are the 'colours' used /inside/ the density statements not read
> as grey tints? That is what I have understood (which doesn't mean
> anything of course). ;-)
>

I looked that up and was put back right on my feet again. I must have an 
alternate universe documentation file in my head... :-)

-- 
Thomas


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From: Stephen
Subject: Re: Media density
Date: 25 Jul 2016 04:32:26
Message: <5795ce9a$1@news.povray.org>
On 7/25/2016 8:21 AM, Thomas de Groot wrote:
> On 25-7-2016 8:57, Thomas de Groot wrote:
>> On 24-7-2016 18:09, clipka wrote:
>>> Am 24.07.2016 um 12:50 schrieb Thomas de Groot:
>>>
>>>> Also be aware that in a density pattern colours are
>>>> interpreted as grey tints.
>>>
>>> Actually, no, they're not. They do modify the media's effective colour.
>>>
>>
>> Yes, but are the 'colours' used /inside/ the density statements not read
>> as grey tints? That is what I have understood (which doesn't mean
>> anything of course). ;-)
>>
>
> I looked that up and was put back right on my feet again. I must have an
> alternate universe documentation file in my head... :-)
>

That's what I thought. That it averaged the colour values.
Where about in the documentation. Do you have a reference?

-- 

Regards
     Stephen


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From: clipka
Subject: Re: Media density
Date: 25 Jul 2016 04:56:26
Message: <5795d43a$1@news.povray.org>
Am 25.07.2016 um 10:32 schrieb Stephen:
> On 7/25/2016 8:21 AM, Thomas de Groot wrote:
>> On 25-7-2016 8:57, Thomas de Groot wrote:
>>> On 24-7-2016 18:09, clipka wrote:
>>>> Am 24.07.2016 um 12:50 schrieb Thomas de Groot:
>>>>
>>>>> Also be aware that in a density pattern colours are
>>>>> interpreted as grey tints.
>>>>
>>>> Actually, no, they're not. They do modify the media's effective colour.
>>>>
>>>
>>> Yes, but are the 'colours' used /inside/ the density statements not read
>>> as grey tints? That is what I have understood (which doesn't mean
>>> anything of course). ;-)
>>
>> I looked that up and was put back right on my feet again. I must have an
>> alternate universe documentation file in my head... :-)
> 
> That's what I thought. That it averaged the colour values.
> Where about in the documentation. Do you have a reference?

It is neither a grey value, nor a plain average.

I suspect your misconceptions may have their roots somewhere in the fact
that there are two knobs available to introduce colour to media: The
`emission`, `scattering` or `absorption` statement, respectively, and
the `density` statement.


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From: Stephen
Subject: Re: Media density
Date: 25 Jul 2016 05:35:34
Message: <5795dd66$1@news.povray.org>
On 7/25/2016 9:56 AM, clipka wrote:
> Am 25.07.2016 um 10:32 schrieb Stephen:
>> On 7/25/2016 8:21 AM, Thomas de Groot wrote:
>>> On 25-7-2016 8:57, Thomas de Groot wrote:
>>>> On 24-7-2016 18:09, clipka wrote:
>>>>> Am 24.07.2016 um 12:50 schrieb Thomas de Groot:
>>>>>
>>>>>> Also be aware that in a density pattern colours are
>>>>>> interpreted as grey tints.
>>>>>
>>>>> Actually, no, they're not. They do modify the media's effective colour.
>>>>>
>>>>
>>>> Yes, but are the 'colours' used /inside/ the density statements not read
>>>> as grey tints? That is what I have understood (which doesn't mean
>>>> anything of course). ;-)
>>>
>>> I looked that up and was put back right on my feet again. I must have an
>>> alternate universe documentation file in my head... :-)
>>
>> That's what I thought. That it averaged the colour values.
>> Where about in the documentation. Do you have a reference?
>
> It is neither a grey value, nor a plain average.
>

And it is?
...

> I suspect your misconceptions may have their roots somewhere in the fact
> that there are two knobs available to introduce colour to media: The
> `emission`, `scattering` or `absorption` statement, respectively, and
> the `density` statement.
>

I'm thinking of the value that the `density` statement passes to the 
media statement. Which it gets from the df3 file.


-- 

Regards
     Stephen


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From: Thomas de Groot
Subject: Re: Media density
Date: 25 Jul 2016 06:58:51
Message: <5795f0eb$1@news.povray.org>
On 25-7-2016 10:32, Stephen wrote:
> On 7/25/2016 8:21 AM, Thomas de Groot wrote:
>> On 25-7-2016 8:57, Thomas de Groot wrote:
>>> On 24-7-2016 18:09, clipka wrote:
>>>> Am 24.07.2016 um 12:50 schrieb Thomas de Groot:
>>>>
>>>>> Also be aware that in a density pattern colours are
>>>>> interpreted as grey tints.
>>>>
>>>> Actually, no, they're not. They do modify the media's effective colour.
>>>>
>>>
>>> Yes, but are the 'colours' used /inside/ the density statements not read
>>> as grey tints? That is what I have understood (which doesn't mean
>>> anything of course). ;-)
>>>
>>
>> I looked that up and was put back right on my feet again. I must have an
>> alternate universe documentation file in my head... :-)
>>
>
> That's what I thought. That it averaged the colour values.
> Where about in the documentation. Do you have a reference?
>

In the media section [3.4.8.4.2 Density with color_map]. In the wiki 
that probably is at a different paragraph number.

Like you, was under the impression that colour values were averaged and 
I don't remember where I got that notion from :-(

-- 
Thomas


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From: omniverse
Subject: Re: Media density
Date: 25 Jul 2016 07:00:00
Message: <web.5795f00c1a150b85b1933f770@news.povray.org>
Stephen <mca### [at] aolcom> wrote:
> I'm thinking of the value that the `density` statement passes to the
> media statement. Which it gets from the df3 file

Is it possible your thinking of the hf_gray_16 output file, of which the docs
say:

height = 0.3 * red + 0.59 * green + 0.11 * blue

I took a look at the documentation regarding df3 and didn't see anything
relating to this same formula, except I'm going to guess it might be used when a
df3 is put into a normal {} statement.

I sure can't say what's what about this, just thought I would mention what it
made me think of and that was the height field formula above.


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From: Stephen
Subject: Re: Media density
Date: 25 Jul 2016 08:20:31
Message: <5796040f$1@news.povray.org>
On 7/25/2016 11:58 AM, Thomas de Groot wrote:
>>> I looked that up and was put back right on my feet again. I must have an
>>> alternate universe documentation file in my head... :-)
>>>
>>
>> That's what I thought. That it averaged the colour values.
>> Where about in the documentation. Do you have a reference?
>>
>
> In the media section [3.4.8.4.2 Density with color_map]. In the wiki
> that probably is at a different paragraph number.
>
> Like you, was under the impression that colour values were averaged and
> I don't remember where I got that notion from :-(

But it says:

The pattern function returns a value from 0.0 to 1.0 and the value is 
passed to the color map to compute what color or blend of colors is used.

When I said "averaged" I meant it in the non technical sense.
So that is what I was thinking about. That value is not a vector.

When I made colour df3's I made them using R, G & Blue filters. Then 
combined them in three media statements. It was clean and simple.

-- 

Regards
     Stephen


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From: Stephen
Subject: Re: Media density
Date: 25 Jul 2016 08:26:48
Message: <57960588$1@news.povray.org>
On 7/25/2016 11:55 AM, omniverse wrote:
> Stephen <mca### [at] aolcom> wrote:
>> I'm thinking of the value that the `density` statement passes to the
>> media statement. Which it gets from the df3 file
>
> Is it possible your thinking of the hf_gray_16 output file, of which the docs
> say:
>
> height = 0.3 * red + 0.59 * green + 0.11 * blue
>

It could very well be. It looks as if some thought has gone into the 
formula. :)

> I took a look at the documentation regarding df3 and didn't see anything
> relating to this same formula, except I'm going to guess it might be used when a
> df3 is put into a normal {} statement.
>

Pause for thought. I've never considered using one in a normal 
statement. I've only used them with media.

> I sure can't say what's what about this, just thought I would mention what it
> made me think of and that was the height field formula above.
>

One of those things we thing we know and when you look closely. You find 
you don't. :)


-- 

Regards
     Stephen


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From: clipka
Subject: Re: Media density
Date: 25 Jul 2016 11:19:50
Message: <57962e16$1@news.povray.org>
Am 25.07.2016 um 11:35 schrieb Stephen:
> On 7/25/2016 9:56 AM, clipka wrote:
>> Am 25.07.2016 um 10:32 schrieb Stephen:
>>> On 7/25/2016 8:21 AM, Thomas de Groot wrote:
>>>> On 25-7-2016 8:57, Thomas de Groot wrote:
>>>>> On 24-7-2016 18:09, clipka wrote:
>>>>>> Am 24.07.2016 um 12:50 schrieb Thomas de Groot:
>>>>>>
>>>>>>> Also be aware that in a density pattern colours are
>>>>>>> interpreted as grey tints.
>>>>>>
>>>>>> Actually, no, they're not. They do modify the media's effective
>>>>>> colour.
>>>>>>
>>>>>
>>>>> Yes, but are the 'colours' used /inside/ the density statements not
>>>>> read
>>>>> as grey tints? That is what I have understood (which doesn't mean
>>>>> anything of course). ;-)
>>>>
>>>> I looked that up and was put back right on my feet again. I must
>>>> have an
>>>> alternate universe documentation file in my head... :-)
>>>
>>> That's what I thought. That it averaged the colour values.
>>> Where about in the documentation. Do you have a reference?
>>
>> It is neither a grey value, nor a plain average.
>>
> 
> And it is?
> ....

Just the plain colour.

>> I suspect your misconceptions may have their roots somewhere in the fact
>> that there are two knobs available to introduce colour to media: The
>> `emission`, `scattering` or `absorption` statement, respectively, and
>> the `density` statement.
>>
> 
> I'm thinking of the value that the `density` statement passes to the
> media statement. Which it gets from the df3 file.

Uh... no, `density` does /not/ get its value from "the df3 file". It
gets its value (which is actually a colour) from a `density_map` and
pattern.

That pattern /can/ be a df3 file, using the `density_file` pattern, but
it is just one of many options.


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