POV-Ray : Newsgroups : povray.general : smooth gradient color_map Server Time: 19 Oct 2017 10:53:03 GMT
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From: Jim Holsenback
Subject: Re: smooth gradient color_map
Date: 23 Jul 2017 14:18:36
Message: <5974b03c$1@news.povray.org>
On 7/23/2017 9:13 AM, Jim Holsenback wrote:
> On 7/23/2017 7:43 AM, Jim Holsenback wrote:
>> On 7/23/2017 2:56 AM, Thomas de Groot wrote:
>>> On 23-7-2017 8:21, omniverse wrote:
>>>> clipka <ano### [at] anonymousorg> wrote:
>>>>> Am 22.07.2017 um 20:21 schrieb omniverse:
>>>>>
>>>>>> And something curious going on, I'm not sure about, when I add 
>>>>>> blend_mode to my
>>>>>> example; I can't get the same appearance as yours, which seems to 
>>>>>> remove the
>>>>>> purple color between blue and red.
>>> [...]
>>>
>>> Now I am completely lost indeed. Where do you put that "blend_mode" 
>>> parameter??? The wiki doesn't show in the examples, while it 
>>> discusses it; something to correct I guess.
>>>
>>
>> true enough no example ... but i thought i hinted about the order with 
>> the syntax diagram
> 
> well ok now ... looking closer i'm not entirely comfortable with that 
> syntax diagram. i think i can do better. i'm trying to get 3.8 docs 
> squared away so we can get back to doing a release ... standby

the syntax diagram has been changed to /correctly/ reflect it's /order/ 
specific nature when using blend_mode:

http://wiki.povray.org/content/Reference:Color_Map
http://wiki.povray.org/content/Reference:Pigment_Map


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From: Thomas de Groot
Subject: Re: smooth gradient color_map
Date: 24 Jul 2017 06:40:23
Message: <59759657$1@news.povray.org>
On 23-7-2017 16:18, Jim Holsenback wrote:
> the syntax diagram has been changed to /correctly/ reflect it's /order/ 
> specific nature when using blend_mode:
> 
> http://wiki.povray.org/content/Reference:Color_Map
> http://wiki.povray.org/content/Reference:Pigment_Map

Thank you indeed Jim, much clearer now.

-- 
Thomas


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From: omniverse
Subject: Re: smooth gradient color_map
Date: 24 Jul 2017 08:15:00
Message: <web.5975ac806b1125dc9c5d6c810@news.povray.org>
Thomas de Groot <tho### [at] degrootorg> wrote:
> On 23-7-2017 16:18, Jim Holsenback wrote:
> > the syntax diagram has been changed to /correctly/ reflect it's /order/
> > specific nature when using blend_mode:
> >
> > http://wiki.povray.org/content/Reference:Color_Map
> > http://wiki.povray.org/content/Reference:Pigment_Map
>
> Thank you indeed Jim, much clearer now.
>
> --
> Thomas

Documentation is 2nd only to the program itself, and sometimes I think of it the
other way around.

Thanks goes to Christoph (clipka) too for that more thorough blend explanation.
Takes me a couple three reads for most things like that. Ahhh that technical
detail stuff!

Bob


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From: Thomas de Groot
Subject: Re: smooth gradient color_map
Date: 24 Jul 2017 10:48:56
Message: <5975d098$1@news.povray.org>
On 24-7-2017 10:14, omniverse wrote:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> On 23-7-2017 16:18, Jim Holsenback wrote:
>>> the syntax diagram has been changed to /correctly/ reflect it's /order/
>>> specific nature when using blend_mode:
>>>
>>> http://wiki.povray.org/content/Reference:Color_Map
>>> http://wiki.povray.org/content/Reference:Pigment_Map
>>
>> Thank you indeed Jim, much clearer now.
>>
>> --
>> Thomas
> 
> Documentation is 2nd only to the program itself, and sometimes I think of it the
> other way around.
> 
> Thanks goes to Christoph (clipka) too for that more thorough blend explanation.
> Takes me a couple three reads for most things like that. Ahhh that technical
> detail stuff!
> 

I fully agree. Would it be going to far to ask if some of that 
explanation could be included into the docs? I think it is not trivial.

-- 
Thomas


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From: Jim Holsenback
Subject: Re: smooth gradient color_map
Date: 24 Jul 2017 11:16:00
Message: <5975d6f0$1@news.povray.org>
On 7/24/2017 6:48 AM, Thomas de Groot wrote:
> On 24-7-2017 10:14, omniverse wrote:
>> Thomas de Groot <tho### [at] degrootorg> wrote:
>>> On 23-7-2017 16:18, Jim Holsenback wrote:
>>>> the syntax diagram has been changed to /correctly/ reflect it's /order/
>>>> specific nature when using blend_mode:
>>>>
>>>> http://wiki.povray.org/content/Reference:Color_Map
>>>> http://wiki.povray.org/content/Reference:Pigment_Map
>>>
>>> Thank you indeed Jim, much clearer now.
>>>
>>> -- 
>>> Thomas
>>
>> Documentation is 2nd only to the program itself, and sometimes I think 
>> of it the
>> other way around.
>>
>> Thanks goes to Christoph (clipka) too for that more thorough blend 
>> explanation.
>> Takes me a couple three reads for most things like that. Ahhh that 
>> technical
>> detail stuff!
>>
> 
> I fully agree. Would it be going to far to ask if some of that 
> explanation could be included into the docs? I think it is not trivial.
> 

i just updated (developer suggested) both syntax diagrams again ... if 
you could help me out by replying here with relevant portions and i'll 
follow up in the morning.


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From: Thomas de Groot
Subject: Re: smooth gradient color_map
Date: 24 Jul 2017 11:59:06
Message: <5975e10a@news.povray.org>
On 24-7-2017 13:15, Jim Holsenback wrote:
> On 7/24/2017 6:48 AM, Thomas de Groot wrote:
>> On 24-7-2017 10:14, omniverse wrote:
>>> Thomas de Groot <tho### [at] degrootorg> wrote:
>>>> On 23-7-2017 16:18, Jim Holsenback wrote:
>>>>> the syntax diagram has been changed to /correctly/ reflect it's 
>>>>> /order/
>>>>> specific nature when using blend_mode:
>>>>>
>>>>> http://wiki.povray.org/content/Reference:Color_Map
>>>>> http://wiki.povray.org/content/Reference:Pigment_Map
>>>>
>>>> Thank you indeed Jim, much clearer now.
>>>>
>>>> -- 
>>>> Thomas
>>>
>>> Documentation is 2nd only to the program itself, and sometimes I 
>>> think of it the
>>> other way around.
>>>
>>> Thanks goes to Christoph (clipka) too for that more thorough blend 
>>> explanation.
>>> Takes me a couple three reads for most things like that. Ahhh that 
>>> technical
>>> detail stuff!
>>>
>>
>> I fully agree. Would it be going to far to ask if some of that 
>> explanation could be included into the docs? I think it is not trivial.
>>
> 
> i just updated (developer suggested) both syntax diagrams again ... if 
> you could help me out by replying here with relevant portions and i'll 
> follow up in the morning.

I shall do that tomorrow if you don't mind. I have to go away now.

-- 
Thomas


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From: clipka
Subject: Re: smooth gradient color_map
Date: 24 Jul 2017 16:57:33
Message: <597626fd$1@news.povray.org>
Am 24.07.2017 um 10:14 schrieb omniverse:

> Thanks goes to Christoph (clipka) too for that more thorough blend explanation.
> Takes me a couple three reads for most things like that. Ahhh that technical
> detail stuff!

I'm not sure if I should get credit for at last explaining the stuff I
implemented myself...


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From: Thomas de Groot
Subject: Re: smooth gradient color_map
Date: 25 Jul 2017 07:42:42
Message: <5976f672$1@news.povray.org>
On 24-7-2017 13:15, Jim Holsenback wrote:

> i just updated (developer suggested) both syntax diagrams again ... if 
> you could help me out by replying here with relevant portions and i'll 
> follow up in the morning.

I /think/ it is quite clear now what is intended and what blend_mode 
does to the color_map entries. I find it a difficult matter altogether 
though. Like always, I need a simple example to play with in order to 
show me the differences. I have not yet done that with Christoph's 
examples but will do so presently....

After playing a bit with that, I think I understand the theory but less 
the (practical) use of blend_mode :-/

-- 
Thomas


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From: clipka
Subject: Re: smooth gradient color_map
Date: 25 Jul 2017 16:07:45
Message: <59776cd1$1@news.povray.org>
Am 25.07.2017 um 09:42 schrieb Thomas de Groot:
> On 24-7-2017 13:15, Jim Holsenback wrote:
> 
>> i just updated (developer suggested) both syntax diagrams again ... if
>> you could help me out by replying here with relevant portions and i'll
>> follow up in the morning.
> 
> I /think/ it is quite clear now what is intended and what blend_mode
> does to the color_map entries. I find it a difficult matter altogether
> though. Like always, I need a simple example to play with in order to
> show me the differences. I have not yet done that with Christoph's
> examples but will do so presently....
> 
> After playing a bit with that, I think I understand the theory but less
> the (practical) use of blend_mode :-/

Problem #1:

Linear greyscale gradients (which is what you get by default with
`assumed_gamma 1.0`) are typically perceived as non-linear.

Solution:

Introduce a mechanism to interpolate colour gradients in a non-linear
fashion. Enter `blend_mode 2`. (`blend_mode 1` was defined as a
mechanism to interpolate gradients in a linear fashion even when
`assumed_gamma 2.2` or similar is used.)


Problem #2:

Non-linear interpolation of colour gradients, if done on RGB values,
causes colour gradients to exhibit a midway dip in brightness and a poor
midway hue (note that this effect can be seen not only with `blend_mode
2`, but also with default blend mode if `assumed_gamma 2.2` or similar
is used).

Solution:

Introduce a mechanism to interpolate brightness in a non-linear fashion
while interpolating chromaticity (the relative ratio of R:G:B) in a
linear fashion. Enter `blend_mode 3`.


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From: Thomas de Groot
Subject: Re: smooth gradient color_map
Date: 26 Jul 2017 06:53:03
Message: <59783c4f$1@news.povray.org>
On 25-7-2017 18:07, clipka wrote:
> Problem #1:
> 
> Linear greyscale gradients (which is what you get by default with
> `assumed_gamma 1.0`) are typically perceived as non-linear.
> 
> Solution:
> 
> Introduce a mechanism to interpolate colour gradients in a non-linear
> fashion. Enter `blend_mode 2`. (`blend_mode 1` was defined as a
> mechanism to interpolate gradients in a linear fashion even when
> `assumed_gamma 2.2` or similar is used.)
> 
> 
> Problem #2:
> 
> Non-linear interpolation of colour gradients, if done on RGB values,
> causes colour gradients to exhibit a midway dip in brightness and a poor
> midway hue (note that this effect can be seen not only with `blend_mode
> 2`, but also with default blend mode if `assumed_gamma 2.2` or similar
> is used).
> 
> Solution:
> 
> Introduce a mechanism to interpolate brightness in a non-linear fashion
> while interpolating chromaticity (the relative ratio of R:G:B) in a
> linear fashion. Enter `blend_mode 3`.
> 

Thank you indeed Christoph, much appreciated. My thoughts were not a 
criticism towards the methods but more a failure from my side to 
/really/ understand what was going on, and I did not go too deep into 
experimentations. Your explanation is (as always) welcome and clear. 
Next time I need some blending I shall certainly explore deeper.

-- 
Thomas


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