In addition to all the post-process requests that have been made in the
past few days, there is one that is particularly important to me, which
is the ability to manipulate separately the highlights/midtone/shadows
proportions (?) of the image. (if this was already mentioned under
another name in one of Glen Berry's message, forget about it).
Many (not all) povray images "out of the render" share a common
characteristic that makes them instantly recognizable, which is to be
too evenly lit : they're too dark, or too bright, and generally lack
contrast and saturation. There are ways in povray to avoid this, but I
find it very difficult to obtain when the scenes involve many light
sources and in fact I'm not sure it can be done for every picture. One
simple post-process trick is to tinker with the highlight/midtone/shadow
proportions, generally by increasing both the hightlights and the
shadows. The price to pay is a loss of detail in both ranges, so this
must be used wisely, but many pictures greatly benefit from this and
appear much more "lively", as if a thin layer of dust had been removed.
I'll post before/after examples in pov.binaries if someone is
interested.

G.

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Yes show me an example :).

Fabian.


> 
> In addition to all the post-process requests that have been made in the
> past few days, there is one that is particularly important to me, which
> is the ability to manipulate separately the highlights/midtone/shadows
> proportions (?) of the image. (if this was already mentioned under
> another name in one of Glen Berry's message, forget about it).
> Many (not all) povray images "out of the render" share a common
> characteristic that makes them instantly recognizable, which is to be
> too evenly lit : they're too dark, or too bright, and generally lack
> contrast and saturation. There are ways in povray to avoid this, but I
> find it very difficult to obtain when the scenes involve many light
> sources and in fact I'm not sure it can be done for every picture. One
> simple post-process trick is to tinker with the highlight/midtone/shadow
> proportions, generally by increasing both the hightlights and the
> shadows. The price to pay is a loss of detail in both ranges, so this
> must be used wisely, but many pictures greatly benefit from this and
> appear much more "lively", as if a thin layer of dust had been removed.
> I'll post before/after examples in pov.binaries if someone is
> interested.
> 
> G.

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On Thu, 27 Apr 2000 11:29:37 +0200, Gilles Tran <tra### [at] inapginrafr>
wrote:

>In addition to all the post-process requests that have been made in the
>past few days, there is one that is particularly important to me, which
>is the ability to manipulate separately the highlights/midtone/shadows
>proportions (?) of the image. (if this was already mentioned under
>another name in one of Glen Berry's message, forget about it).

If we get the ability to alter tonality using things like
"iso-functions", we can achieve much of what you want, if not all.
Some of the toning filters I suggested affect shadows the most ,
midtones somewhat, and the highlights were practically untouched. I'm
sure that different functions could be implemented to affect whatever
portion of the tonal range you want to selectively enhance.

There is also a function in both Photoshop and Gimp called "Auto
Levels" I'm not sure how it works in detail, but it often helps a
typical POV render to perform this function on it. Perhaps a similar
feature could be done inside POV? Basically, it would set the black
point and white point of the image, and scale the tonal range of
everything else to fit between those two points. This makes sure that
the areas that should be black are truely black, the areas that should
be white are truly white, and all the grays in between are evenly
distributed between them.

There is one side-effect of the Photoshop and Gimp filters. They will
sometimes alter the color balance of an image, because they perform
this tonal range optimization on each RGB channel independently. I
suggest that we explore altering each RGB channel the same amount, in
unison. We alter them based upon their value when averaged together.
This would avoid all color shifts.

Gilles, have you tried "auto levels" ?  Does it do anything similar to
what you want?


Later,
Glen Berry

( Remove the "7" from 7no### [at] ezwvcom to email me. )

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It is starting to sound like POV-Ray needs a plugin feature added
with a SDK plug in development environment rather than a whole
bunch of post processing effects that will never meet all of the
requirements that will be asked of it.

-- 
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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On Thu, 27 Apr 2000 11:00:45 -0700, Ken <tyl### [at] pacbellnet> wrote:

>It is starting to sound like POV-Ray needs a plugin feature added
>with a SDK plug in development environment <SNIP>

I had thought of something like this long ago, but as I understand it,
the POV-Team frowns on the idea of plugins. If I'm not mistaken Ron
Parker was asking for plugins a long time ago, and was promptly told
"no."

For post processing, it would be *very* cool if we could use actual
Photoshop compatible plugins, but I doubt this would be very practical
to code, because of the major differences between the two
environments. There are also some data types that are unique to POV
which Photoshop plugins wouldn't be able to take advantage of at all.
If Photoshop compatible plugins were ever useable in POV, we would
still need our own specialized POV plugins to take advantage of those
special geometry related data types, and other POV-unique variables.
Even so, it would still be *very* nice to be able to take advantage of
the large assortment of Photoshop compatible plugins available.
Several of these are even available as freeware.

Later,
Glen Berry

( Remove the "7" from 7no### [at] ezwvcom to email me. )

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Glen Berry wrote:

> I had thought of something like this long ago, but as I understand it,
> the POV-Team frowns on the idea of plugins. If I'm not mistaken Ron
> Parker was asking for plugins a long time ago, and was promptly told
> "no."

Yes, but... Ronald L. Parker is a member of the POV-Team now :)


> If Photoshop compatible plugins were ever useable in POV, we would
> still need our own specialized POV plugins to take advantage of those
> special geometry related data types, and other POV-unique variables.

That is why I recommend a special plugin environment specific to POV-Ray.
A practical suggestion ? I don't know but worth mentioning none the less.

> Even so, it would still be *very* nice to be able to take advantage of
> the large assortment of Photoshop compatible plugins available.
> Several of these are even available as freeware.

It would be nice but I don't know how practical it would be. The older
8bit filters would probably be applicable but with the 16bit and later
filters they came out with a bunch of GUI dependent slider controls
that would be impossible to implement in a cross platform program like
POV-Ray.

-- 
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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On Thu, 27 Apr 2000 11:40:12 -0700, Ken <tyl### [at] pacbellnet> wrote:

>It would be nice but I don't know how practical it would be. The older
>8bit filters would probably be applicable but with the 16bit and later
>filters they came out with a bunch of GUI dependent slider controls
>that would be impossible to implement in a cross platform program like
>POV-Ray.

I would't be surprised if a lot of those slider controlled plugins
couldn't be adapted to run from parameters passed to them from a POV
scene file. Of course, you would lose the "preview" feature, and have
to know what values you wanted to send the plugin, but it might work.
Of course, I could easily be mistaken.   :)

Later,
Glen Berry

( Remove the "7" from 7no### [at] ezwvcom to email me. )

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In article <39080881.2064B6D2@inapg.inra.fr>, Gilles Tran 
<tra### [at] inapginrafr> wrote:

> In addition to all the post-process requests that have been made in the
> past few days, there is one that is particularly important to me, which
> is the ability to manipulate separately the highlights/midtone/shadows
> proportions (?) of the image. (if this was already mentioned under
> another name in one of Glen Berry's message, forget about it).
> Many (not all) povray images "out of the render" share a common
> characteristic that makes them instantly recognizable, which is to be
> too evenly lit : they're too dark, or too bright, and generally lack
> contrast and saturation. There are ways in povray to avoid this, but I
> find it very difficult to obtain when the scenes involve many light
> sources and in fact I'm not sure it can be done for every picture. One
> simple post-process trick is to tinker with the highlight/midtone/shadow
> proportions, generally by increasing both the hightlights and the
> shadows. The price to pay is a loss of detail in both ranges, so this
> must be used wisely, but many pictures greatly benefit from this and
> appear much more "lively", as if a thin layer of dust had been removed.
> I'll post before/after examples in pov.binaries if someone is
> interested.

If you can give me some of the math behind this, I could try to make a 
filter for it. You can already shift the color balance around some using 
the exponent, add, and multiply filters which I added.

-- 
Christopher James Huff - Personal e-mail: chr### [at] yahoocom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://chrishuff.dhs.org/
TAG Web page: http://tag.povray.org/

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Ken wrote in message <3908804D.3FBE5C60@pacbell.net>...
>
>It is starting to sound like POV-Ray needs a plugin feature added
>with a SDK plug in development environment rather than a whole
>bunch of post processing effects that will never meet all of the
>requirements that will be asked of it.


There is one way of implementing a plugin system for POV-Ray that would be
relatively easy and completely platform-independant:  Pov-Script.

Pov-Script plugins could be implemented as a macro in the main scene file,
or in a separate scene or include file specified as part of the filter
definition.  It should be possible to create any post-process filter you
could want using Pov-Script.

To a Pov-Script plugin filter, the image would need to be available as
either an array of structures containing the information for each pixel, or
as a set of arrays containing the information.

Mark

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On Fri, 28 Apr 2000 01:14:58 -0400, "Mark Wagner"
<mar### [at] gtenet> wrote:

>There is one way of implementing a plugin system for POV-Ray that would be
>relatively easy and completely platform-independant:  Pov-Script.

That sounds extremely slow for an image processing system.

( Remove the "7" from 7no### [at] ezwvcom to email me. )

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