In article <=qAEOc9gmlpxWf8+V87kmu2mtM4W@4ax.com>, Glen Berry 
<7no### [at] ezwvcom> wrote:

> I think there was another reason for blurring the negative, in
> addition to worries about film alignment or grain. I think it had to
> do with preserving the high frequency content and "local contrast" of
> the image.

Ah, I see. That way, the smaller features would not be "corrected" out 
of the image, but the larger areas would still be affected.


> I'm trying to find some technical reference material on the subject,
> but haven't yet. I've had to work strictly from my personal memory so
> far, but I'd like to find some technical documentation on this
> subject. The internet turns out to be a very poor place to search for
> this information, because practically all the search engine hits refer
> to the Photoshop unsharp mask effect.

I did a search with Sherlock, and found this page:
http://www.ittc.ukans.edu/~jgauch/kuim/contrast/unsharp.html
This might also be relevant:
http://www.computer.org/proceedings/icip97/8183-439.htm

Some other interesting stuff:
http://www.ph.tn.tudelft.nl/Courses/FIP/noframes/fip-Basic.html
http://perso.club-internet.fr/legault/ip.html


> Also, there *are* things in POV-Ray image that could react to this
> process in a way similar to film grain. High frequency content such as
> crand, fine textures, very small objects, and media "graininess" come
> to mind. Without blurring, I think we would be removing, minimalizing,
> or distorting much of the high frequency content in the image. This
> isn't usually a wanted by-product.

Yes, I understand the technique a bit more now.

-- 
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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On Mon, 24 Apr 2000 15:58:53 -0500, Chris Huff
<chr### [at] yahoocom> wrote:

>I did a search with Sherlock, and found this page:
>http://www.ittc.ukans.edu/~jgauch/kuim/contrast/unsharp.html

I was there earlier today. This page also deals with unsharp masking
as applied to image sharpening. There is no mention of tonal range
manipulation or contrast management. However, there are a *lot* of
post processing techniques discussed at this site. They also provide
source code for each example. It might be a good reference for anyone
wanting to know more about image processing in general. Try their
homepage at this URL:

  http://www.ittc.ukans.edu/~jgauch/kuim/index.html



>This might also be relevant:
>http://www.computer.org/proceedings/icip97/8183-439.htm

This is getting warmer, but no real details are presented here.



>Some other interesting stuff:
>http://www.ph.tn.tudelft.nl/Courses/FIP/noframes/fip-Basic.html
>http://perso.club-internet.fr/legault/ip.html

These are also nice, but still address the use of unsharp masking for
image sharpening, and not the similar technique for contrast
management.

Anyone interested in post-processing would probably want to visit any
of these sites, but for what I am looking for, they are of no help.

I'm still looking...
Glen Berry

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In article <+bUEOels48ML5cOS74XnW16Du5rK@4ax.com>, Glen Berry 
<7no### [at] ezwvcom> wrote:

> Anyone interested in post-processing would probably want to visit any
> of these sites, but for what I am looking for, they are of no help.

Another site in that category is:
http://photo.net/photo/edscott/spectsel.htm
Some interesting stuff here, but I don't see anything that directly 
applies to this problem.

-- 
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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On Mon, 24 Apr 2000 16:26:33 -0500, Chris Huff
<chr### [at] yahoocom> wrote:

>Some interesting stuff here, but I don't see anything that directly 
>applies to this problem.

I figured out something that will help. The more common name for this
technique seems to be "Contrast Masking", and it's also called "Silver
Masking." I swear that once upon a time in the past, I had heard the
technique referred to as "unsharp masking," but apparently that isn't
the term most people use. You can find some information by searching
on combinations of the following phrases:

  contrast masking
  silver masking
  ilfochrome printing
  cibachrome printing
  slide printing

(If you search the photo printing sites, be sure to concentrate on
labs that do professional, custom, hand printing. This is a technique
that isn't used for typical consumer-grade photofinishing.)

When I finish searching, I'll post the best links I found, sometime
tonight.

Hope this helps,
Glen Berry

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Chris Huff <chr### [at] yahoocom> wrote...
> Hmm, it would be nice to have this use the "label" feature, having a new
> "index" feature seems to make for a total of 3 different ways to specify
> an object. The labels could probably be represented internally as an
> index, though...

I have considered that, and that is a good idea.  The current problem is
that if an object is labeled, that is a flag for POV to make it persistent
(when persistent_animation is enabled).  Of course, that could be changed so
you have to set a "persistent true" flag or something like that, then the
labels could be used for stuff like post processing.

> but I have another idea:
> Why not just make this an object pointer? You could add some
> post_process flags to the object, maybe including an ID number(or a
> string, light groups style), and having the pointer to the object
> accessible could also come in handy. It would point to the object at
> Depth, not necessarily the first object.

The problem is that currently the objects in the scene have been destroyed
by the time you get to the post-processing step.  Also, if you tried to do
this with continued renders (or network-distributed renders), you'd run into
major headaches.

> Again, it could be nice to have anti-aliased as well as non anti-aliased
> versions, although that would double the memory usage...maybe just
> include code that could do that if it is needed in the future, and
> comment it out for now.

Already the post-processing buffers can consume lots of memory.  It
currently only allocates specific buffers if you actually use them.  This
same approach could be used for allowing both anti-aliased and
non-antialiased versions.

-Nathan

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I noticed one variable which you seem to have missed: ray direction. The 
normal variables really aren't as useful without this...I can think of a 
couple very interesting uses combining these variables.

-- 
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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In article <UL4EOTVr=tKyJ+48vcVRZtTks0Yd@4ax.com>, Glen Berry 
<7no### [at] ezwvcom> wrote:

> When I finish searching, I'll post the best links I found, sometime
> tonight.

Have you finished yet? Or did I just miss the message...

-- 
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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On Wed, 26 Apr 2000 17:51:55 -0500, Chris Huff
<chr### [at] yahoocom> wrote:

>In article <UL4EOTVr=tKyJ+48vcVRZtTks0Yd@4ax.com>, Glen Berry 
><7no### [at] ezwvcom> wrote:
>
>> When I finish searching, I'll post the best links I found, sometime
>> tonight.
>
>Have you finished yet? Or did I just miss the message...

Sorry Chris,

I've had a bad case of the flu the last few days. I didn't get the
chance to finish later that night, like I thought I would. I'll post
something as soon as I can.  (Assuming I don't catch pneumonia and die
first.)

Later,
Glen Berry


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

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In article <orUIOVMxS0HjTgW9SNP3dMbwXUK8@4ax.com>, Glen Berry 
<7no### [at] ezwvcom> wrote:

> I've had a bad case of the flu the last few days. I didn't get the
> chance to finish later that night, like I thought I would. I'll post
> something as soon as I can. 
> (Assuming I don't catch pneumonia and die first.)

Since I am still recovering from a bad combination cold/flu which I had 
a couple weeks ago, I know how you feel. Get well soon!

-- 
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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