Just a small error correction. PNG does support alpha channels
in index-color mode. The alpha values can be stored in the
palette. (Read it yesterday in a libpng example file)

/ Mathias

Anthony Bennett wrote:
> PNG: developed as a patent-free alternative to GIF, the Portable Network
> Graphics (PNG) format is used for losslessly compressing and displaying
> images on the World Wide Web. Unlike GIF, PNG supports 24-bit images and
> produces background transparency without jagged edges; however, some
> older versions of Web browsers may not support PNG images. The PNG
> format supports grayscale and RGB color modes with a single alpha
> channel, and Bitmap and indexed-color modes without alpha channels. PNG
> uses the saved alpha channel to define transparency in the file.

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Anthony Bennett <ben### [at] panamaphoenixnet> wrote:

: board and is commonly supported by MS-DOS color applications. The Targa
: format supports 32-bit RGB files with a single alpha channel, and
: indexed-color, grayscale, and 16-bit and 24-bit RGB files without alpha
: channels.

  Targa supports also compression. Can you specify which kind of compression?

-- 
main(i,_){for(_?main(i+1,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[--i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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Suggestions for additional topics include:

1. Why raytracers cannot do caustics :
I spent probably 10 hours experimenting with Corel Dream3D trying to get
caustics in an underwater scene by placing refractive, bumpy glass things in
front of my light source.  I was cursing the shareholders of Corel Corp when
I just didn't understand raytracing.

2. Why raytracers cannot make a "homemade" spotlight:
When I first got POV, I probably spent about 10 hours trying to make my own
spotlight with a reflective surface on a parabolic shape and a point light
source in it.  Again, I didn't understand how raytracers worked...

3. Explain compression in the MPEG format by giving exhaustive examples.
This is probably a bit more work, but is still a slight source of confusion.


Nieminen Mika wrote:

>   I started another page with the same idea of the VFAQ page: The
> common misunderstandings page. The intention of the page is to clear up
> some common misunderstanings people have about computer related things
> (mainly about topics related with povray, graphics, etc). The page has
> only one entry right now, which is a very good example of what I mean.
>   Wrong allegations and correct information about them is very welcome.
>   I'll add a link to the page from the VFAQ page if/when I get some more
> entries.
>   The page can be found at:
>
> http://iki.fi/warp/misunderstandings/
>
> --
> main(i,_){for(_?main(i+1,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[--i]
> ):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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On Fri, 12 Mar 1999 08:43:46 -0500, Greg M. Johnson <@aol.com> wrote:
>Suggestions for additional topics include:
>
>1. Why raytracers cannot do caustics :
>2. Why raytracers cannot make a "homemade" spotlight:

These are, of course, both the same topic.  Clearly one would need
to start with a definition of caustics.

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Nieminen Mika <war### [at] cctutfi> writes:

>   Targa supports also compression. Can you specify which kind of
>   compression?

Run length encoding (RLE).  One group of consecutive pixels of the
exact same colour is coded on two (resp. three or four) bytes as a
whole instead of one (resp. two or three) byte for each pixel.  This
allows to use only two bytes to code one hundred pixels if they have
the exact same colour (assuming we are in an eight bits per pixel
image).  Of course, if you have horizontal gradients, this increases
the size of the file instead of diminishing it, but it generally
behaves The Right Way.

Roland.
-- 
Roland Mas


- Genki desu, ture en zinc.

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Ron Parker wrote in message <36e9234a.0@news.povray.org>...
>On Fri, 12 Mar 1999 08:43:46 -0500, Greg M. Johnson <@aol.com> wrote:
>>Suggestions for additional topics include:
>>
>>1. Why raytracers cannot do caustics :
>>2. Why raytracers cannot make a "homemade" spotlight:
>
>These are, of course, both the same topic.  Clearly one would need
>to start with a definition of caustics.

Which is covered in the VFAQ I would guess, and:

Not entirely true anyway, as Nathan is showing us with his new patched
version of POV-Ray.
The statement "cannot do caustics" should be "usually, and with the current
technique - if they are not enhanced with photon-maps or something similar -
cannot do caustics" ;-)

Johannes.

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Nieminen Mika wrote:
> 
>   I started another page with the same idea of the VFAQ page: The
> common misunderstandings page. The intention of the page is to clear up
> some common misunderstanings people have about computer related things
> (mainly about topics related with povray, graphics, etc). The page has
> only one entry right now, which is a very good example of what I mean.
>   Wrong allegations and correct information about them is very welcome.
>   I'll add a link to the page from the VFAQ page if/when I get some more
> entries.

Mis-whatevers:

Q.) Why don't they implement a modeling interface into Pov-Ray

A.) Pov-Ray is a rendering engine. This means it is designed to read a
    text based scene discription language and output an image for it.
    The programming work to keep this working bug free and adding
    features at regular intervals takes a lot time and energy by the all
    volunteer programming team. Adding a modeling interface would add to
    their aleady heavy workload and the progam was never written to be a
    modeling program anyway. There are numerous modeling programs already
    available that are designed with the sole purpose of providing a
    graphical modeling interface to Pov so it really isn't neccessary for
    the programming team to think about adding one.

    And...  or...

Q.) Why can't I use 3ds, dxf, vrml, or whatever models directly without
    having to convert them to triangles first ?

A.) ?


For Ron Parker:

Q.) If I just add the inverse keyword to my triangle meshes shouldn't they
    work in csg operations ?

A.) ?


-- 
Ken Tyler

mailto://tylereng@pacbell.net

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On Fri, 12 Mar 1999 08:42:38 -0800, Ken <tyl### [at] pacbellnet> wrote:
>For Ron Parker:
>
>Q.) If I just add the inverse keyword to my triangle meshes shouldn't they
>    work in csg operations ?
>
>A.) ?

Wow.  Drifting across newsgroup boundaries now.  I'm impressed.

A.) No.  There is no way to find the "inside" of an arbitrary triangle
mesh, so the current implementation just assumes that nothing is inside of
a mesh object.  Adding the inverse keyword would just change it to say
that everything is inside of a mesh object.  The result would be that 
intersecting an inverted mesh with a sphere would leave the entire sphere, 
plus whatever part of the mesh is inside the sphere.  The correct result,
of course, would be to leave only the parts of the sphere that are "outside
the mesh," and only the parts of the mesh that are inside the sphere.  The
problem comes in when POV tries to define "outside the mesh."

The real common misunderstanding here, and one I've been guilty of, is 
"If I want to make an object work in CSG, all I have to do is add an 
insideness test, right?"  The answer is no: you also have to ensure that
the all_intersections routine for your object really does return all of
the intersections for any given ray.  The other common misconception is 
that an insideness test for meshes is as simple as counting intersections.
See the recent and ongoing discussion in povray.programming for more than 
you ever wanted to know about these topics.

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Stephen Lavedas wrote:

> My personal biggest pet peeve, which isn't about POVRay or Graphics is
> when people ask..."Are you on the Internet"  and they mean World Wide
> Web.  The Internet is so much bigger than just the Web that I want to
> smack them one and point out what else is out there.
>
> Steve

As immortalized by Bob Dole (American presidential candidate from a few years
ago, failed, for you who are lucky enough not to live with American politics) :
"The Internet is the fastest way to get on the Web."

--
Josh English
eng### [at] spiritonecom
www.spiritone.com/~english

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Nieminen Mika wrote:
> 
>   I started another page with the same idea of the VFAQ page: The
> common misunderstandings page. The intention of the page is to clear up
> some common misunderstanings people have about computer related things
> (mainly about topics related with povray, graphics, etc). The page has
> only one entry right now, which is a very good example of what I mean.
>   Wrong allegations and correct information about them is very welcome.
>   I'll add a link to the page from the VFAQ page if/when I get some more
> entries.
>   The page can be found at:
> 
> http://iki.fi/warp/misunderstandings/
> 
> --
> main(i,_){for(_?main(i+1,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[--i]
> ):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/


I remember one in c.g.r.r. about the stacks in POVray and the
misunderstanding that they can be increased in autoexec.bat (or
config.sys ?). Somebody wiser than me should give the answer. If I
remember right it's not in the VFAQ.

Marc
--
Marc Schimmler

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