I've been away from playing with Pov-Ray for a few years, so I haven't heard
about this utility. Some of the pictures I've seen in p.b.i. are stunning --
they look like photographs. I'm certainly not looking for advice on how to
use it (I'm back up to the point where I can make a scene with spheres and
boxes without screwing up :-) ), just a sort of basic explanation of what it
is, and how it works. Thanks.

Mark

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From what I know, it's an image which can have color channel values
greater than 1 (normal images can only have values between 0 and 1).
  That's it.

  The reason why that makes a big difference is another story, which I'm
not really qualified to explain, as I don't have any experience at all.

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

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In article <3e205225$1@news.povray.org>,
 "Mark Hanson" <mar### [at] attbicom> wrote:

> I've been away from playing with Pov-Ray for a few years, so I haven't heard
> about this utility. Some of the pictures I've seen in p.b.i. are stunning --
> they look like photographs. I'm certainly not looking for advice on how to
> use it (I'm back up to the point where I can make a scene with spheres and
> boxes without screwing up :-) ), just a sort of basic explanation of what it
> is, and how it works. Thanks.

Basically, to make a really realistic scene, it helps for your objects 
to have realistic surroundings and lighting, especially for things like 
reflections. You can construct this environment entirely in the 
computer, having the computer actually simulate the entire scene, but 
this takes memory, computation time, and is difficult or just time 
consuming.

HDRI means High Dynamic Range Image. Usually, image color values are 
percentages, you can have 0%, 100%, and steps in between. Of course, in 
reality, there is no "100% brightness", it is just a compromise for what 
our display devices can show. High dynamic range images store 
intensities instead of percentages, and can store values brighter than 
"white".

An HDRI image can be used to store lighting values for a scene, either 
precomputed ahead of time or taken from a real-world sample. Since the 
lighting values already exist, it doesn't take as long as having the 
actual scenery there, it is easier to set up, and the lighting is more 
realistic than a background from an ordinary image, with color values 
clipped to a small range.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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Very similar, in fact, to a convolution reverb, which samples the ambience
of a space and applies that to a sound recording, given the recording the
illusion of being in the space.
D.

"Christopher James Huff" <cja### [at] earthlinknet> wrote in message
news:cja### [at] netplexaussieorg...
> In article <3e205225$1@news.povray.org>,
>  "Mark Hanson" <mar### [at] attbicom> wrote:
>
> > I've been away from playing with Pov-Ray for a few years, so I haven't
heard
> > about this utility. Some of the pictures I've seen in p.b.i. are
stunning --
> > they look like photographs. I'm certainly not looking for advice on how
to
> > use it (I'm back up to the point where I can make a scene with spheres
and
> > boxes without screwing up :-) ), just a sort of basic explanation of
what it
> > is, and how it works. Thanks.
>
> Basically, to make a really realistic scene, it helps for your objects
> to have realistic surroundings and lighting, especially for things like
> reflections. You can construct this environment entirely in the
> computer, having the computer actually simulate the entire scene, but
> this takes memory, computation time, and is difficult or just time
> consuming.
>
> HDRI means High Dynamic Range Image. Usually, image color values are
> percentages, you can have 0%, 100%, and steps in between. Of course, in
> reality, there is no "100% brightness", it is just a compromise for what
> our display devices can show. High dynamic range images store
> intensities instead of percentages, and can store values brighter than
> "white".
>
> An HDRI image can be used to store lighting values for a scene, either
> precomputed ahead of time or taken from a real-world sample. Since the
> lighting values already exist, it doesn't take as long as having the
> actual scenery there, it is easier to set up, and the lighting is more
> realistic than a background from an ordinary image, with color values
> clipped to a small range.
>
> --
> Christopher James Huff <cja### [at] earthlinknet>
> http://home.earthlink.net/~cjameshuff/
> POV-Ray TAG: chr### [at] tagpovrayorg
> http://tag.povray.org/

Post a reply to this message

"Christopher James Huff" <cja### [at] earthlinknet> wrote in message
news:cja### [at] netplexaussieorg...
> An HDRI image can be used to store lighting values for a scene, either
> precomputed ahead of time or taken from a real-world sample. Since the
> lighting values already exist, it doesn't take as long as having the
> actual scenery there, it is easier to set up, and the lighting is more
> realistic than a background from an ordinary image, with color values
> clipped to a small range.

Where does the scene come from? A scene you've already rendered? From
reading a few of the posts in p.b.i., it seemed like they were photographs.
Is that it?

Mark

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In article <3e21b1b3$1@news.povray.org>,
 "Mark Hanson" <mar### [at] attbicom> wrote:

> "Christopher James Huff" <cja### [at] earthlinknet> wrote in message
> news:cja### [at] netplexaussieorg...
> > An HDRI image can be used to store lighting values for a scene, either
> > precomputed ahead of time or taken from a real-world sample. Since the
> > lighting values already exist, it doesn't take as long as having the
> > actual scenery there, it is easier to set up, and the lighting is more
> > realistic than a background from an ordinary image, with color values
> > clipped to a small range.
> 
> Where does the scene come from? A scene you've already rendered? From
> reading a few of the posts in p.b.i., it seemed like they were photographs.
> Is that it?

"either precomputed ahead of time or taken from a real-world sample."

It doesn't really matter where it originally came from...could be 
generated with a high-quality renderer, could be taken from a real-world 
location. If the patch allows POV to output images in that format, you 
could generate the images with POV. Then you would have to do the work 
of setting up the scenery, but you would only have to do that and render 
once, and could use the resulting HDRI map in several other scenes, or 
to make a faster rendering animation. Most HDRI maps seem to be 
real-world samples, probably because there isn't much rendering software 
that can output to those images. I think Radiance can do it, or it might 
just use its own RGBE format.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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You can look for "probes" at various sites that have been mentioned
recently.
D.

"Mark Hanson" <mar### [at] attbicom> wrote in message
news:3e21b1b3$1@news.povray.org...
> "Christopher James Huff" <cja### [at] earthlinknet> wrote in message
> news:cja### [at] netplexaussieorg...
> > An HDRI image can be used to store lighting values for a scene, either
> > precomputed ahead of time or taken from a real-world sample. Since the
> > lighting values already exist, it doesn't take as long as having the
> > actual scenery there, it is easier to set up, and the lighting is more
> > realistic than a background from an ordinary image, with color values
> > clipped to a small range.
>
> Where does the scene come from? A scene you've already rendered? From
> reading a few of the posts in p.b.i., it seemed like they were
photographs.
> Is that it?
>
> Mark
>
>

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What made HDRI make sense to me was the idea/fact that it was "invented" to
allow artificial 3D objects to be placed into a "real" scene.

Have you ever watched a program with CGI in an "real" scene where the CGI
just didn't look quite right, but you couldn't quite put your finger on why?
The likely cause was the improper lighting.  HDRI samples light differently
than, say, a single exposure on a digital camera.  From what I understand,
it does this by having multiple exposures of different lengths.  By doing
this, it can approximate the "real" intensity of the light.  By using this
light data, you can then place 3D objects into a "real" scene and have much
better lighting.

A good example is simply sunlight coming trough a window into a dark room.
On a normal photograph, the window may simply look "white".  However, having
a white piece of paper hanging on the wall does not begin to have the same
effect on lighting as sunlight coming through a window.  If you consider
all-white to be rgb<1,1,1>, then sunlight would be something like
rgb<1000,1000,1000>, but a normal digital photo can only show things in the
range rgb<0,0,0> to rgb<1,1,1>, so you'd lose all of that extra light.

I'm not sure if that made sense or not.  If you're like me, you'll be
driving down the road and suddenly go, "Hey, that makes sense now!"

Good Luck,

Slash

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"Slashdolt" <nomail@nomail> wrote in message
news:web.3e24683e552627465543301f0@news.povray.org...

<snip>

> I'm not sure if that made sense or not.  If you're like me, you'll be
> driving down the road and suddenly go, "Hey, that makes sense now!"

Well, I'm getting there. HDRI is a way of approximating real-life situations
that Pov-Ray can't do, or can't do well -- I'm thinking events like depth of
focus, glare, sun flares.

Next: is HDRI a program in itself?

Mark

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>
>Well, I'm getting there. HDRI is a way of approximating real-life situations
>that Pov-Ray can't do, or can't do well -- I'm thinking events like depth of
>focus, glare, sun flares.
>

Not quite.  It really has to do with one thing only, afaik.  Simply the
lighting.

By allowing some things to be brighter than simply "all-white" it allows you
to insert a 3D object into a "real life" photo, and have the same lighting
in the room as you did when the photo was taken.  To use my "sun coming
thru a window" analogy, your 3D object could actually be "lighted" from
where the sun hits on the far side of the room indirectly, and not just
from the actual light source.

I still don't feel I'm explaining this very well.  Maybe if I said something
like, "To some extent, it's like radiosity coming from a photograph rather
than from a light source bouncing off 3D objects in a completely rendered
scene."

Slash

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