"Bill Pragnell" <bil### [at] hotmailcom> wrote:
> Ive <"ive### [at] lilysoftorg"> wrote:
> >  the importand thing is: The 'mirror ball'
> > *projection* is different to the 'angular' *projection*. But I admit
> > they can very easily be confused.
>
> I am well aware of the difference, and that using a 'mirror ball' projection
> with map_type 7 will produce a distorted reflection. All I meant was that in my
> experience (I have used both types of projection in hdri-lit renders), it can be
> good enough (scene geometry and view permitting). Comparing the techniques will
> make the distortion obvious, and an expert may spot it immediately, but it's
> not the end of the world! :-)

Yes, you are right that you can get away with it in certain circumstances
(no-one will know the difference) and it can do in a pinch so long as
significant portions are not visible either directly or via reflection.  The
distortion is not minor and is fairly obvious if enough of the map is visible.

-tgq

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Ive <"ive### [at] lilysoftorg"> wrote:
> Bill Pragnell wrote:
> > I am well aware of the difference, and that using a 'mirror ball' projection
> > with map_type 7 will produce a distorted reflection. All I meant was that in my
> > experience (I have used both types of projection in hdri-lit renders), it can be
> > good enough (scene geometry and view permitting). Comparing the techniques will
> > make the distortion obvious, and an expert may spot it immediately, but it's
> > not the end of the world! :-)
> >
>
> ;) definitely not!
>
> I just wanted to make it clear for everybody that there is a difference
> and (as Trevor also mentioned) I've seen quite some images where this
> resulting distortion *was* visible and it was obviously not the
> intention of the artists but lack of knowledge about those projection types.

Good point, well made :-)

As an aside, I have recently ordered some mirrored spheres from a garden centre
(of all places!) to do exactly what you described, or at least attempt it. I
suspect the actual photography will be the difficult part. My camera's not an
SLR, so I hope it's up to the task... oh well, good excuse to buy me a new toy
if it's not!

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You are great, my friends!! :-)

Thanks a lot to all, as you have cleared up my mind by answering my 
question. I see now when to use map_type 7. In fact, all my hdr maps are of 
the lat/long type, but it is good to know about the other possibilities. The 
megapov docs are rather vague about all this.

Again, thank you very much indeed.

Thomas

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"Bill Pragnell" <bil### [at] hotmailcom> wrote:
> As an aside, I have recently ordered some mirrored spheres from a garden centre
> (of all places!) to do exactly what you described, or at least attempt it. I
> suspect the actual photography will be the difficult part. My camera's not an
> SLR, so I hope it's up to the task... oh well, good excuse to buy me a new toy
> if it's not!

Good luck and have fun!
I have made a few in the past
(http://barberofcivil.deviantart.com/gallery/#HDR-Light-Probes) using a regular
digital camera (Canon S2, with 12X optical zoom though) and steel balls (those
chinese stress balls ~2" diameter).  I used HDRSop and followed the tutorials
to assemble them (http://gl.ict.usc.edu/HDRShop/tutorial/tutorial5.html).

A few pointers for you:

- Make sure you use a good dynamic range.  Check your scene beforehand with your
camera, decrease stops until the scene is mostly dark and light sources are as
dim as possible, then increase until the scene is mostly saturated

- You can make a usuable HDR with as little as 3 exposures, two as noted above,
plus one in between at a balanced exposure.  However, more exposure can be
helpful in ensuring a good dynamic recreation and minimize errors from noise.

- Try to make sure the perpendicular shots are taken from the same distance if
possible to minimize the parallax/perspective difference.  Also try to get
camera as far away from the ball as possible to minimize overall perspective
effects (this is where large zoom can help), however this is not critical so
long as you have sufficient distance.  It also makes a much smaller
camera/photographer reflection to be removed.

- adjust the shutter speed only for exposures.  Aperture and ISO have other
photographic effects that will impact the HDR assembly.

- keep the camera still and stationary.  This makes assembling the HDRs easier,
however, jitter can be adjusted for if necessary, it can just be tedious

- make sure there is minimal movement of background objects (ie, cars driving,
people walking, even fast moving clouds) as this can be quite evident and cause
visual errors in assembling the HDR.

Most of all, have fun!  Try to pick scenes which will produce interesting
reflection or lighting effects.  And by all means post them where I can get
them, I'm always looking to expand my collection.

One further item of interest.  If you have a Canon camera, you may want to check
out CHDK (http://chdk.wikia.com/wiki/Main_Page). I have it installed on my
cameras and it installs easily and doesn't harm the camera at all.  It can give
you a few advantages such as the scripting ability so you can setup your camera
push a button once and wait, minimizing jitter (look in the user-made scripts
section, I actually have a couple in there myself that are for HDR usage).
Also it makes shutter speeds available beyond those avaiable in the standard
camera (available shutter speeds from 64s to as fast as 1/32000 or possibly
even faster, yes that is three zeros) it can make a point and shoot Canon
camera far more powerful than any DSLR money can buy!

-tgq

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"Trevor G Quayle" <Tin### [at] hotmailcom> wrote:
> Good luck and have fun!

I'm looking forward to it - Brasso at the ready in case these spheres aren't
quite what I expect... :-)

> Most of all, have fun!  Try to pick scenes which will produce interesting
> reflection or lighting effects.  And by all means post them where I can get
> them, I'm always looking to expand my collection.

Thanks for the tips, and don't worry, if my exploits are successful I'll
definitely be showing off- er, I mean sharing them!

> One further item of interest.  If you have a Canon camera, you may want to check
> out CHDK (http://chdk.wikia.com/wiki/Main_Page).

Thanks for this link, this looks awesome ! :-D I do have a Canon, it's a
PowerShot A710... need to check my firmware version but this looks good!

Bill

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"Trevor G Quayle" <Tin### [at] hotmailcom> wrote:
> "Bill Pragnell" <bil### [at] hotmailcom> wrote:
> > As an aside, I have recently ordered some mirrored spheres from a garden centre
> > (of all places!) to do exactly what you described, or at least attempt it. I
> > suspect the actual photography will be the difficult part. My camera's not an
> > SLR, so I hope it's up to the task... oh well, good excuse to buy me a new toy
> > if it's not!
>
> Good luck and have fun!
> I have made a few in the past
> (http://barberofcivil.deviantart.com/gallery/#HDR-Light-Probes) using a regular
> digital camera (Canon S2, with 12X optical zoom though) and steel balls (those
> chinese stress balls ~2" diameter).  I used HDRSop and followed the tutorials
> to assemble them (http://gl.ict.usc.edu/HDRShop/tutorial/tutorial5.html).

Ahh! Shooting lightprobes - I've managed to spend some time on that too!

My setup is a chrome-plated pinball, a Canon IXUS 860 (aka the SD 870 in the
US), and a couple of super cheap table-top tripods (one for the camera, one for
the ball).

The pinball by itself was good, but even though it looked very well polished,
when you took close-ups of it, you could see all the almost microscopic
scratches on the surface. They were especially bad with bright lights (the sun,
light bulbs, etc). The first one started to rust after a while too.

Chrome-plating it got rid of the scratches, and finally gave it a true mirror
finish. It should also make it more or less rust-proof as well.

It's interesting to consider that while the perfectly reflective, perfectly
spherical ball is the stereotypical ray-traced object, getting one in real life
is much, much harder than you would think...

I also use CHDK firmware on my Canon, as it lets me automate taking 10 shots,
each one f-stop apart, as well as several other useful tricks, like locking the
focus to the minimum distance the camera will allow, and loading overlays on the
screen so I can exactly place the pinball at the correct distance from the
camera to match that focal distance. I only wish I had a camera that had a
better macro ratio at full zoom.

I use Photoshop to convert the 10 images into an HDR, then HDRShop to convert
that into a lat-long image. I shoot from two positions approx 90 degrees apart,
and combine the two lat-long HDRs into a single one in Photoshop again.

Lately I've started using LightMapGen to give me light dome data from the
images, and also shooting HDR backplates (normal shots of the environment) that
you can use to place in the background of a render. The light probes are almost
always to low res to look good behind objects in your scene, unless they are
very out of focus.

> A few pointers for you:
>
> - Make sure you use a good dynamic range.  Check your scene beforehand with your
> camera, decrease stops until the scene is mostly dark and light sources are as
> dim as possible, then increase until the scene is mostly saturated

I find that two stops over-exposed to seven stops under exposed (which is 10
exposures) captures most environments very well, even those with the sun in
them. I'd suggest at least three shots (2 fstops over, normal, two fstops
under), or four (+2, 0 -2, -4) as a minimum. The underexposed shots capture
lights more accurately, and make reflections look much more realistic.

> - make sure there is minimal movement of background objects (ie, cars driving,
> people walking, even fast moving clouds) as this can be quite evident and cause
> visual errors in assembling the HDR.

Clouds in particular move ore than you think they do...

> Most of all, have fun!  Try to pick scenes which will produce interesting
> reflection or lighting effects.  And by all means post them where I can get
> them, I'm always looking to expand my collection.

Also try to take images with different types of light in the same scene - a
otherwise boring office shot of mine turned out to be a favourite light probe
because it had florescent lighting from the office, and overcast daylight
coming through the windows.

> One further item of interest.  If you have a Canon camera, you may want to check
> out CHDK (http://chdk.wikia.com/wiki/Main_Page). I have it installed on my
> cameras and it installs easily and doesn't harm the camera at all.  It can give
> you a few advantages such as the scripting ability so you can setup your camera
> push a button once and wait, minimizing jitter (look in the user-made scripts
> section, I actually have a couple in there myself that are for HDR usage).
> Also it makes shutter speeds available beyond those avaiable in the standard
> camera (available shutter speeds from 64s to as fast as 1/32000 or possibly
> even faster, yes that is three zeros) it can make a point and shoot Canon
> camera far more powerful than any DSLR money can buy!

I agree - CHDK is an absolute marvel. Definitely check it out if you have a
Canon camera.

> -tgq

Cheers,
Edouard.

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"Edouard" <pov### [at] edouardinfo> wrote:
> My setup is a chrome-plated pinball, a Canon IXUS 860 (aka the SD 870 in the
> US), and a couple of super cheap table-top tripods (one for the camera, one
> for the ball).

When you say pinball, is that as in pinball machine? Basically a large ball
bearing? I thought about trying to find something like that, but I figured
imperfections would be more obvious on a small ball (as you say).

> It's interesting to consider that while the perfectly reflective, perfectly
> spherical ball is the stereotypical ray-traced object, getting one in real
> life is much, much harder than you would think...

I was in a church the other day with a lovely checkered tile floor. Oh for a
mirror ball and a camera... ;-)

> > - make sure there is minimal movement of background objects (ie, cars
> > driving, people walking, even fast moving clouds) as this can be quite
> > evident and cause visual errors in assembling the HDR.
>
> Clouds in particular move ore than you think they do...

I am well versed in this regard, I've been stitching regular rectilinear
panoramics centred on the horizon for some years now. Clouds are not as bad as
foreground parallax errors - I don't have a suitable tripod, so I try to
minimise parallax by rotating myself around the camera lens!

People moving can also be a problem, but as long as they stay out of overlap
regions it can work out (at least for regular panoramas). I took one where my
friend in the foreground appears twice - she skiied on while I was taking the
shots.

Thanks for the tips, both.

Bill

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"Bill Pragnell" <bil### [at] hotmailcom> wrote:
> "Edouard" <pov### [at] edouardinfo> wrote:
> > > - make sure there is minimal movement of background objects (ie, cars
> > > driving, people walking, even fast moving clouds) as this can be quite
> > > evident and cause visual errors in assembling the HDR.
> >
> > Clouds in particular move ore than you think they do...
>
> I am well versed in this regard, I've been stitching regular rectilinear
> panoramics centred on the horizon for some years now. Clouds are not as bad as
> foreground parallax errors - I don't have a suitable tripod, so I try to
> minimise parallax by rotating myself around the camera lens!
>
> People moving can also be a problem, but as long as they stay out of overlap
> regions it can work out (at least for regular panoramas). I took one where my
> friend in the foreground appears twice - she skiied on while I was taking the
> shots.
>
> Thanks for the tips, both.
>
> Bill

With HDRI this is even more pronounced as you are not just dealing with overlap
parallax, but also assembly of several exposures.  While moving objects for
panorama stitching can be hidden or minimized and don't really cause huge
problems other than little ghosting, they can cause ugly noticeable errors in
the calculation and assembly of HDRIs from multiple exposures.  The HDRI
assembler is basically taking the pixel value from the same area for each
exposure and creating a true dynamic value, as sudden change in one exposure
due to a moving object can cause chaos for it.

-tgq

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Whatever they are - they look beautiful! Are these some sort of seeds?

3D Artists Wanted!
http://Evolutions.Jamaica-Focus.com
Evolutions!  - The Game

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"Sven Littkowski" <Sve### [at] Jamaica-Focuscom> schreef in bericht 
news:4a0870eb$1@news.povray.org...
> Whatever they are - they look beautiful! Are these some sort of seeds?

he he... no. They are narcissic mirror balls for vain beholders :-)  Only 
the beholder is not present here...  hmmm makes me remember I 'did' a scene 
like that a long time ago....

Thomas

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