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Old 09-02-2012, 07:36 AM   #1
johansvensson3d
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Question HRD Light Probe

Hi

I will photograph a mirror ball, then use it for a HDR lighting. (I will only photo from 1 view, and I only need 1 view in the reflection.)

Then I guess my "HDR Layout" will be like my attached image, a "sperical ball light probe," But my question is now.

How do I use this type of HDR layout?

I`m often using "HDR 360 Panoramas" but this time I need to use a "Sperical Ligt probe" layout instead, like attached image. But I can`t figure out how to apply it, and use it.

Anyone know?

 
Old 09-02-2012, 10:59 AM   #2
EricM
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You have to unwrap it as an equirectangular map. Some 3D software can do it natively (C4D for instance) otherwise you need to go through a soft like HDRLab or flexify plugin for photoshop.

Best
 
Old 09-02-2012, 12:16 PM   #3
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The env ball node can be used in Maya to load a mirror ball image and use it as a reflection map.
 
Old 09-02-2012, 09:38 PM   #4
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Is there any particular reason you aren't just taking a multiangle 360 hdr and stitching it after?

I can't remember the last time I used a mirrorball on a shoot.

There are so many advantages to just shooting your own equilateral hdr.
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Old 09-03-2012, 08:10 AM   #5
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Mirror ball is so much faster and cheaper, while good enough for CG lighting and reflections in most cases. Only drawback usually is that it's too low resolution for backdrops. This aside, you only need a couple of bracketed shots with a long focal length and get rid of your own reflection in PS.

Paul Debevec presented at last siggraph a way to reconstruct HDR probes from a single LDR shot with a special mirror ball with reflective tape. There's a very informative FXguide podcast about it, so it's hardly a "thing of the past". It can even be done with the same camera doing principal photography if you're on a shoot.

Full 360 equirectangular is best but requires a set of 10 to 50 shots depending on your focal length, multiplied by you bracketing steps (say 3 or 5) and in a best case scenario a panoramic head and a wider lense. Then a stitching program (PS may not be enough if lense distortion is extreme) and deal with ghosting if people or things are moving between your shots.

So eventually it's more expensive and time consuming if you want to do it right (and you do, of course, otherwise you would go the mirror ball way).

I've been doing both, and I can see why a mirror ball can be the best options in some situations.
 
Old 09-03-2012, 09:16 PM   #6
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Quote:
Originally Posted by EricM
Mirror ball is so much faster and cheaper, while good enough for CG lighting and reflections in most cases. Only drawback usually is that it's too low resolution for backdrops. This aside, you only need a couple of bracketed shots with a long focal length and get rid of your own reflection in PS.

Paul Debevec presented at last siggraph a way to reconstruct HDR probes from a single LDR shot with a special mirror ball with reflective tape. There's a very informative FXguide podcast about it, so it's hardly a "thing of the past". It can even be done with the same camera doing principal photography if you're on a shoot.

Full 360 equirectangular is best but requires a set of 10 to 50 shots depending on your focal length, multiplied by you bracketing steps (say 3 or 5) and in a best case scenario a panoramic head and a wider lense. Then a stitching program (PS may not be enough if lense distortion is extreme) and deal with ghosting if people or things are moving between your shots.

So eventually it's more expensive and time consuming if you want to do it right (and you do, of course, otherwise you would go the mirror ball way).

I've been doing both, and I can see why a mirror ball can be the best options in some situations.


Great post, and very true. Both methods have their strengths, its just about the situation on set / location and the requirements for your shots.
 
Old 09-03-2012, 09:31 PM   #7
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The times i have made full panos i used my 8mm lens and a bracketing tool on a nindendo DS, i am looking forward to making another one with the new magic lantern firmware on my 5d2. Granted setting up the tripod can be a bit awkward, but overall i think it works pretty ok.
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Old 09-04-2012, 02:37 AM   #8
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Oh wow, after listening to the FXGuide podcast, I would love to find out more information about the new HDR probes.

Anyone know if the paper is floating around?
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Old 09-04-2012, 05:38 PM   #9
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Definitely some things require or can benefit from a Chromeball, but I have found that at HD resolultions, they tend to fall apart (at the edges in particular) for shiny objects like cars.

As far as speed, well, that depends greatly on your rig.

With a Canon T2i, or 550d
Magic Lantern Firmware (free)
4.5mm Sigma Fisheye
an Atome 360 Pano-head
a reasonable tripod base
and PTGui (normal, not pro version)

I can take 9 exposures at 1-3 EVs apart, 3 angles

under a minute

and you get an 8k equilateral HDR that has an exposure range going from near black to almost pure white.

Depending on what you call expensive or not, that rig will cost you under $2000

The only times that I might prefer a chrome ball would be if the location is particularly small or tight, or dangerous in which it is easier to hang a chromeball off a C-stand or something
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Old 09-08-2012, 05:49 PM   #10
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In VFX light probes (both grey and chrome) come in handy when used as additional plate reference taken from the same camera used to take the shot.

This gives you a few things. It gives you a better idea of the camera-to-lights relationship of that particular shot, something that you don't get from a stitched environment map. As a starting point for your lighting you can easily adjust the rotation of your stitched environment map and your sunlight to match CG grey and chrome balls with the real ones.

For use as reflection maps light probes may be limited, but for use in IBL they are fine, general best practice these days is to remove high-intensity light sources (ie. the sun) from the HDR anyway and place them on area-lights or reflection cards so taking non-bracketed reference of light probes is fine - in cases like this you'd take bracketed images of the sun or lights used on-set in order to get the intensity (HDR) of those lights. Disconnecting these high-intensity lights from your IBL maps makes it easier to adjust your lighting to get it looking right (and I believe also makes importance-sampling of environment maps easier).
 
Old 09-08-2012, 05:49 PM   #11
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