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realgray
09-01-2009, 05:33 AM
Hi all, I'm currently studying HDRI and loving it but I'm having a hard time finding information about the gray matte ball. Does anyone know of any good resources explaining this technique and what it's used for? You'll see what I'm talking about 30 sec. into this video on Iron Man cgi.

http://www.youtube.com/watch?v=Q4ga6OV0lkc

I don't know what the gray ball does but I'm sure it's important.
Thanks for any tips.
Gray

akademus
09-01-2009, 05:59 AM
I believe you can accurately capture the environment lighting and surrounding using only the chrome ball and shooting HDR for yourself.

If you can't afford pro chrome ball, there are cheaper equivalents in metallic garden balls.

Hope this helps.

Nowhere Man
09-01-2009, 05:59 AM
Hi realgray, as far as I know, the gray ball is not used for HDRI acquisition. It's just there as a visual reference for lighting artists (fe. if they are going to set up a traditional lighing).

In other words, it isn't that important :thumbsup:

RebelHill
09-01-2009, 06:03 AM
So far as I know, the grey ball is used for lighting reference for performing manual lighting. You can however also use it, or mroe often a matte white ball for HDR capture, the difference from the mirror ball being that it gives you the environmental illumination (diffused) as opposed to the environmental reflection. SImilar to the effect of blurring your HDR mirror ball...

Basically, the more data you can get of the lighting environment, the better.

realgray
09-01-2009, 06:27 AM
Ah that makes sense. I figured it had something to do with capturing the direction of shadows. Very interesting. Thanks all the help.

AdamAvenali
09-01-2009, 07:10 AM
at my last studio we did a few little tests capturing our own HDR's with a garden ball. we also got a second garden ball and painted it with grey primer to have for light intensity purposes. granted, we didnt really know what we were doing, but it was fun to play around with haha

realgray
09-01-2009, 08:09 AM
I'm seeing some pros using Autodesk Stitcher for putting together their environment maps. Is stitcher doing something I can't do in photoshop?

bjornkn
09-01-2009, 08:23 AM
I'm seeing some pros using Autodesk Stitcher for putting together their environment maps. Is stitcher doing something I can't do in photoshop?
Yes. Stitcher and other programs like Hugin (free) and PTGui (my choice -great program!) can stitch a set of images, fisheye or normal, into a spherical panorama, which is what you apply with spherical projection in LW.
Mirror balls will always be much lower resolution, and to get it all (with no camera/photographer) you need to take 2 sequences from different angles to fill in the "holes" from the background behind the ball and the camera.
OTOH it may be much more work to shoot 4-100 sequences with a panohead/wideangle if all you need is a small and blurred HDR for lighting your scene.

Mike_RB
09-01-2009, 08:28 AM
Thats my shot! :) It just gives feedback on lighting angles and color on matte surfaces, same as the reflective one (the reflective one also heled us line up the pano HDR to the right spot). The HDR for that shot was captured shooting multiple exposures in a panorama, the reflective ball was not used to capture image probe HDR's, thats old school.

Mike

tischbein3
09-01-2009, 12:03 PM
thats old school.

But still a very fast and save method to have luckily at hand when stiching goes "picasso".

"old school" zssszsss.

:)

jeremyhardin
09-01-2009, 12:24 PM
Nice one Mike_RB! Stellar work.

Yeah, we use the grey ball to measure diffuse response, and when setting up the HDR lighting, we make sure that our CG 18% grey diffuse ball sits at about the same exposure as the one in the plate (when lit with the HDR acquired from the set).

Intuition
09-03-2009, 02:10 PM
Nice one Mike_RB! Stellar work.

Yeah, we use the grey ball to measure diffuse response, and when setting up the HDR lighting, we make sure that our CG 18% grey diffuse ball sits at about the same exposure as the one in the plate (when lit with the HDR acquired from the set).

Same method we use as well, 18% grey diffuse which is matched in linear colorspace for lighting value.

Very handy for diffuse amount and direction. An HDR from the location is always handy as well. ;D

What stunned me about Mike's, and the Embassy crew's, work on Iron Man was that, if I remember correctly, it was rendered in Lightwave.

By that point I had wussed out for Mental Ray and Vray and seeing these guys push LW that way was great. :D

Mike_RB
09-04-2009, 06:53 PM
why 18% grey?

Muhahahahaha, that question is like opening the Ark of the Covenant in Indy.... prepare to melt your brain...

18% in linear at gamma 2.2 = 50%

:)

JBT27
09-05-2009, 01:31 AM
This PDF over at Adobe might help a bit:

http://www.adobe.com/digitalimag/pdfs/linear_gamma.pdf

This stuff gives me headaches, to be truthful :)

Julian.

3DGFXStudios
09-05-2009, 03:54 AM
Here you can find everything you need to know http://smartibl.com/sibl/index.html


REALLY

RebelHill
09-05-2009, 05:01 AM
18% grey has also been considered for years as the "medium" colour for exposure. An old photgraphers trick for decades now, when confronted with a scene to shoot with a high brightness range going on, has been to take an 18% grey card, and meter the exposure to that, for the lighting conditions that you are in.

JBT27
09-05-2009, 05:41 AM
18% grey has also been considered for years as the "medium" colour for exposure. An old photgraphers trick for decades now, when confronted with a scene to shoot with a high brightness range going on, has been to take an 18% grey card, and meter the exposure to that, for the lighting conditions that you are in.

Ah, the old Kodak 18% Grey Card and my trusty Weston EuroMaster light meter ..... I still have them both! Standard kit back in the day when I was doing my City and Guilds 744 Photography!!!

Julian.

revengeofmonty
09-05-2009, 07:00 AM
Completely thick question:

So how does the 18% matte ball come into the workflow??

gordonrobb
09-05-2009, 09:13 AM
My assumptions on this are that you use the mirror ball to create an HDRI of the environment. this is used through Image World as lighting and reflection map. I think that you can then put a CG ball in your CG scene that is 18% and you compair how it is lit to the shot of the grey ball in the live plate, and use this to increse/decrease the brightness of your lighting. Interested to know if I am even close though.

realgray
09-05-2009, 12:18 PM
@Mike_RB
Loved the Shot!:thumbsup:
Could you explain when you captured the HDRI for Iron Man did you use a Sigma Fisheye? Do you have any recommended reading for learning this topic? (general workflow)

I'm up for a little brain melting :)


There's a great interview with the Embassy including a little on the HDRI workflow for District 9

http://www.fxguide.com/fxpodcast.html

Sigma Fisheye/Canon 5D/Manfrotto Nodal Head

jeremyhardin
09-07-2009, 08:29 AM
My assumptions on this are that you use the mirror ball to create an HDRI of the environment. this is used through Image World as lighting and reflection map. I think that you can then put a CG ball in your CG scene that is 18% and you compair how it is lit to the shot of the grey ball in the live plate, and use this to increse/decrease the brightness of your lighting. Interested to know if I am even close though.

Bingo. If your CG 18% grey ball reacts like 18% grey in the real environment, then your HDR lighting is spot-on.

gordonrobb
09-07-2009, 11:11 AM
Cool. And just to check. Is 18% grey 128,128,128 rgb?

revengeofmonty
09-07-2009, 11:30 AM
I feel a dim lightbulb starting to glow slowly......ever so slowly.....

Mike_RB
09-07-2009, 11:31 AM
Cool. And just to check. Is 18% grey 128,128,128 rgb?

no, thats 50%. You want 46,46,46 RGB

bjornkn
09-07-2009, 02:10 PM
no, thats 50%. You want 46,46,46 RGB
Oh?
I believe you got that upside down?
Shouldn't it be 209,209,209?
After all 100% black is 0,0,0.

jeremyhardin
09-07-2009, 02:17 PM
Nope. He's got it right. It's 255* 0.18. Luminance is 18%.

Mike_RB
09-07-2009, 03:39 PM
Oh?
I believe you got that upside down?
Shouldn't it be 209,209,209?
After all 100% black is 0,0,0.

I know how this stuff works. A linear pipeline is a mind bender. Quick put the lid back on the ark, while you still can.

Intuition
09-08-2009, 06:30 PM
I don't even see the linear pipeline anymore, I just set my gamma to...blonde, brunette, ....redhead.

:thumbsup:

realgray
09-25-2009, 11:52 AM
does anyone know of a website that the grey ball can be purchased from? Where would you get something like that?
Thanks,
Gray