Hdrx to hdri 32 floating point for 3d lighting

[Christopher Lowden]

Hello
I had a revelation recently when someone asked me how to optimize a shoot where there would be 3d objects intergration in post. Normal procedure is to shoot scenes on a motion picture cam and have a vfx person shoot 360 degree hdri plates on a stills cam. This often becomes a time consuming affair, having 2 cams that should be in the same place etc. So I realized that maybe using the hdrx functionality I could shoot and have high quality hdris, except I don't really know what the spec of the hdrx files are. I figure that if I have had this idea, there certainly someone who has already done it.

Is my thought true or just a naive dream?
Many thanks

[Phil Holland]

I do this work, create software, and build rigs that capture this type of imagery. I've done lots of testing. Lots.

While HDRx is exceptionally useful for maintaining latitude within shots, it's not quite up to snuff for spherical high dynamic range imaging. You still need to change exposures within the camera to capture a proper full range HDRI. And due to the nature of the best it would appropriate to black shade when you get down to slower exposures. Adjusting the ISO isn't suitable to capture in this case either.

Not linking to it here, but Gnomon just released a presentation on shooting spherical HDRIs that I did a while back that includes tons of info about capturing and processing. It's a great place to start if this is new to you.

After saying that, it can be done with Epic and Scarlet. It's infinitely easier, faster, more accurate, and more compact utilizing DSLRs for this specialized imaging. The rigs I put together are fast too. Less than 20 seconds for a typical HDR capture used for image based lighting. Higher resolution images though require a bit more time.

[Eric Pascarelli]

Generally you want to shoot HDRIs not from the position of the motion picture camera but from the position of the the virtual object, character etc. This is because you want to record the light falling on the object and reflected from the object. This is not the same as the camera POV in most shooting situations. And if you want a sphere, you should ideally use a 180° fisheye lens.

Also, the dynamic range, while large at a potential of 18 stops, is somewhat anemic for environment spheres which sometimes need 20+.

You can create nice linear EXR frames (same as what might be used for 3D) from HDRx using REDCINE. While not that useful for CG integration they are useful for many things. Great for time lapse with post exposure compensation. See this thread:

http://www.reduser.net/forum/showthr...tone-mapped-QT

Here's a test of this I did:

http://www.youtube.com/watch?v=mWxz9...e_gdata_player

[Christopher Lowden]

many thanks for the quick reply. Phil, I probably could not have a reply from a higher authority on this subject. I recently saw your HDRI presentation. It was extremely informative.

Truth be told, the question is more production driven. I don't work on feature films for this sort of stuff, but more for low end commercials and pop videos. There is a large want to augment production value with reduced budgets and one option is "theoretically" 3D. The thing that kills a 3d route is that it is expensive and often its integration is not photo real. This is often as not due to poor lighting that makes decent compositing pretty impossible. ( I am talking about adding for example cars in a street or props to a scene). Yet IBL changes all this. It immediately puts 3d objects in the right ball park. But budgets often will not extend to having a dedicated person for this.
Yes it is a compromise, but a compromise that fits a certain diffusion quality and a scarlet economy.

Eric, you are absolutely right about where the HDRI should be taken. Again I am looking at ways to cut corners (shame on me). Thanks for confirming the HDRX largest latitude and the video that proves it.

[Christopher Lowden]

This morning's thought: hdrx has not got enough latitude for ibl. But the scarlet can be a stills cam (of sorts). The issue then becomes how to remotely automate the capture of these images. A quick look at the redmote manual did not show me a way to remote this procedure. I am sure that it could be easily programmed as a script but the cam does not seem to have this available to my knowledge. Therefore, do you know if there exists a scarlet compatible remote that could?

[Phil Holland]

It's a toughie. Even some major productions don't dedicate a single individual to this task. It's often been set data collectors, ACs, and even PA/Coordinators we've trained up to do the capturing. These day's I've even operated and have jumped in with the rig when necessary.

The real issue with using HDRx to capture this type of imagery is how many exposures and how many stops apart each exposure is. HDRx really only get's you a two image dynamic range. Which is awesome for shooting, but not enough range for a meaty HDRI.

I'm cracked open the Canon SDK to see if we could put a dummy program on cards, but between the built in HDR bracketing and different controllers out there it's just easier to achieve this through another device. I didn't want to worry about updating firmware and what not with every new camera. Especially now since we've made a couple of Nikon rigs too!

[Christopher Lowden]

Philip, thank you for the reply. I must confess that it saddens me to see how everyone is becoming a jack of all trades. Recently, I worked on a commercial where time-lapse sunrise was needed. The assistants were briefed to take hdri files (can't tell you why) and they had 2 5ds to cover daily event. Due to bad luck, badly adapted equipment and sheer incompetence they screwed it twice causing an insurance claim. The question is, why give delicate work to incompetents? Because there is a belief that even if you put a chimp in front of a 5d, you'll be alright !
that said, I too want to cut corners but by optimizing the gear rather than the crew. One day I will take the time to analyze the flight case to non shooting time ratio. the accessories needed for a modern shoot is astonishing. When I think that many of the greatest images were shot on an Arri 2c, I realize just how important the gear has become, often to the detriment of crews and training.
So in short, a competent Dop should be able to crack out hdri on a scarlet. The question is how to automate this task.

[Jose Lomeña]

Phil I do HDR spheric movies for plates with my epic. I like HDRX, it has enough stops, at least for me. In fact, the most time I use +4 or +5. 18Stops is enough the most of the time. What I only need is less compression at 24fps HDR. But I only need to wait for the "porche" new media.

I prefer same color processing than use a 5D. And with 5D you can't shoot Spheric HDR video.

[Christopher Lowden]

what is porche media?

[Jose Lomeña]

The new turbo 512GB ssd media, announced at NAB... porsche because it is faster and expensive :-)