As I alluded to in my previous post, I have a HDR sky project I’m really excited about, but also a little scared! Namely…
Timelapse, Hemispherical, HDRI Skies.
A CG project I always admired was Paul Debevec’s and the USC/ICT Graphic Lab’s “Direct HDR Capture of the Sun and Sky”. Almost 10 years ago he and his colleagues created a time lapse HDRI sky and used it both to light the Parthenon and as an animated background. The sky timelapse sequence was shot on a Canon DSLR with an 8mm Sigma Fisheye lens pointed straight up to capture the sky from morning to midday to sunset over the course of a day. When this sky sequence was merged into a high dynamic range image and dropped into this 3D scene of the Parthenon, the HDR sky actually lights the scene, and the result is dramatic:
The pdf they published was technically in depth – there were scripts, custom camera controllers, colour balancing and geometric lens corrections(!). I always wanted to recreate it but what held me back was the feeling that I’d be wasting my time due to the low resolution that sensors had even just a few years ago. I could go to great lengths with all the hardware, but then nothing can make up for those fuzzy pixels. Having said that, looking at the Parthenon shots with the sky passing overhead – the motion can really help when the resolution is low, the end result still looks great.
I honestly always wondered as well whether all the technical aspects were necessary or not. Would I have to work with a programmer to get an accurate, usable end result? This is something I’ll be investigating and comparing as I develop my first test shots. I plan to do some side by side tests with Debevec’s HDRIs and my own, and while obviously its hard to compare the results when the sky is different, it should be an interesting exercise.
Finally, while the lighting for the Parthenon did use the HDR sky, they ended up clipping the sun and using a direct light source due to limitations with image based lighting (IBL) at the time. Today, software like VRay and even Blender’s IBL solutions offer “importance sampling” which can focus more rays on the sun, and use that light source more accurately to light the whole scene, without the need for a separate light.
Last year when the D800 was released, I thought once again about trying my own time lapse HDR sky. The resolution this DSLR provides is similar to most medium format digital cameras, meaning that a single shot can yield a pretty nice horizontal resolution of ~9500 pixels. Over the past few weeks I’ve been testing my new setup, which includes a sigma 8mm fisheye, ND filters and Promote Control – and here’s a sneak peak!
So while this looks like its essentially complete, this is just one exposure rendered out as jpgs, pretty easy! I still have to merge them to HDR, remove any horizon elements, grade the white balance over time, remove birds/planes/bugs, and… more! 🙂
Here’s the day-length time lapse HDR sky shot by Paul et al:
So, while I’m pretty comfortable these days shooting static HDRI skies, this will be somewhat more challenging. I’m still not sure if I’ll really have to go to the same lengths in terms of technical lens and colour corrections, or if current day software can mostly manage. I’m planning on doing some test renders with my own HDRI sky frames, and then comparing them with Paul’s, and see what difference there is – mostly in terms of colour balance, shadow quality and dynamic range.
I’ve still got a lot of workflow challenges ahead too. I’m going to document every step, so you can follow along and see how the set develops.
I’m creating this timelapse sky set for 3d artists in film, games and architectural visualisation – I think these time lapses will create some really dramatic show case animations and I’d love to be able to provide people with a solution that produces a real wow factor for their lighting and backgrounds. Especially if you can basically drop in the sky and let it do its work lighting the scene for you.
If you work as a CG artist with a HDRI workflow, I’d love to hear from you! Or click here to be notified by email of future updates to this timelapse making-of. I’ll notify you whenever an update is made. I’d love to work with some of you before this goes live, so that I can get the best feedback from the people who will be using it the most. If you email me, please don’t use a gmail address, so I know who you are and so I can check out your website. Also please don’t be offended if I decline, I can only work with so many people at once!
Have a go with a HDR time lapse sky now
The University of Southern California’s ICT lab has had the light probes available on their site for some time now, check them out and have a go! Would love to hear how you went and what results you achieved. I believe these are half the resolution of the end result, probably due to the file sizes (yet another challenge I’ll be facing!).
The next few posts I’ll be sharing with you (sometimes through text, sometimes video, sometimes screen casts) how I go about putting this challenging timelapse sky together, the hardware I’m using, how its setup, workflows, samples and tutorials. Once again I’d love to hear from you, and if this interests you, click here to sign up for the newsletter.
See you next time!