sky replacements

[Roberflowers]

hello all,

I've been discussing the sky replacements with my director, and I've seen the blip on the web with guy doing it in after effects. I'm wondering if anyone has experience with this. After I have shot the scenes that I intend to do the replacement, is their any considerations for what I use as the replacement. Do I have to shoot those sky shots with 35mm motion picture film as well, can it be digital still? if so at what resolution and what format?

 

We've shot test footage that is being scanned at 2K this week, so we'll be able to manipulate it soon and try different things before we begin principal photography

 

any thoughts.

 

Just for FYI our workflow is this

originate on 35mm,

edit dvcam

2k scan to dpx files

input in Assimulate Scratch

conform/color

output to DS Nitris

output to HD D5 Master

[Phil Rhodes]

If you do decide to go the DSLR route, other than obviously avoiding shooting clipped electronic highlights, be aware that the average high end postproduction station probably won't be able to read RAW image files from it as there's a distressing amount of proprietary stuff floating around at the moment. Therefore, while you will clearly wish to shoot raw, you'll also want to convert your shots to a known and more standard format, such as TIFF, on the station where you usually handle your digital photography, presumably one with the camera manufacturer's software available. You will want to ensure that the high bit depth of the original raw image is maintained. Photoshop, given the camera plugins, is capable of creating a 16-bit TIFF from an imported raw image.

 

Ironically, the more expensive the post system, the more likely it is to be unable to read bog-standard formats!

 

You'll probably want to shoot at least a ten or twelve megapixel image through decent glass (not the coke bottle that comes with the EOS-400D!) in order to outresolve the 35mm motion picture plate, so you're softening and adding grain to the DSLR image, not trying to go the other way!

 

Phil

[e gustavo petersen]

Phil offers great advice. I would add that you might also want to try shooting time lapse footage of the sky if you want to give some movement with clouds. It doesn't have to be lots of footage (shots) but just enough to give the sky a little movement. You'll, of course, need to have some clouds. Otherwise if you don't need the movement, just capture a still of the kind of sky you need.

 

If you chose to shot some time lapse, you'll likely use the software that came with the camera. I use a Canon XTi and the EOS Utility software. Then I give the footage (either converted or as is) to the post folks who stitch it together in After Effects, Final Cut, or Shake as an image sequence.

 

You should check with your post house to find out which kind of files you'll need to give them. As Phil mentioned, your DSLR files might need to be converted to either DPX, TIFF, or TGA.

[Roberflowers]

Thanks guys for your input. I believe we may attempt a test this weekend with DSLR camera, and I'll try doing some time lapse stuff. We are definately wanting clouds, we're shooting in Santa Clarita at one of the movie ranches up there, and of course there are never clouds:) So our plan is to go to AZ, where I'm originally from and shoot some nice skies there after we wrap principal photography. The monsoon season there gives a ton of clouds in the skies.

 

I'll let you know how it goes

[Phil Rhodes]

I built a timelapse controller for EOS series cameras which allows it to just sit and operate on its own, untethered. It's quite easy to do as they only need a closing contact. Worth thinking about.

 

Phil

[brian jennings]

I've done quite a bit of this stuff and have a few suggestions. I work in 2K and have used many digital images from a Nikon d-70 to replace skies. I lived in New Mexico and like you have seen fantastic sunsets and clouds.

 

Its good to answer these questions before shooting. Get all that figured out so when you are on set you can concentrate on getting what you need. I don't know how many times I've gone to prep only to find out the visual effects happen the next day.

 

Never underestimate the power of good planing. I plan carefully because I know when I get on set every thing is there and waiting on me.

 

I know most of you know this but just in case.

 

1. keep track of the lens information.

2. you want your clouds to match. Wide angle clouds or sky need to closely match the lighting and lens distortion of you foreground. best to shoot with same lens.

3. if you are needing to pull mattes off the sky be careful and you will get a clean Luma or Green screen . DP can help with your issues and help match color space between a raw still and whatever stock he is using.

4. keep in mind you may want or need to do some tracking. You need a spot to place a tracking mark or two in the shot.

 

Hope I helped some. If you solve the technical issues during prep you will be free to be creative and possibly get some goods shots.

 

BMJ

 

 

 

 

 

 

quote name='Roberflowers' date='Aug 9 2007, 02:32 AM' post='187185']

hello all,

I've been discussing the sky replacements with my director, and I've seen the blip on the web with guy doing it in after effects. I'm wondering if anyone has experience with this. After I have shot the scenes that I intend to do the replacement, is their any considerations for what I use as the replacement. Do I have to shoot those sky shots with 35mm motion picture film as well, can it be digital still? if so at what resolution and what format?

 

 

 

 

 

We've shot test footage that is being scanned at 2K this week, so we'll be able to manipulate it soon and try different things before we begin principal photography.

 

any thoughts.

 

Just for FYI our workflow is this

originate on 35mm,

edit dvcam

2k scan to dpx files

input in Assimulate Scratch

conform/color

output to DS Nitris

output to HD D5 Master

've

[Stuart McCammon]

Two words: cloud tank

 

The cheap, always-predictable, easily redoable solution)

[e gustavo petersen]

Two words: cloud tank

 

The cheap, always-predictable, easily redoable solution)

 

I would have to disagree. The last time I shot a cloud tank it was anything but cheap, predictable or re-doable. It took a whole day with a complete crew including the VFX gents. Just refiling the 100 gallon tank took an immense about of time and we had a water truck. Given what Robert is trying to achieve, the DSLR solution is most convincing and inexpensive option.

[Roberflowers]

So is the DSLR solution better and more convincing than shooting the skies with 35mm footage? Should I be concerned with having the grain matching in the sky replacement and the original photography? We are shooting 5274. I have one more emulsion test where we'll see if we like it pushed one stop.

 

Cloud tank sound like there's more involved for what we're trying to do, with the financial constraints we have.

[Stephen Williams]

So is the DSLR solution better and more convincing than shooting the skies with 35mm footage?

 

Hi,

 

Probably not better or more convincing, but possibly cheaper.

 

Stephen

[Will Earl]

Sky replacements are fairly common these days, and the dSLR route is typically the way it's done (using cloud tanks and cotton are rare these days). The limited dynamic range (that's relative of course to film) of a dSLR image can be solved using HDR images (floating point EXRs and TIFs are the commonly used formats). Movement can be added to the clouds by warping or panning the BG plate in post. Grain can be added by sampling the grain from the FG plate or depending on the tool used, by selecting a filmstock from a bunch of presets.

[Stuart McCammon]

I just thought that, compared to a potentially large investment in time waiting for the right sky, the expense of a tank (not necessarily 100-gal.), hot and cold water and some paint sounded cheap, and certainly much more controllable than Mother Nature)