Cinematography Mailing List - CML

Polar Bear on Blue Screen


I have an up coming Blue Screen shoot. We will shoot a White Mother Polar Bear against; and standing on a Chroma Blue Screen floor. 4K RED Cameras. The bear footage will be comped onto footage that was shot in the Arctic under sun and shade. There is much concern about spill onto the bear. We will create soft skylight; and sun in order to match our plates. We cannot use real snow for the floor. I have stated to the producers: What is required is that the bear is lit to match the environment that the plates were shot in. The matching sky light we will recreate is white in colour. The spill light is that which is reflected/bounced off the Blue floor. The Bear will be standing on a Blue floor. Any light hitting the bear will also bounce off the blue floor. Thus creating "spill".

If we were only shooting the bear against a Blue Screen (and not on a floor) ; spill would not be an issue as the would be far from the Blue Screen and not standing on it.

I can add ground level light onto the bear to make up for the lack of "natural" snow bounce. Am I missing anything here?

Many thanks, Peter Wunstorf, ASC US, Canadian Cinematographer


Since Polar bears aren't actually white, wouldn't it be better to shoot it on a white floor? There would be no colour spill, and you'd get a snow like bounce. Comp it onto the arctic footage using a soft edged travelling matte and you probably won't see the join between white floor and white snow.

Just a thought...


Edinburgh Film Studios, UK.


I don't think white is a good idea, because it's close enough to the actual color to make pulling a matte a nightmare.

I would suggest a blue screen instead of green, just so any left over spill or bounce would be closer to the cool polar ice, than green

Steve Hullfish author, "The Art and Technique of Digital Color Correction"


I wasn't suggesting pulling a key, rather hand animating a fairly rough travelling mask/matte.


Edinburgh Film Studios UK


Well, a polar bear presents particular challenges, so these options may be impractical, but whenever I think of shooting anything head to toe on a chroma color limbo I consider the advantages and compromises of either having them stand on mirror plexi (which reflects the chroma screen bg, but adds no color bounce to the subject) or raising the subject off the floor on clear plexi (thereby eliminating shadows on the floor and limiting color bounce onto the subject).

Reflections in the surface (plexi) ahead of the subject must be cleaned up, but in some cases that's easier than managing the effects of spill and/or shadows. In some cases the back edge of clear plexi can cause issues, but they are usually minimal.

It would help to know the angle from which the plates were photographed.

Fortunato Procopio DP NYC/LA


Don't shoot the bear on a white floor.

There are spill supression systems in modern compositing tools that are designed specifically to help solve the problems you're concerned about.

Shoot the bear on full blue screen, and yes add a bit of underlighting as you suggest to mimic the bounce from the snow.

Is your delivery format HD / 2K ? If so, then 4K is a good idea and will provide you enough hair detail for great mattes. Do not attempt the white on white travelling matte, it will look bad.

Keep your blue screen levels at, or even a half stop over your shoot stop. You want your blue screen levels to be similar to what your BG plate is. If you were shooting for comping against a late afternoon sky for example, you would bring the screen levels down. In any case, keep a close eye on your noise levels in blue and shadow areas.

Primatte in nuke is exceptional for keying hair detail and removing spill color. Since it's an all white polar bear it will be a snap to bring the blue spill colors to white or grey. When it's a multicolored object then it becomes a little more tricky. The comper will have to do a bit of holdout matting.

In cases like this, the best approach is to bring a vfx sup with a laptop and a comping tool such as nuke, smoke, or even AE on set as well as a pix 240i or other high quality recorder to grab shots from the video feed. They can also grab the r3d files directly but this is a little more time consuming/render heavy. The vfx sup can do rough comps and quickly identify problem areas which can be resolved with minor lighting/fill fixes.

Lee Towndrow Nuke Artist, Flame Artist, dp, etc.


I thought of the same thing, mirror plex. Then I had this terrible thought of the poor big bear sliding around and having his feet slide out from under him on the very slick plexi surface. You don't want an unhappy polar bear in a studio with you!

Roberto Schaefer, asc, aic Venice Beach, CA. / New Orleans, LA.


As always, the devil is in the details My first conversation might be with the trainer with regard to what the polar bear is likely to tolerate with regard to surface.

Personally I don't think mirrorplex is a great idea with 750-1200lbs of bear...

My second conversation would be with the post house... it may turn out that rotosocoping the bottom of the polar bear off a neutral gray floor might be preferable to dealing with the bounce up from the green or blue.


Given the possibility of the polar bear relieving itself or worse, you might consider laying out and painting a big piece of linoleum for the intended work area and have another one painted and ready to go... seamless paper would be easier but doubtful that it would outlast one or two direction changes on the part of the bear.


That would mean painting the floor (or linoleum) gray - yes there is a line between the floor and the background but maybe thats easier to deal with than a dingy color tinging the bottom third and shadow areas of a moving bear -

We always talk about how good spill suppression is but its better at some things than other things. different kinds of hair or fir handle strong saturated edgelight differently (as in your bounce from screen and floor)


Thirdly, remember that you only need the green or blue or gray or whatever right around the outline of the bear on any given frame....

once you have a working area, maybe you can put out white muslin elsewhere on the floor to pick up light and add that low fill that will help sell the comp

foamcore is easier but muslin might be less freaky for the polar bear to walk on if that becomes an issue

Fourth - and this has fallen out of fashion, but only light the portion of the cyc you need for the comp... Most people light a big green and leave it hot even when they dont need it and squirt all sorts of green around that they dont need... you only need a handful of pixels around the animal - all the rest is garbage mattable...

Me, I would hang whites on tracks in front of the green and tease them in to the edge of frame and bounce light on them to emulate the back-plate's ambience...

Have fun - and try not to look, sound, or smell like a baby seal.

Weingartner la dp vfx


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