Chroma Key and Compositing

[Rocket]

Hi Guys,

I finally got to see Pirates of the Carribean 3 last night on the big screen, and I could notice almost every scene where they had obviously shot blue screen and chroma keyed the actors over the background scene.

Why in this day and technological age is this still so hard to get right. I couldn't put my finger on it. There was no halo to speak of, but for some reason it just didn't blend, lighting maybe?

Will digital aquisition at 4K make this any easier to perfect?

Rich

 

[Richard Andrewski]

Lighting in my opinion. Its so hard to duplicate the look of really being outdoors with the look of being in a studio with artificial lighting. In the fifties and sixties, even with elaborate sets that duplicated an outdoor scene, somehow it never looked real and you could just tell. While I'm sure 4K will make keying easier and cleaner, I doubt it will help any with the lighting issues and the "feel" of really being outdoors in an all digital CGI matte painting background, even with accurate tracking of camera position in relation to the matte painting.

 

[Ace]

There really is no excuse.. With all the tools available today, if it didn't look 100% real then a bad job was done. No excuses when you have budgets of that size.

 

[Richard Andrewski]

Well look at any of the bigger budget movies where much of the action is on a green screen stage. Sky Captain, 300, Star Wars I, II and III. Did any of them really look like the outdoor scenes were outdoors? I don't think so personally. It's not that the keys weren't good either because they're very good. It's just that it doesn't really look like someone is outdoors yet.

 

[GlennChan]

Check out some CG/VFX-generated lighting for chroma key sets:
http://gl.ict.usc.edu/research/LS5/

Paul Debevec does academic research and if you read all of it, you realize what he's doing goes way beyond the original problem (making a single composite look real). But what that webpage is showing is that you can get stuff looking very real if you surround that person with the correct lighting. In his tests, the subject is lit from almost every angle.

2- In non-chromakey situations, we know that it's possible to get away with certain cheats. e.g. a softlight placed close (angularly) to a practical light will look like light coming from the practical. So the full-blown approach that Debevec takes may not be necessary.

I played around with lighting a chroma key realistically, but it didn't quite work because the light sources I used were not big/powerful enough. I think for things like sky illumination, you have to bounce it off large surfaces (which obviously reduces output significantly).

3- IMO, the robots in Transformers looks great throughout, indoors and outdoors. Compositing them in is the same idea as chromakey (and you don't have to deal with spill; but if you wanted to shoot real subjects without spill, you can do that with a difference key and/or rotoscoping). Except a lot harder because you have to make the CG robots look right (including reflections of the scene).

Movies like LOTR and Harry Potter also show good chromakey work IMO; you don't notice it. IMO, movies like 300 don't look right because the backgrounds are stylistic and not realistic/real. For real backgrounds, the helicopter stuff in Charlie's Angels 1 didn't quite look right IMO.

 

[Jim Arthurs]

Today's "perfect" key work will look less than perfect in a few years as visual taste and the general audience's perception increases.

I remember seeing DragonSlayer and Poltergiest in my youth, thinking how great some of the bluescreen was and that it would never get better than that. It did. Film bluescreen probably was at its best with Willow or Hook, which both pushed the techniques to the limit.

Using the same source images, the most mediocre digital compositor in the world running a 500 dollar PC with After Effects will do cleaner matte work than the best trained optical techs in the world running a quarter million dollar optical printer fifteen years ago.

I'm humbled having worked in both worlds, optical and digital, and the power/speed we have now.

The Pirate movie has been well documented as a rush job and a nightmare to work on...

http://www.variety.com/article/VR1117965871.html?categoryid=2520&cs=1

 

[Jason Murphy]

The Pirate movie has been well documented as a rush job and a nightmare to work on...

I think this explains a lot of the less than perfect compositing and FX work on the movie. If you have the time, even if the lighting is off, you can certainly make things look more seamless (if not 'perfect'), assuming you have the time. Almost every FX heavy summer blockbuster these days doesn't have the time; some of them are locked into a release date before shooting begins, and the FX work is finished in a massive panicked crunch two weeks before the premiere. It shows, more often than not.

 

[Jim Arthurs]

Lighting in my opinion. Its so hard to duplicate the look of really being outdoors with the look of being in a studio with artificial lighting.

Oh yes, lighting is key (pun intended). Lighting a subject in front of a blue or greenscreen is fairly tricky for DP's without the background in it.

For starters, the blue or green spill is seen by the eye and evaluated as actual back or side lighting, when in fact, it is actually "negative lighting" and won't be represented in the composite. In order to see the lighting as it really is, it is sometimes helpful to fly in a large black behind the talent... as this is how the matting plugin views the foreground after the spill is removed. In almost all cases, extra white fill is needed to replace the areas where spill is happening, else the edges go dark on you.

Another factor, besides lighting, is the slight of hand of the shot itself... you see twenty copies of a talent side by side and know it's a comp. You see the hero standing in front of a vast alien cityscape and know it's a comp. It's the shots that you're not expecting to be an effect that always stand the best chance of slipping by the audience regardless of visual experience in the area...

An example of this trickery was with a bluescreen shot I did and posted back on DVXUser done with the HVX when testing it. By posting a clip of talent in front of a nature setting and asking for lighting advice on the nature of my talent "interview" lighting, I diverted attention away from the shot as a potential comp and put the attention on the talent lighting. It helps that the comp was good, but a bit of verbal slight of hand kept the true nature of the shoot as a bluescreen from being discovered for several pages of posts...

I did get very helpful advice on talent lighting, however...


http://www.imageshoppe.com/HVX_bluescreen2.html

 

[Charles Angus]

C

Movies like LOTR and Harry Potter also show good chromakey work IMO; you don't notice it. IMO, movies like 300 don't look right because the backgrounds are stylistic and not realistic/real. For real backgrounds, the helicopter stuff in Charlie's Angels 1 didn't quite look right IMO.

Really? I watched Lord of the Rings (the first one) again the other day, and I almost laughed at how unrealistic the lighting looked. Not that I could do better, but I don't get paid the big bucks those DPs do...

 

[Chris Nuzzaco]

Really? I watched Lord of the Rings (the first one) again the other day, and I almost laughed at how unrealistic the lighting looked. Not that I could do better, but I don't get paid the big bucks those DPs do...

The lighting was never supposed to look real... watch the documentaries, they wanted it to look like a story book of sorts. I think they pulled it off fantastically, course, I'm a big Andrew Lesnie fan....

 

[Jason Murphy]

Anyone interested in seeing some really excellent lighting/comp work in a recent film should check out David Fincher's Zodiac (out today). There's a surprising amount of it, and it's pretty much entirely seamless in the film. Probably the best example would be the investigation sequence on the corner of Washington and Cherry; it's entirely greenscreened since the location isn't the same as it was in 1969 (not to mention that the current residents weren't about to put up with a film crew moving onto the block for a week).

The effectiveness of these shots also goes to highlight what Jim Arthur rightly said a few posts above, when he mentioned that the shot itself is usually more effective when compositionally it does not draw attention to the fact that it's a composite. Very true.

 

[Jason Murphy]

Really? I watched Lord of the Rings (the first one) again the other day, and I almost laughed at how unrealistic the lighting looked. Not that I could do better, but I don't get paid the big bucks those DPs do...

The cinematography is unrealistic for sure (assuming that 'realism' should be held up as a criterion for a story about hobbits, elves, etc. trying to destroy an incredibly evil ring in a volcano in the south of a mythic historical England), but it is pretty effective nonetheless. There's a bit too much unmotivated lighting for my tastes (for example, the fact that in the middle of the night you have Black Riders silhouetted by an obscenely bright light coming from just over the horizon of a hill - gotta love HMIs), but then again, 'realism' would dictate that it would be more or less impossible to see a black-cloaked figure on a dark moonless night, especially at a time/place when electric lighting shouldn't exist. And it may just be me, but a totally black screen full of rustling and screaming and hobbits yelling for 10 minutes just doesn't strike me nearly as gripping as actually being able to see the little guys run...

 

[Gavin Greenwalt]

Hi Guys,

I finally got to see Pirates of the Carribean 3 last night on the big screen, and I could notice almost every scene where they had obviously shot blue screen and chroma keyed the actors over the background scene.

Why in this day and technological age is this still so hard to get right. I couldn't put my finger on it. There was no halo to speak of, but for some reason it just didn't blend, lighting maybe?

Rich

That's because there were some reallly badly made composites in Pirates 3. Some really really basic things like black levels were off. Also some shots the greenscreen footage was slightly out of focus while the plate was sharp... I was less than impressed with many shots.

That being said it was almost always the integration not the extraction that was the problem.

 

[Rocket]

Well, thanks for all your input. I guess I'll put it down to time in the case of Pirates. It's amazing how much this type of compositing is considered standard fare in almost any movie these days, not only in the case that the actual location can't be shot, or isn't accessible but that it could just be cheaper.

I'd imagine that if I was shooting a sequence in the middle of Time Square for instance, like at the beginning of Vanilla Sky, I'd probably consider modelling Time Square in all it's detail, and compositing the shot over the 3D rendered location. This probably wasn't a viable option when Vanilla Sky was shot.

I shot a corporate video earlier in the year (well, 4 x 30 min videos) that were entirely shot in a green screen studio. I was shooting with two DVX100's in 25p and had a really good lighting tech that came with the studio we rented. The lighting, for the interior scenes we were going to composite, was perfect, but the keying in the end was less than perfect, mostly due to the fact we were recording miniDV, and I really think the compression is a killer in overall quality of the job. I will never record a chroma shoot in DV again.

Now, I find myself doing another one, but this time things need to be right because the entire 10 minute video is filled with Matrix style effects and compositing over CG background. So, this time I'm shooting HDCAM in the hopes I'll get a good result.

Anyone here managed to do it sucessfully with DV?

 

[Jim Arthurs]

Now, I find myself doing another one, but this time things need to be right because the entire 10 minute video is filled with Matrix style effects and compositing over CG background. So, this time I'm shooting HDCAM in the hopes I'll get a good result.

Anyone here managed to do it sucessfully with DV?

HDCAM is far better than DV of course, as it's 3:1:1 vrs 4:1:1 or 4:2:0, but needs a certain amount of care as if you push it too far you'll see the compression artifacts. Make sure you're right on with exposures for screen and subject with the flattest screen exposure possible is the best advice.

Asking someone to define success with keying in DV is a tricky question to ask. Some will jump in and say "yes", others will say "never"... realize that it's case dependent and camera dependent and people have different tolerance levels for what they consider "good" or "great".

Most work with any format is spoiled if the detail is turned up too high. I've not done work with DV or HDV that I consider excellent, though HDV can do nicely if the end product is SD and the source footage scaled down for the composite.

In regards to keying, HVX-200 is the best bang for the buck shy of its 2/3" bigger brother that just hit the market. It performs with both blue and green equally well. I make good money with it, but it has situations where the noise in the picture make for difficulties.

All semi-affordable cameras will pale next to the RED in matting quality. I will treat the RED the way I treat the HVX, in that the HVX makes for great SD final product when scaled down, and the RED will produce the best possible HD from the downscaled 4K...

 

[Bruce Allen]

The lighting, for the interior scenes we were going to composite, was perfect, but the keying in the end was less than perfect, mostly due to the fact we were recording miniDV, and I really think the compression is a killer in overall quality of the job. I will never record a chroma shoot in DV again.

Agreed. Shooting DV makes no sense when you can shoot HDV for the same price and get a better SD image out of it. What were you using to pull the key?

Now, I find myself doing another one, but this time things need to be right because the entire 10 minute video is filled with Matrix style effects and compositing over CG background. So, this time I'm shooting HDCAM in the hopes I'll get a good result.

If you're finishing HD or film, you'll need a lot of light wrap, etc. Even HDCAM has problems on the edges - once you take the green out, they tend to go a bit grey... so you have to do a few tricks to make it look good.

Bruce Allen
www.boacinema.com

 

[Chris Nuzzaco]

.........or you could hire me and I'll shoot your green screen with my Andromeda


http://www.reduser.net/forum/showthread.php?t=3098

 

[Michael Schrengohst]

The Pirate movie has been well documented as a rush job and a nightmare to work on...

http://www.variety.com/article/VR1117965871.html?categoryid=2520&cs=1

Shit rolls down hill, as the studio tells the producer, who yells at the director
who yells at the DP who yells at the gaffer and then the best boy down
to the grunts....the grunts could give a crap and they want to go home.
So everyone rushes it out the door because they are getting tired of
hearing the $15,000,000 actor whine about the hang nail he has....
Yada, Yada......

 

[Richard Andrewski]

Today's "perfect" key work will look less than perfect in a few years as visual taste and the general audience's perception increases.

I remember seeing DragonSlayer and Poltergiest in my youth, thinking how great some of the bluescreen was and that it would never get better than that. It did. Film bluescreen probably was at its best with Willow or Hook, which both pushed the techniques to the limit.

Using the same source images, the most mediocre digital compositor in the world running a 500 dollar PC with After Effects will do cleaner matte work than the best trained optical techs in the world running a quarter million dollar optical printer fifteen years ago.

I'm humbled having worked in both worlds, optical and digital, and the power/speed we have now.

The Pirate movie has been well documented as a rush job and a nightmare to work on...

http://www.variety.com/article/VR1117965871.html?categoryid=2520&cs=1

How about that Dragonslayer? That was really great blue screen work by Brian Johnson (Empire and Space 1999). I remember the article on that in American Cinematographer. They had a huge blue screen that was backlit with DC operated, blue tinted fluorescent bulbs. DC of course to eliminate any chance of flicker as electronic ballasts didn't really exist in 1981. Very clean keys. Look at the shot of the wizard on the mountain top at the end. With his white hair blowing in the wind. Not that real looking mind you (because of subject lighting and background too perfect) but very clean.

I think looking real is a subjective thing anyway. I look at a lot of older movies where they used rear projection on car shots (Casablanca for example) and its easy to forgive because the movie was so great and the cheesy rear projection is actually a part of the experience. In fact, you almost feel the movie wouldn't be the same without the stylized elements like that.

The 1950's War of the Worlds was mostly shot in stages at Paramount, even many of the "outdoor" scenes at the beginning of the movie, but its easy to overlook because the movie is such a classic and really set records for number and quality of effects shots in a movie.

Maybe something looking very clean (no obviously bad edges for example) but not real is okay as it lends to the overall fantasy of the movie. Everyone will have different opinions on this though.

 

[Alex Boothby]

There was an interesting discussion about over/under exposing green screens on fxguidetv, episode 3:

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

The Australian Cinematographer Society did a shoot with FX-PHD to test green screen lighting and keying for digital cameras such as the F-23. Ross Emmery (fx DOP for Superman Returns & The Matrix) recommended to OVER-EXPOSE the green screen by 2 stops - to much surprise all round.... And it turns out that he was right. The episode then goes on to demonstrate that a cleaner key is indeed pulled from an over-exposed green screen (for digital cameras at least, they say).

I found all this very interesting - but I think it's an over simplifications. First of all, the chances of unwanted green spill increase as you increase the light on the green screen (I think they assume that the subject is always far enough away from the screen to avoid spill, which is not always possible.) Second, an over-exposed green screen may indeed yield a better key, but at the cost of chroma and luma corruption of the subject's outer edge. This can produce the tell-tail white halo or 'perpetual rim light' look in composites.

I certainly plan to test this more. In the past I have always considered the background. If the subject is to be comped into a dark environment, then it is preferable to under-expose the green screen. Likewise if the subject is to be comped into a very bright environment, then over-expose the green screen. But never more than 1 stop. Personally I don't mind a bit more work pulling a perfect matte (or even garbage matting or rotoscoping) so long as the edge looks natural.

Thoughts anyone?