Blue Screen Techniques

[pnut]

I am in the pre-production stage of creating a music video using mostly blue screen and black matting techniques.

Does anyone have any info or links to diffinitive guides of colour spectrums and their reationship to keying?

We are at the stage of deciding on the colour pallet for the video, and i would like to, at all costs ovoid using colours on costumes,props and the set that may compromise full and effective keying of the action. By this i mean bleading through any other colours that are not blue or green.

What are the differences between a Blue Screen and a Green Screen, i was told one was better for celluloid and the other digital, but this i am unsure of.

Any help would be greatly appreciated,

Tanks

Faltown Pirate

[markmyvideo]

have been flame artist for some time and did a lot of keying...
green is used because in rgb signal, green is least present in human flesh colour and therefore easiest.

any experience with difference key? this works very well as long as you have your camera fixed or using motion controlled cameras...
shoot one empty clean plate and the other with talent...

-my twopence-

[pnut]

What editing platform do you use?

I Use the RGB difference in Premier Pro. Im really after info on the colour ranges that determain which end of the scale in keyed.

There are some complex costume and set designs, and i really want to be able to avoid having problems with certain colours in the edit.

Which colours should be avoided?

which colours will be of exact oposites of the green or blue screen? Therefor ok to encorporate into the costume and set designs?

[sleepytom]

green is used because its more acuratly represented in the 4:2:0 DV colourspace.

premiere is really terrible at keying - i would try using combustion (or aftereffects) i suggest that you search this website and use google to search the web - there are a lot of very good keying resources out their.

good keying is mainly about lighting - this is where you need to put the most effort in..

[evomedia]

Agreed Premier keying is poor, I use the ultimatte advantage for keying, it even works as a plugin for premier/AE or occassional serious magic. Either are seriously good keyers

[holly]

Agree with Tom. Software can key any vivid color nicely, but the lighting is what will kill your shot. Blue vs green is not as important as evenness of color for the backdrop and enough light on your subject to provide good contrast. The original chromakey color was yellow....

[deepvisual]

and...
avoid reflective and white fabrics, jewellery, even glasses.

[evomedia]

The chroma paints are interesting if you just a have a big plain wall somewhere.

Lighting is the most important especially if your using cheap DV cams. White balance needs to be carefully adjusted for best results.

[pnut]

We are shooting on a budget and need to get maximum results from available software.

The costumes and props are going to be mostly black and grey scale, using vivid highlights.

Just want to ensure costume / cinematogropher / stay away from any compromising spectrums of the colour scale.

Does AE 5.0 key very effectively?

ta

[sleepytom]

no AE is not really all that good at keying, combustion or Commotion are better or get one of the ultimatte plugins for AE.

[holly]

Do you know what the final background(s) will look like? Big budget productions will often change colors based on the individual needs of the shoot. For example, if everyone is supposed to be tromping around in the forest green is likely the way to go because the difficult key moments (where you just can't get that bleed out of the shot without crunching too hard on your edges) will blend in to a mostly green background. Blue is also used for obvious reasons (sky is a likely background outdoors) and also sky light has a slightly blueish tint (compared to most electrical lighting) so blue lightwrap is less an issue than green. I was dumbfounded in the second (fifth?) StarWars movie when Senator Palpatine's office was chromakey blue. I immediately thought they had to make the backgrounds match because they couldn't get a clean key.... It's a valid solution, however. Many decisions are made because you HAVE to fix the shot in post, not because blue is derrived as a subtraction of luminance after the inversion of the green channel... or whatever the "technical" logics behind green v blue. In the real world you don't get to split hairs that fine.

Rolls of photo backdrop paper are not very expensive and might give you a few more options than paint for the price..., but if the backgrounds are constantly changing abstractions of vivid color you might run into the issue that some backgrounds naturally camoflage keying flaws while other backgrounds make them more noticable.

My suggestion to you is, set up your shooting environment LONG BEFORE your actual shoot with the band. Run lots of test footage through your entire keying process. No software can fix problem footage. It is best to focus on your shooting environment to get good shots you can work with later, than to try to fix it once it's too late.
Good luck!

[MrJustin]

and...
avoid reflective and white fabrics, jewellery, even glasses.

For shiny things utterly necessary in the shot (chrome frets, steel drums etc) , a quick squirt of hair spray or two (or similar matte effect lacquer) can really help diffuse the reflection. Note 'can' and not 'will'... have a play with the lighting and certainly take Holly's advice on testing the shots first.

Good luck pnut,

Justin

[labmeta]

AE is fine for keying if you can get Ultimatte or my favourite Keylight.

Keylight has a lot of settings to tweak the keying matte and at a push if your clever with building up several layers of keyed footage, ie one layer for the inside, another for the edges, and maybe another for any hair you can even get good results from badly lit green screens. Some times even the biggest production companies fuck up the green screen lighting.

The main thing i would say is dont shoot on DV or HDV, cos thats always a nightmare.

If you do, a cheeky trick is to get a DV deck with an SDI output, capture it via that with some form of 10bit uncompressed codec and some how, i cant explain it technically, the edges arent anywhere as near as jaggy.

[deepvisual]

anyone use the ultimatte box???

it pulls a real time key and is shit hot when combined with reflecmedia.

[Entheogen]

Apple's motion is very good at keying, using the Primatte RT Filter.

If the lighting isn't right then it will be very difficult to key, you may end up having to mask frame by frame if it isn't right.

Someone with some experience with lighting and a light meter are important.

The further the light source is from the subject the better as you will get a flatter light on your subject. The further away the subject is from the green screen is better too as you'll get less spill from the chroma screen. Spill is coloured light from reflecting from your chroma screen and will make it harder to key. Although spill suppression filters can reduce this.

If you're in the London area I'm up for helping if you need access to Final Cut Pro /Motion.

[holly]

anyone use the ultimatte box???

it pulls a real time key and is shit hot when combined with reflecmedia.
Yeah, I have the new one, the UltimatteDV. It is indeed shit hot. I never want to render again....

I have an old one too from ebay, Ultimatte5 which is destined to become an end table....

[holly]

The main thing i would say is dont shoot on DV or HDV, cos thats always a nightmare.

If you do, a cheeky trick is to get a DV deck with an SDI output, capture it via that with some form of 10bit uncompressed codec and some how, i cant explain it technically, the edges arent anywhere as near as jaggy.
The technical explanation is that DV codec is a crap. :P It stores less color information per frame than light/dark information. When in motion it all seems to smooth out, but when keying just one color you are working with only 25% the resolution -- hence the jaggies. You can read a more technical explaination by looking up DV's colorspace (4:1:1). HDV is mpeg2 (4:2:0 colorspace) which is better for keying, but HDV is a comparably low bitrate for the image size so there is more compression noise.

[Meierhans]

Did some keying from HDV, recorded in Sonys "Cineframe" Mode. This trows away half of the lines but also reduces the compression noise due to less res/details that need to be compressed. In general the background does not take alot, so there is enough bandwidth for object.
With Ultimatte (in DV mode) results where pretty good, at least when resized to SD it looked like a key on 4:2:2 Betamax.

[vjpixylight]

have been flame artist for some time and did a lot of keying...
green is used because in rgb signal, green is least present in human flesh colour and therefore easiest.


-my twopence-
That funny cause I remember being told that Blue is the opposit of skin flesh tone and is best for keying flesh tones.

Anyhow, it really matters what colors the costumes are.(unless you are doing alot of closeups and facial shots)