rules for chroma shoot!

[adolf]

can any body please tell me what basic rules should we follow while a chroma shoot? and what is the difference between blue and green screen shoot?

[metalrahul]

Man as far as i know, there isn't any standard rule for doing that thing. its depends upon the situation. if your actor is wearing a blue shirt go for green screen, if your forground got some foilage or grass then you must go for blue screen.. And if your ur actor is black then go for green screen bcos blue got some elements of black. (hmm i have read about it some where not sure..)


check ou this these links, they gonna help you a lot..

http://www.computerarts.co.uk/tutori...and__animation
http://www.creativecow.net/articles/...l/shooting_3d/


cheers
Rahul.

[Rafs Ome]

The best discussions I have found on this subject are cinamatography.net and fxsoup.com:
summerized and linked on miafx.com wiki:
http://www.miafx.com/23/tiki-index.php?page_ref_id=125
http://www.miafx.com/23/tiki-index.php?page_ref_id=287

[rohitm]

the most important things are distance of the screen from the target and the LIGHTing... some cameramen like to light up the screen which is usually the worst thing to do! its the difference tween lightness and brightness..but thats a long explanation....also some cameramen use high speed low light film stock cos that saves them loads of lighting time...but ruins the key..always avoid high speed stock for chroma keys..and if yr worried about matching the film stock detail to the ret of the shots...use flames grain management tools

[adolf]

hi rohit
thanks for ur help but could u please explain me in detail the issue of film stock and lighting ? ur reply could be very precious for me!
adolf

[michaelmovies]

The higher the speed of the film stock the more grain, the more grain the more chatter in the blue/green screen, the more chatter the harder it is to pull a good key. So slower speed, fine grain film is better, which means you need to rent more lights, and more lights makes it harder to eliminate shadows on the screen, which means you need to find a better DP. Kodak makes SFX200 specifically for blue/greenscreen work, and apparently it's a good balance of all characteristics needed.

Ideally the object of interest should be as far from the green/bluescreen as possible to minimize spill. The screen should be clean, consistent, very evenly lit, with no visible seams, flaws, or areas that are darker or lighter than others. The color chosen should provide a good strong contrast with the subject (ie if the screen is green the subject should NOT be green or have areas with a high proportion of green unless you want these to be transparent).

Most important rules: don't move the camera during the shot unless A) you've got a motion control rig or B) you've got useful tracking marks. If A) then great, shoot the action then shoot the clean plate. If B) then make sure your marks contrast both with the screen and with the subject in color, and make sure there's enough room between them that the comper can use one track to paint over the marker for another, etc.

Better yet ... JUST DONT MOVE THE CAMERA!!! And shoot a plate of 5-10 seconds with just the green/blue screen and any objects that do not move during the shot. Make sure the tripod is really REALLY well locked off before you roll on the clean plate, then don't let anyone touch it until after you've finished shooting all the action. This will make your compositors life a dream.

[quantum mechanic]

Chances are quite good that your dp will want to use blue gel on his/her light (1/4 or 1/2 CTB to balance colour temperature) if this is the case then you definitely want a green screen as the blue will effect your key.

Also make sure you have a decent back light to kill any spill from the screen. Even if your subject is 20ft. from the screen you will get some spill. If you don't chances are your screen is not lit properly.

SHUTTER ANGLE!!! make sure your dp isn't killing you with tons of motion blur and while you are at it don't let her/him use any promist filters.

And make the dp meter the screen after it's lit, if only I had a dime for every time I've seen a dp meter everything in the shot and then glance at the screen and say "that looks even".

DP's don't light for effects artists they light for directors and subjects, it can be a pain sometimes getting them to understand that you also have requirements to get your job done.

[martindisenio]

and
What's the right saturation for background chomakey?

When i order to paint a chroma green / blue background; What color must be request?

[michaelmovies]

http://www.rosco.com/us/scenic/digicomp.asp

Rosco has a Brazil office and website where you can order more locally.

This paint and tape are not cheap, but they are very standardised. The green tape over the green paint will be pretty nearly perfect. I see rosco paints being used all over Hollywood.

It's only worth the trouble though if you are also using good lighting: ie daylight or tungsten balanced photographic lights, and no mixing of the two on the screen itself.

Michael

[adolf]

hi mikes and everybody !
i am writing u whatever i am aware of chroma ( green / blue / black ) shoot !
please fel free to correct me !
1) for dv shoot on green screen as the video signal is compressed and some color information is lost !
2) if its uncompressed highend format then use blue screen ! for compressed use green !
3)avoid clothing matching the color of chroma screen !
4) light screen from front
5) there should be no shadows on screen
6)use gels to neutralize the color spill on foreground objects backlight
7)keep at least 12 feet distance between fg ( foreground ) and screen
8) use no special filters while shoting
9)check the uniformity of lighting with a spot meter
10)avoid shiny objects with glossy surface or shiny surface
11)never use dimmers with lighting the screen as it lowers the color temperature, making the blue more orange
12)capture with better sampling ratios . 4:2;2.
13)check what stock the dop is shooting on
14)the dop should not use fog, difussion,superfrost or smoke when shooting chroma
15)light your screen for its hue and not just to make it bright
16) there should be no reflection of the screen on fg object or talent
17)shoot light colored objects with dark blue screen and adrk objects with green
18 ) use a flat lighting scheme as far as posible
can nebody help me shooting on black ?
thanks
please feel free to correct me !
adolf

[michaelmovies]

1) for dv shoot on green screen as the video signal is compressed and some color information is lost !

NO. Choose the color based on the subject, not the camera. If you are shooting DV make sure you read up on preparing DV for compositing (ie blurring the Red + Blue channels horizontally to make up for the loss of resolution in 4:1:1)

2) if its uncompressed hghend format then use blue screen ! for compressed use green !

NO. Choose the color based on the subject, not the camera. Yes most video holds more information in the green area, but compression is just as bad for blue as it is for green. ALWAYS shoot uncompressed if possible.

3)avoid clothing matching the color of chroma screen !

YES, but not just clothing. There should be no similar color on the subject as on the screen unless you want it to be transparent. The reason Green is so often chosen is because it is much less likely to appear in any normal subject (ie people) than red or blue, but ALWAYS choose the screen that contrasts best with the subject. If your subject is bright green then a Redscreen may be best, etc.

4) light screen from front

Yes, normally.

5) there should be no shadows on screen

Yes. No shadows, no darker areas. Get a spot meter and check the entire backdrop, do not rely on an incident light meter (the ones with the white plastic domes).

6)use gels to neutralize the color spill on foreground objects backlight

If possible, yes, but most people cannot balance the color correctly, and it will play havoc with your grading. Normally light the subject as you would normally light it in the space it is supposed to be in. Use the backlight to seperate the subject from the backdrop and try to minimize spill, but unless you want the backlight in the final shot to be colored dont use the gels.

7)keep at least 12 feet distance between fg ( foreground ) and screen

Not always possible, but yes, a good idea. The main thing is getting the screen lit correctly, but the further the subject is from the screen the less the incident spill.

8) use no special filters while shoting

YES, very very true. Unless absolutely necessary do all filters in post. Good idea to shoot a test shot with the filter and then do the proper clean plate without. Give both to compositor, so they have a visual reference of the effect.

9)check the uniformity of lighting with a spot meter

YES!

10)avoid shiny objects with glossy surface or shiny surface

If possible, yes. Very hard to eliminate a specular spill.

11)never use dimmers with lighting the screen as it lowers the color temperature, making the blue more orange.

Yes, unless you use a proper photographic dimmer. Simple magnetic dimmers will always lower the temperature, but expensive professional electronic dimmers do not.

12)capture with better sampling ratios . 4:2;2.

Yes. 4:4:4 is even better. Film is best. Work in 10 bit uncompressed instead of 8 bit. Learn about Log formats.

13)check what stock the dop is shooting on

Yes, very helpful in grain matching.

14)the dop should not use fog, difussion,superfrost or smoke when shooting chroma

Already answered, but most DOPs will do it anyway.

15)light your screen for its hue and not just to make it bright

Yes.

16) there should be no reflection of the screen on fg object or talent

If possible.

17)shoot light colored objects with dark blue screen and adrk objects with green

Depends on the color of the subject. The main thing is to not let the edge of the subject disappear into the screen ... there must be contrast.

18 ) use a flat lighting scheme as far as posible

On the screen yes, but not on the subject. Light the subject based on how it is supposed to fit into the final shot. If it's supposed to be in a side lit high contrast room then it should be lit that way, not flat.

18a) can nebody help me shooting on black ?

Yes, make sure the subject is flame or light or something else that provides its own light. If it's a person rim light them and get the fill and key right so they (and especially their hair) do not blend into the background. Black screen is usually for explosions, fire, or light effects.

Michael

[adolf]

hey mike !
thanks for correcting me ! i got to learn a lot from u ! can you tell me :
how do we achieve very good lighting for the fg and screen !
how do we mix the live action cg very realistically !
what are the things we should generally carry on vfx shoots ( plz can nebody send me what each thing does and its use )
how do we achieve complex motion tracking shots without using motion control camera?
how do we shoot miniatures and integrate them with live action and cg !
Optical flow - how to shoot for optical flow on set
Keying theory - the algorithms behind the keyers
Shooting hires with mini-dv & mini-HDV - tricks for upresing and compositing
Lighting greenscreen - how to do it and how to get the best results
Shooting minatures - on set with the DOP discussing lighting and shooting
what to take on set, how to get great reference
we show how to design a complex shot and then comp it.

[rohitm]

and most important ! MAKE SURE THE TELECINE COLORIST DOESNT ADJUST THE BLUE OR GREEN [WHICHVER U FINALLY USE] COLOR OF THE SCREEN WHILE GRADING AND TRANSFERRING

[rohitm]

they have this nasty habit sometimes of bringing up the bightness or saturation of the screen color with totally screws the edges of the key

[rohitm]

is u really need to grade the shot in telecine..make sure the colorist gives u a clean flat RGB pass with the same timecode and TKpan etc settings