blue/green chroma .why this color?

[beaker]

Pretty basic color theory. Most cameras capture the three primary colors separatly RGB. So it would make sense that it is easier to separate out those individual colors in the background from the foreground.

Red is fairly comon in our skin pigment, so you really don't want to use that. The blue channel is always very grainy, dark and it is a common color in clothing. Green tends to be a good medium, it is bright and tends to be less in people clothing.

http://www.seanet.com/Users/bradford/bluscrn.html

[Ecleposs]

ohh..thank alot beaker
:)

[j-man]

It gets a alittle more complicated than that...

Most consumer (and broadcast!) video is recorded in component form, Y'CBCR 4:2:2 which basically it has a luma channel, and two colour-difference channels, not three colour signals as you might expect (RGB, 8-bit). The first number (4) is the l;uma horizontal sampling, the next two the colour difference horizontal sampling, and vertical sampling, and if there is another number after this, the aplha (as in 4:2:2:4).

4:2:2 means there are twice the number of luminace samples for the two colour difference channels (on an 2 by 2 grid, there will be 2Y, 1CB,and CR). Consumer DV takes this even further to 4:1:1 Why? so that you can get more information into the same signal.
Wheres the trick? the two colour difference chanels are Luminece (Y)-red, and Y-blue, and the green is calculated from the remaining luminance, essentially meaning that there is more colour information for green than red and blue.
The best situation would be to use 4:4:4 but unless you have some fancy equipment this is going to be pretty unlikely.
I hope this explains something! I suggest you do a good search and read on the internet since this is a pretty complicated concept.

Cheers,

[VFX Follower]

As stated above it is simple color theory, but there is a little more to it. First of all you have to determine in what medium you are capturing your footage. Film works better with blue screen and video works well with green screen. However, you also have to consider the shot as well. There are many factors that can dictate what color screen is used:

Actors clothing
Time of day
Color cast of live elements
Overall lighting mood.

These are just a small sample of possible factors that will determine the screen used. If you have access to it, I would recommend you check out the Matrix Ultra Collection. I would look at the Re-visited discs and watch the visual effects sections. These topics are discussed on the discs. They used 3 different color screen for a variety of their visual effects shots. It takes some time to watch alot of the material on the discs, but I guarantee that it is well worth it. I hope this helps.

JB...

[hiphopcr]

Or the director will shoot on whatever the heck color he wants and not worry about lighting or even if the actor is in front of the green/blue screen cuz he knows it will be fixed in the post. It seems like 60% of VFX work nowadays is just clean up.

[@lias]

. If you have access to it, I would recommend you check out the Matrix Ultra Collection.

JB...

what is exactly is that..and how can i puy it or download it from? can you provied a link please?

[VFX Follower]

@lias,

The collection can be be found here:

http://www.thematrix.com

However, I am not sure if it is available outside the U.S. I am sure it would be. The Matrix movies have a large fan-base around the world. I hope this answers your question.

JB...

[beaker]

It gets a alittle more complicated than that...

Most consumer (and broadcast!) video is recorded in component form, Y'CBCR 4:2:2 which basically it has a luma channel, and two colour-difference channels, not three colour signals as you might expect (RGB, 8-bit). The first number (4) is the l;uma horizontal sampling, the next two the colour difference horizontal sampling, and vertical sampling, and if there is another number after this, the aplha (as in 4:2:2:4).

4:2:2 means there are twice the number of luminace samples for the two colour difference channels (on an 2 by 2 grid, there will be 2Y, 1CB,and CR). Consumer DV takes this even further to 4:1:1 Why? so that you can get more information into the same signal.
Wheres the trick? the two colour difference chanels are Luminece (Y)-red, and Y-blue, and the green is calculated from the remaining luminance, essentially meaning that there is more colour information for green than red and blue.
The best situation would be to use 4:4:4 but unless you have some fancy equipment this is going to be pretty unlikely.
I hope this explains something! I suggest you do a good search and read on the internet since this is a pretty complicated concept.

Cheers,I should have more specific and put the word "film" before the word "camera". In which case it is RGB. Also many of the highend 4:4:4 digital film camera's that go strait to hard drive, record RGB(yuv is optional though).

When you work with it every day you tend to forget about the ugly world of dv and other "fun" digital mediums :)

[Voldron]

yeah I am in a class right now for broadcasting, all of it is shot live to tape. So we had to learn all about that. I am wondering if the luminance can be recorded into a format rather then just going straight RGB, and if yes is this related to bit depth?

[beaker]

It depends your capture card/codec/medium you are going from into the computer. Some codecs capture YUV, some change convert strait to RGB at capture.

[Voldron]

good to know, thanks. Any codecs you know of that do YUV?

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