For those into visual fx, what is the difference between using blue or green screen for vfx work? Having in mind the fact that most of our cameras these days shoot interlaced footage.

From my mini experience, I'd prefer Green Screen cos' I think it's easier to setup (lights,etc), but from my studies, blue is a colour that isn't in the skin tone. I'd advice we use Green Screen in Nigeria. This topic is a very long story.

Nice pointer wilsonhaze. I have noticed that even in heavy vfx Hollywood blockbusters, they use green for studio setups and I rarely see blue these days. I don't know though.
I have been using green for a while and well, it has been good and I would like to try out blue and see if i get better results.

You guys are speaking in tongues here

O'course, this thread is for Video Fx buffs I recommend we novices sit back, watch and learn.

From my experience and research, digital cameras shoot a lot of detail in the green spectrum therefore making it easier to get a key. But that is if you are really pushing it. For most requirements green and blue are pretty interchangeable. It just depends on what you are shooting and on the lighting conditions. For example we are going to use green screen on an outdoor sunny shoot. This is because the sky is blue and the bluish diffused/bounced light will reflect on the filmed subjects. This will make it harder to get a key if the bluescreen is used. And none of the subjects are wearing green.

As Wilsonhaze said, it's a topic you can really get deep into. That's some of the info I've picked up and applied along the way.

@ AdamuW, Oh!!!!!! No wonder. Just remembering some hellish experiences with outdoor blue screen a very long while back. Thanks.
So technically it is safe to say green is the way to go. Another issue I have had is selecting the right chroma material.
Which is the cheapest and most readily available material (that I can get in Yaba market for eg).

I've had my share of nightmares too. However, I am not an authority on this so I can't definitely say which one is better.

I can't help you regarding the material to get. All I know is that it shouldn't wrinkle easily and should diffuse the light evenly as possible. I'm just going to invest in a portable rig with 'professional' chroma blue and green muslin material to save us the hassle of a home made one. Once we get it and test it out will I feel able to recommend it or not.

Sorry I can't be of more help.

In actual fact it realy doesn't matter whether you use green, blue, white or whatever color of screen. What you should be more concerned about are
1). Is the color of the background distinctly different from the color of the object(s) on the fore ground? The clothes, props and other items you wish to retain in your video should not have the same color as the background.
2). Is the background homogenoeusly lit? If the lighting on the background is not homogeneous either due to too much wrinkles in the background material or uneven arangement of background ligthing (you should have a seperate set of lights for the background) or whatever reason, then you will have problems in knocking off the background due to uneven tone.
3). Is the shadow of the fore ground object casted on the background? This is another problem area. If the shadow of the foreground object falls on the background, then the color of the background in no more honogeneous and it will be hard to knock it off. Try to give as much space as possible between your forground objects and your background and set the fore ground lights at such angles as to make their shadows not fall on the background , making sure the foreground objects are well lit of course.
4). Do you have transparent objects in the foreground? If foreground objects such as bottles or wine glasses are present and the background shows through them then you will have a real dificult time knocking off the background in those areas . Softwares like "Serious magic ultra chroma" are designed for just such situations though.

Compliments of the season, one and all.

@tomX, It really matters a lot contrary to what you have said. The way the human eye works is entirely different from the way the video camera works. What the human eye sees is different from what the chips of the camera records. The reason why green and blue have been the most widely used colours for chroma is because the are the least colours that can be similar to the common colours we come in contact with eg skintone. A yellow/orange/red chroma cloth will most likely NOT key.
As per the software for keying, basic keying filters in compositing apps like after effects will do the job. Keylight (comes free with After effects professional) is my favourite. Another thing visual effects artist miss out is utilising the matte tools like matte choker and using garbage mattes. Then combining skills and the rules as you have listed will give you Hollywood-class keying.
Good luck to us all.

In the makings of movies, I noticed that blue screen is used for sky shots, underwater shots and some night scenes

@sojioguns,
Thanks for the heads up. Now shoot a video using a green screen as a background and let one of your actors wear a green costume with green designs on it then try knocking off the background. The result is like what you see on AIT's Kaakaki when a guest appears on screen and part of his cap or atire seems invisible.

sojioguns:

The reason why green and blue have been the most widely used colours for chroma is because the are the least colours that can be similar to the common colours we come in contact with eg skintone. A yellow/orange/red chroma cloth will most likely NOT key.

Have you ever wondered why in the matte options in your favourite video editor, apart from the popular green screen and blue screen you have the choice to pick any matte color using a color picker? I have done splendid chroma works using even white screen. Any single color background chroma will key properly if the background is homogeneously lit and its color is of a distinct tone from anything in the foreground. This is even on the easy side.

It is possible (and I have done it a lot) to even knock of the backgroung of a video without even using any form of screen. You just have to broaden your understading of the matte concept. How do you think such video works where an actor plays a dual and interactive role in a scene is achieved. Imagine a scene where a character is lying on a bed gisting and interacting with his twin (actualy himself) and there is full interaction between the subject(s) and other elements in the shot. If you are presented with such a story board trust me simple chroma keying will not cut it.

sojioguns:

As per the software for keying, basic keying filters in compositing apps like after effects will do the job.

People don't spend millions of dollars inventing specialist keying softwares when they know that "basic keying filters" in available editors and compositing softwares will do the trick. Set up a minature set for yourself with your favourite green screen or blue screen. Place a transparent red toned glass cup infront of the screen and shoot. Then try keying out the background as seen through the glass cup with out lossing the lustre of the glass (good luck with your after effects).
Take a video that involes small area artifacts like wisps of hair strands shot against a chroma background and try keying using your basic software keying function (once again goodluck).
Finaly consider a situation where an amature shoots a chroma video with poor lighting and lots of shadows (a basic chroma nightmare). You are then presented with such a video to key in the studio. You can either complain and rightly pass the blame to the poor footage and the amature who shot it (like many editors would do) or you can get magical with "Serious Magic Ultra Chroma". It was built for such scenerios. Try it before you D-I-S it.

sojioguns:

, Good luck to us all.

When it comes to Chroma I trust more on research and practical experience and expertise than luck. But hey, we all need some luck right!

@tomX:

@sojioguns,
Thanks for the heads up. Now shoot a video using a green screen as a background and let one of your actors wear a green costume with green designs on it then try knocking off the background. The result is like what you see on AIT's Kaakaki when a guest appears on screen and part of his cap or atire seems invisible.

I agreed with your last post. You gave us a list of dos and donts for chroma keying.

@tomX:

It is possible (and I have done it a lot) to even knock of the backgroung of a video without even using any form of screen. You just have to broaden your understading of the matte concept.

Yes there are several methods of keying out backgrounds apart from simple chroma keying (rotoscoping, etc) but let us try to stay within topic. I will create another thread so vfx guys can share how best they would achieve using a 'twin' character on the same set.

@tomX:

How do you think such video works where an actor plays a dual and interactive role in a scene is achieved. Imagine a scene where a character is lying on a bed gisting and interacting with his twin (actualy himself) and there is full interaction between the subject(s) and other elements in the shot. If you are presented with such a story board trust me simple chroma keying will not cut it.

For the effect you are trying to create, the simplest method that has been used is actually planning shots and locking the camera then bla bla bla, (Check the next thread)

@tomX:

People don't spend millions of dollars inventing specialist keying softwares when they know that "basic keying filters" in available editors and compositing softwares will do the trick. Set up a minature set for yourself with your favourite green screen or blue screen. Place a transparent red toned glass cup infront of the screen and shoot. Then try keying out the background as seen through the glass cup with out lossing the lustre of the glass (good luck with your after effects).
Take a video that involes small area artifacts like wisps of hair strands shot against a chroma background and try keying using your basic software keying function (once again goodluck).

The difference between Hollywood chroma keying and ours is actually the acquisition format. You cannot compare full res HD 4:4:4 footage to DV and HDV 4:2:0 or even DVCPRO HD 4:2:2. There is more information in the full res footage and it even makes keying easier. Why would blockbusters like The Aviator use After effects if they could easily have used Shake, Inferno, Toxic and other high end VFX tools? After effects is a VERY POWERFUL tool, Andrew Kramer would attest to that.
As for the glass chroma effect, the trick lies in the lighting. You could treat the glass with some sort of film to reduce the lustre and make sure the lighting is indirect (ie bonced off surfaces).
As for the artifacts like loose hair. The resolution of the camera needs to be very high and the motion blur has to be at the bearest minimum. Motion blur can be added later with tools like Boris Continuum 4. For a video camera, use the highest possible shutter speed so the motion blur is lowest. If using a film camera then you could shoot at higher frame rates (slow mo mode) so there are more frames to key out.
One trick I do though is when I am faced with poorly shot chroma footage, I would work in a 16-bit project (I would also convert the original footage to uncompressed). Technically I am not supposed to gain anything here but it improves the chances of getting a better key.
Primatte keyer is also another good plugin and is very easy to use. You can select bg, fg and even clean up bg and fg by simply dragging over the image. (Smart tool)

We are comming closer to a converging point now. When you are faced with a challenging keying situation as you just confessed you will probably have to go through a lot more dilly-dallying with some softwares as compared with others. I can achieve the result I want even using premiere pro (without after-effects) but I get better result using softwares that were built for just those kinds of challenge.

sojioguns:

The difference between Hollywood chroma keying and ours is actually the acquisition format. You cannot compare full res HD 4:4:4 footage to DV and HDV 4:2:0 or even DVCPRO HD 4:2:2.

And before the advent of HDV cameras what were the Hollywooders doing? Even if you shoot your video with a camera phone and you follow the tips I gave earlier viz

1). Is the color of the background distinctly different from the color of the object(s) on the fore ground? The clothes, props and other items you wish to retain in your video should not have the same color as the background.
2). Is the background homogenoeusly lit? If the lighting on the background is not homogeneous either due to too much wrinkles in the background material or uneven arangement of background ligthing (you should have a seperate set of lights for the background) or whatever reason, then you will have problems in knocking off the background due to uneven tone.
3). Is the shadow of the fore ground object casted on the background? This is another problem area. If the shadow of the foreground object falls on the background, then the color of the background in no more honogeneous and it will be hard to knock it off. Try to give as much space as possible between your forground objects and your background and set the fore ground lights at such angles as to make their shadows not fall on the background , making sure the foreground objects are well lit of course.
4). Do you have transparent objects in the foreground? If foreground objects such as bottles or wine glasses are present and the background shows through them then you will have a real dificult time knocking off the background in those areas . Softwares like "Serious magic ultra chroma" are designed for just such situations though.

you'd still get good results with your chroma.

I remember once when I witnessed a friend trying to shoot a low budget musical. They had so much difficulting editing the messed up chroma shots and he called me to aid him. His next attempt was not much better though he had "Stepped-up" somwhat and rented a Cannon XLS.

At his third attempt I forwarded my arguements to him convinved him to let me arrange his set for him. Honest to God all we hav to work with was a couple of 500watt hallogen (no gels), a number of 100 watt bulbs and a white cloth to use as a background. I suppervised the costumes to make sure they where color compliant and shot the video for him with a Mini-DV camcoder (CCD not even 3CCD). He had no problems with his keying on those rushes.
If we could achive such good results under those horribly frugal conditions then I think more amazing feats could be expected with higher budget and proper equipments.

All said and done, while there is a myraid of hardware and softwares out there to help us come that much closer to keying nirvana, understanding the fundamentals in keying is one of the greatest weapon we should have in our arsenal. It will save us a bundle in time and cash.

Yeah we are already digressing from the primary issue, the whole point I am trying to make is that while blue and green are the two most widely used keying colors (for good reasons too), being well grounded in your fundamentals will ensure you get a great result irrespective of the color you use for your background of the softwre you use for compositing.  And at very difficult spots, there are third party softwares that come in very handy and some are more effective than others.
Adobe affter-effects may have a cult following amongst its users but there are other softwares that are great out there. Use what works best for you. But for me as far as after-effects is concerned, used-it-dumped-it-and-not-a-fan!!!

Question 1: You have an entirely chroma video to shoot in a studio. Which would you use, green or blue?

Question 2: What is your workflow for keying? I mean what software do you use?

Ans to question 1)
If you restrict me to Green or Blue then my first consideration is the prevalent tones in my foreground objects. If the foreground tends more towards lighter hues of colors then I will go for Blue since it will contrast better. If the foreground tends towards darker hues then I will use green (since it is lighter) it will contrast better.

Ans to question 2)
Depends on the scope of the project and the difficulties I have.
For Basic video editing with motion graphics effect, I Key with my editors, I use Premier Pro Or Ulead Media Studio 8. Since I also work alot with Flash, I am biased to ULEAD Media studio 8since it supports direct importation of swf format which premier pro dosen't.
For difficult keying situations that my Editors cant handle elegantly, I use srious magic Ultra kEy.

That is sooo different from my very common workflow. I like people that practise what they preach. Ulead media studio and Serious magic. Let me look into the current versions. You are well grounded. Nice job in your research.
You have broken it down for a lot of people. Nice!

I tend to agree with @tomx, from my experience , both green and blue screens work as well . What really matters is lighting evenly;Prefarably lighting the background seperate from the subject (If u have enough lights),

I will also agree with sojioguns by saying that while one can get some relatively good results with proper lighing on DV footage, HDV footage with the same quality lighting will ALWAYS produce a much better key

Don't let the "H" in HDV deceive you oh. It only means more pixels and processor hungry playback. It has the same colour depth as DVCAM. I do NOT use HDV and neither do a lot of industry professionals. DVCPRO HD is ten times better. Even AVCHD a new codec (wilsonhaze, the codec that my small Sony camcorder uses) is better than HDV if handled well.
For me I would use the Panasonic HVX 200 P2 camera (readily available for rent) and shoot either 1080i or 720p. I would shoot 720p for fast moving objects to avoid interlacing artefacts in 1080i.
The Sony EX1 and EX3 have sharper images due to larger chips but I haven't really played with them.

This is what I found. Very useful. From http://boards.theforce.net/message.asp?topic=13919927

This is a old and routine debate around here, but I had some (possibly) new thoughts on the subject.

A lot has been said about the 4:1:1 color space of DV compression making a green screen more favorable than a bluescreen. The thinking behind this is that there are four "green" pixels for every one blue/red pair, more is better, so green is better.

So here's the "new" thought,
While green is stored at a higher resolution, chroma keying is not based on green alone, even when using a green screen.

Presumably, your subject in front of the screen uses contrasting colors. Unless your subject is entirely very dark, a significant factor of these constrasting colors colors is going to be falling in the :1:1 part of the DV compression scheme, so you haven't improved anything by using a green background.

Example:
A reddish-yellowish face in front of a green screen.
A possible RGB for a face pixel might be 238:238:180.
Note that the Green channel value isn't very far from a perfect 255 green, and there will be even less contrast (or none at all) within the NTSC/PAL color space. As a result, any keying will be entirely dependent on the RED & BLUE color resolutions.

Even more common, BTW, is the use of a kicker light to highlight the edges of the subject. The resulting white, or nearly white, edges you get will also have little to no contrast at all in the green channel when using a green screen !!!! So much for the "4" part of 4:1:1 being of any help.

So, what IS a good way to select color: My contention is that it should be primarily based on your foreground subject.

With proper planning, you can make the wardrobe contrast with anything, and virtually all human skin has a lot of red, so these don't really factor into the screen color selection too much, but HAIR does.
The basic rule of thumb is that Dark Hair subjects will work best with a green screen and light hair will work better with blue. This will provide the most contrast possible in that crucial "4" channel. happy

Thoughts from anyone else
Have fun!

@tomX:

Ans to question 1)
If you restrict me to Green or Blue then my first consideration is the prevalent tones in my foreground objects. If the foreground tends more towards lighter hues of colors then I will go for Blue since it will contrast better. If the foreground tends towards darker hues then I will use green (since it is lighter) it will contrast better.

With proper planning, you can make the wardrobe contrast with anything, and virtually all human skin has a lot of red, so these don't really factor into the screen color selection too much, but HAIR does.
The basic rule of thumb is that Dark Hair subjects will work best with a green screen and light hair will work better with blue. . . .

I think there is a point of agreement there. Don't also overlook the point he made about proper planning of the wardrobe. Don't go shooting with green screen if your subject is wearing green or hues close to it.

@tomx, you didn't answer my last question, "Are you in lagos?"

Yes @solioguns, I stay in Lagos.

Cheers.

Hi there,

Which keyer do you guys think works best with either of the blue/green backgrounds

Depending on your workflow:
1. Keylight, comes free with adobe after effects professional
2. Primatte keyer nice click and drag functions
3. Color key within after effects (okay)

The options above are limited to adobe after effects only.