Send the link below via email or IMCopy
Present to your audienceStart remote presentation
- Invited audience members will follow you as you navigate and present
- People invited to a presentation do not need a Prezi account
- This link expires 10 minutes after you close the presentation
- A maximum of 30 users can follow your presentation
- Learn more about this feature in our knowledge base article
Petro Vlahos/Green Screen
Transcript of Petro Vlahos/Green Screen
Green screening is the process of separating a subject from its background. This is done by creating a screen of colour behind a subject then keying said colour out leaving the subject with a transparent background. It is also important to have a nice flat evenly lit screen and avoid shadows for a good key as this prevents multiple shades of the same colour.
Although the process can be done with any colour, green and blue are the most widely used. This is because these two colours are the furthest from the tones in human skin and are least likely to affect the subject when keying. Petro Vlahos/Green screen This case study is an investigation into the compositing of live action footage captured on a green screen, specifically the methods developed by Petro Vlahos, a special-effects pioneer who reinvented the way in which we use green screens today. VS Good Bad A leap forward
Vlahos is not credited with the invention of the green screen as it was invented by a man called Larry Butler for his 1940s film “The Thief of Bagdad” but he is credited with developing a way to use it that minimised some objects appearing to have a surrounding unwanted glow especially on more difficult elements like glassware, cigarette smoke and hair. (Kelion, 2013) Mr Vlahos's breakthrough was to create
a complicated laboratory process which involved separating the blue, green and red parts of each frame before combining them back together in a certain order. He named his invention “the colour difference traveling matte scheme.” (Anita Gates, 2013) Green screen vs Rotoscoping
Using a green screen is not the only way to remove a subject from a background. Another method of doing this is called rotoscoping which consist of a rotoscope artist systematically tracing around a subject frame by frame in order to separate it from its background. This method can take a very long time and be quite costly. This is not to say that the creation of the green screen has eliminated the need for rotoscoping as many people today have careers built around it and achieve great results, it just means that for certain shots a green screen can accomplish the same result without being hugely time consuming and expensive. Petro Vlahos In the visual effects pipe line there is almost always someone waiting to take over a piece of work from where someone else left off so getting the job done as quickly as possible (without quality suffering ) and at minimal cost is important. Green screen in the VFX pipeline
The visual effects pipeline is made up of three main sections, pre-production, production and post-production and each of these consists of many interdependent departments. Green screen lies in the post production section with others such as effects, texturing and compositing. Compositing is the last process in the chain where all the CG, elements and the scanned plates are brought together to create a seamless finished image. (Andrew-whitehurst.net)(no date) Strength to strength
Moviemakers use visual effects to create a variety of enhancements to movies of every genre and Vlahos's technology has been used in some classic big name films such as William Wyler’s “Ben-Hur,” Alfred Hitchcock’s “The Birds,” and more modern films like Ang Lee’s “Life of Pi” and James Cameron’s “Avatar” one of the top grossing movies to this date to which its stunning visual effects probably played a big part in.
Mr Vlahos ultimately racked up more than 35 movie-related patents and went on to co-found his company, Ultimatte Corp, with his son Paul in 1976. (Kelion, 2013) Vlahos's original innovations have grown over the years which have evolved into the advanced digital hardware and software it is today. One of the software’s that comes as standard with ultimatte keyer is a powerful compositing program called Nuke. By David Morrison Experiments
There are multiple different keying nodes in nuke that have their individual strengths and weaknesses and for the sake of this case study I’m going to pit two of my favourites against each other (Ultimatte and Keylight) and see which one comes out on top. I will do this by performing a set of controlled mini experiments, looking at how each one copes with some of the more difficult areas like hair detail, motion blur, smoke and glassware also what tool provides the quickest, easiest solutions with the best results. Kelion, J., 2013. Blue and green-screen effects pioneer Petro Vlahos dies. BBC NEWS TECHNOLIGY, [Online] (last updated at 22:34 14th February 2013) Available at: http://www.bbc.co.uk/news/technology-21463817 [Accessed on 20th Feb 2013].
Gates, A., 2013. Petro Vlahos, Special-Effects Innovator, Dies at 96. The New York Times Movies, [Online] (last updated 14 February 2013) Available at: http://www.nytimes.com/2013/02/20/movies/petro-vlahos-special-effects-innovator-dies-at-96.html?hpw&_r=1& [Accessed on 21st Feb 2013].
Whitehurst, A., 2013? The Visual Effects Pipeline. andrew-whitehurst.net, [online] (Last updated n.d.) http://www.andrew-whitehurst.net/pipeline.html [Accessed on 15th Feb 2013].
Whitehurst, A, 2013 (n.d). The Visual Effects Pipeline. [Image online] Available at: http://www.andrew-whitehurst.net/pipeline.html [Accessed on 15th Feb 2013].
complit323, 2009. "I'm Free!" - The Thief of Bagdad (1940) . [video online] Available at:<http://www.youtube.com/watch?v=ugMmyjCdpoQ> [Accessed 22 February 2013].
[HPX500 not good for green screen?] n.d. [image online] Available at: <http://www.dvxuser.com/V6/showthread.php?148594-HPX500-not-good-for-green-screen > [Accessed 25 February 2013].
[Avatar (2009) 720p BDRiP MP4 SendSpace] n.d. [image online] Available at: <http://moviesfreedownloadz.blogspot.co.uk/2012/03/avatar-2009-720p-bdrip-avi-mediafire.html> [Accessed 26 February 2013].
Charles Salmon, 2010 (n.d). Chroma-Keying in Photoshop. [image online] Available at: <http://www.techwow.com/chroma-keying-in-photoshop/> [Accessed on 1st March 2013].
Alberto E. Rodriguez/Getty Images, 2013 (February 20, 2013 ). Petro Vlahos . [Image online] Available at: <http://www.nytimes.com/2013/02/20/movies/petro-vlahos-special-effects-innovator-dies-at-96.html?hpw&_r=1&> [Accessed on 18 February 2013].
Archive for The Thief of Bagdad 1940 (September 24, 2012). [image online] Available at: < http://tomzone.wordpress.com/tag/the-thief-of-bagdad-1940/> [Accessed 24 February 2013].
[Rotoscoped car] n.d. [image online] Available at: <http://help.apple.com/motion/mac/5.0/fr/motion/usermanual/index.html#chapter=20%26section=16%26tasks=true> [Accessed 28 February 2013]. 1st Experiment In this first experiment Ultimatte was used to see how it would handle the extraction of this woman and her hair while trying not to lose most of the fine details. After hooking up Ultimatte and just selecting the screen colour it was quite surprising how well it performed at just this early stage as it had gotten rid of all the green without leaving any left over shades or the need for a garbage matte and although fine tuning still had to be done first impressions where good. However after allot of time fine tuning to try and bring some of the fine detail back Ultimatte proved unsuccessful leaving allot of artifacting and not much fine detail. Outcome Unsuccessful 2nd Experiment Conclusion When done using Keylight there didn't appear to be as good a result at first but after fine tuning with different settings much better results where achieved with finer details. When it comes to speed Ultimatte was the victor but if you want to preserve fine detail when keying hair its worth spending that little bit more time on it using Keylight. Ultimatte V Keylight In this experiment an image was picked that had stronger edges plus good contrasting colours to the green in the background. Starting with Keylight there seemed to be problems straight away. After pulling a key on the green background the image was left with allot of cleaning up to do but playing around with the screen gain and the screen balance gave better results but this did leave a strange red glow around their hair. Ultimatte V Keylight After pulling the same key in Ultimatte you could already see much better results. Ultimatte removed the green background withiout almost any need for further intervention with exception to a little almost unseen glow around the subjects. This was fixed this by selecting clean up and adding a slight shrink around them and softening the edges a little. Plus there was no issue with a strange red glow. REFERENCES After experimenting with both these keying tools I could not decide which one should be the winner. It took me longer to get a good key with Keylight than it did with Ultimatte but Keylight produced much finer detail in the experiment with the hair however when keying with an image with high contrasting colours Ultimatte gave a much cleaner key in half the time. I think the solution may lie with not just using one or the other but swapping between which ever one is more suited to the job at the time. Blue glow around subject.