Hello Readers, today through this blog we will discuss about an exclusive Green Screen Technique developed by the famous Disney Studio.
Green Screen Keying or Chroma Keying is one of the major tasks for VFX artists during post-production stage.
Chroma-keying or Green Screen Keying technique helps in layering two images based on color range.
In other words it is a technique for combining two images by replacing a colour in one frame with that from another frame.
This technique is widely used in audio/video medium like news-casting, motion pictures and video game industry to remove background from an image.
Chroma-Keying can be done with Blue or Green Screen; the selection of blue or green screen background depends upon the effect required and what color actor is wearing.
Shooting With Green Screen Background
Green Screen Keying Technique has become a vital part of contemporary feature films and television shows.
Most of the shootings now days take place in the indoor studio set ups with the green screen to cut down the production cost.
Green Screen Technique enables the director to achieve complex shots which would be impossible to capture in real scenario.
For example in the above picture; the director can easily remove the green screen from the background of the lady and insert some snow covered mountains at the back which will give the effect as if the lady is standing in chilled mountain area.
Moreover green screen technique can become expensive and herculean task if the shooting is not done in proper way.
Adjusting different color ranges can become strenuous in case of bad green screen shooting.
Compositing artist will have to spend lot more time in correcting green screen shots.
When Green Screen Shot Turns Useless
There are few situations when green screen shots turn out to be useless for example
- Low light condition shooting
- Uneven shades or patches on green cloth
- Chroma or green cloth and actor’s cloth are of same color
- Actor is very close to the green screen
- Motion blurred and Defocus shooting.
In case of above mentioned situations the compositing artist spends long time in correcting the imperfect green screen shots using various chroma removal tools like Primatte Keyer available in After Effects or IBK Keyer from Nuke.
When the character is very close to the green screen, spill issue creates on character’s edges which must be fixed.
Rotoscopy tool comes to great help to separate the actor from the background when length of green cloth is lesser than the acting area.
Disney’s Method Of Color Unmixing
Custom Keying is an advanced technical process to remove chroma or green screen without using any of the standard chroma removing software tools and third party plug-ins.
In Custom Keying various mathematical operations are achieved on color channels to rectify the green screen shots and to suppress the color spills.
In other words this is a high quality interactive green screen removal technique through color un-mixing developed by Disney Research Team.
The research team has scientists Tunç Aydin, Aljoscha Smolis, Yagiz Aksoy and Marc Pollefeys from ETH Zurich Lab.
This green screen keying method utilizes energy minimization-based Color Unmixing algorithm.
Markus Gross, Vice President at Disney Research said that “Keying is vital in adding backgrounds and objects smoothly into live-action shots. So this fast high-quality keying method will create a good impact on the production of feature films”.
The research team has already compared their output with the above mentioned standard keying software tools used in the industry and it is proved that their result is better than the other tools.
Color un-mixing algorithm method consumes less amount of time in post-production stage and delivers superior results compared to other available green screen keying solution.
One of the scientists from research team Tunç Aydin mentioned that “Number of software tools is available in the market for compositing artist to perform keying but those tools are difficult to use for the removal of green screen background when the colors of objects mix with each other”.
In the above picture we can see spill of green color on the extreme right white dress from the background green screen.
When the color spills on the object or mixes with each other it becomes a laborious work for the artist to correct those regions manually.
But the unmixing algorithm method is effective enough to remove color spills, as we can see the clear effect on the left white dress in the above picture.
The newly created method of color unmixing algorithm can extract the multiple color layers using a color model of the image.
The research team has developed user friendly interface that allows the artist to create a color model of the image simply by scribbling over each visible colored area of the image.
In the above image we can see scribbling has been done with red colored lines.
Here the shape of the scribble is not the factor the program only needs to identify each area of color so that it can create representation of all the colors in the scene.
The algorithm helps to figure out the underlying colors and their mixing ratios for each area.
Applicable On Non-Green Screen
Method of unmixing algorithm is applicable for keying scenes with non-green screen backgrounds also.
“Unlike standard method this advanced algorithm method also has the ability to represent the image with multiple color layers rather than just foreground and background layers. Colors of objects in a scene can be changed” said scientist Tunç Aydin.
Disney’s unmixing algorithm can preserve the intricate details in the keying method.
Unmixing algorithm can also be used to generate multi-layered representation of images which can be used for photo re-coloring.
Through this interactive high-quality green screen keying method Disney is continuing its legacy of creativity and innovation.
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