The Art Of Compositing 01 Pertemuan 06

Matakuliah : UO666 / DKV Visual FXTahun : 2009

Bina Nusantara

Keying is such a vital area of visual effects,

research continues to both improve the

quality of the key and easy of use of

the module.While it is not strictly keying

in the greenscreen sense - there are a

host of new matte generating tools that

extract mattes via a range of different

technologies.

Digital Keying

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The age old question is should one shoot against

blue or green screen. Many factors influence

the decision, the most obvious being what

colours are represented in the foreground

subject. For a while prior to the Vision 2

stocks - the film stock itself was grainier in the

blue channel, and hence green screen grew

in popularity. One urban myth is that human

skin contains a lot more green than blue and

so blue screen should be better, in fact this is

only true of blond hair - which is often better

shot against blue - but human skin while not

equally balanced in its green and blue

components - easily keys from either blue or

green screen.

Green or Blue?

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Zmatte

The standalone Zbig Software was available on the market since 1998 as a chroma key/compositing program and as a plug-in for many standard programs, (Fusion, Illusion and others)

A unique feature of Zbig Software is the automatic and dynamic application of background color reflections onto the composed foreground, resulting in an extremely convincing composition.

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Keylight

The keyer is effectively a colour difference keyer, so it works better on primary colour, and according to the Foundry's Bruno Nicoletti "to work well it needs a high primary saturation" in the keying background. Keylight's strength comes from the algorithm that allow the spill removal to become an intrinsic part of the process. Recently, it has been upgraded to a full float implementation on Shake, but this is only currently as a plugin. The version shipping with Shake 4 now respects Float and no longer clamps to 16 bit. Even with Keylight's great foreground colour correct, in a floating pipeline in Shake, it is often only used for key or matte generation and not for the key & comp of the foreground and background. The work of CFC in pioneering their compositing pipeline caused them to get a technical achievement award in 1996. Keylight anecdotally is thought to be best on transparent items such as sheer fabric - glass ware and say soft hair. There is now Linux & Burn support for Keylight. When using the Keylight controls fg bias work best with near neutral colours. Nicoletti has also written a great new 64 bit version of Keylight for Discreet (A M&E) products which also has improvements to the matte processing and colour correction tools.

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Primatte

Primatte today runs on a wide variety of OS - LINUX, OSX, NT IRIX etc. Primatte is one of the most widely available plugin keyers, from Flame, Smoke to Fusion, Shake, Quantel, AE, Photoshop, Nuke and others. When using Primatte's controls the fgbias effect the f/g colour & Matte opacity, the key controls are the shadow gain, mid gain and highlight gain.

For a full discussion of Primatte listen to our fxpodcast with Scott Gross of IMAGICA Corporation of America by clicking the links at the top of this page. Scott has been involved with Primatte from the beginning and he explains not only the keyer's approach but much of its history.

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Ultra Keyer (Fusion keyer)

- Five modes of spill suppression to eliminate difficult reflection halos.- Animated garbage mattes for isolating rigging and set elements.- Adjustable edge gamma and fringe color correction.- Matte thresholding for semi-transparent region replacement.- Matte blur, gamma, and contrast control for post key processing of the

matte.- Advanced color selection includes a more varied range than traditional

"select" and "soften" style keyers

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