Using keyer like Flame,s modular keyer.

[PIL]

Hi all. I have worked several years with Flame and I love the modular keyer, that allows you to use different settings in different areas of the live action plate. You can reach a nice control over your result and avoid the classic problems when the croma is horrible or you need a lot of detail in the hair but not in other areas. In Shake you can combine a lot of keyer nodes to have a similar result.
My question is about what,s the best way to do the same in Combustion. For example, how to aply three or four discreet keyers with different settings of tolerance, softness, etc, in the same footage. Repeating the same layer several times and using masks+keyer can be a good option, but I would like to listen other options and tricks.

Thank,s a lot.

[Anonymous]

Hi..

Here are some Tips & Tricks on pulling better keys……………………

Anyone who has attempted to pull a good chroma key from lousy source footage knows what a headache it can be… Video clips with poor lighting, incorrect blue/green paint, footage with DV-Compression, etc. can ALL contribute to a nightmare……

Greg Niles posted an excellent summary on how to pull green/blue screen chroma keys from that type of tough source material. Greg Niles is an ex-combustion developer who departed Discreet just after the release of Cv2. He had been working with the software since the very beginning: back when it was called paint/effect and before Discreet bought it.

I have edited and summarized his tips below…

The best tip to getting good keys from a poor background is to do multiple selection passes to extract an alpha channel. This means to apply many keys to extract alpha channel layers. The fact is, although this trick is well-known in Photoshop, most people still try to create a “perfect” one-click keys in motion compositing programs. The fact is that the reality of a “One-Click Best Key” RARELY lead to A PERFECT KEY, especially very often given the moving nature of the source material, backgrounds lights and shadows, poor green/blue screen, etc. Although it may work sometimes, most of the time it WON’T.

The trick is not to beat your head against the wall and keep compromising different areas of the key in order find a “magic” number of tolerance vs. softness, but to simply create many spcific keys and stack up their operations when you run into a problem area.

For example: If a key you’ve created works for the body but not the hair, then don’t force it – leave the settings alone for the body and then create a NEW key specifically for the hair with new settings. Then, stack the keys.

And this is done very easily in combustion. Here’s how:

1) Add a Selection operator (Draw Selection works well), and draw around a region you want to key, for example the body.
2) Now add your key (the selection can be done after adding the key, BTW, if you create the selection operator and drag it underneath the existing keyer). Now you can modify the keying parameters, but it will only affect that one region. ‘
3) To start keying in another region, simply add another Selection, draw the region you want, and add a new Keyer. The new selection will replace the old one by default.

Even the most difficult keys often shouldn’t take more than two or three “passes” with this technique. And unlike Photoshop, this leaves you with the option of tweaking any of the the key passes anytime you want, something you wouldn’t get with bitmap alpha extraction automatically. You can also tweak and animate the selection regions anytime you want, which is another useful trick.

Note that this is one of the big “secrets” of the VFX pros when it comes to blue/greenscreen compositing – they ALL do things in multiple passes, even when they’re using a third-party keyer like Ultimatte or Primatte. The reason why the discreet combustion keyer has the reputation it does is because when you use this technique, you have as much flexibility and can get as good results as a third-party keyer, without spending the money.

Greg goes on to say that he has found a great easy key is to use Channel mode, then use the histogram controls in the matte controls to push the dark areas black and the light areas white while keeping the middle ranges relatively intact. You can pull keys really fast with this technique.

So, to sum up, while the combustion keyer isn’t always “one-click” like Primatte and Ultimatte can be, but it works very well in a large variety of circumstances, once you know these key Tips & Tricks. This technique assures that, in those touchy situations where you don’t get the perfect key right off the bat, you can still quickly and easily do it.

Special Thanks to Greg Niles for his input !

bye,

Jack

[Author]

Posts