There are some nice tutorials about IBK in the following link,
http://compositingmentor.com
This is pretty much amazing! Thank you pretty much, Tony.
IBK node which IBK Colour and IBK Gizmo have it inside themselves can be broken down into the following formula.
alpha = (Ag-Ar*rw-Ab*gbw)<=0?1:clamp(1-(Ag-Ar*rw-Ab*gbw)/(Bg-Br*rw-Bb*gbw))
A is pfg and B is c. and this is the the case of "Green" keying, I mean we choose "Green" on IBK.
rw is the value of "red weight" and gbw is the value of "green/blur weight".
So, When preparing clean plate with IBK Colour, we need to tweak the value of the "darks" and the "lights" on itself. The "darks" is the "offset" of the Grade node which affects on input plate in IBK Colour. The "lights" is the "multiple" of the Grade node as well.
Anyway, we compare green and red + blue. If the pixel goes "green > red + blue", the pixel would be remained. Or if the pixel goes to "green < red + blue", the pixel would be turned to black. I mean IBK Colour-wise.
When the green in the green screen looks saturated, I usually take the red or the blue value of "lights" up.
When the green in the green screen doesn't so saturated, I usually take the red or the blue value of "lights" down. This is the case of Green screen.
 |
| the top node(IBK Colour) of IBK Stack, this is the case of "Saturated" |
 |
| the top node(IBK Colour) of IBK Stack, this is the case of "Less Saturated" |
the clean plate which is the resulted of IBK stack.
 |
| checking for key extract |
And "use bkg luminance" on "IBK Gizmo" works like "Additive Keyer"
See http://www.nukepedia.com/written-tutorials/additive-keyer/
This is also awesome great tutorial.
(CC) Blender Foundation | mango.blender.org
