Adv Post week 6: Color Keying

Week 6 keying
Color channels: red, green and blue.
in 8-bit color, 256 shades of red green and blue.

combining the 3 colors makes all the others.

computer breaks down each color channel into shades of grey
White=the pixel is at 100% ON of any color.
Black=the pixel shows none of that color
Grey=the pixel kinda shows some of that color.

Keying is a way to avoid excessive roto
-selecting an area of the screen to keep or remove, based on its color.
-Effect/Keying.

Ways avoid roto:
-Shoot well on a well-lit screen
-Screen should not contain any colors that are present in your subject.
-Bad colors: black, cream, white, brown
-Good colors: green (brighter the better), blue, magenta
-Good lighting on your screen.
-As many lamps as you can sign out of checkout.
-And some.
-Bounce cards
-Lotta stands
-Things to diffuse your light
-Help
-Time

Diffuse light that bounces onto your screen
-no hot-spots
space between your actor and the screen
-avoid shadows on the screen
light your actor with his/her own lights when possible.

blondes should be shot on bluescreen.
the shadows from their hair go toward green.

1-shoot it properly
-make sure it's lit well, it's high-res as possible, and the focus is sharp
-do test footage to make sure your setup is good. bring a laptop and proper cables on set to check my key in AE before the shoot.
-if shooting someone tall, turn the camera instead of short-changing your composite
-this allows for possibility to shoot SD output HD
No black or white clothes or accessories.
Grey is ok
shoot as High-Res as possible.
Autofocus OFF. zoom in, focus. turn off auto, zoom out.

2-import it properly.
import it at the size it was shot at.
3-look at it.
-try a simple keyer, like color key or linear color key

-turn on the channels, one at a time.
-see which one gives the highest contrast.
-it might be a channel other than the obvious.

4-create a matte

Draw 3 circles on your screen
-Use the Shape tool set to Ellipse, change stroke value to 0 and these values for each circle:
-Red:255, others 0
-Green 255, others 0
-Blue 255, others 0
-set the blending mode to Add for all of these.

each pixel has 4 values.
Red green blue and alpha
see a b&w picture of each of these in Olympics symbol (located next to resolution below comp window)

the best keys are based on a good matte.
matte is a window thru which we see our footage.
-matte can be black-and-white
-or have alpha.

Color Key: 4 values
key color: eyedropper the color of screen
tolerance: higher the number=more pixels picked.
edge thin: sucks in your edge
feather: makes the edge so Soft.

Always do the following when keying:
-change the BG color to Yellow, Hot Pink
-Look at it thru the Alpha channel
-View it in High Res and 100% zoom
-look around your image with the Hand tool
this way you stay at 100% and you can see each part of pic.

Don't scale footage up more than 115%
-edges and pixels will go to crap otherwise

Edges of your matte should be sharp when dealing with solid stuff, soft when dealing with fluff, hair, fur.

Linear color key (LCK): has more settings than regular color key.
-Turn off the little Fx in the effect controls for LCK
-Click eyedropper and click the background
-For an average of pixel values, hold apple-key while clickdragging in your screen color.
-Default matching softness is 10%: too high.
-2-3%
-Change matching tolerance up from default value of 0%
(Apple-scrub on any slider to change the value to something in the 10ths, or click change the value by typing in numbers.

After Effects Studio Techniques by Mark Christiansen

Creating a matte:
-drag our footage from proj win to below proj window (comp icon)
-draw garbage masks using pen tool to get rid of bluescreen stands
-Set the Mask mode to Subtract

wineglass: channel keying
Photoshop Channel Chops
-Duplicate your layer
-remove all effects: Ap Shift E
-delete other masks
-rough roto of wineglass, 2 sec min
-look at channels indiv.
-apply the effect Shift Channels
-Alpha=alpha
-all others=blue (or which is high-con)
-levels, move sliders to ends of mtns,
move grey till you like what your matte looks like.
(red giant software Composite Wizard)
-add blurs as needed

Name this layer "glass matte"
Edit/Duplicate
-layer 2: call it glass. remove all effects (apple shift E) but keep masks
Rt-click the column heading and choose Modes
Set the TrkMat column of layer 2 (glass)
to Luma Inverted Matte the top layer (glass matte)
-uses the b&w info of the top layer as a window for the bottom layer.
-inverts that.

delete mask off of top layer if you're getting a line

Apply the effect "spill suppressor" to the glass and the girl.

precomp glass and glass matte, then add
simple choker
channel blur

homework:
shoot something with green
keying footage available here if you don't want to be clever:
http://antidotefx.com/afx_hdtestftg.zip