header
gray shim
T354 Week 12 - Spring 2014

Announcements:

  • Your final project proposals are due Thursday of next week (4/17).

Agenda:

  • Tuesday Jim will be attending the NAB conference.We won't have lab but there is a 5-point exercise you need to do on your own. (Multi-part motion tracking exercise)
  • Thursday Jim will be back and we'll look at homework and practice keying.

For Tuesday (no lab but carry out on your own) you will need your book.

Multipart Tracking Exercise (5 points)

In this exercise, you'll show you can track an object, even though it moves out of the frame. You'll need 1 piece of media from the Meyer DVD:

This was in the video files which were in last week's lecture notes.

Instructions

  • Follow the instructions in the Multipart Track tutorial (on page 511 from Chapter 30)
  • Make a 4x3 DV-sized comp to place the LS_hihat_snare.mov in
  • Look at the video. The goal is to create three different elements, which will be tracked along with the camera movement. The first element will appear in the green area underneath the hi-hat. It will follow/track the hi-hat as it moves up, out of the frame. Another element will track up, along with and over the white drum head (using the white drum head as a background). The third element will track down, again in the green space following the camera move. These elements could be text, or anything else you want.
  • Make a null layer to apply the track to
  • Track the movement of the LS_hihat_snare video. (The trick is to hold the "option" key to move the search and track square to another part of the video as needed.)
  • Only use the Y (up and down) axis before applying to the Null layer
  • Use the Smoother (Found under the "Window" menu to smooth out the bumps a bit.
  • Make 2 separate elements to tie to the motion (1 for the camera tilting down, the other for the camera tilting up)
  • Parent these to the Null layer
  • Adjsut for a pleasing look
  • When you are finished, render out a full-size (H.264) version in your week 12 folder.
  • Make sure it's called "multipart"

Be sure you know about these resrouces:

Motion Tracking (cont.) & Perspective Corner Pinning

Motion Tracking uses a technique similar to Motion Stabilization, but applies the tracking data to a different layer.

An interesting variation of Motion Tracking is Perspective Corner Pinning. This can be used to replace signs on billboards or other moving shots.

Want to try it? Experiment on the KD_streetsign_DV.mov file which was in the zipped folder from last week.

Thursday -------------------------------

Review homework

Keying in AE

There are some bluescreen files you can use in this 70 MB zip file:

  • Blue Dance
  • blue screen.mov
  • GI_CoolCharacters_sml.mov
  • PM_Alex.tif

In the AE pro bundle you will find several different types of color keys. Many good keyers are made by 3rd party companies (Ultimatte, Keylight, Boris, etc.). An excellent one (Keylight has been built into the CS3 release of AE. it is possible to get good keying out of AE's built-in keying tools- but the footage should be lit well and recorded into a codec with good color sampling.

Review color sampling (4:1:1, 4:2:2) and need for evenly lit blue/green screen footage. Note the different codecs in Blue Dance (DV) and blue screen.mov (Animation).

Garbage matte (aka junk matte) - Often when subjects are shot for chroma keying, there are areas not masked or covered by the blue or green screen material or paint. These are typically outside of the subject's area of motion. Because they aren't the uniform blue or green required for color keying, we use what's called a garbage matte to get rid of them. In AE it's easy to use the pen tool to make a mask that serves as a garbage matte.

Color Key

This is the basic color keyer in AE. It can work well if the footage was created in a 3D program with a highly uniform color background.
While it works well with really uniform color keying, it's hard to get some bluescreen footage to work, as it's not extremely uniform.
A little edge feather can conceal bad footage or lighting but will lose the fine details.

Luma key

Luma keys work on brightness (as opposed to color). They are good if shooting against a solid white or black background.

Linear Color Key

This is a more sophisticated and easy to use color keyer with the interesting feature: you can use the + eyedropper tool to add to your matte or the - eyedropper tool to subtract multple times.

Mattes

The matte choler and simple choker let you modify the matte created by the key. This is a quick and dirty way to eliminate the fringing

Color Difference Key

This key will get you much closer, as its additive eyedropper tool allows you to more easily create a good matte. It might be overwhelming for those new to keying.

Color Range

This is frequently used for video work. It is simple to use and has additive and subtractive eyedropper tools.

Difference Matte

A difference matte compares one layer to another and then keys out the info that's "different." This is usually used with footage shot from stationary cameras, or from motion controlled (repeatable) rigs. Imagine you have two layers, one is a static shot of a room. Another layer has the same shot, but a subject walks in. Using a Difference Matte, we can key out the subject.

Keylight

This is an excellent keyer provided with AE. Check out the links below for additional tutorials on how to use it and make better mattes.

General tips:

Any good keyer will allow you to examine the matte. Ideally you want to adjust the settings until you get only black and white (what's keyed out and what remains visible).

Note that with all of the keyers, you will likely need to add an effect to get rid of an unwanted color fringe. The maniuplating the Hue / Saturation helps. You can use AE's spill supresser and the simple choker to clean up nasty edges.

Additional Keying Help:

Check out the on-line help, the book, or these tutorials:

In-class Exercise

There are several bluescreen clips listed above. Use the keying tools and the info in the tutorial to put any of these clips together against any background you choose. (E.g. you could have the dancers dancing on the moon.) Can you add a shadow to make it more realistic?

Leave a full-sized, square pixel movie (H.264) in your week 12 folder. Make sure it's called "bluescreen".

If time allows - show Shape Layers

Homework:

  • Read & work through Meyer, Chapter 32 (Shape Layers)
  • Make a 15 or 30 second fake (or real) ad. It must have:
    • audio
    • at least two Shape Layers (read the book!)
    • a layer that is motion tracked to another
    • Turn in a square pixel H.264 version.
    • Be sure to note what you did and how you carried out the motion tracking in the accompanying critique form.
  • Bring in your finalized Final Project Proposal & Storyboard (for Thursday)

Back to Jim's T354 Home page