Using Premiere or the standard edition of After Effect.
The goal of this tutorial is to create a moving object/person that can then
be pulled from the background and placed into another scene. This is not unlike
selecting a part of an image in Photoshop with the Magic Wand tool and pasting
the portion onto another picture. The difference with video is that the colour in
every frame of your video must be pulled rather than just a single image. While
there are great plugins, such as Ultimatte to help you complete professional
grade projects, this tutorial will only cover tools that come standard with your
Adobe After Effects or Adobe Premiere product. In other words, this is for those
who are making their effects on the cheap.
This tutorial assumes that you know how to start a New Project in Premiere
and a New Composition in After Effects. The Production Bundle is not
needed to complete these instructions.
You will be introduced to the following concepts and tools:
Bluescreen
Alpha Matte
Masks
For this tutorial miniDV footage was used and captured using a Firewire/IEEE
1394/iLink connection. You can still complete this tutorial using anologue
capture, but you are hoping for the greatest colour consistency and analogue
does not always hold up.
Final Note: Avoid wearing blue during filming. It will
become invisible when compositing.
Pre-Filming: Things to think about before filming
When looking for a bluescreen to film against there are many options,
however, a fabric is best. It can be draped over odd shaped objects and easily
transported to different locations. If you decide to use fabric, iron out as
many of the wrinkles as possible. Any hard shadows will be black, not blue, and
will not be keyed out once you apply the bluescreen technique.
In ideal situations, you will be able to light your background seperately
from your talent. Unfortunatly, this is not always an option and extra care must
be taken to avoid unintended shadows directly behind the talent. The above
graphic shows many shadows caused by creases.
Finally, if you do not have a bluescreen, or any other coloured screen for
that matter, don't forget that any shot taken on a nice clear day with a blue
sky in the background will do the trick very nicely.
Part One: Using Premiere for quick and simple bluescreen
Once the footage is captured to the computer, import the video into Premiere
and drag it onto the timeline. Video 2 track or above must be used to obtain the
TRANSPARENCY settings required.
Right click on the footage and choose TRANSPARENCY
From the pull down options entitled KEY TYPE, choose BLUE
SCREEN
Use the THRESHOLD slider to choose how strongly the blue is pulled
form the video.
Use the CUTOFF slider to leave out areas that may have blue in it,
but not as strongly as the bluescreen itself.
If you would like to soften the edges, choose SMOOTHING and select
low or high.
Once completed, put any video behind the bluescreen image and render for
visual check.
Part Two: After Effects, Color Key, and Masking
Using Premiere for bluescreen is a good method for some situations, but
really falls apart on others. The problem is that there are bound to be poor
lighting conditions on parts of the image, causing unwanted artifacts. Also,
some parts of the image being bluescreened are unecessary in the final shot.
This is where After Effects can be used to solve the problem.
Color Key:
Import the bluescreen footage and background footage you would like to
use.
Drag the bluescreen file to the timeline
Select the Effect option from the top menu bar and select
Keying and finally Color Key
This option menu will allow you to choose one of the shades of blue in the
bluescreen in order to remove the colour. Unfortunately, not all of the blue
will probably be removed and it will be necessary to reapply the effect and
select a different colour blue. For the example pictured above, three blues
needed to be keyed out.
Notice that a blue halo seems to surround the talent. This can be removed,
to a point, by using the Edge Thin option on the colour that is closest
to the talent. By selecting a positive number, you slightly choke the matte
and as a result remove the halo, but also shave off part of the talent.
Masks:
The footage is now prepared quite closely to what Premiere was able to do
earlier. However, the advantage now is that masks can be created to hide the
problem areas that cannot be removed with the Color Key process.
Double click on the bluescreened footage. A new window will appear that
looks like your original. In fact it is, but you have the ability to create
masks.
Choose the Pen tool and click an area around the problem artifacts.
You will notice that everything else disappears and all that remains is the
artifact.
In the example provided, you would have to change the mask property from
Add to Subtract, as shown above. If you do not see the same menu
as what is depicted, then you simply need to click the Switches /
Modes button at the bottom of the timeline window, or Right Click
on the Source Name title and choose Panels | Modes to
bring up that menu option.
Do the same for other problem areas.
What makes these masks even more powerful is that they are animatable. If
desired, a mask could have been drawn around the talent, only the above example
had very little movement with the masked off artifacts and animating every time
the talent moved would have taken much longer.
As a final idea of what you can produce, I have provided an effect created
entirely in After Effects. Masks were used for much more than cropping out
artifacts, but shows how far these powerful features can be taken in combination
with bluescreen techniques.