We look at the individual components of each pixel
(red, green, and blue) and calculate an alpha (transparency) value
for that pixel based on these other values.
Based on Luminance and Chrominance
Luminance (Y) is made up of a certain percentage of each color component:
GREEN --- 0.587
BLUE --- 0.114
We can then use the values:
Red - Luminance --- (R - Y) or (V)
to determine which pixels to drop out.
If the (R - Y) value of a given pixel is within a certain range, and its (B - Y) value is within another given range, then the pixel can be dropped out.
We can take this a step further and compare the (R - Y) and (B - Y) values of the pixel to their upper and lower bounds independantly:
Rmax - (R - Y) > 0
(B - Y) - Bmin > 0
Bmax - (B - Y) > 0
We can see how this works by plotting each pixel on a graph. The (B - Y) is plotted on the horizontal axis, and the (R - Y) on the vertical, similar to a vector scope. We can also draw the bounding box created by the upper and lower limits of (R - Y) and (B - Y) values. The pixels that lie within this bounding box on the graph are the ones that will be made transparent.
Sometimes the video daemon gets confused. To make sure that it is working properly, start up vcp. If it opens up all right, try opening Utilities->Live Video Input. If that seems to be working properly, exit Video In and vcp, you're ready to proceed. If either Video In or vcp itself failed, reboot the machine to reset the video daemon.
Start up VAgui and run it in the background (VAgui &)
Start up VAip (make sure that it is run in the foreground.)
Once VAip has been started and all of the graphics windows are updating, you need to make a dummy recording to finish setting up the recording process. Press the Record button in the VAgui window. The graphics windows will temporarily stop updating. The winterm window will prompt you to press "Enter" on the keyboard. Do so with the cursor in the winterm window. You will then be prompted to press the Continue button in the VAgui window. The graphics windows should resume updating, and you're ready to drop out the background.
The VideoAvatar image processor window shows the full image which will be recorded. The area within the red box represents the area which will actually be used for the VideoAvatar. This area can be adjusted. When the cursor is inside the box, the box will turn BLUE, indicating that it can be selected, using the left mouse button. When it is selected, it becomes GREEN, indicating that it can be moved. It should be positioned so that the blue of the backdrop fills the capture area, with the person's feet as close to the right side as possible (or to the bottom in the VideoAvatar processed image window.) The polygon which these textures are eventually mapped on to are a fixed size of 6.5 feet. So if you want the avatar to be approximately to scale, you should leave the appropriate amount of space above the person's head. You may also need to make some adjustment from the camera to do this properly.
As described the the Chroma Keying section above, in the VideoAvatar vector window the bounding box of the (R - Y) and (B - Y) minimum and maximum values determine which pixels get dropped out. These values can be adjusted individually or all together. Just as the capture area in the VideoAvatar processed image window, the box (or portion of the box) will turn BLUE when it can be selected, and GREEN when it is selected and can be adjusted.
When you are ready to record, press the Record button in the VAgui window. Again the graphics windows will stop updating, and this time you will be prompted to enter a BaseName. This BaseName will be used for the movie file and the chroma keying information file (BaseName.vamv and BaseName.vachroma, respectively.) Once you've entered the BaseName you will again be asked to press "Enter" on the keyboard. IMPORTANT: You should begin recording when the person on the turntable is facing to the left from the camera's point of view. After the person has turned out complete revolution (15 seconds) the recording is complete and you will once again be prompted to press the Continue button in the VAgui window. Repeat to capture another avatar, or kill the process from the winterm window to exit.
Don't forget to copy your files to your home directory, or where ever you plan to store them, as the automatic purge of files in usr/tmp is once again working.