2D Tracking - Nuke 101: Professional Compositing and Visual Effects - page 217

3. Make sure you are viewing Read1 in the Viewer and press the Play button to
watch the clip ( FIGURE 5.14 ) . Remember to stop playback when you're done.
Figure 5.14. A picture frame on a table.
What you are seeing is a picture frame on a table with a handheld camera going
around it. You need to replace the picture in the frame. The movement happens
in more than two dimensions (though, of course, as far as the screen is concerned
everythingismovingjustintwodimensions).Thepicturechangesitsperspective
throughouttheshot.Thatmeansyouwillhavetotrackfourindividualpoints,one
for each corner of the frame, to be able to mimic the movement.
The Tracker node has the ability to track up to four tracking points.
4. Insert a Tracker node after Read1.
5. Turn on all four tracking points by checking the boxes to the left of Tracker 2, 3,
and 4. The one next to Tracker 1 is checked by default ( FIGURE 5.15 ).
Figure 5.15. Activating all four tracking points.