Apple Final Cut Pro 5 - Manual (Page 1709)

358 Part V Appendixes
These days, the biggest challenge comes when exchanging graphics between
applications that use different pixel aspect ratios, or when using an application that
does not support rectangular pixels with one that does. The key to a simple workflow is
to use applications that can work at the native, nonsquare pixel image dimensions and
compensate on the computer display. Fortunately, major video and graphics
applications such as Photoshop, After Effects, Final Cut Pro, and DVD Studio Pro can
work with graphics and video at native resolutions. This way, you are always working
with the exact pixel dimensions that you will eventually output to video tape or DVD.
Frame Rate
The frame rate of any motion picture, whether film or video, defines how often pictures
are taken per second. The higher the frame rate, the more accurately you capture
moments in time and reduce flicker during playback. To achieve double the perceived
frame rate (flicker), film projectors actually double or triple the shutter speed, even
though the same frame is repeated two or three times, respectively. This is because a
faster flicker creates more convincing motion. Video uses a similar, although more
complicated, technique called interlacing. For more information about interlacing, see
the next section, “
Scanning Method .” For more details about frame rate, see
Appendix B, “ Frame Rate and Timecode ,” on page 377.
Scanning Method
A video frame is made of horizontal lines that are scanned from one side of a display to
the other. Progressive video scanning happens when each line of a video frame is
scanned one after another. Interlaced scanning fills the entire frame with only half the
lines, which requires half the time, thus doubling the perceived frame rate and
reducing flicker.
About Interlaced Scanning
Frame rates lower than 40 fps cause noticeable flicker. When NTSC and PAL were
invented, faster frame rates were not practical to implement. Interlaced scanning was
devised to create a perceived frame rate of 60 fps (NTSC) or 50 fps (PAL). Interlaced
video scans the display twice, using two fields, to complete a single frame. A single field
contains only the odd lines (1, 3, 5, 7, and so on) or the even lines (2, 4, 6, 8, and so on)
of the frame. If you could stop the video scanning process to observe a single video
field, you would see that every other line is missing, like venetian blinds or a comb.