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Chapter 1: Basic Concepts And Tips
About Video Formats
Video is comprised of a series of still images called frames. When the frames are
displayed in rapid succession, the eye interprets the changes between frames as motion.
The NTSC video format displays 29.97 frames per second (often referred to as 30 fps).
The PAL video format displays at 25 fps.
The resolution or dimensions of a video frame is described as the number of pixels in each
line by the number of lines. The lines within each video frame are actually a series of
horizontal lines which are called scan lines. In the NTSC format, there are a total of 525
lines. Not all of these lines are part of the image. Some contain synchronization and other
information. The TARGA 3000 digitizes CCIR 601 at 720 x 486 for NTSC, and
720 x 576 for PAL.
The odd and even numbered scan lines (counting from the top) are separated into two
groups, called fields. When the frame is displayed, one field (odd or even) is scanned first.
Then the system goes back to the top of the screen and scans the other field. In this way,
the two fields are alternately drawn. This is called interlaced display because the two
fields interlace on the screen. While one field is fading, the other is drawn, so that the
screen is constantly and uniformly refreshed.
The sound track that accompanies most videos is a completely separate set of data. The
only relationship the sound track has to the video is synchronization.
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