Hello Shakeel,

Sunday, October 24, 1999, 11:41:31 AM, you wrote:

SR> But it was not what i really meant. By "full action" i mean, action scenes
SR> i.e the running of a man...then you see cristal squares being displayed in
SR> the background on the screen. But whenever the image is focused on someone
SR> or something, then it is ok. you 've got clear crystal image. A close friend
SR> of mine has also reported the same problem and unable to know what exactly
SR> causes this.

In the format you view the video, the bit rate (amount of information
transferrable per second) is limited. The still scenes are what they
are - the picture doesn't change much; may be lip movement and facial
expressions, some 10-20% of the screen, and those changes can be
described in fine detail (while the not-changed parts are inherited
from the previous frame).

On the other extreme, action scenes have 90-100% of the screen
changing from frame to frame, and to keep the bitrate in bounds the
picture has to be compressed with image loss, and quite severely. This is
what you see - the squares are the result of approximated color
described by some arcane math formula, and it is normal.

The same result can be seen in two more things : one is JPEG
compression. In some sense, size of JPEG can be viewed as a bitrate
and then the quality degrades if the bitrate must be limited.

The other is a size/speed consideration of animated GIFs - small
changes take little space, while full-screen animation takes loads of
it, and (for example) full-screen scrolling might force the image to
16 colors to keep the animation file's size in limits of acceptable.

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