[Jerry Avins]

Radium wrote:
On Aug 19, 6:08 pm, Jerry Avins wrote:

Radium wrote:

This would be a start if I want to decrease the frequency of a video
signal without decreasing the playback speed.

Various compression schemes do that with varying degrees of resulting
quality.

I am talking about:

1. Decreasing the temporal frequency of the video signal without low-
pass filtering or decreasing the playback speed - an example of which
would be decreasing the rate at which a bird [in the movie] flaps its
wings. Hummingbirds flap their wings too fast for the human eye to
see. So the flap-rate of the wings could be decreased until the
flapping is visible to the human eye - without decreasing the playback
speed of the video. This decrease in flap-rate without slowing
playback is visually-analogous to decreasing the pitch of a recorded
sound without decreasing the playback speed. In this case, low-pass
filter would involve attenuating rapidly-changing images while
amplifying slowly-changing images -- I don't want this.

You convinced me: there are stupid questions. Video and movies work by
displaying a succession of still pictures close enough together in time
and and position to give us the illusion of continuous motion. Think
about how slow motion is accomplished with film photography. Speculate
about how this might be done with analog video, and extrapolate to
digitized video.

2. Decreasing the spatial frequency of the images in the video-signal
without low-pass filtering the images or increasing their sizes. An
example of this would be making the sharp areas of an image look
duller without decreasing the "sharpness" setting [an example of low-
pass filtering] on the monitor or increasing the size of the image.
Normally, when the size of an image is decreased, its sharpness
increases [it's like compressing a lower-frequency sound wave into a
higher-frequency one]. Likewise, when the size of an image is
increased, it looks duller [like stretching a higher-frequency sound
wave into a lower-frequency one]. Low-pass filtering simply decreasing
the sharpness of an image while increasing its dull characteristics --
which is what I don't want.

That's a reasonable summary of what you don't want to do. What do you
think you might do instead?

#1 Decreases the rate at which objects in the video move without
decreasing the video's playback speed or eliminating originally-
rapidly-moving objects [such as the rapidly flapping wings]

Something has to give. If the flapping of the wings is slowed, so is the
motion of everything else.

#2 Decreases makes a still image less sharp by stretching everything
within the image without increasing the size of the image or
eliminating sharp portions of the original image

Huh?

Both #1 and #2 are visual-equivalents of decreasing the pitch of a
recorded audio signal without decreasing the audio's playback speed.

Says who? You're reasoning from false analogy again.

Jerry
--
Engineering is the art of making what you want from things you can get.
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