[opendtv] Re: opendtv Digest V7 #147
- From: "M. Olivier HOUOT" <olho_avatar_i@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sun, 20 Jun 2010 00:25:10 +0200
In audio, the samples are held and low pass filtered in the player. The output
of the player is a signal that is mathematically identical to the original
physical sound, at least within the limits of the 20 khz bandwidth designed in
the system (neglecting any defects in the construction of the player, of
course).
Hence, without knowing the insides of the brain, we know it will react just
like it would to the original sound since, to all practical purposes, it is
precisely what the player is providing.
In cinema, the projector holds the sample (the individual frame) for 1/24 th of
a second minus the time needed to move film, a black gap that is filled by POV
(not needed in digital cinema).
The low pass filter is the brain slow processing speed. Seen from behind this
filter, the sampled and held output of the projector and the original
continuous motion would appear as mathematically identical, at least within the
12 Hz banwidth that seem to be the limit of brain motion processing speed (if
we accept that 24 frames per second is a good enough sampling rate). Since we
have identical signals, we don't need to know more about brain circuitry, they
can only produce the same effect in the end.
It could be interesting to calculate the effect of an incomplete hold (without
the pov to fill in the black gap). I suspect it would not ruin the whole thing.
Of course if some in depth study of the brain
were to reveal that POV is somehow a byproduct of the slow processing speed,
the argument would become meaningless.
Albert Manfredi wrote:
Olivier Houot wrote:
> Hence, explanation of cinema does not require any specific analysis
> of the brain behavior, it is just standard sampling theory.
Hmmm. I'm not a film professional by any means, but I think this question is
more math/engineering related.
I see no contradiction here. In order to understand how the eye/brain decodes a
sampled signal, you need to do this analysis of brain behavior.
It seems to me that sampling theory requires sample and hold (for a very short
time, but long enough that the sample can be stored accurately) during the A/D
conversion process, and then low-pass filtering of the sampled signal train in
decoding, to recreate the continuous signal. And sampling theory also assumes
that the original continuous signal is in fact a continuous signal (i.e. max
frequency content of signal less than half the sampling frequency). Not
unrelated images or unrelated bursts of noise.
In sampled audio, if the separate audio samples occur so frequently that the
bandwidth of hearing cannot detect the discontinuity, the sound is perceived as
a constant tone. The ear/brain behave as the low-pass filter of the decoding
process. But of course, the samples must be related, or the decoded signal
would just be white noise. So, doesn't this require brain behavior analysis?
In visual perception, I think it works the same way. If you interpret
"persistence of vision" to be the required sample and hold in the A/D
conversion process, then there's no disagreement here. You take multiple
samples over time. If the subsequent samples are related to one another, and
occur quickly enough that the brain cannot decode them as separate images (like
audio samples occurring at higher rate than the ear's bandwidth), then the
image is interpreted as motion. But if the samples are unrelated, or are too
slow, then the visual process will perceive distinct images (or just mush).
I agree that POV alone is not enough to explain the phenomenon, but I think
that POV is one of the elemnts you need in the process.
Bert
------------------------------
End of opendtv Digest V7 #147
*****************************
----------------------------------------------------------------------
You can UNSUBSCRIBE from the OpenDTV list in two ways:
- Using the UNSUBSCRIBE command in your user configuration settings at
FreeLists.org
- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
unsubscribe in the subject line.
----------------------------------------------------------------------
You can UNSUBSCRIBE from the OpenDTV list in two ways:
- Using the UNSUBSCRIBE command in your user configuration settings at
FreeLists.org
- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
unsubscribe in the subject line.
Other related posts:
