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Date:	Sun, 11 Jul 2004 18:03:16 PDT7
From:	Peter Skye <pskye@peterskye.com >
Reply-To:	scoug-help@scoug.com
To:	scoug-help@scoug.com
Subject:	SCOUG-Help: Re: Supposed OS/2 Port of FFMPEG (?)

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Michael Rakijas wrote:
>

Oh boy! Somebody to argue with!

> Most people find TV refresh rates acceptable
> despite the 30 Hz image rate.

This is incorrect. TV images (NTSC, standard North American television)
are refreshed at 60 images per second.

> > Our television system uses a 60 Hz rate
>
> Slight correction. TV images are refreshed at the rate of half an image 60
> times per second or one full new image 30 times per second. Each half
> image is interlaced (every other scan line) with the other half image.

That's still 60 flashes per second. :)

> > Hewlett Packard's research on eye flicker for illuminating
> > with LEDs found a 100 Hz rate acceptable.
>
> Again, for what?

The digital displays on their calculators. If you wave your old H-P
calculator while looking at it, you'll see digits frozen in the air
where the LEDs blink on.

> > Fluorescent tubes flicker at 120 Hz (in North America).
>
> Most people cannot see flicker at 120 Hz but I believe that there is still a
> primary light generation rate of 60 Hz.

No, the tubes fluoresce on each half wave.

> This is why viewing computer images
> refreshed at 60 Hz in ambient fluorescent light to be one of the most harshest
> environments. The flourescent light tends to "beat" against the 60 Hz of the
> image refresh, also leading to headaches in some, fatigue in others, and
> sometimes no effect.

Yes, absolutely correct. You've nailed this one.

> This beating can be seen in other circumstances say, when
> a TV image containing a computer monitor showing an image. Unless the two (TV
> and computer monitor) refreshes are locked against one another, you will see the
> rolling horizontal black bar in the TV image of the computer monitor.

Also when motion picture film has a television in the image. Sort of
like those wagon wheels that spin backwards when the horses slow down.

> > Many people don't realize that television (NTSC) is shot at 60 images
> > per second.
>
> Again, see above - this is the half image rate.

Rocky, there are still 60 flashes per second. Each flash contains an
updated view of the image, i.e. the image 1/60th of a second later.
This is why NTSC is so much smoother than 24fps.

> There are two things going on here that shouldn't be confused:

And why not? I _am_ a life-long registered Republican.

> double the source intensity yields double the brightness of the image

Hoo haa, you'll fall over if you ever look at the transfer curves.

> Videotape looks cleaner mostly because of its improved characteristics
> in color fidelity and linearity relative to film

No. Videotape looks much better than film even when viewed on a black
and white television. And film has far superior shadow characteristics.

> but most don't find it acceptable for movies because
> the film going public has been conditioned to expect film and its
> characteristics, that is, the softness and relative warmness (opposite of
> harshness) relative to videotape.

I went to see Two Brothers on Friday (the film about the tiger cubs).
Part of it was shot in HDTV for production reasons and then transferred
to film. I looked hard but couldn't see the difference.

> Flickeryness and smoothness of motion are related to . . .
> video capture rate and image capture (shutter) speed.

Capture rate yes. Shutter speed yes with the caveat that blurred motion
is smoother than "strobed" motion.

> This has led to the process of filmmakers using video first (for the added convenience as
> well) and then transferring to film to cater to the film going public.

Not a chance. Filmmakers use video for 1) its lower cost, 2) there are
production problems which video resolves (like putting cameras in tight
places or where low weight is required or where you need to set up a lot
of cameras), 3) they simply want that particular "look" (talk to the
lighting director and find out how hot and shadow you'll deal with).

> > Note that the eye can "see" extremely short "changes". A photographic
> > strobe light might be "on" for just 1/1000th of a second and yet we
> > still see it.
>
> Even neurons have a persistence to them. I don't think the question here is
> how short of an image change one can see (the eye has an integrating effect) but
> how far apart two strobe pulses need to be before you perceive them as two
> separate pulses. I guarantee that two 1/1000th of a second pulses separated by
> 1/1000th of a second will be perceived as one pulse. It's been a long time
> since I've looked at this stuff but I think that they have to be separated by at
> least low 10s of milliseconds to be perceived separately.

Try flashing those pulses on two different sides of an object. Or
flashing them in different colors. I don't know what the results will
be but I know the eye is non-linear with respect to the three cones,
i.e. they resolve differently.

Glad to know somebody read my message. Whatcha up to, Rocky?

- Peter

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