> > 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.
No, 60 half images.
> That's still 60 flashes per second. :)
60 flashes or a 60 refreshes but not 60 full images. If there are 525
horizontal lines per TV image and you get 262 every 1/60th of a second, what's
your image rate?
> 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.
And that's got what to do with TV? or anything, for that matter?
> > > 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.
60 flashes a second does not mean a 60 Hz image rate. Every 60th of a second,
you get every other line of the transmitted image. You don't get all 525 lines
of the image until two flashes have gone by. Are you saying there's no
difference? Then I presume you save money by going with interlaced computer
displays, too.
> This is why NTSC is so much smoother than 24fps.
A 30 Hz frame rate is better 24. Even with that, text (like credits in a film)
looks better in film than they do on TV. You're looking at it too
simplistically. It's more than just the frame rate. I can make 60 Hz frame
rate material look less smooth than 30 Hz by changing the optical capture
characteristic. Frame rate is not the end of the story.
> > There are two things going on here that shouldn't be confused:
>
> And why not? I _am_ a life-long registered Republican.
No comment.
> > 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.
I guess we'll just have to disagree on this one. One indication that videotape
does not "look" better than film is that movies still use film for presentation
- movies would have transitioned a long time ago. I'm not saying that video
isn't better. There isn't an objective characteristic that videotape can't
equal or exceed film (except possibly dynamic range which is what would be
reflected in the shadow characteristics mentioned above). Yet film "looks"
better because it's what we're accustomed to. People have long reacted to going
to movies that were basically transfers of video as looking 'cheap', or like a
TV show. They go to a movie and they don't expect it to be 'cheap' in quality
despite the fact that video is objectively higher in quality. So, we continue
to see film and probably will continue to see "film" (in digitized transfers)
even when we get to all digital transmission systems.
> > 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.
That explains a lot more. In fact, a great deal of effort has gone into making
computer generated and videotaped productions as pleasing to the eye as film.
The simple method is just to transfer to film. My guess is that this will
transition to digitally processed productions in which the film "look" is
imposed on the image sequence of digitally captured or generated video.
> > 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.
I guess we'll just disagree some more. At 30 Hz, you can't see "strobed"
motion. However, at a fixed refresh rate (say 30 Hz), you can see the
difference between film/video/image where the shutter speed varies between the
minimum, which is the inverse of the image rate (or 1/30th sec in this example)
and say 1/1000th of a second where the shutter is very fast and is capturing a
less blurred still image each frame. I think you would call this "strobed"
motion but each image is, in fact, cleaner just as it would be in photographs
and yield a better movie. In this case, "better" means cleaner (objectively
measured) to see rather than more pleasing in the film versus video debate
above.
> > 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).
Then why do they transfer to film after they're done?
> > > 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.
Timing is extremely important. If you flash on two different objects close
enough together, you get a mixing effect.
> Glad to know somebody read my message. Whatcha up to, Rocky?
Eh, just real busy as evidenced by the time it took for me to respond to your
challenge. We should probably carry on with this off line so as not to go to
off-topic for the group. I won't be able to go to the next meeting (visiting
relatives in Philly) but maybe the next meeting.
> - Peter
-Rocky
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