On Aug 20, 3:15 am, Richard Dobson <richarddob...@blueyonder.co.uk> wrote:> Radium wrote:> > 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.> There are some mixed metaphors here. There is a video equivalent to > audio pitch shifting. think of the latter represetned in the frequency > domain (spectrum) - the peak correspindsing to the source partial moves > down (or up). the video equivalent is colour cycling or shifting. But > most simply, reds would be shifted to orange, green shifted to blue, > violet to ultra-violet (and hence llost to view). An alternatyive > stratgy is colour rotation using the artists colour wheel, where, > ideally, diametrically opposite colours are complementary. There is no > equivalent that I know of to colour complemenariness in audio.Never thought of it this way. My description of visual "pitch- shifting" is to alter the temporal and spatial frequencies of a video signal without using low/high-pass-filtering, changing the speed of the video or changing the size of the images that make up the movie. Real-time pitch-shifting is done for audio on the phone. Certain voice- changing devices allow women to sound like men on the phone, without decreasing the speed at which they talk. The pitch of the audio is decreased but the speed remains the same. I would like something similar to be done with the spatial and temporal of a video signal in real-time. I would like to be able to work not only for recorded video but also for video signals that are being transmitted/received in real-time -- such as a live TV show.> I ~think~ I get what Radium wants - he wants to be able to modify a > recorded scene the way one can modify a CGI virtual scene, e.g. by > setting a slower wing flapping rate while leaving other parts of the > scene unchanged.Actually I don't want other parts to be unchanged. What I would like is the temporal frequencies [of all parts of the video] to be decreased but without decreasing the speed of the video signal.> The only audio parallel I can think > of is wanting to pitch shift just one instrument in a polyphonic > texture, leaving other voices unchanged.The audio parallel is the following: http://www.adobe.com/products/audition/overview2.html#kmhead3 "Time and pitch processing: shift pitch without changing tempo - and never introduce audio artifacts."
Questions about equivalents of audio/video and digital/analog.
Started by ●August 19, 2007
Reply by ●August 20, 20072007-08-20
Reply by ●August 20, 20072007-08-20
Radium wrote: (snip)> Real-time pitch-shifting is done for audio on the phone. Certain voice- > changing devices allow women to sound like men on the phone, without > decreasing the speed at which they talk. The pitch of the audio is > decreased but the speed remains the same.> I would like something similar to be done with the spatial and > temporal of a video signal in real-time. I would like to be able to > work not only for recorded video but also for video signals that are > being transmitted/received in real-time -- such as a live TV show.Normally this is done by removing the appropriate frames (samples), or duplicating them. One example is the 3-2 pulldown used to convert 24 frame/second movies to 59.94 field/second video.>>I ~think~ I get what Radium wants - he wants to be able to modify a >>recorded scene the way one can modify a CGI virtual scene, e.g. by >>setting a slower wing flapping rate while leaving other parts of the >>scene unchanged.> Actually I don't want other parts to be unchanged. What I would like > is the temporal frequencies [of all parts of the video] to be > decreased but without decreasing the speed of the video signal.That might be harder. For audio, it can be chopped, such as removing 1/60th of a second every 1/20th to speed it up by 1.5. If that is done faster than the modulation (vocalization), and slower than the frequencies of interest (maybe 400Hz-3.5kHz for voice) it works pretty well. Probably less well for music. As far as I know, that is usually done asynchronously to the source signal. One could imagine removing cycles of a 1.23kHz voice, for example. For video the modulation (wing flapping) is not separate from the source frequency. If you know you are trying to separate wing flapping, it could be done by cutting out whole flap cycles, assuming only one bird is in the scene, and is doing most of the motion. Otherwise, I don't think there is anything you could do. -- glen
Reply by ●August 20, 20072007-08-20
In article <6M2dner4stOKoVfbnZ2dnUVZ_qelnZ2d@comcast.com>, glen herrmannsfeldt <gah@ugcs.caltech.edu> wrote:>> Actually I don't want other parts to be unchanged. What I would like >> is the temporal frequencies [of all parts of the video] to be >> decreased but without decreasing the speed of the video signal. > >That might be harder. For audio, it can be chopped, such as >removing 1/60th of a second every 1/20th to speed it up by 1.5. >If that is done faster than the modulation (vocalization), >and slower than the frequencies of interest (maybe 400Hz-3.5kHz >for voice) it works pretty well. Probably less well for music. > >As far as I know, that is usually done asynchronously to the >source signal. One could imagine removing cycles of a 1.23kHz >voice, for example. > >For video the modulation (wing flapping) is not separate from >the source frequency. If you know you are trying to separate >wing flapping, it could be done by cutting out whole flap >cycles, assuming only one bird is in the scene, and is doing >most of the motion. Otherwise, I don't think there is anything >you could do.Some of the TV networks are speeding up syndicated reruns by using this sort of technique. They appear to be using the "chop out audio samples" method to speed up the dialog (without pitch-shifting it) and dropping out complete frames of the video. This works fairly well when watching scenes with little action, but causes an odd stuttering-jerk effect when the camera pans or somebody walks across the screen. I think I prefer it to the old technique of cutting out whole scenes or sub-scenes, though. -- Dave Platt <dplatt@radagast.org> AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads!
Reply by ●August 20, 20072007-08-20
Floyd L. Davidson wrote:> Jerry Avins <jya@ieee.org> wrote:...>> I can >> demonstrate a circuit using analog components that >> transforms a continuous ramp input into a staircase >> output. Moreover, the output levels can be individually >> adjusted. Is the output digital? (We're discussing an >> arbitrary definition here. There is no wrong answer.) > > The output is apparenlty analog. At least you have said > *nothing* that indicates otherwise.Apparently analog but actually digital? That would be in keeping with your assertion that quantizing an otherwise analog signal digitizes it.> Do you think all digital signals are square waves and > anything that has square waves is digital? Your example > above suggests that you might, but it simply isn't true.By old vacuum-tube signal generator was certainly analog. It produced square waves among other wave shapes. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●August 20, 20072007-08-20
Floyd L. Davidson wrote: (snip)> Actually I suspect it is open to debate as to whether a > sample is actually PAM until it is quantized. (Until it > is, it's just a sample of an analog signal.) But > whatever, if the sample itself actually is PAM, then yes > that is an analog signal.Phase modulation can be done continuously, and so can amplitude modulation. The NTSC chroma subcarrier is pretty much PAM, where the phase indicates the hue and amplitude the intensity of the color. NTSC isn't actually described that way due to the desire to get just a little more resolution out of the signal. The eye is more sensitive to spatial resolution between some colors than others (and not along the obvious R-G-B axes), and NTSC encodes that. Only very recently were TV receivers built to decode that extra information, at about the same time ATSC tuners are taking over. -- glen
Reply by ●August 20, 20072007-08-20
Floyd L. Davidson wrote:> Jerry Avins <jya@ieee.org> wrote:>> ... A signal can be >> quantized without any need to measure it or describe it >> with a number. > > That isn't true. In order to quantize it you *must* > decide on non-overlapping ranges of *values*, and a > specific quantity value that equates to those values. > >> An example is the signal being measured >> in a quantum Hall-effect experiment. > > Explain.http://www.warwick.ac.uk/~phsbm/qhe.htm Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●August 20, 20072007-08-20
Floyd L. Davidson wrote: ...> Anything that is quantized is digitized.A signal can be quantized without having been measured. How doe that fit your scheme? Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●August 20, 20072007-08-20
On Aug 20, 7:15 pm, glen herrmannsfeldt <g...@ugcs.caltech.edu> wrote:> For video the modulation (wing flapping) is not separate from > the source frequency. If you know you are trying to separate > wing flapping, it could be done by cutting out whole flap > cycles, assuming only one bird is in the scene, and is doing > most of the motion. Otherwise, I don't think there is anything > you could do.I don't want to separate the wing-flapping or anything from the video. I want all temporal components of the video signal to be slowed without changing the length or speed of the video. Just like Adobe Audition and certain voice-changers allow the pitch of the audio signal to be decreased without changing the length or speed of the audio.
Reply by ●August 20, 20072007-08-20
Radium wrote:
...
> Actually I don't want other parts to be unchanged. What I would like
> is the temporal frequencies [of all parts of the video] to be
> decreased but without decreasing the speed of the video signal.
...
> The audio parallel is the following:
>
> http://www.adobe.com/products/audition/overview2.html#kmhead3
>
> "Time and pitch processing: shift pitch without changing tempo - and
> never introduce audio artifacts."
The video analog of acoustic pitch is color. Both are our biological
response to frequency.
Jerry
--
Engineering is the art of making what you want from things you can get.
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Reply by ●August 20, 20072007-08-20
On Aug 20, 12:37 am, Jerry Avins <j...@ieee.org> wrote:> Radium wrote:> > I wish I knew. This 'pitch-shifting' is a lot more confusing than I > > thought. Yet I still find it so interesting. Sorry.> Don't be sorry. If you work out the details, I'll help you to see the > inherent contradictions they impose, but I won't argue with you about it.The problem is, I have a hard time accepting when I'm told that there is no video-equivalent to pitch-shifting-without-changing-tempo.> > Similarly an imaging device with insufficient spatial bandwidth will > > result in image distortion if excessively fine detail is put into the > > camera.> That's true only if you mean spatial aliasing. Otherwise, you're using > "distortion" in a non-standard way.Okay.> > Just like if you have an 11.025-KHz-sample-rate digital audio device, > > you need to make sure the pitch of the audio you are inputting into > > the device does not exceed 5.5125 KHz.> How does that make for "decent imagery? It amounts to a low-pass filter, > about which you remarked, "ugh".Well, the image looked bad. It's similar to what happens when you set the "sharpness" setting on a PC-monitor or TV-screen too low.> > Spatial frequency is how fine or dull an image is. Pitch is determined > > by audio frequency. I am using the spatial frequency as an analogy.> Stop with analogies. Say what you mean.I am saying what I mean -- or at least what I think I mean.> Here's the picture of you that I have in my head: You were a precocious > kid, and impressed those around by asking questions that were further > out than what most kids asked. (Reading a lot leads one to do that.) The > adults around you patted you on the head and praised you for digging > into subjects they knew little or nothing about.* They knew so little > about it that they didn't understand much of what you talked about, and > so couldn't set you back on the rails when you wandered away from > reality. No matter, the praise kept coming anyway, and you learned that > if you imagined something, it was golden. It wasn't really, but those > around you taught you to believe that it was. Now you find yourself > going on about your imaginings with people who _do_ understand the > subject you fantasize about and their reaction hurts, but you're finding > it very hard to get out of bullshit mode and ask basic questions. It > hasn't sunk in yet that you don't even have basic answers because you > still believe that the fantasies you construct are real. I hope you get > over that. In the meanwhile, I feel sorry for you.Well, I've always had a special interest in things that I find difficult to answer or make sense of. Video-equivalents-of-audio- entities are certainly one of them.
