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  #16  
Old 08-04-2012, 05:32 AM
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Quote:
Originally Posted by NewVista View Post
This should be a no-brainer yet only movie people use 4k cameras!
Always wondered why HDTV cameras 2k? Naive?
Depends on the tradeoffs when you're making the sensors. In the early days of CCDs they were struggling to make them work at all, you got as many pixels as you could reasonably make work at all. There are also 2 tradeoffs that may well be fundamental. For a given image size on the chip, if you have more pixels each one is smaller and hence collects less light. Also the fill factor, the fraction of the chip's surface that's sensitive to light, goes down. While a theoretically ideal sampler has infinitesimally small pixels it would also have infinitesimal sensitivity. Hence the sensor designer strives to fill as much of the space as possible with pixels and leave minimum space between them.

Image size is important. For cine camera replacement you want to be able to use your existing stock of 35mm prime lenses. Hence the sensor size needs to replicate 35mm film area. For TV the sensors are smaller.

I haven't looked at what size sensors Super Hi-Vision uses but the fundamental resolution is about 8k x 4k. I saw a demonstration a few days ago at BBC Broadcasting House, some recordings from the Olympics. NHK and BBC have worked together to televise parts of the olympics on this new system. Only 3 cameras so a refreshing return to old fashioned production values, lots of lingering wide shots, minimal pans or zooms. You don't need closeups when you have that much resolution available. From my seat, about 30 feet from a 25 foot screen the pictures were perfectly detailed and flawless, even under difficult lighting conditions such as fireworks.

The pictures were also being relayed to Bradford, Glasgow, Washington DC, Tokyo and Fukushima so some of you may have had a chance to see them.
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  #17  
Old 08-04-2012, 09:07 AM
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Quote:
Originally Posted by ppppenguin View Post
..For a given image size on the chip, if you have more pixels each one is smaller and hence collects less light..
I hadn't considered that issue. HD clearly needs to migrate to a larger format chips
and cinema camera innovations will drive this change.

Have not noticed any Olympics motion artifacts with BBC?originated HD in 50HZ?
but probably 60HZ for HiVision?

The EBU needs to continue to push for 1080p for 7 & 8 mhz channels and dual 50/60hz standard
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  #18  
Old 08-04-2012, 09:16 AM
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Perhaps the EBU need not worry about Interlace given the present
availability of 50/60p cameras:
With an alternate method of interlace generation, motion artifact
could be avoided in a similar manner to film scanning (see diagram)
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  #19  
Old 08-05-2012, 02:36 AM
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In digital broadcasting there isn't really any such thing as "an interlaced channel". Just a coding standard and a bit rate. I don't have a citation to hand but it's probably easier to get a good picture at a lower bit rate when you start with a progressive source. As 1080/50p (and 60p) equipment becomes more readily available I think it will become standard for originating material. Hence removing the compomise between 1080/50i, 720/50p and 1080/25p. And the 60Hz related equivalents.

In the set of SMPTE standards for handling full bandwidth HD digits there are 2 basic bit rates, 1.5GB/s and 3GB/s. The latter is needed for 1080/50p and 1080/60p where the pixel clock is 148.5MHz. All the others (1080/50i, 720/60p and lots more) fit happily in 1.5GB/s with a 74.25MHz pixel clock. To add to the proliferation of standards all the 30Hz and 24Hz related standards have a variant with the pxiel clock multiplied by 1000/1001 to fit with the 59.94Hz NTSC field rate. This has always caused trouble with timecode. Now that NTSC is just about officially dead for broadcasting I can't see any reason for originating programme material on these standards.

NewVista's sketch is not unlike 1080/24psF. This is effectively 48 Hz interlaced int he channel but carrying 24Hz progressive. This allows material originated at 24Hz to be displayed on a CRT monitor without undue flicker.

Standards, don't you just love them. So lets have lots of them
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  #20  
Old 08-05-2012, 10:11 PM
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All right, I see they have a name for it: "30PsF". So my sketch
which I thought of a while back will not will not earn a patent

But it would obviate the need for complex & flawed motion comp
in deinterlacers if broadcasts could be somehow flagged to switch
off/bypass motion processor as for film sourced programming
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  #21  
Old 08-06-2012, 01:00 AM
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30psf isn't actually in the list of SMPTE standards Implicitly 25psf has been used for years in Europe for film material where 24fps film has traditionally been shown at 25fps. The 4% fater running time is just accepted as normal, the sound pitch likewise or it can be corrected.

The US has suffered badly from its standards. 59.9Hz fouls up timecode for the prodcution people. 3:2 pulldown fouls up transmission of 24fps film. This can be overcome with advanced standards converters. These can convert 24Hz material to 30Hz without significant quality loss. They can also recognise and remove 3:2 artefacts.
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  #22  
Old 08-07-2012, 11:43 AM
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Quote:
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.. 59.9Hz fouls up timecode for the prodcution people..
Were there problems editing with dropframe timecode?
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  #23  
Old 08-08-2012, 02:29 AM
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Drop frame doesn't work too badly on short programmes, as all editing software has been designed to cope with its peculiarities. Generating it in the long term requires all sorts of corrections as there is no simple relationship between clock time and dropframe TC.

It's all due to a decision made at the start of NTSC colour, long before TC was invented. The relationship beween colour SC and sound carrier had to be set to minimise certain crossmodulation problems. It was felt that moving the sound carrier by 0.1% would upset too many existing receivers so they moved H, V and SC frequencies instead. We've been living with the consequences ever since TC was invented.
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  #24  
Old 08-18-2012, 01:44 AM
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Quote:
Originally Posted by ppppenguin View Post
Drop frame doesn't work too badly on short programmes, as all editing software has been designed to cope with its peculiarities. Generating it in the long term requires all sorts of corrections as there is no simple relationship between clock time and dropframe TC.

It's all due to a decision made at the start of NTSC colour, long before TC was invented. The relationship beween colour SC and sound carrier had to be set to minimise certain crossmodulation problems. It was felt that moving the sound carrier by 0.1% would upset too many existing receivers so they moved H, V and SC frequencies instead. We've been living with the consequences ever since TC was invented.
The original color subcarrier frequency tested by RCA was 3.583125 MHZ which worked perfectly with 60/15750 on color receivers. However it caused visible moire patterns in received images on B&W intercarrier receivers during the tests because it beat against the 4.5 MHZ audio subcarrier.

Changing the H & V frequencies slightly to 15734.26 and 59.94 and reducing the color subcarrier to 3.579545 MHZ resolved the problem for the B&W sets, although it was never a problem for the new color sets.

Much Later, this change proved to be the undoing of videotape editing, special effects, standards conversion, and digital video.

Life in the engineering department would have been so much easier if they'd left it alone.
Cliff

Last edited by cbenham; 08-18-2012 at 05:40 PM. Reason: clarity
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  #25  
Old 08-28-2012, 03:20 PM
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More on Hi-Vision experiment
http://www.bbc.com/news/technology-19370582
Article says UK HD is 25 FpS
With 8mhz channels they should have followed EBU with 50p FpS
Especially since they have 12.5% more bandwidth than Continent
--and 25% more Bw than US channel (which can do 720 @ 60p )
As 25 FpS is really poor motion sampling rate
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  #26  
Old 11-29-2012, 12:17 PM
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Some good points here. I recall John Watkinson wrote a paper in 1998 on Video Oversampling. He stated that because of the optical filtering ahead of the sensor, it is not necessary to use so many lines to deliver HD. If on the otherhand, the number of pixels on the sensor is substantially higher followed by the optical low pass filter, rescaling to fewer lines will not result in loss of spatial resolution. The only caveat is that oversampling only really works with non-interlaced video.

I believe we now underestimate the resolution of Image Orthicon video since resolution was limited by the structure of the target element and not by a digital imager's pixel array. Hence higher number of pixel imagers, rescaling and progressive scan is the future.

Nevertheless, I would have liked to have seen what a 4" IO tube could yield in terms of spatial resolution.
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  #27  
Old 11-30-2012, 09:06 AM
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Otto Schade did research in which the raster was reduced in size. With a fine beam, it showed that the target was capable of finer resolution.

In pickup tubes, it is necessary to have the beam wide enough to produce complete discharge of the target in one field (not one frame). Otherwise, there is an inverse raster of unread charge remaining on the target. The next scan will then produce a coarse moire' or flicker as it scans slightly out of register with the original scan. This can occur for either interlace or progressive. Of course, for interlace, the beam must be twice as wide as for progressive with the same number of total lines per frame. In old recordings, you can sometimes see this flicker in areas where the beam focus was too good. A similar effect could occur on kinescope recordings when they were rebroadcast, but there the moire' was more often a higher frequency swirly line pattern because the rescan had a much worse match to the original scan than the two fields in a camera.

In CCD pickups, it was found that using every other line of elements for interlaced scanning resulted in far too much vertical resolution, producing excessive interline flicker in interlaced CRT displays. Therefore, rows were combined (with a coefficient that was adjustable to set the vertical peaking in high-end gear). This was the equivalent of the wide scanning beam in tube pickups.
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  #28  
Old 12-12-2012, 04:33 PM
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More on "PsF", now being used more widely for 30fps!
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  #29  
Old 12-13-2012, 02:03 AM
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I hadn't realised that PsF was proliferating. I know about 24pSF which is used to dress up progressive film material to look like interlace. Now they're doing it for 25, 29.97 and 30Hz.

I though that we were trying to abolish interlace but it's a hardy weed.
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  #30  
Old 12-13-2012, 09:48 PM
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I think this is welcome news given the ubiquity 1080/60i, with even ABC switching to this after a decade of 720p - and maybe this is why: They now have more confidence for artifact-free images now that PsF can be originated from new generation cameras? (It's all done in the camera)
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