Interlacing and channel bandwidth

[NewVista]

Originally Posted by ppppenguin

. This suggests using a sensor with more pixels than needed for your TV system and filtering the output..

This should be a no-brainer yet only movie people use 4k cameras!
Always wondered why HDTV cameras 2k? Naive?

[ppppenguin]

Originally Posted by NewVista

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.

[NewVista]

Originally Posted by ppppenguin

..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

[Penthode]

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.