DTV on standard 4:3 TVs and CRT damage

[dr.ido]

Aspect ratio switching can be handled automatically using the flags that already exist in the the standards - as long as the broadcasters use those flags correctly. Unfortunately most channels would set the flag to 16:9 for everything and either hard encode the black bars onto 4:3 programs or crop it to fit a 16:9 frame. In either case the only way to get what was originally a 4:3 program to display in full screen on a 4:3 TV is to manually mess with the settings - on a case by case basis.

On the (in the minority) channels that did use the flags correctly (both OTA and cable) the set top box would adjust on a program by program basis - sometimes it would even correctly adjust for commercials in a different aspect ratio to the program and correctly switch back when the program returned. 4:3 programs in full screen on a 4:3 TV - 16:9 programs either letterboxed or center cut depending on your setting.

The Pace cable box I had even supported the wide screen switching signals so it didn't have to resize anything to fit the chosen setting. It could display everything in it's native aspect ratio and just control the aspect ratio/zoom setting in the TV. I could unplug the 4:3 set, hot plug in a 16:9 set and without changing a single setting on the cable box everything would automatically display correctly.

Of course these features only work when programs are broadcast with the flags set correctly and 4:3 shows haven't been butchered to fit a 16:9 frame.

[andy]

...

[zenith2134]

As far as burnt phosphor is concerned, NOTHING I've seen can beat an original Ms. Pacman arcade cabinet I saw circa 2007 in a L.I. bowling alley..It was unplugged, and there was a perfect, distinct burnt-in image of the pacman home screen, with high-score and everything. It was amazing, like a photograph.

[jr_tech]

Originally Posted by andy

It's rare, but I have seen burn in on an LCD. This is different from image retention which goes away after a few minutes. It only happens in extreme circumstances, but it can happen.

What is the mechanism for this rare, but long term "burn"... is there a small amount of UV light from the backlight that causes the dye in the color filters to fade in areas of long exposure?

jr

[wa2ise]

That screen size would approximately simulate the pre-war 441i scanning standard. Showing the resolution that pre-war standard would have given us...
So we have stepped forward AND backward with the implementation of HD....Brilliant!

You could construct a fake prewar TV by getting a small CRT display (like one of those Chinese AM-FM-TV portable sets) and build a wooden cabinet (in the style of the day), set that set to really overscan horizontally and vertically so a B&W signal from a coupon eligible converter box (set to letterbox mode) shows visibly on the CRT around 441i line scanning. The overscan essentially throws away 84 lines, and the letterbox mode makes those thrown away lines black anyway. The horiz overscan would throw away the extreme left and right portions of the 16:9 image, so it would look reasonably geometrically correct on the CRT.

As for the audio, back before the war, the sound carrier was to be AM, not FM. So we'd need to degrade the sound quality a little, maybe add some video related buzz. Probably best approximated with a cap, to pass a little video signal above around 10KHz into the audio...

[ChrisW6ATV]

Originally Posted by jr_tech

What is the mechanism for this rare, but long term "burn"...

JR-

The problem with "burned-in" LCD images (whether or not it can be fixed; I have not yet had an opportunity to try) is supposedly that the liquid crystal elements or molecules get "lazy" or something roughly like that. So, with a given voltage they will no longer change polarity/position as much as they originally did. One of the "repair" theories I have heard is to run some kind of test video on such a damaged screen that would make the "lazy" elements or pixels eventually respond properly again.

[ChrisW6ATV]

Originally Posted by dr.ido

Aspect ratio switching can be handled automatically using the flags that already exist in the the standards - as long as the broadcasters use those flags correctly.

Dr. Ido-

Like a number of other nice technologies used elsewhere in the world, aspect-ratio flagging has either never been used here in the USA, or no sets sold here have been designed to follow the flags, or both.

It does not help that sets such as Samsung LCDs can not even be made to remember the manually-chosen aspect-ratio settings on a per-channel (or specifically, per-subchannel) basis. One station here has a 480p or 480i subchannel (the equivalent of your 576p/i ones) showing 4:3 content but pillarboxed and coded as 16:9. My Samsung can remember aspect-ratio settings based only on the resolutions of various channels or subchannels. So, I either get that one subchannel double-pillarboxed (with everything on the screen super-thin) or, worse, I get all of the other 480p/i channels (which are all 4:3) stretched out wide and fat, filling the screen.

[Electronic M]

My Zenith DTV box does a decent job of interpreting aspect ratio flags and remembering settings, but I have cable so it is rarely used, and analog cable don't let me pick how they send it down the pipe (which can often be retarded particularly if the engineer at a given channel is dumb).

[ChrisW6ATV]

The Zenith DTT-900 and DTT-901 are among the tuners (built-in or external) that DO let you set and remember aspect-ratio settings on a per-channel/subchannel basis. Don't ever let go of it!

[jr_tech]

Originally Posted by ChrisW6ATV

The problem with "burned-in" LCD images (whether or not it can be fixed; I have not yet had an opportunity to try) is supposedly that the liquid crystal elements or molecules get "lazy" or something roughly like that. So, with a given voltage they will no longer change polarity/position as much as they originally did.

Interesting, Thanks!
Then I would guess that there might be some variation of this "ageing" phenomenon depending upon quality/purity/type of the LC material, cell construction, etc. Perhaps this is why it is rarely observed?

jr

[dr.ido]

I've seen videos of flashing test patterns that are supposed to fix lazy or stuck pixels if you run them long enough. I've also noticed that sometimes rubbing the panel in the affected area will get a stuck pixel to work temporarily, but I've only tried this with individual stuck pixels that were an inherent defect in that panel. I've never had a panel with "Aged" from image retention.

Originally Posted by ChrisW6ATV

Like a number of other nice technologies used elsewhere in the world, aspect-ratio flagging has either never been used here in the USA, or no sets sold here have been designed to follow the flags, or both.

I thought that the aspect ratio flag was part of the MPEG2 spec - or does that only apply to DVDs?

[ChrisW6ATV]

I may be thinking more of the analog TV days, when other countries widely adopted 16:9 programming and had an aspect ratio flag in the signal. Yes, on some digital TV sets, I have seen an indication of the aspect ratio in addition to the resolution when the "Info" or "Display" or similar button is pressed, so you must be right about it being part of MPEG-2 video.