General > General Technical Chat

The Mehikon - broadcast TV color eraser

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tooki:

--- Quote from: BrianHG on August 24, 2020, 11:14:12 pm ---
--- Quote from: tooki on August 21, 2020, 05:16:57 am --- (How many CRT HDTVs are there out there, really??)

--- End quote ---
What the hell.  My 37inch multiscan Mitsubishi back in 1993 did HDTV in RGB fine once the standard became available.
Ok, well, brand new at the time, it was a 20K$ monitor.

And yes, 5 years later when I could finally reliably play DVDs on a PC, I ran the screen at 72fps progressive making the motion in movies perfectly v-synced.  Well, once in awhile, you could catch a dropped frame as the video card's 72Hz wasn't in perfect tune with the DVD player software of the time which I believe locked onto the sound card's 48KHz clock since it had to sync AC3 without disruption.

My desktop screens were all running at either 96Hz or 120Hz.  No flicker at all.

--- End quote ---
I wasn’t talking about computer displays, which is why I said “CRT HDTVs”, not just “CRTs”. I assume your 37” Mitsu was a computer display (or broadcast monitor), not a TV, right?

Anyhow, I didn’t say there were no CRT HDTVs. Just a vanishingly small number, compared to the number of flat-panel HDTVs sold over the years.

tooki:

--- Quote from: vk6zgo on August 25, 2020, 02:17:51 am ---With the invention, & subsequent miniaturisation of frame stores, system conversion has become a trivial task.

--- End quote ---
Well, I wouldn’t call it trivial. If the sole thing you’re converting is color system (e.g. PAL <-> SECAM), then it’s trivial. If you have to rescale a resolution, it’s a smidgen harder. But any time you have frame rate conversion or interlacing involved, it gets a LOT hairier. Good converters do similar things as the motion smoothing in our TVs: object tracking and interpolation. If you don’t do this, you get jerky movement and (on interlaced source material) combing.

igendel:
Funny thing, I've heard a lot about the Mehikon (I'm just a couple of years too young to have any personal recollection of it) - but it always bugged me, how color can be restored to a B/W picture, and no one could explain so I stopped asking I guess. Now I finally understand... thanks!  :D

Ultrapurple:
Fascinating info from basinstreetdesign - thank you!

The 50/60Hz thing lives on today. I was recently looking at the possibility of acquiring a '4k' TV. Reading the small print in the spec, it's amazing how many of them quote a 120Hz refresh rate for the panel. What's wrong with that? I live in a 50Hz country and if you watch 50Hz (100Hz) material on a 60Hz (120Hz) screen you get awful judder. Once you see it you'll hate it forever.

I have yet to see a domestic TV that specifically says it adapts the panel refresh rate to suit the source material (though I admit I haven't done an exhaustive market survey).

As an aside, the first couple of generations of Roku-based boxes used for the NowTV service were hard-wired 60Hz - which made as much sense as a chocolate teapot because all the native source material (basically, UK broadcast TV) would be 50Hz.

I find it quite nausea-inducing to watch an American show that has been standards converted from 60Hz to 50Hz, converted back to 60Hz in the Roku box, and finally played on a 50Hz screen. Yet my partner doesn't even notice it.

tom66:

--- Quote from: Ultrapurple on August 25, 2020, 10:08:31 am ---I have yet to see a domestic TV that specifically says it adapts the panel refresh rate to suit the source material (though I admit I haven't done an exhaustive market survey).

--- End quote ---

Perhaps it's different nowadays, but my 2012 Panasonic plasma has a 100Hz, 60Hz and 72Hz mode.  The 100Hz mode is for 50Hz (frame doubling with low flicker), the 60Hz mode is of course for NTSC/60Hz content and the 72Hz mode is for frame-tripled 24fps content.  You could see, on an oscilloscope, the drive waveforms changing between these modes, with the screen briefly blanking.  The reset pulse, ramp timings etc all changed slightly and indeed the '100Hz' and '72Hz' modes had a slightly lower black level as they could refresh the panel more often without 'mal-discharge'.

My older 2008 Panasonic plasma had 48Hz, 50Hz and 60Hz modes for a similar purpose, although the 48Hz mode was very close to the flicker-fusion point and so you often could see flickering in your peripheral vision.

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