The Mehikon - broadcast TV color eraser

[Bud]

A curious piece of history of broadcast television in Israel that I never heard of before (source: Wikipedia):
 

Color eraser (Mehikon)   
In the '70s, the Israeli government considered the import of color televisions as frivolous and a luxury that would increase social gaps. Therefore, the government ordered the Israel Broadcasting Authority to cease broadcasting in color. As it was impractical to strip out the chrominance signal from material recorded in color, this was accomplished by simply omitting the burst phase signal from the broadcast. The "damaged" signal triggered the "color killer" mechanism, installed in color TV sets to prevent the appearance of color. This method was named Mehikon (Hebrew: מחיקון‎ "eraser").

Soon after its introduction of the "Color eraser", special TV sets with an Anti-Mehikon (Hebrew: אנטי-מחיקון‎ "anti-eraser") device were offered. This device re-constructed the burst phase signal according to several known standards. The client had to turn a knob until the pictures on the screen appeared in natural colors. According to a report in Yediot Aharonoth from January 1979,[4] clients had to adjust the knob every 15 minutes on average in normal conditions, or up to 10 times an hour when special problems occurred, in order to restore natural colors or if the picture suddenly turned black and white.

Based on information from owners of electricity appliance stores, the report estimated that 90% of those who bought color TV sets also bought the Anti-Mehikon device, which added about 5–10% to the price of the television.

Eventually, the Mehikon idea was proven to be futile, and the Israeli television stopped using it in 1980, allowing color transmissions to be received freely.

[tom66]

This reminds me of the reason that SECAM was popular behind the Iron Curtain:  because most of Europe used PAL, it made it difficult to receive (in colour) European signals without illegal imported sets.  Of course, black and white video was still receivable, as SECAM and PAL did not differ there.

It also gives rise to the alternate acronym for SECAM:  System Entirely Contrary to the American Method.

[janoc]

This reminds me of the reason that SECAM was popular behind the Iron Curtain:  because most of Europe used PAL, it made it difficult to receive (in colour) European signals without illegal imported sets.  Of course, black and white video was still receivable, as SECAM and PAL did not differ there.

It also gives rise to the alternate acronym for SECAM:  System Entirely Contrary to the American Method.

That is nice story but very unlikely to be true.

The originally French (and European standard) SECAM was used in the Eastern bloc because it was used in Soviet Union since 1967. For example, Czechoslovakia didn't start with regular color broadcasts until 1973-75. So it was logical that they picked the same technical standard as what was used by the Soviets already (all the labor division within COMECOM).

Why Soviets picked SECAM is likely due to the fact that it was an European standard, it wasn't German (all the WWII stuff) and, crucially, PAL didn't even exist when the decisions were made yet.

And given the geography, people in Moscow (and most of the Soviet Union, really) really didn't need to worry about receiving any illegal foreign signals in offensive color.

FYI, both SECAM & PAL were designed explicitly to fix the problems of the "American method" (aka NTSC).

[Benta]

This reminds me of the reason that SECAM was popular behind the Iron Curtain:  because most of Europe used PAL, it made it difficult to receive (in colour) European signals without illegal imported sets.  Of course, black and white video was still receivable, as SECAM and PAL did not differ there.

It also gives rise to the alternate acronym for SECAM:  System Entirely Contrary to the American Method.

Like janoc says, nice story for the pub, but that's about it.

All the systems have B/W compatibility, only colour coding is the issue. SECAM was probably chosen by the USSR as it seemed the most mature system (development started in the 1950s).

More efficient in the East Block when warding off "imperialist television" was the audio carrier frequency offset, which gave the option of either seeing a western broadcast without sound, or just hearing the audio.

[Halcyon]

FYI, both SECAM & PAL were designed explicitly to fix the problems of the "American method" (aka NTSC).

There is a reason why NTSC was commonly referred to as "Never Twice the Same Colour". I always did appreciate the extra resolution of PAL.

[tooki]

FYI, both SECAM & PAL were designed explicitly to fix the problems of the "American method" (aka NTSC).

There is a reason why NTSC was commonly referred to as "Never Twice the Same Colour". I always did appreciate the extra resolution of PAL.

Whereas to me, as a highly flicker-sensitive individual, the trivially lower resolution of NTSC was more than a fair price to not have to deal with the flicker of a standard 50Hz PAL TV.

[TimFox]

The reason why North America used approximately 60 Hz frame rate while Europe used approximately 50 Hz is the local mains frequency, unrelated to PAL/SECAM/NTSC standards.  The North American b/w standard is actually 60 Hz.  If there be line-related noise on the (color) video, a "hum bar" results, moving vertically with a repetition frequency equal to the beat between 60 Hz and 59.94 Hz frame rates.

[schmitt trigger]

Interesting Israeli story.
It shows how an absurd government regulation, even a well-meant one, will always provide incentives for people to break it.

Speaking of the PAL system....people sometimes forget that there were several PAL "flavors". The most common was the PAL-B/G, and the oddest one was PAL-M, used exclusively on Brazil and which was a bizarre mix of PAL and NTSC.

[NiHaoMike]

The part I like least about NTSC nowadays is the oddball 29.97 FPS frame rate, specifically because it's sometimes used in modern video standards instead of being rounded up to 30 FPS. The tolerances on analog TVs are loose enough that they won't even notice a slight increase in frame rate.

[Halcyon]

The part I like least about NTSC nowadays is the oddball 29.97 FPS frame rate, specifically because it's sometimes used in modern video standards instead of being rounded up to 30 FPS. The tolerances on analog TVs are loose enough that they won't even notice a slight increase in frame rate.

Although these days, that is all mostly irrelevant. Many countries, including Australia did away with analog TV transmissions years ago. Now all we have to do is get rid of interlacing and everything will be peachy.

[vk6zgo]

The part I like least about NTSC nowadays is the oddball 29.97 FPS frame rate, specifically because it's sometimes used in modern video standards instead of being rounded up to 30 FPS. The tolerances on analog TVs are loose enough that they won't even notice a slight increase in frame rate.

The old BW system was exactly 30Hz-----when NTSC colour came along, the horizontal rate was changed to avoid interference problems with the colour subcarrier frequency, so the vertical field (& frame) rate had to be changed as well, to maintain the normal raster.

Analog TV is interesting----if you look at a BW (luma) video signal with a Spectrum Analyser, you will notice that the signal actually consists of multiple harmonics of the 15kHz horizontal rate, each with sidebands at multiples of field rate.
There are gaps in the spectrum between these.

For colour TV, the colour information is quadrature modulated upon the colour subcarrier (3.58MHz approx in NTSC).
This signal also has a spectrum with large gaps between the sidebands.
By judicious choice of the subcarrier frequency, these sidebands fit in the gaps in the luma signal spectrum.
What might be called "frequency interlace"!

This is why the strange  frequencies are used as horizontal, vertical & colour subcarrier rates.

[NiHaoMike]

The old BW system was exactly 30Hz-----when NTSC colour came along, the horizontal rate was changed to avoid interference problems with the colour subcarrier frequency, so the vertical field (& frame) rate had to be changed as well, to maintain the normal raster.

Analog TV is interesting----if you look at a BW (luma) video signal with a Spectrum Analyser, you will notice that the signal actually consists of multiple harmonics of the 15kHz horizontal rate, each with sidebands at multiples of field rate.
There are gaps in the spectrum between these.

For colour TV, the colour information is quadrature modulated upon the colour subcarrier (3.58MHz approx in NTSC).
This signal also has a spectrum with large gaps between the sidebands.
By judicious choice of the subcarrier frequency, these sidebands fit in the gaps in the luma signal spectrum.
What might be called "frequency interlace"!

This is why the strange  frequencies are used as horizontal, vertical & colour subcarrier rates.

If you speed up all those frequencies in proportion so that the frame rate is exactly 30 FPS, wouldn't they still have the same relation to each other?

[vk6zgo]

FYI, both SECAM & PAL were designed explicitly to fix the problems of the "American method" (aka NTSC).

There is a reason why NTSC was commonly referred to as "Never Twice the Same Colour". I always did appreciate the extra resolution of PAL.

Whereas to me, as a highly flicker-sensitive individual, the trivially lower resolution of NTSC was more than a fair price to not have to deal with the flicker of a standard 50Hz PAL TV.

Was that with normal TV programming  or did you have problems using a PAL TV as a monitor, as many of us did with the Commodore 64, etc?

On the resolution side of things, before I went to the UK in 1971, I assumed I would see a huge difference in resolution between the BW 625 line system used in Australia, & the Brit 405 line system.
As most of the Brit TV shows I'd seen were "kines" so were pretty dire, I had a definitely jaundiced view.

The first "guest house" I stayed at had a "dual standard" BW TV for us "guests".
Watching both 625 & 405 line Stations, I was surprised that the difference was quite slight.
OK, the line structure, which was apparent with both, was a bit coarser, so vertical definition suffered slightly, but the horizontal resolution was pretty much the same.

As the horizontal rate is slower, with 405, a given resolution requires lower frequency response, so, the narrower passband doesn't matter that much.

One thing which was immediately noticeable was that with positive modulation, occasional very bright pictures would cause loss of vertical syncs.
On the BBC, these  were rare, but on the commercial channels, they did occur in the form of ads.

[vk6zgo]

The old BW system was exactly 30Hz-----when NTSC colour came along, the horizontal rate was changed to avoid interference problems with the colour subcarrier frequency, so the vertical field (& frame) rate had to be changed as well, to maintain the normal raster.

Analog TV is interesting----if you look at a BW (luma) video signal with a Spectrum Analyser, you will notice that the signal actually consists of multiple harmonics of the 15kHz horizontal rate, each with sidebands at multiples of field rate.
There are gaps in the spectrum between these.

For colour TV, the colour information is quadrature modulated upon the colour subcarrier (3.58MHz approx in NTSC).
This signal also has a spectrum with large gaps between the sidebands.
By judicious choice of the subcarrier frequency, these sidebands fit in the gaps in the luma signal spectrum.
What might be called "frequency interlace"!

This is why the strange  frequencies are used as horizontal, vertical & colour subcarrier rates.

If you speed up all those frequencies in proportion so that the frame rate is exactly 30 FPS, wouldn't they still have the same relation to each other?

No, the spectrum gaps don't quite work out.
Bear in mind, this was designed as a whole system to be used in thousands of units, so they could afford to be "fussy".
We could probably tweak it to exactly 30Hz & not notice, but the FCC would have!

It's ages since I read the complete specs for 625 line PAL, but I'm pretty certain they kept 50Hz  & adjusted the other frequencies.
I do remember that the "slack" way of looking at a field rate signal with a 'scope was to just trigger from the 50Hz Mains.
The display did drift, but it was so slow as to be effectively imperceptible.
.
30Hz/30fps frame rate put the designers of telecine chains in a world of hurt, as there was no easy relationship between that & the 24 fps used for film.
 
They devised ingenious mechanical systems which presented the same frame several times to get around this.
Very, very, clever, & very complex to explain, especially for myself, as I never had to work with them.

50Hz systems just "cheated", ran their projectors at 25 fps, & said "to hell with the 4% difference!"

[basinstreetdesign]

If you speed up all those frequencies in proportion so that the frame rate is exactly 30 FPS, wouldn't they still have the same relation to each other?

Yes it would but you would have to move the sound carrier up by the same amount to avoid the original problem:  If there were any non-linearities in the video system then an annoying stationary dot pattern would be caused by the sound carrier at 4.5 MHz.  In that case, all NTSC receivers would have to be returned as well, and that wasn't about to happen.

All other components of the signal were slowed down to maintain their respective relationships, of course, and this lowered the frame rate from 30 Hz to 29.97002997… Hz, or approximately 0.1%.  The exact ratio of new frequency to old is 1000/1001.  This seemed innocuous enough for the system designers since their first priority was to make sure that the system stayed compatible with all of the installed receivers in America; and a shift of about 0.1% was sufficiently small that those TV sets could easily track the change in scanning rate.

However, when this was done the distinction between video time and real time came into sharp focus.  With the widespread usage of time code 1 hours worth of video, or 108,000 frames of videotape would last too long!  It now became 60 x 60 x 29.97… = 107,892 frames, or 108 frames too short!  It was imperative for the producers (and sponsors) of an hour’s worth of programming to see that the length of a show was exactly one hour.  This discrepancy was fixed in the application of the code by losing or “dropping” 108 frame counts spread over the course of the hour.  So, during the progress of the frame count through the hour, two frames (the counts only NOT the actual frames of video), numbers 00 and 01 were skipped or “dropped” at the start of each minute with the exception of minutes which were a multiple of ten.  Sounds complicated?  It gets worse.

Now every manufacturer of equipment that generated, read, computed, or otherwise used “drop frame” time code had to take this stuttering time reference into account when dealing with programming length.  Every producer, director, editor who wishes to create accurately timed commercials or programs had to be aware of this disjoint “real-time” reference.

As it happens, the above discrepancy of time is not exactly 108 frames per hour.  I rounded the frame rate to 29.97 f/s but it is actually a repeating decimal, 29.97002997002997…  This means that a fraction of a frame is left over each hour.  In fact a real hour is 107,892.1079… frames long.  If the time code generator were to run for an entire day it would count 2,589,410.589... frames.  It would NOT be an even number of frames due to the repeating decimal.  The “drop frame” code would reach the terminal count of 24:00:00:00 with an error of [2,589,410.589 - (30 x 60 x 60 x 24) - (108 x 24)] or 2.5894 frames or 86.4 milliseconds.  Each and every day a time code generator would be this amount out of time every day.

It drove many people nuts to have to deal with this crap until the software in the editing systems became sophisticated enough to remove much of the burden from the users.  It also gave the Europeans much cause for amusement to look at the mess the TV engineers across the pond had created for themselves.

[tooki]

The part I like least about NTSC nowadays is the oddball 29.97 FPS frame rate, specifically because it's sometimes used in modern video standards instead of being rounded up to 30 FPS. The tolerances on analog TVs are loose enough that they won't even notice a slight increase in frame rate.

Although these days, that is all mostly irrelevant. Many countries, including Australia did away with analog TV transmissions years ago. Now all we have to do is get rid of interlacing and everything will be peachy.

Hear, hear!!!

I am actually irrationally angry that digital video standards (other than than 480i, which matched the analog SD signal, and which predates the HD standards) even include interlaced modes. It never made sense for 1080i to even exist, given that practically no TVs exist that can display it truly natively! (How many CRT HDTVs are there out there, really??)

[Bud]

With interlaced method of transmission you send half of the picture 50 or 60 times per second. With progressive method you send full picture at full resolution each time, therefore doubling the bandwidth. I can speculate that 1080i may have to do with lower bandwidth media including perhaps interconnecting cables. It would be less demanding to the system throughput than 1080p.

[Halcyon]

With interlaced method of transmission you send half of the picture 50 or 60 times per second. With progressive method you send full picture at full resolution each time, therefore doubling the bandwidth. I can speculate that 1080i may have to do with lower bandwidth media including perhaps interconnecting cables. It would be less demanding to the system throughput than 1080p.

It looks shit, mainly on LCDs.

[janoc]

Whereas to me, as a highly flicker-sensitive individual, the trivially lower resolution of NTSC was more than a fair price to not have to deal with the flicker of a standard 50Hz PAL TV.

Tooki, don't tell me that you can see the difference between 50Hz and 60Hz flicker with a naked eye and in the absence of flickering ambient lighting (i.e. no fluorescents or flickering LEDs around).

[tooki]

Whereas to me, as a highly flicker-sensitive individual, the trivially lower resolution of NTSC was more than a fair price to not have to deal with the flicker of a standard 50Hz PAL TV.

Tooki, don't tell me that you can see the difference between 50Hz and 60Hz flicker with a naked eye and in the absence of flickering ambient lighting (i.e. no fluorescents or flickering LEDs around).

With regards to CRT TVs? Absolutely. It’s clearly visible, especially in peripheral vision. 60Hz really is the lower bound for being flicker free, 50Hz is just below it. There’s a reason 100Hz (50Hz x2) TVs were developed, but nobody ever had to make 120Hz (60Hz x2) TVs. It’s why cinemas used, at rock bottom minimum, frame rate doubling projectors (48fps) but preferred frame-tripling (72fps) to ensure no flicker.

[tooki]

With interlaced method of transmission you send half of the picture 50 or 60 times per second. With progressive method you send full picture at full resolution each time, therefore doubling the bandwidth. I can speculate that 1080i may have to do with lower bandwidth media including perhaps interconnecting cables. It would be less demanding to the system throughput than 1080p.

Interlacing was originally invented to reduce the demands on the circuitry of TV receivers, limited by 1930s technology.

It (sorta) made sense to preserve that in digital video standards intended to be displayed on CRT SD TVs. In digital, they should have just made it 1080p30 instead of 1080i. (The things where you’d want the extra frame rate of p60 are also the ones where you want the clear movement of progressive, which is why sports, for example, typically got broadcast in 720p rather than 1080i.)

[NiHaoMike]

Yes it would but you would have to move the sound carrier up by the same amount to avoid the original problem:  If there were any non-linearities in the video system then an annoying stationary dot pattern would be caused by the sound carrier at 4.5 MHz.  In that case, all NTSC receivers would have to be returned as well, and that wasn't about to happen.

So then move the sound carrier that slight amount.

With interlaced method of transmission you send half of the picture 50 or 60 times per second. With progressive method you send full picture at full resolution each time, therefore doubling the bandwidth. I can speculate that 1080i may have to do with lower bandwidth media including perhaps interconnecting cables. It would be less demanding to the system throughput than 1080p.

1080p at 30 FPS would be exactly the same pixel rate. Also, since the video is compressed, doubling the frame rate does not double the bandwidth.

Instead of interlacing, they could have "checkerboarded" the half frames so that the artifacts would just appear as a blurred image instead of more visible lines.

[janoc]

With regards to CRT TVs? Absolutely. It’s clearly visible, especially in peripheral vision. 60Hz really is the lower bound for being flicker free, 50Hz is just below it.

I think the issue is more that if you watched a 60Hz TV you didn't have any 60Hz light sources around (everything being 50Hz in Switzerland), so you didn't get the beating effect that makes it much more visible. Or you have superhuman eyes.

There’s a reason 100Hz (50Hz x2) TVs were developed, but nobody ever had to make 120Hz (60Hz x2) TVs.

That's not true, for example 120Hz CRTmonitors were completely common (and expensive!). And pretty much all 100Hz TVs were multi-standard, they were able to double both 50Hz PAL/SECAM signals and 60Hz NTSC.

[Bud]

1080p at 30 FPS would be exactly the same pixel rate. Also, since the video is compressed, doubling the frame rate does not double the bandwidth.

..and you would get horrible flicker as a bonus

Instead of interlacing, they could have "checkerboarded" the half frames so that the artifacts would just appear as a blurred image instead of more visible lines.

All that shenanigan just because someone wanted even 30Hz ?

[tooki]

With regards to CRT TVs? Absolutely. It’s clearly visible, especially in peripheral vision. 60Hz really is the lower bound for being flicker free, 50Hz is just below it.

I think the issue is more that if you watched a 60Hz TV you didn't have any 60Hz light sources around (everything being 50Hz in Switzerland), so you didn't get the beating effect that makes it much more visible. Or you have superhuman eyes.

There’s a reason 100Hz (50Hz x2) TVs were developed, but nobody ever had to make 120Hz (60Hz x2) TVs.

That's not true, for example 120Hz CRTmonitors were completely common (and expensive!). And pretty much all 100Hz TVs were multi-standard, they were able to double both 50Hz PAL/SECAM signals and 60Hz NTSC.

Sorry, your assumptions are just all wrong.

When I moved from USA to Switzerland (obviously not bringing any TVs with us, since they wouldn’t work), I immediately noticed how TVs here were flickery. Nothing to do with lighting artifacts, nor with a side by side comparison, but rather something that I was readily able to detect in isolation. This has nothing to do with “superhuman” vision: It’s widely documented that human peripheral vision is easily capable of much faster flicker detection than central vision.

It’s my understanding that if a 100Hz TV supported NTSC input (which was FAR from universal!), that 60Hz was not frame-doubled. Maybe some could. Either way, that’s neither here nor there, since NTSC countries didn’t have 120Hz TVs. They never existed because 60Hz didn’t flicker the way 50Hz does. Nobody in an NTSC country would have had a 100Hz TV, even if it could do 120Hz.

120Hz-capable computer displays were common among high end CRTs, but that’s got nothing to do with TVs.