Analog cable stations broadcast at 10 bit-depth which is a very low grade picture
 

I have learned that the SMPTE has issued a recommendation to television stations that they should broadcast a 20 bit-depth (color depth) picture when they broadcast in high definition and that they should broadcast at 10 bit-depth (about 3 bits for each primary color) when they broadcast in standard definition.

To give you an idea of what 10 bit-depth picture (about 3 bits for each primary color) is like, it is something like watching the picture on one of those old computer monitors from the 1980s, which is a dismal picture. An extremely low grade picture; I would say you can't get a lower grade picture than that. And even if you use one of those old analog TVs you will still get that picture.

And that is a real shame. I loved to watch my old analog Zenith TV. The picture was so rich and vivid, it was fantastic!

Yet another way in which the powers that be want to screw folks who haven't bought the latest Chinese POC and or like old shows.

This is probably to keep folks from making a decent analog loophole based bootleg of ota broadcasted content while also forcing them to buy a copy the the program to see it in any reasonable amount of quality.

I've been recording analog TV programs since the transition, and have had no problems with picture quality. My cable carries all local TV stations in SD and HD, and, again, I see no loss of image quality (except that the picture does not fill the screen on my 19" flat panel TV) when viewing the SD feed. The tapes are perfectly watchable when I play them back on my Panasonic VCR; in fact, I just recently watched a tape I had made of an episode of "Criminal Minds" on ION TV (channel 23 in my area). Again, no loss of picture quality that I could see when I watched the program.

Could you provide a reference for this SMPTE recommendation please.

I work primarily with uncompressed SDI interfaces. In the SMPTE documents that specify these (125M, 292M, 424M etc) the standard colour depth is 10 bit, which means 10 bits per component per pixel. That is 10 bits each for Y, Pb and Pr. When handling the signals as parallel data (before serialisation or after deserialisation) the interface can be specified as either 10 bit (with Y and C multiplexed on a single 10 bit bus) or 20 bit (with Y and C on separate 10 bit buses).

When compressing signals for transmission the MPEG2 or MPEG4/H264 encoder uses at least 8 of the 10 bits per pixel per component, depending on the profile.

I had read about that recommendation by the SMPTE on a reputable page on the Internet but I didn't copy it then so I do not know the specific details.

I think that they use 10 bits per channel when they produce HDTV programs in ATSC but when they broadcast the programs the use 8 bits per channel (or 24 bits total).

I know also that they also use 8 bits per channel when they broadcast programs in DVB-T and DVB-T2 where you live in England. Actually, they do the same thing there on Freeview, that they broadcast the standard definition PAL programs at a much lower bit depth than the HD programs.

AFAIK all the MPEG2 encoders used for SD programs in the UK use 8 bits per component. The HD MPEG4/H264 encoders may use 10 bits rather than 8 but I have no evidence. The improvement when moving from 8 to 10 bits is very marginal on real pictures. It can of course be seen on special test signals such as shallow ramps.

PAL is no longer used in the UK and quite likely not anywhere else in Europe. Any material originated in PAL would be decoded to components before being used. Even an inexpensive single chip decoder can work remarkably well, leaving very few artifacts. The BBC and others have developed sophisticated 3D comb decoders that can convert PAL to component with essentially no artifacts. Quite a few people say "PAL" when the really mean 625 line, 50Hz. Just as some say NTSC when they mean 525 line, 59.94Hz. Likewise a lot of people say YUV when they really mean YCbCr or YPbPr. U and V are strictly speaking the weighted colour difference components immediately before being modulated on to a colour subcarrier. U and V have no place in a component system.

I cannot believe that anyone anywhere is using 3 bits per component at the input to the encoder. The pictures would be unbelievably and utterly impossibly bad.

Many years ago I experimentally digitised composite PAL video at 1 bit per pixel. As you would expect the pictures (in monochrome) looked truly horrible. The surprise was that in highly coloured areas the PAL subcarrier acted as a dither signal and made the picture vastly better. This was a demonstration of how you can trade quantising errors (limited bit depth) for noise. You can make a 3 bits per component picture without the posterisation errors you would expect simply by adding enough random noise. It will then look like a snowstorm.

Hey Electronic M, we still have NTSC in Milwaukee! The signal should reach you in Delafield as it's coming from that big tower near Capitol Dr!

I'm getting a kick out of watching REAL NTSC,
(Don't have to travel to SA, Caribbean, Mexico, Canada or Burma to see the real thing!)

I'll have to see if I can tune it. Out here analog wise what is on the air and where it is on the dial varies(though last couple of times I tried, some time ago, I got zilch). I'm not into watching Spanish language programing though it would be an interesting way of gauging UHF tuner performance of my sets.

I agree with ppppenguin - you must have confused the SDI interface specs with the number of bits per pixel for coding. Broadcast coding uses 8 bits per component pretty universally.

I would note also, however, that 8 bits per component can have visible artifacts on some picture material when viewed on a high-contrast capable display in a dimly lit room. If you want to produce shows that use the kind of dynamic range long used in the movies to contrast indoor/outdoor and day/night, the extra bits help.

Viewers have gradually been trained (over a period of decades) to higher quality in terms of noise level and contrast range. The TASO study that set signal-to-noise for analog TV coverage in the 50s would probably get a one grade lower result (on a 5-step scale) today.

"Color Depth" should refer to Gamut not A/D spec?

Color depth (or bit depth) is not the same as gamut. Color depth means just that, the depth of the colors in the picture. Bit depth started with HDTV because it is all digital; bit depth is not applicable to analog TV because the signal there is continuous (not in bits of information), although someone can say that analog NTSC signal had the equivalent of something like 32 bit depth.

The reason why HD broadcasting systems see fit to broadcast a 24 bit depth (or 8 bits per component) picture instead of the equivalent of a 32 bit depth one that analog NTSC used to have is because they believe that the human eye cannot tell the difference above 10 million colors, and actually a 24 bit depth picture has about 16 million colors.

I have read somewhere that television and motion picture engineers believe that the 3 most important things about a picture are gamut, contrast and color depth. Perhaps, they overlook the color depth somewhat nowadays.

Where do I start. Let's separate colour gamut and number of different colours.

The gamut is set first by the system primary colours. The current primaries for PAL/NTSC differ slightly from the original NTSC primaries. The HD primaries (Rec709) differ slightly again giving a slightly larger gamut than PAL/NTSC. This theoretical gamut is then restricted further by the cameras and displays. CRTs have, if anything, got worse over time though the introduction of rare earth phosphors helped a bit. More with brightness than gamut. In practice it's not too important. The TV camera and CRT makers have done a pretty good job. Gamut limitations only affect the most saturated colours. The various flat panel technologies are all over the place. None match the CRT phosphors but the best are pretty good.

Number of different colours is more difficult to quantify. I've seen CIE diagrams with arrows showing the least colour change the eye can see in different areas. This can only be established by subjective tests and varies with actual colour.

An 8 bit per component digital system can meet the eye's requirements here. The problem is that certain sorts of pictures can make the quantisation very obvious. The engineering test waveform "shallow ramps" is designed to expose this. Even a 10 bit per component system can be exposed this way. 32 bits are irrelevant. No TV system has ever used a total of 32 bits.

Now let's look at analogue. Although this allows an infinite number of colours the practical limit is set by signal to noise ratio. 48dB SNR is roughly equivalent to 8 bits. You would be very lucky to get that all the way from camera to receiver in an all analogue chain. Chroma SNR is worse than luma so even a superb analogue chain is probably working at the equivalent of 20 to 22 bits overall. Ever since the 1970s there have been digital islands within the analogue system. More recently the only analogue parts have been the camera head, transmitter and receiver. Eveything else has been digital. Often 8 bits, more recently 10 bits.

In a digital system you can trade quantising errors with noise. If you add a small amount of random noise to a shallow ramps test waveform the step effects will disappear while the noise itself will be impreceptible.

None of this addresses what happens during compression, more properly called data rate reduction. This is more complex.

Speaking of Wide Color Gamut, the opening animation of Wheel of Fortune (Sony Columbia Studios) is particularly wide!
Especially on my Samsung DLP using High Intensity tri-color LEDs (2006)
No longer produced due to cost - no doubt the widest color gamut of any TV
I run it in WIDE mode for dazzling spectral extension.

No broadcast is especially wide gamut. All are standardized as Rec 709 colorimetry. If you enjoy the extra color saturation, fine, but it is only your TV set's guess of when to expand it.

What is sRGB mode? (not that I want to give up the Garish - but pretty - "WIDE")