Issues with TV-Feed

[philwjan]

Hi,
first off all, this is a great site with a staggering amount of resources that should be enough to finally rid all these silly conspiracy theories (well, we all know, this will never happen, but one can dream though )

On the page www.clavius.org/tvqual.html titled "Technology - Television" I found a little imprecision regarding the reduction in the amount of data by reducing a TV signal from color to BW. It is not like you assert, that all three colors use the same amount of bandwidth, thus a BW broadcast only using a third of a color one. Much rather a technique called croma subsampling is being used. Other than your example postulates no RGB-Signal is used, but a composite signal of a full-resolution luminance channel and two chrominance channels with lower resolution (YCbCr). While the luminance channel will carry the full frequency (every pixel has its own luminance value), the chrominance information is only transmitted with half or a fourth of the frequency. This is usually expressed as ratios in the form of 4:2:0. This is used in television and means that the chroma subchannel is half the frequency of the luminance channel. The chroma information alternates from line to line between Cb and Cr.

Thus I would think that the amount of bandwidth needed to transmit Color TV should roughly be 150% of that needed for BW. The estimation of 66% savings due to the BW seems a bit excessive to me.

As a starting point for further information see:
en.wikipedia.org/wiki/Chroma_subsampling

While this is in no way intended to either encourage any Hoaxer's criticism in this website, I think that we should try to be as precise as possible and have our facts as well together as we can.

Cheers,
Philipp

[echnaton]

Welcome to the board, Philipp.

Just to let you know, JayUtah who operates the Clavius site, has not been around much in the past month due to the commitments in his real life aside from his web site. In the past he has welcomed people that have offered corrections and were he here regularly would respond to your post quickly. Please fell free to hang around and make more contributions to the board.

[philwjan]

Hi,

and thanks for the kind welcome.

I understand, real life sometimes sucks and keeps you from all the important things. Maybe he'll eventually find the time again an find this interesting.

I'll definitely stick around for a while!

Philipp

[Kiwi]

Welcome Philwjan.

Have a look through Dwight's posts.
apollohoax.proboards21.com/index.cgi?action=viewprofile&user=dwight

Dwight made many valuable contributions about video and TV, so you and he should be on the same wavelength.

Jay's TV page is one of my favourites at Clavius because he does such a good of explaining the Apollo 11 TV transmission for laypeole, so it's interesting that you can suggest an improvement, which I'm sure he will appreciate.

On the old Apollo Hoax board we continually ran a "Typos" thread for posting to when ever we found any typos at Clavius, and Jay fixed them.

[philwjan]

I agree Kiwi, the page is really good apart from the color/BW issue.

As a teacher I know the problem of didactic reduction (literal translation, is there such a thing in English?). i.e. dumbing down things enough to make them comprehensible but short of making them factually wrong. In doubt I'd opt for no explanation rather than a factually incorrect one.

Philipp

[ajv]

Remember that even when the Apollo surface cameras were color they still did not use YCbCr. The early static color cameras (Apollo 12-14) and the later LRV mounted color cameras were field sequential RGB (black and white cameras with a color wheel). Combining the individual color frames was done on the ground. This avoided having either three vidicons or complicated/bulky delay circuits built into the lunar surface camera - a weight saving. So based on the history of the Apollo TV cameras, a black and white image was only a third of the color bandwidth.

[gillianren]

philwjan said:

As a teacher I know the problem of didactic reduction (literal translation, is there such a thing in English?). i.e. dumbing down things enough to make them comprehensible but short of making them factually wrong.

I (an English literature major) tend to just call it "dumbing things down enough to make them comprehensible but not actually wrong." There may be a simpler term for it, but I don't know it.

[Kiwi]

philwjan said:

As a teacher I know the problem of didactic reduction (literal translation, is there such a thing in English?). i.e. dumbing down things enough to make them comprehensible but short of making them factually wrong. In doubt I'd opt for no explanation rather than a factually incorrect one.

In that case, you must hang around here. In 50-odd years I don't think I have ever come across anyone who is better than Jay at explaining technical matters to laypeople. I recall one time trying hard to follow his description of the two types of complex systems. Getting near the end I started to think, "Yeah, Jay, I think I'm getting it," but wasn't sure. Then he made it all fall into place: The Post Office is an example of one type of complex system and a nuclear power plant is an example of the other.

Not only that, he comes up with a few quotables, such as:
You paint a totally wrong picture of space as a wholly unknown entity full of the physical equivalent of krakens and sea serpents, the existence and nature of which cannot be known except by throwing monkeys to them. Pure handwaving.
apollohoax.proboards21.com/index.cgi?board=theories&action=display&thread=1144878798&page=9#1148307763

ajv said:

Remember that even when the Apollo surface cameras were color they still did not use YCbCr. The early static color cameras (Apollo 12-14) and the later LRV mounted color cameras were field sequential RGB (black and white cameras with a color wheel). Combining the individual color frames was done on the ground. This avoided having either three vidicons or complicated/bulky delay circuits built into the lunar surface camera - a weight saving. So based on the history of the Apollo TV cameras, a black and white image was only a third of the color bandwidth.

When reading your first post Philwjan, I wondered whether you had taken the RGB colour wheels into account, but don't have the expertise to figure it out.

[PhantomWolf]

Not only that, he comes up with a few quotables

While I like the one in my quote, I'm quite partial to "If you rub your face with fish, everything smells fishy."

[Joe Durnavich]

It is not like you assert, that all three colors use the same amount of bandwidth, thus a BW broadcast only using a third of a color one.

I have always thought that Jay's graphic is correct. It does start out with "color (RGB)", after all, and not one of the chroma-subsampling schemes. The accompying text can be a little confusing because it refers to a "a standard full color signal" and a "standard television signal" and it is not clear if he meant those to refer to the same thing.

[dwight]

Moin moin philwjan.

I think Jay's post does refer to straight RGB. However, the TV cameras used on the lunar surface after A11 were all sequential colour. The signal they sent back was indeed a black and white signal encoded with RGB colour information sequentially. (ie the red frame followed by the blue, and then the green).

If you see the start of TV transmission, occassionally the straight B&W image is seen. It is extremely flickery due to the undecoded colour values. The feed was routed through an Ampex HS200 video disc system which then matrixed the three colours into a composite NTSC signal on the earth.

I have the docuntation describing exactly how TV was encoded for the missions, but not at hand, so I am going from memory. I am unsure if any subsampling would have been anticipated in comparison of full colour TV and the system used on Apollo through to the shuttle. If you want a more accurate explanation of TV compression techniques, it would be better to say the TV signal was required to stay within its given bandwidth parameters. On A11 it was extremely limited (thus the B&W, slow-scan, 10fps camera) while the later missions were able to enjoy full frame rate at 525 line resolution.

However, as mentioned before all TV from space during Apollo was sequential colour. One thing often overlooked as to why the TV was so noisy (apart from signal strength, satellite relays etc) was that each field as it arrived at the ground station had its noise. As the frame was matrixed together with two other fields in the HS200 this had the effect of trebling the noise ratio. After A15 John Lowry was applying noise reduction resulting in near broadcast quality TV, especially on A17.

Hope that helps.
Dwight

[ka9q]

NASA kept using those sequential color cameras well into the Shuttle era. I could never figure out why, except maybe they didn't want to fly non-US-made cameras.

The sequential color cameras had a serious artifact that made them very easy to spot: moving objects broke up into their primary colors. This reached its extreme on the lunar liftoffs as bits of insulation flew out from under the ascent stage engine looking like colored confetti.

I bet that if the original raw signal recordings are available somebody could figure how to reprocess them to get rid of many of those artifacts and even much of the noise. Much Apollo video was pretty static and there's certainly no reason the noise could not be averaged out of those areas.

Imagine what we could do today with high quality CCD imagers and digital transmission.

[Al Johnston]

Nov 7, 2006 17:37:22 GMT -4 gillianren said:

philwjan said:

As a teacher I know the problem of didactic reduction (literal translation, is there such a thing in English?). i.e. dumbing down things enough to make them comprehensible but short of making them factually wrong.

I (an English literature major) tend to just call it "dumbing things down enough to make them comprehensible but not actually wrong." There may be a simpler term for it, but I don't know it.

Jack Cohen called it "Lying to Children"

[Ginnie]

"Yeah, Jay, I think I'm getting it,"

;D
That's what I always say to myself reading Jay's posts. Sometimes I actually do get it.

[dwight]

G'day ka9q,

If I didn't thank you for the TV xl sheets you sent me, I'm doing so now and hoping you'll excuse my rudeness if I forgot to do so before.

The images from Apollo 16 and 17 were processed on the day by John Lowry (who now does the major cleanup on films like Star Wars and Indianna Jones). I have the downlink set made with digital conversion of the RBG signal and it looks breathtaking compared to anything else I have seen (including Spacecraftfilms stuff). The only problem being that whoever re-matrixed did so with the frame buffer sequence RGB and not RBG so the hue is way off. It can be fixed with tint control, but it still is not the full donut.

Contrary to HB folklore, not all raw TV telemetry tapes have gone astray. A16 is a prime example.

As far as field sequential colour on the shuttle, RCA was the winning contractor. Westinghouse realised they couldn't compete with RCA in the fixed price bidding and so opted out. RCA lost a lot of money on the shuttle TV system, and I guess NASA never upgraded due to the financial benefit of sticking with a proving system that supplied usable pictures. I also imagine the bandwidth limitations were still an issue in early shuttle days. The only major overhaul to the NASA TV system was the digital-sequential-conversion-equipment upgrade done in part by Charles Poynton.

As an interesting side note, the Russians were using sequential colour well into the early-mid 90's. Using specs from stolen East German secret police Westinghouse blueprints of their Apollo TV cameras!!