The encoding used by both NTSC and PAL for colour was similar, except PAL alternated the phase on alternate lines allowing the receiver to reduce the effect of any phase errors. There was also vertical colour resolution reduction in PAL as a delay line was typically used in the decoder as part of the phase correction process.
NTSC = Never Twice the Same Colour.
What composite colour standard does the RPi output? I have one working here on PAL.
Thanks for that. I remember seeing a description of NTSC encoding in one of the early DIY computer books (probably one of Don Lancaster's) but have never seen or, I must admit, looked for equivalent descriptions of PAL or SECAM encoding.
;-)
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martin@ | Martin Gregorie
gregorie. | Essex, UK
org |
Thanks - good description. I'd noticed that the monochrome image had to be separate because its noticably sharper. This is particularly obvious if you see a YouTube capture of some old analogue NTSC footage.
Your comment about the eye being forgiving is what I meant by saying that those brought up with analogue NTSC probably didn't notice the colour blurring because 'thats just how TV is'.
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martin@ | Martin Gregorie
gregorie. | Essex, UK
org |
The simple mistake of allowing the most fragile element of the transmission - phase - to not be cancelled by alternate line transmissions essentially destroyed terrestrial colour TV in the States and made cable what it is.
Not sure how they are doing with digital terrestrial.
--
the biggest threat to humanity comes from socialism, which has utterly
diverted our attention away from what really matters to our existential
survival, to indulging in navel gazing and faux moral investigations
into what the world ought to be, whilst we fail utterly to deal with
what it actually is.
I always liked SABENA : Such A Bad Experience - Never Again. I flew them once...
--
the biggest threat to humanity comes from socialism, which has utterly
diverted our attention away from what really matters to our existential
survival, to indulging in navel gazing and faux moral investigations
into what the world ought to be, whilst we fail utterly to deal with
what it actually is.
That also described Crossair, which is now part of Swiss International Airlines, to perfection. In the late 1990s I was using it for a weekly commute between London City and Zurich. The outward run was generally more or less on time, probably because London was one end of the route, but coming back you could guarantee they would be 30 mins late into Zurich at at least that late into London, depending only on how long they spent pissing about at Zurich. They were using RJ100s (Bae146), which I like.
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martin@ | Martin Gregorie
gregorie. | Essex, UK
org |
All modern color encoding schemes, starting with NTSC, are based upon studies of human visual perception.
And, though early color TV sets were less accurate in their color rendition, this was largely a result of users idiosyncratic settings of the "hue" (phase) and "saturation" (chrominance amplitude) controls. By the time the Trinitron arrived, these "controls" had become mostly automatic, and NTSC color receivers produced excellent color.
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-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
--
the biggest threat to humanity comes from socialism, which has utterly
diverted our attention away from what really matters to our existential
survival, to indulging in navel gazing and faux moral investigations
into what the world ought to be, whilst we fail utterly to deal with
what it actually is.
Note that color rendition problems of NTSC (and the necessity of a HUE control) has absolutely nothing to do with convergence problems of the CRT and the effect of technologies like Trinitron on that.
I wasn't objecting to colour rendition. What I was on about was the failure of a colour to stay within the boundaries of the object it should be colouring.
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martin@ | Martin Gregorie
gregorie. | Essex, UK
org |
What we were talking about was the failure of the color to be even close to what it ought to be, inside boundaries or not
--
the biggest threat to humanity comes from socialism, which has utterly
diverted our attention away from what really matters to our existential
survival, to indulging in navel gazing and faux moral investigations
into what the world ought to be, whilst we fail utterly to deal with
what it actually is.
Thats been true of majority of CRT TVs and almost every NTSC set I've seen. Since, for my taste, the colours are generally too saturated on many LCD and OLED sets as well, a reasonable guess is that they're that way because that's what what most punters like.
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martin@ | Martin Gregorie
gregorie. | Essex, UK
org |
SECAM uses FM for the sub-carrier modulation rather than QAM that NTSC and PAL use. PAL alternating the phase between adjacent colour lines, hence the name Phase Alternate Line. By alternating the phase and storing the previous line of colour info you can average out phase errors in the transmission. The resulting phase errors alter the saturation of the colour with PAL where the errors result in the colour changing with NTSC.
PAL was patented by Telefunken and all PAL televisions had to pay a licence fee to Telefunken. Apart from SONY who ISTR transcoded the PAL signal to something else and decoded that thus avoiding the fee.
The luminence was sent as normal amplitude modulation. The colour using phase modulation needs a phase = 0 reference. This was transmitted as 8 cycles of 4.43MHz at the start of each scan line used to lock the local reference. To ensure that colour signals decoded on BW TVs, the luminence bandwidth was limited to less that 4.43MHz so the luminence did not compromise the colour information. Because the colour signal was effectively offset 4.43MHz from the the luminence carrier it just disappeared on BW sets as all of them didn't have sufficient receiver bandwidth to make use of all the luminence causing little problems.
As a teenager trying to understand how modulation schemes for TV and radio worked was challenging as I didn't have the maths knowledge. I was
14 when FM stereo multiplex finally came clear. It was a few more years till I got I understood QAM. The modern digital modulation schemes are very clever but apart from the maths behind Reed Solomon, Golay coding etc. which is rather complex, the rest is quite straightforward and you only need sufficient computational horsepower to decode the signal and then fix the errors. Analog schemes such as PAL have a wonderful elegance to them which echoes a gentler time.
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