▲What if the Apple ][ had run on Field-Sequential?(nicole.express)
87 points by zdw 15 hours ago | 7 comments
▲Zak 12 hours ago
I had a camera with a field-sequential electronic viewfinder. Because it relies on persistence of vision to mix RGB colors, it could be pretty distracting if I moved my eye quickly, breaking the illusion, and I think it would be similarly annoying on a TV or computer display.
▲CamperBob2 12 hours ago
Tektronix built a lot of test equipment based on color-shutter CRTs in the 1990s. It was simultaneously nifty and awful. They could render rich, well-defined color waveforms, but as soon as you moved your eyes, the illusion would break apart into rainbow-colored fragments. It was like watching a movie on a DLP projector, only much worse.

Meanwhile, HP OEM'ed a bunch of Trinitron monitors from Sony and called it a day.

▲Animats 9 hours ago
Right. Field sequential display means heavy flicker. Do not want.
▲jrdres 1 hour ago
The CBS field-sequential color system did have one application after the 1950's: it was the system used for color transmissions from the Apollo moon landings.

https://en.wikipedia.org/wiki/Apollo_TV_camera#Westinghouse_...

If you watch footage of the Apollo 17 LEM liftoff from the moon, you can see color artifacts in the burst of fragments off the platform. Their motion is too fast to stay in the same color band.

▲thought_alarm 11 hours ago
Hypothetical question:

Let's say that back in 1930s when they were assigning frequencies for the broadcast television channels, they allocated enough extra bandwidth for a future color (chroma) signal, apart from the existing monochrome (luma) signal.

If the bandwidth was available, would it have been possible to include separate chroma and luma components in the broadcast signal without the two interfering with each other, thereby producing a much cleaner color image while maintaining backward compatibility with the original B&W TV sets?

▲badlibrarian 11 hours ago
You could argue that if extra bandwidth were available it might be better allocated elsewhere for improved picture quality. But yes. It would've reduced lots of engineering complexity and probably would've looked very much like PALplus.

https://en.wikipedia.org/wiki/PALplus

▲tlb 8 hours ago
Isn't that essentially what happened? In the 1930s, the channels were allocated at 6 MHz spacing, but only needed about 3 MHz of bandwidth for the luma channel. There might have been some foresight involved, but the gaps between channels also allowed for cheaper, less precise tuners. Then in the 1950s they added a 1 MHz chroma signal on a 3.58 MHz upper sideband, expanding the channel bandwidth to just under 6 MHz.
▲badlibrarian 8 hours ago
6 MHz was there from the start. If it wasn't, the CBS field-sequential might have won. Both government (FCC) and industry (RCA) were pushing for a backward compatible system and there was enough bandwidth to pull it off. OP asks what would've happened had chroma been given its own separate, non-overlapping band. That was not possible while maintaining compatibility.
▲dzdt 10 hours ago
I think in this alternate universe the Apple-II analog would be the first cheap computer that could run a spreadsheet. That really takes a 40 column display. So I think it would have waited for the 2mhz 6502 to handle the doubled line frequency.
▲dlcarrier 13 hours ago
Does anyone know why they call it artifact colors? It creates a valid colorburst signal, so the colors are exactly as expected. It's high-resolution black-and-white imagery that's more of an artifact.
▲dzdt 8 hours ago
Guessing not knowledge but I expect it was called that from the accidental occurence of color on broadcast TV wben the image includes something with black-and-white stripes at the right spacing. So the name predates the intentional usage by the comphter system.
▲Dwedit 12 hours ago
Because they're square waves and not proper modulated signals.
▲ 11 hours ago
▲dn3500 13 hours ago
It's a specific technique where you deliberately modulate the signal so as to interfere with the color subcarrier. This can be used to produce colors that are otherwise not available.

https://en.wikipedia.org/wiki/Composite_artifact_colors

▲rayiner 12 hours ago
> But we are saving the lives of ~3 million people so who’s to say what is bad

Korea’s GDP per capita in 1950 was similar to that of Bangladesh around the same time: https://www.nationmaster.com/country-info/stats/Economy/GDP-.... In the alternate timeline where there isn’t a capitalist south korea, the Korean peninsula has 100 million+ people living in poverty and squalor, like Bangladesh today. The cost of that is tens of millions of lost lives resulting from higher infant and child mortality rates.

▲kryptiskt 8 hours ago
The simplest way to have no Korean war is if Kim Il-Sung decides that an invasion is too risky and concentrates on internal matters.
▲nicole_express 12 hours ago
Interesting that your takeaway is "capitalist South Korea doesn't exist" when I also said the 38th parallel held?

Also I guess now we're discussing the Repugnant Conclusion, which is a bit out of scope

▲CamperBob2 12 hours ago
See also the arguments that more Koreans would be alive and well today if MacArthur's plans to nuke the Norks had been greenlighted by Truman.
▲theturtle 5 hours ago
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