Here is a loopy idea.
Has anyone tried to emulate a NTSC encoder in software, or is anyone familiar with an effort to do so?
The next question is, why? I dunno, just something to do. Here in the U.S., there are still low-power TV stations broadcasting in analog NTSC.
It's easy to convert RGB into luminance using NTSC coefficients, but to be a true emulation you would need to synthesize a subcarrier.
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there is workflows around for about 20 years,
they might take VHS, if they still take them,
or NTSC DV tape, you can use some NLE like Magix Vegas,
they might take some appropriate mpg as a file, you'd need to ask for specs, but if you encode it with Magix Vegas, there should be no problem, these files could be easily tested on a distance
before exporting in Vegas (or other NLE) just use some broadcast colors effect, (7.5 IRE, or custom luma, chroma, composite) or even to 16-235 RGB (Vegas can apply this) , audio balanced with a desired -6dB or something, 48000Hz.
NTSC is as good as obsolete. I can't imagine Vegas or any NLE program supporting it because the output would be basically useless; it wouldn't be compatible with anything. The few low-power TV stations still broadcasting analog NTSC probably use hardware encoders, just like the old days.
There are people in this world who restore steam locomotives and vacuum tube radios as hobby projects, and they enjoy it. You wouldn't run a railroad with steam locomotives in revenue service in this day and age, though.
What do VHS tapes have to do with the topic at hand?
Digital files? We didn't have digital files in 1970. It's 2020 now. In 2020 NTSC is a dinosaur.
What the heck are you talking about? What NTSC encoder even means?
You want to emulate something from 1960 before digital era with those analog rules? I just told you, you take a video and then throw a bunch of filters on it to simulate NTSC. Am I in Twilight Zone or something? In 1960 you had recording in analog to tape and broadcasted it was as such with specific hardware with bunch of knobs turning left and right making a signal out of it and receiving it and specific viewing CRT at the end also equipped with bunch of knobs. What part of it do you wish to simulate? Just one part of it at the end, receiving signal? How? It was analog.
I got the NTSC encoder working except for interlace.
I had thought about synthesizing a subcarrier but the math is way over my head. Much simpler to use the equations from Poynton.
I found the following to convert YIQ to a composite NTSC signal. It was in SMPTE 170M - 2004.
Anybody want to take a crack at converting this back to YIQ? The math is way over my head. This is a "just for fun" project so don't knock yourself out.
double N = (0.925 * Y + 7.5 + 0.925 * Q * Sin(2 * PI * fsct + 33)) + (0.925 * I * Cos (2 * PI * fsct + 33))
// RGB to YIQ
double Y = R * 0.299 + G * 0.587 + B * 0.114
double I = (0.5959 * R) - (0.2746 * G) - ( 0.3213 * B)
double Q = (0.2115 * R) - (0.5227 * G) + (0.3112 * B)
// YIQ to RGB
double R = Y + 0.955986*I + 0.620825 * Q
double G = Y - 0.272013 * I - 0.647204 * Q
double B = Y - 1.106740 * I + 1.704230 * Q
Last edited by chris319; 26th Jul 2020 at 21:24.
If you want to synthesize NTSC (which has absolutely nothing to do with VHS) yes, you can do it in software but the result is a digital stream anyway. You still have to convert it back to analog using a fast DAC so it becomes rather pointless when there are cheap hardware solutions that can directly convert RGB or YUV costing only a few $$. You would be emulating an IC like the AD720 series in software. If you really want to try it, the first place to search is for VHDL models of the AD72x series as these will have most of the math in them already.
Hi Brian -
I don't know where you got the notion of VHS tapes or hardware. This is strictly a software emulation at a cost of 0. I already have it encoding Y, I and Q. That was the easy part.
Theoretically I am generating the composite signal "N"; I just don't know how to decode it back to YIQ.