6 ms·

I know what NTSC is, and what Matlab is, what would be interesting to hear about now is how you got an NTSC signal turned into Matlab data. Was there some kind

I know what NTSC is, and what Matlab is, what would be interesting to hear about now is how you got an NTSC signal turned into Matlab data. Was there some kind of video input hardware to digitise composite video for you, or were you just working from example data? Sounds like fun either way.

anyfoo 4y ago
It's a good question! I simply sampled the composite output of my Blu-ray player using my oscilloscope, and exported it as CSV. The bandwidth for NTSC or PAL is 6MHz at best, so even the most crummy digital oscilloscope should do (provided it has enough memory to hold at least a full frame's worth of data). The only Blu-ray I had lying around was Back to the Future II, so that's what I used. Here is one of the very first pictures from my decoder, you can see dot crawl artifacts all over the place from my shoddy filtering (if I filtered at all at that stage): https://i.imgur.com/k2ZiCrH.png https://i.imgur.com/k2ZiCrH.png You can also see the insanely overkill sample rate I used (whatever my oscilloscope was set to, it could do 300MHz) by the numbers on the bottom. That's horizontal resolution, as sampled. But you won't get more than at most ~700 really discernible pixels with SD composite video's bandwidth. Finally, this picture shows everything: The (green) color burst on the left, the data in the sync gap at the top, and the vsync pulses at the bottom.
- jamiek88 4y ago
  Wow that picture is so cool. It has a ‘portal’ look to it, I feel like I’m in a sci fi future looking through a floating portal to the past. Or maybe the video output from a terminator robot being sent back to the future (pun intended) me in my evil lair. It has this unreal retro future feel that I’m struggling to put my finger on. This whole thread was fascinating as well.
  - anyfoo 4y ago
    Heh yeah, I know what you mean. It's also just really interesting to me how analog video degrades over bad transmissions[1]. With digital video, you usually don't get much more than just a disappearing stream, but analog video has/had all sorts of different failure modes, and they revealed a lot about the underlying encoding. And they all had their particular "look and feel" to it. There was also a third color modulation scheme, SECAM, which was very different from NTSC/PAL (PAL is really just "NTSC 2.0"). It added the two color signals using plain FM. When degrading, it gave rise to something sometimes called "SECAM fire", and anyone who spent some time in France back then, me included, might subconsciously remember it: https://www.scheida.at/scheida/TV_SEITE/SECAM_Screenshot_Secamfire_lowRF.jpg https://www.scheida.at/scheida/TV_SEITE/SECAM_Screenshot_Sec... http://www.scheida.at/scheida/TV_SEITE/SECAM_Screenshot_Secamfire_Scart_Insert.jpg http://www.scheida.at/scheida/TV_SEITE/SECAM_Screenshot_Seca... (Those pictures are not from me, just found on the Internet.) To the casual onlooker that probably just looks like noisy pictures, what's the big deal... But to me it's interesting because the noise is different. [1] Of course, my picture is not a bad transmission, just bad decoding.

anyfoo 4y ago

It's a good question! I simply sampled the composite output of my Blu-ray player using my oscilloscope, and exported it as CSV. The bandwidth for NTSC or PAL is 6MHz at best, so even the most crummy digital oscilloscope should do (provided it has enough memory to hold at least a full frame's worth of data). The only Blu-ray I had lying around was Back to the Future II, so that's what I used. Here is one of the very first pictures from my decoder, you can see dot crawl artifacts all over the place from my shoddy filtering (if I filtered at all at that stage): https://i.imgur.com/k2ZiCrH.png https://i.imgur.com/k2ZiCrH.png You can also see the insanely overkill sample rate I used (whatever my oscilloscope was set to, it could do 300MHz) by the numbers on the bottom. That's horizontal resolution, as sampled. But you won't get more than at most ~700 really discernible pixels with SD composite video's bandwidth. Finally, this picture shows everything: The (green) color burst on the left, the data in the sync gap at the top, and the vsync pulses at the bottom.

jamiek88 4y ago
Wow that picture is so cool. It has a ‘portal’ look to it, I feel like I’m in a sci fi future looking through a floating portal to the past. Or maybe the video output from a terminator robot being sent back to the future (pun intended) me in my evil lair. It has this unreal retro future feel that I’m struggling to put my finger on. This whole thread was fascinating as well.
- anyfoo 4y ago
  Heh yeah, I know what you mean. It's also just really interesting to me how analog video degrades over bad transmissions[1]. With digital video, you usually don't get much more than just a disappearing stream, but analog video has/had all sorts of different failure modes, and they revealed a lot about the underlying encoding. And they all had their particular "look and feel" to it. There was also a third color modulation scheme, SECAM, which was very different from NTSC/PAL (PAL is really just "NTSC 2.0"). It added the two color signals using plain FM. When degrading, it gave rise to something sometimes called "SECAM fire", and anyone who spent some time in France back then, me included, might subconsciously remember it: https://www.scheida.at/scheida/TV_SEITE/SECAM_Screenshot_Secamfire_lowRF.jpg https://www.scheida.at/scheida/TV_SEITE/SECAM_Screenshot_Sec... http://www.scheida.at/scheida/TV_SEITE/SECAM_Screenshot_Secamfire_Scart_Insert.jpg http://www.scheida.at/scheida/TV_SEITE/SECAM_Screenshot_Seca... (Those pictures are not from me, just found on the Internet.) To the casual onlooker that probably just looks like noisy pictures, what's the big deal... But to me it's interesting because the noise is different. [1] Of course, my picture is not a bad transmission, just bad decoding.