Looking into stuff on video generation for PAL or NTSC. Composite colour, basically:
- This is part of a discussion where someone captured a PAL NES (actually famiclone) raw video signal output signal and saved it as a PNG:
- Captures are referenced here with discussion about how the "phase alternating" part works.
- 250MHz capture
- 53.2MHz downsampling i.e. (12× subcarrier frequency).
- Note that both of these capture just one "field" of 312 lines. I found I could get the right aspect ratio by scaling up on the Y axis by 32× (using "Nearest Neighbor" scaling in Photoshop, for example, i.e. just repeating pixels rather than filtering).
- There's also a 500MHz capture referenced here.
- NOTE: I'm not sure what this is actually meant to look like. Obviously lots of colour cells. Probably comes from this. Interesting what the patterning looks like. I can see how the phase "shifts" a little on every other line, but then what's the purpose of the full inversion on the next 2 lines?
- Actually this (from above) might be a great place to learn more, including through the rest of the discussion.
- Info on Composite artifact colors.
- Lots of detail on composite CGA 1024-colour (including some details about NTSC and quadrature colour).
- A lot of NES NTSC detail here including colour phase stuff, and example C code for generating the signals.
- Video Signal Fundamentals
- Consider searching for "CVBS" to refer to "Color Video, Blanking and Sync" (aka Composite Video).
- Also search for QAM ("Quadrature amplitude modulation"). Re PAL, see: this.
- More on 640x200 dot patterns: https://forums.nesdev.com/viewtopic.php?f=2&t=7853&start=30
- More: https://forums.nesdev.com/viewtopic.php?f=2&t=15080
- Crazy QuickBASIC NES emulator code including some colour processing stuff.
- What about this?
- Here's some info on decoding PAL colour: http://www.techmind.org/vd/paldec.html (see program link at the bottom). More info from that author here.
