NTSC and PAL video emulation

[NJRoadfan]

Mods feel free to move this if this isn't the right location.

One of my other interests has been computer emulation of various sorts. Some recent work has gone into accurately emulating the composite video output of classic computers to look more like the real hardware. This work might be of interest to the video restoration community for simulating video to test various filters... or to take it in the other direction, to add a "patina" to modern video sources for an added retro touch.

Check it out at: http://code.google.com/p/openemulato...VideoEmulation

[jmac698]

Thanks, I think it's cool There's some details you need to know, for example c64 has odd-only video lines at 60Hz. There are some advanced tweaks to output interlaced video too.
Some links:

http://techmind.org/vd/paldec.html
software PAL/NTSC video decoder (windows), includes the famous "BBC PAL" artefact-free color decoding.

http://sites.google.com/site/h2obses...C128/Interlace
Details of vic-ii video signal and software interlace trick

I see that you captured a raw PAL frame, I was wondering if you could capture a frame from a VCR? I'd really like to investigate jitter, and write a software decoder to remove it.

Too bad I don't have a Mac, but I'd like to see a C version that I could turn into an avisynth plugin, this would send video through an encode-decode loop to create a simulated composite signal.

[NJRoadfan]

The work shown isn't mine, although I have been investigating adding it to an emulator I have contributed to in the past. The source code is available and has been used in other emulators on various platforms.

Most older computers and game consoles like the C64 output NTSC/PAL video in a tweaked "240/288p" mode, they trick the monitor by eliminating the half scanline at the beginning and end of the field. It causes grief for some capture cards and TBCs, particularly with S-video inputs. The chroma channel will show a checkerboard effect via S-video if the card doesn't properly detect 240p video, composite seems unaffected since the video has to go through a comb filter. A lot of cards won't even lock onto the signal to begin with. This is likely the reason why some capture cards won't show a VCR's onboard menus or blue screen, most are output as 240p to avoid flickering.

[jmac698]

Yes there's source but I don't want to try to dissect GPU code, now straight C I could read. I guess it's OpenGL code.

[admin]

Quote:

Originally Posted by NJRoadfan

a VCR's onboard menus or blue screen, most are output as 240p to avoid flickering.

Interesting!

[gortu]

Hi everybody!

I'm the author of the OpenEmulator NTSC/PAL emulation! I found this post just by chance while googling for my project, and wanted to join the discussion as I find it very interesting :-).

Just a quick intro: it all started with an Apple II emulator. Then I wanted to be able to add devices on the fly. Then I decided to emulate any kind of computer, and in the end I decided to use actual composite signals, so the computer-monitor interface would be as close as possible to the original. In short, I'm in big trouble :-D.

I'm also glad to hear about all this positive feedback here in this forum! So if you can think of any other kind of (d)effect of real NTSC/PAL monitors, please let me know!

[jmac698]

Hi,
I'll think about that. Could you tell me your filter taps and type for separating the chroma and filtering the luma. I think that's all I need to make my composite effect filter.
Thanks
p.s. also could you digitize the full raw frame from a VCR, I'd be very interested! Just record some rec601 colorbars.

[gortu]

Hi there!

Unfortunately I don't have a video digitizer available, and used a PAL video frame I was able to find on the web.

Regarding the filter: It's a simple Lanczos lowpass filter with variable cutoff. I also multiply this filter with a Tchebyshev window, so that the stopband is consistently below a certain level (I use 50 dB, which corresponds to the SNR of a typical eye).

Hope this was useful.

Best wishes,

Marc.-