Re: NTSC Emulation

["Michael J. Mahon" <mjmahon@aol.com>]

Sheldon Simms wrote:
> MDJ mentioned NTSC video emulation yesterday and that piqued my
> interest because I have been working on Apple II video emulation by
> NTSC decoding/demodulation in software.
>
> Theoretically I could display a regular NTSC composite TV signal with
> my program assuming I had a suitable A/D converter, but as it stands
> I take some shortcuts specific to Apple II video that save some cycles
> like, for example, inferring sync signals and color burst from the current
> values of the horizontal and vertical counters, which are emulated
> Apple II counters, instead of trying to extract them from the signal.
>
> The sample outputs from the image-converting program I've also been
> working on recently were created by loading the output files into the
> video emulator and capturing the screen.
>
> http://wsxyz.net/tohgr.html
>
> I have also captured a movie (9Mb H.264) of the video emulator
> displaying a mixed Lores screen as first "brightness", then "contrast",
> and then "tint" is "adjusted".
>
> http://wsxyz.net/images/video.html

Very nice--it was just such an emulation that I envisioned being
the method of populating a table of 4096 32-bit color entries,
each corresponding to the NTSC response to the previous 12 bits
of (14MHz) Apple video signal.

Something looks a little off in your colors, however.  What filter
bandwidths are you using for Y, U, and V signals?  Then there's
the delay in the Y signal to compensate for the U and V filters...
Gamma may also be an issue...

-michael

NadaNet 3.1 for Apple II parallel computing!
Home page:  http://home.comcast.net/~mjmahon/

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