Mexican Mystery

[yagosaga]

Originally Posted by oldeurope

Next time I'll build a mexican colour adapter for TV.

If you try it, why not thinking about building a mexican color adapter for NBTV signal with 32 lines vertical and 12.5 frames/second? I need a converter which makes it possible to record video, color and sound on a single CD. With two colors it might be easier to realize it than with true RGB. One channel is for sound and the second channel for video with color. If you use an alternating subcarrier of 11 KHz for example for mexican color, and a hue control, it might be possible.

Kind regards,
Eckhard

[Dave A]

I just found this web article today while on another search. It does describe a two-color attempt by the author in his youth. The portion that we would be interested in is quoted.

"I modified my Emerson rear-projection TV console to accommodate two Norelco video projectors. There wasn't space for a third, so I settled on displaying the luminance signal on both projection CRTs while feeding the chrominance signal to a push-pull chroma demodulator and recovering the I component. The +I chroma went to the grid of one CRT, the -I signal to the other. In the common light path I mounted a dichroic mirror which reflected the orange colored Y+I modulated light, while it transmitted the Y-I blue modulated light.

Both images arrived at the screen and were laboriously registered. I couldn't reproduce pure red, green or blue, but on the other hand, flesh tones looked natural, and there were no green or purple people on my screen. This project may have lead to my being hired by Tektronix and what followed was a wonderful career building instrumentation for NTSC, PAL, PAL-M (Brazil) and SECAM applications."

The full article can be seen at;

http://tvtechnology.com/features/dig...s_rhodes.shtml

Who wants to try this version?

Dave A

[wa2ise]

All these things are fun to play with, but you need 3 separate signals to get true color TV. At the TV studio you start with R, G, B. That's converted to Y, U, V or Y, I, Q or Y, R-Y, B-Y. As the human eye's ability to distinguish differing color detail is about jalf that of differing brightness detail levels, Y is twice the vertical and twice the horizontal resolution of U or V. So we save some bandwidth with this conversion. At the TV set, the chroma subcarrier (which is a quadature AM signal, U is sine, V cosine gives us the R-Y and B-Y or UV or IQ. Then add Y to R-Y and you get R, same for B. What about the green? Well, if you invert R-Y and multiply by a coefficient, and invert B-Y and multiply by another coefficient (so you'd get a vector pointing "southwest"), That becomes G-Y. and add Y and you have green. RGB.

The above Mexican schemes only have 2 signals, roughly a red signal, and the 2nd is a cyan signal. No luma only. Thus you can never get true RGB from just that.

[oldeurope]

Originally Posted by wa2ise

The above Mexican schemes only have 2 signals, roughly a red signal, and the 2nd is a cyan signal. No luma only. Thus you can never get true RGB from just that.

Don't agree , if you are able to delay a frame, it is possible .
The mexican system uses two colours because the picture is double
interlaced. If you have a tripple interlace it can make RGB . The problem
here is colour flicker . Today this could be solved with frame stroe devices,
this causes of course artefacts in quick moving colours... and this makes
it all complicated .
The advantage of the described mexican colour is that it is very easy.
For example it can be recorded on a B&W vcr without any modificationes .
If you watch some old colour recordings, with its bad noisy colour, I think
the mexican system gives the better results here.

Kind regards,
Darius