Mexican Mystery

[wa2ise]

About 26 years ago I was working at some defense contractor, and we were using a few red and green color CRTs. One electron gun, you vary the very high voltage to change the color. This changed the energy the electrons in the beam would have when they hit the special phosper mix on the tube face, and thus cause the different colors from red to green to glow. No blue. At first you'd think there is no convergence issues as there is only one electron gun, but the very high voltage varying causes the image size to bloom or shrink. So we had to modulate the amplitudes of the horizontal and vertical deflection feeding the yoke. What fun...

This system was used only for simple graphics (like heads up displays in fighter jets) and not for displaying live video images. Disconnect the blue gun feed on a normal RGB CRT and you can get an idea what this above would look like. SO this would not be a tube you could sell to consumer TV use. Looks bad without blue. And you trade the convergence circuits used for shadowmask 3 gun CRTs for the deflection modulation circuits. You don't come out ahead in cost, and the picture looks awful, so there's no point in building color TVs this way.

[old_tv_nut]

Originally Posted by David Roper

I'm *supposedly* colorblind. FWIW here's what the blind man sees:

Despite Wayne's caption, it's the picture on the far right that's original color. The center picture overall looks very natural to my eyes, though I can see by the colorbar that yellow has become beige...or parchment.... The left picture is definitely not acceptable. It looks like a black & white photo that somebody started to hand color, but got interupted before they could start on the fleshtones.

You are correct! I thought they would show up by file name, not just as thumbnails, and the the thumbnails are in the order you describe:
Original on the right, Y+I (orange or cyan) in the center, and Y+Q on the left (green or magenta)

[old_tv_nut]

Originally Posted by oldeurope

Hi old_tv_nut,
this is not mexican colour. You wrote copyright do not repost.
Is it allowed to pose the pics in mexican colour here?
I made some screenshots of your pic in three and two colour and in red and cyan only.

Kind regards,
Darius

YOou're roight, It's not "Mexican color" as described in the article, but the Y+I version shows about the optimum choice for color axis of a two color system, whihc is more orange-red than red.

You may post your versions if you include in the posting "Original photo copyright Wayne Bretl, used by permission." Thanks!

[Tom_Ryan]

Originally Posted by old_tv_nut

BTW, it seems silly that there are limits on the image dimensions and file size you can post, but you can cut it up into pieces that total more than the original and the files will be accepted. Any comments from an administrator, please?

ZIP the file and you can send megabytes. Not sure of the limit but it's considerably much much larger than a picture file.

[old_tv_nut]

Oldeurope, what happened? I am looking forward to see your Mexican color versions.

[oldeurope]

Originally Posted by old_tv_nut

Oldeurope, what happened? I am looking forward to see your Mexican color versions.

I am not sure to show them because of copyright.
But I can sent them to you via email, please give me your email adress
in a PM.
I made a pic of the mexican parlament too, and guess what, there is no
visible difference between three and two colour .

Kind regards,
Darius

[old_tv_nut]

Originally Posted by oldeurope

I am not sure to show them because of copyright.
Darius

Hi Darius,

The original photo is copyright by me, not by anyone else, so when I tell you that you may post your versions here with the notice in the text "Original photo copyright Wayne Bretl, used by permission", that is all that you need to do.

This is a legal statement of non-exclusive license to only you to do only this. It is not permission to do anyting else with the photo or derivative work, such as post to another site. It is not permission to post your derived versions anywhere else.

Any one else wishing to use the photo needs to ask my permission in a similar way.

I want to encourage this thread of discussion, I just want to be clear that I an not generally releasing rights to that photo to be freely published or used for derivative works without specific permission in each case.

All that said, I generally give permission when asked!

[oldeurope]

Originally Posted by old_tv_nut

Hi Darius,

The original photo is copyright by me, not by anyone else, so when I tell you that you may post your versions here with the notice in the text "Original photo copyright Wayne Bretl, used by permission", that is all that you need to do.

This is a legal statement of non-exclusive license to only you to do only this. It is not permission to do anyting else with the photo or derivative work, such as post to another site. It is not permission to post your derived versions anywhere else.

Any one else wishing to use the photo needs to ask my permission in a similar way.

I want to encourage this thread of discussion, I just want to be clear that I an not generally releasing rights to that photo to be freely published or used for derivative works without specific permission in each case.

All that said, I generally give permission when asked!

Ah, sorry I did not understand that you are Wayne Bretl.

Ok, here they are. The resolution is not high because the pics are screenshots.

"Original photo copyright Wayne Bretl, used by permission",
Kind regards,
Darius

[old_tv_nut]

OK!

The pictures seem to be suffering by being screen shots (look overexposed to me).

Are you using a Windows machine? You can copy the active window to the clipboard by pressing "ALT" and "prtscrn" simultaneously. Then open the Paint program (found under Progtams ... Accessories) and paste the image into Paint. Then you can Save As a jpg file and you will have somethng to post without the imtermediate screen photo step

Actually, instead of Paint, I recommend the free program "Irfanview", (www.irfanview.com), which will allow you to easily crop and resize your images for posting.

[oldeurope]

You can copy the active window to the clipboard by pressing "ALT" and "prtscrn" simultaneously

Hi Wayne,
I can not because the mexican colour adapter is between the graphic card and the monitor. Thus the computer does not know that I am watching mexican colours.

Kind regards,
Darius

BTW:You must see the pic from the mexican parament, it is impressive!

[old_tv_nut]

OH - I forgot it's done with hardware. Can you re-take your photos and reduce the exposure?

[oldeurope]

Hi, I can not adjust the camera.
I just got the 10SP4 from Bob for my tesla tv . It takes all my spare time at the moment.
Please test the VGA adapter yourself. It is not complicated. Next time I'll build a mexican colour adapter for TV. I want to know how much is the colour
flicker and brightness loss.
The odd/even output of the LM1881 can be used for switching .

Kind regards,
Darius

[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.