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by zackbloom 1314 days ago
> I went out of my way to feed the Apple ][ video into the luminance pin of an S-Video port for this segment to make the text more readable at the expense of color.

I found this to be the most interesting part of the whole post, I'd love to see a schematic of how that works.
2 comments
krallja 1314 days ago
The schematic would just be a wire connecting two pins.

    RCA             Mini DIN
    __________________________
    COMP o--------o LUM
          --------o CHROM 
     GND o--------o GND
S-Video has two pins (plus ground): luminance and chrominance. Composite has only one pin (plus ground). A composite video signal is a hack (for backwards compatibility with B&W TV) that has both of these signals (and some timing signals, called "sync", which happen outside the visible area of the image) combined together into a single "composite" waveform. De-composing the two signals is what causes color bleed and color artifacts with NTSC color images: it's not easy for a monitor to reverse the math, especially on abrupt brightness edges (like the kind computer pixels are prone to causing, with their decidedly discrete color transitions), since they look an awful lot like the color carrier shifting phase.

S-Video is exactly the same two visible signals as a composite image, but the color data gets its own dedicated pin. So, if you send a black and white composite signal on the luminance pin, and no signal at all on chroma, you get a completely clear B&W picture output, with 0 color bleed (since there is no color information).

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duskwuff 1314 days ago
Some early computer monitors had a "mono/color" switch which could disable chroma separation. Set to "mono" for text mode; "color" for games. :)
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nicole_express 1314 days ago
It's pretty easy to get a breakout cable for chrominance and luminance separately into an S-Video port; at that point I just plugged in the Apple II's output into luminance and left chrominance unconnected.

This works particularly well on the Apple II because all of its color actually comes from creating dot patterns that cause luminance to interfere with decoding of chrominance, it has no "real" chrominance signal.

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