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Re: Apple II Video Generator

On Saturday, October 20, 2012 10:15:19 PM UTC-5, Kevin wrote:
> ugh stupid google ... let me confuse you some more 10 HGR2 20 HCOLOR = 2 30 HPLOT 0,0 40 CALL -3082 omit that part, I just hit enter while editing the message, its the same, I thought I saw another waveform packed in there but it was just noise. >Let's talk about luma wave while color burst is NOT enabled. >How do NTSC monitor interpret square wave into monochrome? I suspect all 15 >colors run at 7 MHz as true grayscale as monochrome. >If NTSC monitor's frequency is higher enough to sustain 14 MHz instead of 7 >MHz, then grayscale does not show and true black & white monochrome shows. >Are you positive sure monochrome does not use luma wave? >What is the filter name do NTSC monitor use to display grayscale as monochrome? its pretty simple, NTSC is a analog signal, the apple is sending out a digital signal so its either on or off, thus a black or white only mono signal. In normal video applications that voltage can be anywhere it wants to be between black and white, giving shades of grey.

I understand, but NTSC monitor does not provide sufficient information how square wave is converted into luma and chrominance waves.

I will discuss chrominance later.  Let's talk about luma.  NTSC monitor is supposed to show only five colors in monochrome.  Five colors are black (0%), dark gray (25%), gray (50%), light gray (75%), and white (100%).

The NTSC monitor is supposed to use luma by recognizing the percentage between 0% and 100%.

Let's talk about 16 colors.

If color=1, 2, 4, 8, 5, & 10 is chosen, then dark gray (25%) is used.
If color=3, 6, 9, & 12 is chosen, then gray (50%) is used.
If color=7, 11, 13, & 14 is chosen, then light gray (75%) is used.
If color=15 is chosen, then white (100%) is used.

Are you going to agree that all 5 colors in monochrome run at 7 MHz inside NTSC monitor?

I do not know how, but I try to figure out.

If NTSC monitor runs monochrome at 7 MHz, then 80 column text is 75% readable.
If NTSC monitor runs monochrome at 3.58 MHz, then 80 column text is 50% unreadable and 40 column text is 75% readable.

If RGB monitor runs monochrome at 14 MHz, then both 40 / 80 column text are 100% readable.

Bryan