Re: NTSC's Three Dots Per One Pixel

["Bryan Parkoff" <bryanparkoff@nospam.com>]

Michael,

    Thank you for the information.  I do understand that Apple II's picture
signal always outputs one dot per pixel, but video monitor displays three
dots per pixel that is called shadow mask CRT.  It does make sense that it
is how NTSC is designed to use shadow mask CRT unlike Apple IIgs' RGB
monitor.
    I am trying to simulate RGB pixel into NTSC's shadow mask CRT.  I would
not be able to find any information on the website using google search.  My
goal is to write C++ source code by translating RGB pixel into NTSC's shadow
mask CRT.  NTSC screen will look real on SVGA monitor.
    Can you please help me to find the information like source code, graphic
/ video functions including shadow mask CRT formula and YIQ formula for
translating from RGB to NTSC while I am searching right now.
    Thanks...

-- 
Bryan Parkoff
"Michael J. Mahon" <mjmahon@aol.com> wrote in message
20040626040152.16528.00000476@mb-m22.aol.com">news:20040626040152.16528.00000476@mb-m22.aol.com...
> Bryan Parkoff wrote:
>
> >   Do you see that Apple IIgs' RGB monitor displays one dot per pixel?
If
> >you type in Applesoft BASIC like below.
> >
> >10 HGR
> >20 HCOLOR=2
> >30 HPLOT 0,0 TO 100,100
> >RUN
> >
> >    It displays a violet line from (0,0) to (100,100).  Do you notice
that a
> >pair of pixels do not get close together that it only displays one dot
per
> >pixel?  Now, compare to NTSC.  Do you notice that it displays three dots
per
> >pixel?  It is because NTSC's beam to light three dots per pixel, but it
> >looks like that it is really five dots or six dots per pixel.
>
> I believe that you are confusing the dots created by the CRT's shadow
> mask with pixels.
>
> Try plotting a single point and look at the screen.  Then plot two
adjacent
> points (which will appear to be white) and look at the screen.
>
> Apple pixels are, indeed, single pixels, but when sent to a monitor
> using NTSC encoding, the bandwidth is limited and the dots are
> smeared somewhat.  If you see multiple discrete dots in a single
> Apple pixel, this is not in the video signal, but in the shadow mask
> just behind the CRT's screen.
>
> If you want to see what is actually going on, you should look at
> the Apple video signal with an oscilloscope.  That will make it quite
> clear that an Apple pixel is a single pulse, regardless of "color".
>
> The color of a displayed pixel is an artifact of the phase (timing)
> of the pulse with respect to the color reference burst.  The video
> signal is simply a sequence of pulses, one per "on" pixel, each
> of the same amplitude (even the "runt pulse" that occurs when
> a pixel pulse is cut short by a change in "color set" between
> video bytes).  It is the location and duration of these pulses
> that produce the apparent color of the display.
>
> -michael
>
> Check out amazing quality sound for 8-bit Apples on my
> Home page:  http://members.aol.com/MJMahon/