Re: NTSC's Three Dots Per One Pixel

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

Michael,

    Okay, I have downloaded MAME32 already, but I don't know how to install
Apple II's ROMs into it because it has no documents for Apple II to work
with MAME32.  Please provide the information as possible.  Thanks...

-- 
Bryan Parkoff
"Michael J. Mahon" <mjmahon@aol.com> wrote in message
20040627132209.11511.00000707@mb-m11.aol.com">news:20040627132209.11511.00000707@mb-m11.aol.com...
> Bryan Parkoff wrote:
>
> >"Michael J. Mahon" <mjmahon@aol.com> wrote in message
> >20040626202439.12238.00000767@mb-m01.aol.com">news:20040626202439.12238.00000767@mb-m01.aol.com...
>
> <snip>
>
> >> I didn't bother to invert the RGB-to-YIQ matrix an earlier respondent
> >> supplied, but I did happen to come across an YCrCb-to-RGB matrix.
> >> There are various such matrices dependent on exact color models,
> >> but this is one typical of TV (with all components from 0..256):
> >>
> >> R = 1.164*(Y-16) + 1.596*(Cr-128)
> >> G = 1.164*(Y-16) - 0.813*(Cr-128)-0.392*(Cb-128)
> >> B = 1.164*(Y-16) +2.017*(Cb-128)
> >>
> >> Note that the Cr and Cb values are excess-128 signed, while the
> >> Y values are absolute.  Also note that in TV signals, there is a
> >> luminance "setup" of 16 units to provide margin for the blanking
> >> signals to be "blacker than black".
> >
> >    I agree with you that one pixel is stretched to cover mask holes on
> >Apple NTSC Monitor.  I have no idea why stretching pixel is done that it
> >looks like 5 dots (mask hole) for violet and green color and 6 dots (mask
> >hole) for white color.
>
> For one thing, white is only produced in Apple II video by the
> illumination of two _adjacent_ pixels, each having "complementary"
> colors in the IQ colorspace--that is with 180 degree phase
> difference, such as green-violet, or blue-orange.
>
> >    I have put violet color and green color into YIQ.
> >
> >    Look at my example.
> >
> >Y = 0.299(221) + 0.587(0) + 0.114(221) --> 91
> >I = 0.596(221) - 0.274(0) - 0.322(221) --> 61
> >Q = 0.211(221) - 0.523(0) + 0.312(221) --> 116
> >Violet
> >
> >Y = 0.299(0) + 0.587(221) + 0.114(0) --> 130
> >I = 0.596(0) - 0.274(221) - 0.322(0) --> 61
> >Q = 0.211(0) - 0.523(221) + 0.312(0) --> 116
> >Green
>
> There is something wrong here.  Violet and green are complementary,
> but your conversion has them differing only in luminance--like dark green
> and light green.  (Also, you are converting _into_ YIQ space from RGB,
> when I thought you wanted to convert in the other direction.)
>
> >    The problem is that SVGA has RGB 24 Bits per pixel.  Red is 8 Bit,
Green
> >is 8 Bit, and Blue is 8 Bit.  Each pixel contains four bytes into video
> >memory before it can display in SVGA screen.  I can't figure that Y
should
> >be in Red byte, I should be in Green byte, and Q should be in Blue byte.
It
> >does not work that way.
> >    It is why I have to create color palette for YIQ so color palette for
> >YIQ is always in RGB 24 Bits.  Do you know what I mean?
>
> You are doing it backwards.  You need to convert from the YIQ space to
> the RGB space if you want RGB pixels.  The usual formulas work with
> 8-bit representations of the components, so they naturally produce
> 24-bit pixel values.
>
> If you want to "emulate" Apple NTSC video on a high resolution screen,
> I'd suggest using DSP techniques to filter the chroma signal from the
> Apple video signal (a signal which is either 0 or 255), with appropriate
> bandpass filtering, quadrature demodulation, and subsequent matrixing
> into RGB.  Perhaps this is what you are intending.
>
> If you don't understand digital filtering, demodulation, etc., then you
> will need to read up on this.  (Perhaps MAME has already done the
> job, but I haven't looked at it.)
>
> -michael
>
> Check out amazing quality sound for 8-bit Apples on my
> Home page:  http://members.aol.com/MJMahon/