## Re: [stella] tia hue luminance

 Subject: Re: [stella] tia hue luminance From: Glenn Saunders Date: Sat, 27 Sep 2003 23:31:38 -0700
It should also be noted that measuring the output of a particular 2600, especially through RF, is not the best way to judge what the chip does.

Sure, maybe it's authentic in the sense that you are getting out what you would have seen in the 70s, but it's not representing the raw output of the TIA.

There are too many ways that the signal can get altered both by the motherboard (the chroma knob for instance) or the signal path outside of the 2600 that using a capture card isn't the best approach.

So I think using a formula is better, as it represents a theoretical ideal at the chip level.

Once you have this ideal you have your baseline and at least for emulators, modify it to simulate things like signal degradation through RF or adjustments to the chroma knob if you really want to.

At 11:53 AM 9/27/2003, you wrote:
```The base equations are well known, but the specific scaling factors used by
the TIA aren't as well known.  I believe what was done for the latest Z26
was to use the RGB output of a video capture card.```

But if you are interested, here are the NTSC formulas.

```R8 = 255 * ( Y + 1.402 * Pr )
G8 = 255 * ( Y - 0.344136 * Pb - 0.714136 * Pr )
B8 = 255 * ( Y + 1.772 * Pb )```

```where
Y = ( COLU AND 15 ) / ( luminance )
Pb = saturation * cos ( hue )
Pr = saturation * sin ( hue )
hue = 180 degrees - ( COLU / 16 - 1 ) * 24 degrees
saturation = 0 if ( COLU / 16 == 0 ), otherwise some value between 0 & 0.5
luminance = some value 14 or greater```

(base formula from http://www.poynton.com/PDFs/ColorFAQ.pdf)

```----- Original Message -----
To: <stella@xxxxxxxxxxx>
Sent: Friday, September 26, 2003 2:04 PM
Subject: Re: [stella] tia hue luminance```

```> On Wed, 24 Sep 2003, Adam Wozniak wrote:
> > What equations are used to convert 4 bit hue / 3 bit luminance to
> > RGB 8/8/8 ?
> >
> > I've seen tables for the conversions, but I'd like to know what
equations
> > are used.
> >
> > I am interested in both NTSC and PAL.
>
> Nobody knows?
>
> --
> Will code for food.          http://cuddlepuddle.org/~adam/resume.html
> "The dinosaurs are not around today because they did not have a space
program."
>   -- Arthur C. Clarke
>
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