Re: [stella] tia hue luminance

Subject: Re: [stella] tia hue luminance
From: Adam Wozniak <adam@xxxxxxxxxxxxxxxx>
Date: Thu, 11 Dec 2003 08:11:17 -0800 (PST)
On Wed, 10 Dec 2003, Glenn Saunders wrote:
> At 08:05 AM 12/10/2003, you wrote:
> >The only way to get a true white for col=0 lu=7 is to use a ypmult >= 1/14.
> >This tends to wash out the other colors though.
> What do you consider a true white?
> I know from my Toaster/Flyer days that you can't generate a video-legal RGB 
> 255,255,255.  The top end of composite video is something around 190-220 or 
> so.  I can't remember the actual cutoff.  Beyond that it generates IRE 
> values above the legal threshold.
> NTSC has a compressed colorspace and therefore can not generate a full 
> 24-bit display.  The blacks are not true black and the whites are not true 
> white.  I think the blackest black in NTSC is something around 34,34,34.

Eric Ball's equations yeild #000000 for col=0,lu=0 (blackest black)
and #A0A0A0 for col=0,lu=7 (whitest white).

Before your post, I would have expected them to range from #000000 to
#FFFFFF, because I'm a sort of an algorithmic purist.  But now I see we're 
trying to emulate real hardware, or idealized real hardware, or some similar
critter, and I have no clue what to expect.

> Now, it's been stated on multiple occasions that the 2600 doesn't generate 
> a totally in-spec NTSC signal so I'm not sure if its blackest black and its 
> whitest white even conforms to NTSC guidelines.

Which makes it even worse.

Will code for food.
"The dinosaurs are not around today because they did not have a space program."
  -- Arthur C. Clarke

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