Re: [stella] tia hue luminance

Subject: Re: [stella] tia hue luminance
From: Adam Wozniak <adam@xxxxxxxxxxxxxxxx>
Date: Tue, 9 Dec 2003 20:17:30 -0800 (PST)
On Tue, 9 Dec 2003, Eric Ball wrote:
> Y' = ( COLU AND 15 ) * 0.045
> hue = 180 degrees - ( COLU / 16 - 1 ) * 24 degrees
> saturation = 0 if ( COLU / 16 == 0 ), otherwise saturation = 20 / 92.5
> U' = saturation * cos ( hue )
> V' = saturation * sin ( hue )
> 
> R' = 1.140V' + Y'
> G' = Y' - 0.3947U' - 0.5808V'
> B' = 2.033U' + Y'
> 
> Clip the values of R'G'B' to the range 0.0 - 1.0.
> 
> I'm not sure why my colors are off.  I thought it might have been that I
> reversed something somewhere, but I just double checked my spreadsheet and
> don't see any problems.  Maybe Adam will have better luck with his program.

http://cuddlepuddle.org/~adam/z.html

My calculated value agreed with your web page, +/-1, for the few colors
I spot checked.

I still think it's a little dark, and col=F is a little off.

Can I extrapolate a little?  If I wanted to add "brightness/saturation/hue"
adjustments...

would "brightness" affect the 0.045 multiplier for Y'?
would "saturation" affect the 20/92.5 value?
would "hue" phase shift the hue value?

-- 
adam@xxxxxxxxxxxxxxxx        http://cuddlepuddle.org/~adam/pgp.html
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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