ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab) (06/29/88)
[ "Penny is cute..." ]
What are the YIQ values of the C64 colors?
More specifically, what are their CIE-XYZ coordinates, and
subsequently, their RGB equivalents?
And I don't mean theoretical ideal values; I want as close to
reality as possible.
I'll settle for YIQ, since I can get to RGB from there...
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Leo L. Schwab -- The Guy in The Cape ihnp4!pacbell -\ <-- Under destruction
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"Hmm, you're right. Air is made up of suspended meat loaf." -- Josh Siegeldwl10@amdahl.uts.amdahl.com (Dave Lowrey) (07/01/88)
Status: R > What are the YIQ values of the C64 colors? How deep is a hole? :-) Seriously, though... the C-64 generates a pseudo-NTSC directly, without benefit of actual I & Q. Because of the simplicity of the circuitry used, the subcarrier phase is somewhat predictable but its amplitude is whatever it turns out to be, so there's no way to accurately compute the resulting I & Q values. At best, one can measure them on a specific C-64. Of course, neither the phase nor the amplitude of the subcarrier are absolute color predictors anyway; the phase is modified by the setting of the "tint" control on the monitor, and the amplitude by the "color" control. > And I don't mean theoretical ideal values; I want as close to >reality as possible. You'll have to settle for theoretical... A C-64 is hardly a precision color-generation instrument, and there can be wide variations between units. Also, there has been more than one design of the C-64's video system, which introduces further differences. Even more significant is the variation which exists between monitors and monitor interfaces. The following info applies to NTSC C-64's; subcarrier phase is in degrees leading, referenced to the color burst: Color Luminance S/C Phase Theoretically Correct Phase ---------- --------- --------- --------------------------- Black 0% none no subcarrier modulation White 100% none no subcarrier modulation Red 25% +90 +76.5 Cyan 75% +225 +256.5 Purple 50% +135 +119.9 for Magenta Green 50% +315 +299.9 Blue 25% +180 +192.0 Yellow 75% +0 +12.0 Orange 50% +45 +34 approximately Brown 25% +45 Lt. Red 50% +90 +76.5 Dk. Grey 25% none no subcarrier modulation Med. Grey 50% none no subcarrier modulation Lt. Green 75% +315 +299.9 Lt. Blue 50% +180 +192.0 Lt. Grey 75% none no subcarrier modulation Theoretical I axis: +57 Theoretical Q axis: +147 You'll notice the absence of saturation information. Saturation on the C-64 is essentially uncontrolled. The amplitude of the chroma signal is either zero (for black/white/grey) or some constant value (for all other colors). When connected by the 3-plug cable to an external monitor, that's about all you can say about saturation. The saturation level's all up to the monitor. For the C-64's composite output, the chroma amplitude is excessive for those colors which have luminance levels of 25% or 75%, especially on older units. Well there you are then. I doubt that this dissertation has been very helpful, but I do hope it was at least enlightening. -- Doug Pardee {ames,hplabs,sun,amdahl,allegra}!oliveb!edge!doug Edge Computer Corp., Scottsdale, AZ uunet!ism780c!edge!doug -- ------------------------------------------------------------------- "This isn't Heaven, this is Cleveland!!!!" Dave Lowrey Amdahl Corp. Houston, Texas (713)-850-8828 ...!{ames,sun,decwrl,uunet,....}!amdahl!dwl10 [ The opinions expressed <may> be those of the author and not necessarily those of his most eminent employer. ]