CTIA/GTIA Palette - Obtaining RGB Triplets

[ColecoFan1981]

Hi,

 

Please help me: Is there any way to determine what the RGB triplets to all of the standard 16 CTIA (Colleen's TIA) / GTIA (George's TIA) colors??? Of course, this may involve using some conversion formulas as devised by Charles Poynton and others. Again, I am searching for help on how to obtain values that I can use with the Poynton formulae (YPbPr to RGB, YIQ to RGB, etc.).

 

This page mentions the names of the sixteen C/GTIA colors, but are described only in value, hue and luminance (disregarding phase angle and chrominance).

http://www.atariarchives.org/agagd/chapter1.php

 

This page explains, somewhat, the colors and their phase angles, but still it lacks some decent formulae:

http://www.xmission.com/~trevin/atari/video_notes.html

 

Thank you,

 

 

 

Ben Edge

[gauntman]

There was a fairly in-depth discussion of this recently. This thread might provide what you are looking for:

http://www.atariage.com/forums/topic/107853-need-the-256-colors/page__st__25

[ColecoFan1981]

Thanks, however, I have one problem with a formula: Although the "S" means "saturation," do I have to use different color saturation values in this one equation?

 

The formula goes as such:

R = Y + S * sin(angle)

G = Y - 0.5094 * S * sin(angle) - 0.1887 * S * cos(angle)

B = Y + S * cos(angle)

 

Again, would S be the same value for all three components in the equation??? In determining the relationship between RGB and black and white, it was found each of the three RGB components contribute the following amounts to the overall brightness:

Red = 30% (0.3)

Green = 58.9% (0.5889)

Blue = 11.1% (0.1111)

 

Thank you,

 

 

 

Ben

Edited October 9, 2009 by ColecoFan1981

[atariksi]

Thanks, however, I have one problem with a formula: Although the "S" means "saturation," do I have to use different color saturation values in this one equation?

 

The formula goes as such:

R = Y + S * sin(angle)

G = Y - 0.5094 * S * sin(angle) - 0.1887 * S * cos(angle)

B = Y + S * cos(angle)

 

Again, would S be the same value for all three components in the equation??? In determining the relationship between RGB and black and white, it was found each of the three RGB components contribute the following amounts to the overall brightness:

Red = 30% (0.3)

Green = 58.9% (0.5889)

Blue = 11.1% (0.1111)

 

Thank you,

 

 

 

Ben

 

The standard equation for luminance is Y = 0.299*R+0.587*G+0.114*B.

[ClausB]

Here's Atari's say on the topic, from this document:

http://www.atariage.com/forums/topic/134096-antic-on-a-breadboard/page__p__1617584entry1617584

[Rybags]

From what I've been led to believe, the actual colour saturation level doesn't change at all relative to luminence.

 

As such, luma values 0-2 are over-saturated, and the ones near the top of the scale tend to be a bit washed out.

 

Aside from all this stuff, also note that the colour wheel is different for PAL. Colour 3 is closest to true Red, colour 4 is actually closer to violet.

[ClausB]

Here's Atari's say on the topic, from this document:

http://www.atariage.com/forums/topic/134096-antic-on-a-breadboard/page__p__1617584entry1617584

If you prefer tables over graphs:

[Kr0tki]

Also, you might find this topic interesting.