Re: [stella] PAL<->NTSC colors

Subject: Re: [stella] PAL<->NTSC colors
From: Eckhard_Stolberg@xxxxxxxxxxxxxxxxxxxxx (Eckhard Stolberg)
Date: Wed, 16 Apr 1997 12:52:06 +0200
>I've finally burned an Eprom in order to run Eckhard test programs.
>The description of PAL colours that Eckhard sent some time ago seems quite
>accurate - perhaps 'gold' is more 'brown-gold' than 'gold' - but I think
>that finding accurate descriptions isn't so important.

Thanks for testing it. Does that mean you see grey four times too, but no real

>Instead, in order to write a multi-standard game, here are some things that
>I must understand:
>- Is the number of hues the same in PAL and NTSC, or does one of the two TV
>standards have more colours?

There should be 16 hues on both systems, but there is not nessessarily a
corresponding hue for each hue in the other system.

>- How can colors be mapped between the two systems, I mean can I write a
>table made of lines like: NTSC X (green) = PAL Y (the same green), or at
>least: NTSC X (green) = PAL Z (the PAL green nearest to NTSC green)?

The colours are encoded in YIQ on NTSC and in YUV on PAL.

Y stands for the luminance, but I don't know if they are exactly the same on 
both systems. Other than on the NTSC emulators the darker colours appear
allmost black on my PAL TV whereas the brighter colours appear allmost white,
but that might be due to my badly tuned TV set.

IQ and UV are coordinates in a hue plain. Imagine a square with the hues green,
red, magenta and cyan in it's corners. Each of these hues runs from full
intensity in it's corner to no intensity in the other three corners. So on the
side between green and red there would be yellow and in the center of the sqare
would be grey.

NTSC uses as it's coordinate system I (cyan-orange balance) and Q (magenta-green
balance), whereas PAL uses U (red-cyan balance) and V (yellow-blue balance).
Since the TIA chip is the same for both systems it produces the same coordinates
in different coordinate systems. Therefore it produces totally different colours
on PAL and NTSC.

Someone with more knowledge on this subject than me could probably calculate RGB
values for both systems, so that we could see whitch colours correspond, but I

I really hope I got all this right.

Ciao, Eckhard Stolberg

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