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Re: RGB colors
Knut wrote:
I'm wondering about that the gray "colors" are the same. All the emulators
do Grey 1 darker than Grey 2 but when I look at NTSC I agree with your
calculation, they are same. Is this correct?
Most definitely, yes. For Grey 1 the NTSC video circuits produce "0101
0101 0101"...., for Grey 2 it's "1010 1010 1010".... i.e. in both cases
zeroes and ones alternate. It's not difficult to see that the average
value (which determines luminance) is 0.5 in both cases. The only
difference between the two greys is the way they interact with other
colors to their immediate left or right -- the color fringe effects will
be somewhat different.
Is the difference something
that came with RGB cards and RGB output of IIc and/or IIgs?
Yes.
I think there
was a difference on PAL but I might be mistaking there
There wouldn't be a difference if the resistor values in the NTSC-to-PAL
conversion matrix were perfect, and if the two color balance pots were
perfectly adjusted. Since Apple used normal 5% tolerance resistors in
this place and since the pots might be slightly deadjusted, a slight
difference between the two greys, not in brigtness, but in hue and/or
saturation, is possible.
(it's a pity I never
grabbed an image there, the frame grabber does both NTSC and PAL). Or is
there a difference between II, II+ or IIe.
Shouldn't be. They work pretty much the same way when it comes to NTSC
or PAL video output.
I was toying with the idea to make a summing-network for XRGB (RGBI) to
create the proper colors on an analog monitor (or TV with RGB in scart). I
would use a PAL (actually GAL) to control a couple of resistors for each
color but I need to know what to make... To mimic the KEGS emulator might be
a good idea.
Depends on what you want to achieve, IIgs look-alike or NTSC look-alike.
Both should certainly be doable.
I should note that the saturation of the colors in my "calculated"
colors might be a bit lower than on a real Apple. I assumed perfectly
rectangular output. A real logic chip of course doesn't produce
perfectly rectangular output; the flanks will be less steep in reality,
which means that the result will be more sine-wave-like than a perfect
rectangular wave. This higher "sine-ness" changes the first Fourier
coefficient and thus increases the saturation.
--
Linards Ticmanis