Re: Deep Thoughts => More than 3200 or More than 16 grays

[johnmac@fawlty.towers.oz.au (John MacLean)]

In article <1993May11.034555.20918@fawlty.towers.oz.au> neville@fawlty.towers.oz.au (Neville Smith) writes:
>>Question:  With the nice pallette switch techniques, would it be possible for
>>one to re-draw two different pallettes.  The eye would most posibly merge
>>the images into one.
>>--Ken >Wirehead< Wronkiewicz
>
>Are you possibly talking about the following idea :
>Set up two different pallettes (sp?).
>Then every alternate time the electron beam redraws the screen,
>flip the SCBs to the alternate pallette (or flip the pallette back and forth).
>
>Thus say we have gray1 and gray2 in the same colour position in the pallette.
>The first redraw we would see gray1, and the second time we'd see gray2
>in effect producing gray1.5.
>
>This way we'd get 8192 possible colours.
>
>plusses :	- should be just as easy if not easier than 3200 to implement.
>		- there are quite a few 32 colour gifs (made on amigas?)
>
>minuses :	- effectively a 25Hz screen rate (or 30 for Europeans (US?)).

On each scan line you either have:

A) The pixel values constant, but the palettes flipping, in which case you
only get 16 colors per scanline, or 3200 colours (even if each colour is
1/2 way in between the colors in each of the flipped palettes).
You may well get a choice of more effective colors, but this would not help
you very much as the number of effective colours on the screen at any one
time would not increase.

B) The pixels and the palettes flipping on each screen refresh.
This should effectively give you up to 16 * 16 = 256 colors per scanline.
(ie: for each pixel/palette value on refresh 1, you could have 16 different
pixel/palette values on refresh 2).
This equates to a maximum of 512000 colors per screen.
Unfortunately, approach B) does not work (on a stock GS), because there is
only just enough time to flip palettes, let alone pixel values, on every
refresh.

You should however be able to use approach B if you have a VOC installed,
because you have two video buffers (one in bank $E0 and one in bank $E1).
I started work on it once, but gave up - it had to be under P8 because
you can't use the $E0 memory when in GS/OS, and who would want it after
all.

>I think the FTA(ACS) did this on their Animaga disk.
>They had a screen showing 32 shades of gray.

You can't have 32 pure shades of gray (ie: Red=Blue=Green) even in 3200
mode because there are only 16 shades of red/blue/green.
You can get more by adding bluey-grays, greeny-grays, and redy-grays
(for want of better terms).

>Neville Smith
>neville@fawlty.towers.oz.au	BH +61 2 427 2999	Have a nice compile.

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