Re: Double HIgh Resolution Question

[mjmahon@aol.com (Michael J. Mahon)]

Andy McFadden wrote:

<snip>

>The trouble with DHR is that you need a 12-bit lookup table to determine
>the color of each pixel.  You have to consider the four bits that "should"
>be determining the color, plus the previous 4 bits, plus the following 4
>bits, because the color can be different depending on what came before or
>after.  And there isn't a simple logic function that explains it.  (If
>there is, it has eluded me.)

This is interesting--and strange.

What we are calling a 4-bit pixel is just the display's "interpretation"
of the luminance and chrominance components of some composite
"wiggles".

I have not examined the logic that synthesizes RGB outputs
from the composite luminince-chrominance signal synthesized
by the Apple, but I would be surprised if it took much of the
following 4-bit group into account when determining its current
outputs.

Since what we are calling a 4-bit pixel is just the display's
"interpretation" of the luminance and chrominance components
of some composite "wiggles", but we choose to focus on the
wiggles four bits at a time, then it is possible that an efficient
way to look at them is as four bits centered in an 8-bit byte,
with the last two bits of the preceding pixel and the first two
bits of the succeeding one.  This might provide enough context
to allow accurate mapping to the displayed appearance of the
middle four bits with only an 8-bit lookup table.

-michael

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