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From: izumi@fugitive.berkeley.edu (Izumi Ohzawa)
Newsgroups: comp.sys.next
Subject: Re: NeXTdimension board - multiple heads on a cube?
Message-ID: <1990Sep25.062019.20821@agate.berkeley.edu>
Date: 25 Sep 90 06:20:19 GMT
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In article <50958@brunix.UUCP> rca@cs.brown.edu (Ronald C.F. Antony) writes:
>In article <1990Sep24.084343.3794@agate.berkeley.edu> izumi@fugitive.berkeley.edu (Izumi Ohzawa) writes:
>>How about LUTs (Color lookup tables)?  Do they exists on NeXTdimension
>>boards?
>
>Can you tell me what colors you want to look up that 24-bit color does
>not bring to a screen directly without a look-up?

There are uses for LUTs even for 24-bit color systems.  I suspect
that most people associate LUT as a workaround to produce
reasonable looking color image with 8-bit 256 color systems.
That's not entirely correct.

One thing LUT makes it easy is to do accurate color calibration
to compensate for variations of RGB guns in the display and
D/A converter gain imbalances.  Any system boasting "true color"
capability should be able to calibrate color accurately if the
user wants to do it.  I think Display PostScript is the wrong
place to do this.

Another thing LUT allows is LUT animation, the kind you might see
in weather forecasts on TV where, e.g., jet stream snakes
over the map of the continental US, represented as alternating
stripe patterns.  That kind of animation where image change
must occur in non-rectangular area extending potentially the whole
screen is next-to-impossible by bit-blitting to VRAMs.
Even with NeXT's fast compositing by i860, I am not sure
the NeXTdimension board can do it.  Can it do compositing to
the whole screen area within a ONE frame period (14msec),
assuming you can do alternately map two separate VRAM areas
to the displayed area (Large memory config. for NeXTdimension
seems to allow this kind of use, where you can write into
one frame while the other area is displayed.).

AT&T, in the old TARGA board, made the same mistake of
not putting LUTs on their board.

Most of the old style true color systems such as ADAGE
have LUTs, in fact that has TWO LUTs.

Actually, if NeXTdimension board uses BrookTree RAMDAC, then
it must have LUTs.  Let's see the picture of the board...

What do you say?


Izumi Ohzawa, izumi@violet.berkeley.edu

I am not sure if