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From: johnl@auscso.UUCP (John Lange)
Newsgroups: mod.computers.workstations
Subject: Graphics on SUN's;  SUN tape drive operations
Message-ID: <14@auscso.UUCP>
Date: Mon, 16-Mar-87 12:55:32 EST
Article-I.D.: auscso.14
Posted: Mon Mar 16 12:55:32 1987
Date-Received: Tue, 17-Mar-87 04:17:42 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: world
Organization: Austin UNIX User's Group, Austin, Tx.
Lines: 38
Keywords: Choosing 256 colors, speeding up tape drives, bug in tape driver
Approved: works@red.rutgers.edu

I have recently begun to play with the graphics capabilities of our
SUN3/160.  It has a color display that is capable of displaying a
total of 256 colors on the screen at one time.  This is done by
choosing from a pallette of 2^24 colors.  To set the colormap of 256
colors, it is necessary to specify red, green, and blue indeces of
[0] to [255].  In my endeavors, I have discovered that approx. the
first 100 levels of indeces in the red, green, and blue come out
looking virtually identical - they are all VERY dark.  This may be a
hardware problem with our particular SUN.  It seems a bit wasteful to
have 256 indeces when only the last 150 or so look different.  It
would be MUCH more practical and useful to make the 256 indeces about
equal perceptually.  Most high quality pictures are digitized in this
manner.  Thus, to display a picture using as many perceptually
different colors as possible requires the use of logarithmic scaling
of the indeces.  THERE'S GOT TO BE A BETTER WAY!!

My next question is also SUN specific. Does anyone know why the tape
drives only work at 1600 bpi???  Even the lowly IBM RT can save at
6250 bpi.  I can't think of a good reason why the SUN workstations
couldn't save at 6250.  The speed increase would be about a factor of
4 with very little additional hardware or software.  While I'm on the
subject, why is the default blocking factor so low??  All SUN's that
I have used work with at least 126, and again, it's a lot faster.


One other bug on the SUN's: I have a problem with our machines
getting hung when the tape is not rewound before usage (with the 'mt
rewind' command).  It only shows up once in a while - not every time.
When it happens, it looks like it's hung in the tape driver.  I have
read of other people's similar problems, and am wondering if anyone
has found the cause or a solution.


Reply to:
John Lange
Radian Corporation
voice: 512-454-4797 x. 5747
net: altair!johnl or whatever it says at the top of this