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Path: utzoo!utgpu!water!watnot!watmath!clyde!cbatt!ihnp4!ptsfa!lll-lcc!pyramid!voder!apple!dgold
From: dgold@apple.UUCP
Newsgroups: comp.sys.mac
Subject: Re: Mac II
Message-ID: <506@apple.UUCP>
Date: Wed, 4-Mar-87 12:22:35 EST
Article-I.D.: apple.506
Posted: Wed Mar  4 12:22:35 1987
Date-Received: Fri, 6-Mar-87 07:09:20 EST
References: <10231@teknowledge-vaxc.ARPA> <1338@husc6.UUCP>
Reply-To: dgold@apple.UUCP (David Goldsmith)
Organization: Apple Computer Inc., Cupertino, USA
Lines: 41

In article <1338@husc6.UUCP> hadeishi@husc7.UUCP (Mitsuharu Hadeishi) writes:
>Re: Mac having 15- versus 8- bit color
>	As far as I know (haven't seen the spec sheets from Apple yet)
>the software of the color workstation will support up to a full 16-bits
>per R, G, B.  The software queries the display device by sending it
>a 16-bit RGB value (16-bits per R, G, and B) and getting back the
>"closest" value the display device can handle.

Color QuickDraw's architecture supports 48-bit RGB (16+16+16) and up to 32
bits per pixel, chunky, planar, or chunky-planar.  The first implementation
(in the Mac II) only support up to eight bits per pixel, chunky.  The full
48-bit RGB space is supported.

In order to support multiple display devices from different vendors (with
more than one possibly connected at a time), each video card must have a
video driver, which takes care of mapping the 48-bit RGB color to the
capabilities of the device.  QuickDraw supports three kinds of video
devices:  those with a color lookup table, those with a fixed set of
colors, and those with direct RGB.  The Apple Video Card is a color lookup
table device; its color table has room for 256 entries, with a palette of
16 million (eight bits of resolution for each of R, G, and B).  Although
the color table has 256 entries, the base configuration of the card only
has enough memory to support configurations of 1, 2, and 4 bits per pixel,
allowing 2, 4, and 16 colors on screen simultaneously (out of the palette
of 16 million).  With an expansion kit (which consists of more video ram),
you can go up to the full 8 bits per pixel, with 256 colors (or shades of
gray) on screen out of the palette of 16 million.  Apple's card supports
640x480 pixels; SuperMac has a card with the same capabilities that supports
up to 1024x768 pixels (theirs is more expensive, however).  Because of
this video driver approach, Color QuickDraw is capable of supporting a
wide variety of video cards, from inexpensive fixed color (or monochrome)
cards up to to very fancy high-end devices.
-- 
David Goldsmith
Apple Computer, Inc.
MacApp Group

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