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From: fnf@mcdsun.UUCP
Newsgroups: comp.sys.mac
Subject: Re: Mac II
Message-ID: <257@mcdsun.UUCP>
Date: Wed, 4-Mar-87 11:17:27 EST
Article-I.D.: mcdsun.257
Posted: Wed Mar  4 11:17:27 1987
Date-Received: Fri, 6-Mar-87 23:12:22 EST
References: <10231@teknowledge-vaxc.ARPA>
Reply-To: fnf@mcdsun.UUCP (Fred Fish)
Organization: Motorola Microcomputer Division
Lines: 65

In article <10231@teknowledge-vaxc.ARPA> rburns@teknowledge-vaxc.ARPA (Randy Burns) writes:
>I had heard that the Mac II would have 15 bits of color per pixel. It 
>sounds like this has been reduced to 8 bits per pixel. Is this true?

According to the advance preview posted to BIX and due for the April 87
Byte:

	"The old Macintoshes use a bitmap to represent the screen--
	there, one bit represents one pixel, and only two colors are 
	possible: black and white. The Mac II generalizes this to 1, 2, 
	4, 8, 16, or 32 bits per pixel. Apple's first video board will 
	use either 4- or 8-bit pixels, thereby allowing 16 or 256 
	different colors, respectively. On the high end, a 32-bit pixel 
	gives a  theoretical limit of 4,294,867,296 different colors 
	onscreen at one time--from a 48-bit wide palette representing 
	over 280 trillion colors. (These numbers far execeed other 
	system contraints.)"

>Also does the new mac handle its color as 8 seperate planes or is each 
>pixel a contiguous are in the bitmap.

Again, from the BIX preview:

	"The design of Color QuickDraw allows the support of three 
	different layouts of video memory. In planar layout, the video 
	display comprises one or more bitplanes, where the number of 
	colors or shades of gray possible equals 2**n, where n is the 
	number of bitplanes. Here, adjacent bits in a bitplane 
	contribute to the definition of different pixels, but the n 
	bits that define a given pixel are scattered throughout memory. 
	Color QuickDraw supports the monochrome 1-plane graphics and 
	the 8-fixed-color 3-plane graphics supported by previous 
	Macintoshes."

	"The second layout is the one Apple supports completely: chunky 
	pixels. In this layout, all the bits for one pixel are adjacent 
	and are followed by all the bits for the next pixel. Each pixel 
	is defined by 1, 2, 4, 8, 16, or 32 adjacent bits in memory. 
	This layout works well with Apple's preferred design of 
	graphics output devices, which use color lookup tables. These 
	cards use the numeric value stored in the pixel's memory to 
	index into a known table of colors from a much larger color 
	spectrum. In the case of Apple's first video card, the actual 
	(Apple calls it concrete) color is 24 bits wide, giving 
	16,777,216 colors from which to choose."

	"The last layout is a hybrid of the first two, chunky-planar. 
	This layout would have separate memory areas for the red, 
	green, and blue components of its pixels, with the individual 
	components being chunky--that is, 1, 2, 4, or 8 adjacent bits 
	describing a given component. This layout might be used someday 
	to drive a very high-resolution color device that would use 
	three slots for its three bitplanes. The current implementation 
	of Color QuickDraw does not support this, but the overall 
	design permits it."

-Fred



-- 
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Fred Fish  Motorola Computer Division, 3013 S 52nd St, Tempe, Az 85282  USA
{seismo!noao!mcdsun,hplabs!well}!fnf    (602) 438-5976
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