Subject: Re: Color Depth (was: Re: NetBSD and Battery Level tool?)
To: None <port-mac68k@netbsd.org>
From: Michael G. Schabert <mikeride@prez.org>
List: port-mac68k
Date: 08/17/1999 15:02:17
>I know I'm not telling most of you anything new but FWIW this is 16 bit
>colour, e.g. 2^16 = 65536.  32768 is 15 bit e.g. 2^15.  16bit is a
>supported resolution, 15 bit is not, in the monitors control panel.  In
>my NeXT color Station it has 12 bit color (4096) w/ a switch on the fly
>color map which allows it to drive large monitors w/ near
>photo-realalistic, albeit slow, output.

Although technically, there is no such beast as 16-bit color on the Mac,
the same as there's no such thing as 32-bit color. Video color tables
generally go:
B&W (1-bit)
4-color (2bit)
16-color (4bit)
256-color (8bit)
32768-color (CALLED 16-bit)
16.7mill-color (CALLED either 24-bit or 32-bit, depending on the manufacturer)

The reason that they add in the extra bits is because there really is that
much info travelling down the line...the extra bits are just used for
"extra" control info instead of the color data itself.

> Umm, well actually on the Mac 16-bit colour is actually 15-bit colour. You
> have 3 colours, and 3 doesn't go into 16, so they pack 3 5-bit values into
> a 16-bit word & don't use the upper bit.

Well, it's used...just not for the CLUT.

>Does that mean the pb540c does 32768 colors and NetBSD is reporting it
>wrongly as 65536 colors?

Basically, yes...it just knows that there's a 16-bit signal coming down the
line.

Mike
Bikers don't *DO* taglines.