PowerMac 8550 Video Problems with YDL 3.0

[Tim Seufert]

On Thursday, August 21, 2003, at 03:56  PM, Longman, Bill wrote:

>> I found another thread in the message list from 02/2001 where
>> someone stated
>> that the on their 8600 16 didn't work but switching to 15 did.
>>
>> I'm not sure what the heck 15bit depth is but it works!
>
> 11111 - R
> 11111 - G
> 11111 - B
>
> Where does the other bit go? (On 16, that is....)

Pixels are still 16-bit words, they just don't use the 16th bit.  It's 
along for the ride, so to speak.

Apple uses 15-bit color rather than 16 because they actually care about 
color.  Adding 1 extra bit to one of the channels (typically it's added 
to green because your eyes are most sensitive to green) causes some 
problems with color.  For example, usually you'd like all zeroes in 
every channel to be black, and all ones to be white, but doing so with 
565 RGB means you end up having problems representing grays: there will 
be few if any true gray shades representable, so you have to live with 
tinted grays.  The solution for that problem requires red and blue to 
have less intensity at all ones than green, which can also be 
considered a problem.  (But in most implementations I've ever seen, 
they just live with tinted gray levels.)