Re: Decoding in bidirectional mode: 4bpp?

• To: Nelson Minar <nelson@santafe.edu>
• Subject: Re: Decoding in bidirectional mode: 4bpp?
• From: Craig Milo Rogers <rogers@ISI.EDU>
• Date: Fri, 02 Feb 96 08:35:55 PST
• Cc: linux-connectix@crynwr.com
• From ISI.EDU!rogers Fri Feb 2 12: 43:46 1996
• In-Reply-To: Your message of "Fri, 02 Feb 1996 01:53:25 MST." <199602020853.BAA02987@nelson.santafe.edu>

>I haven't quite figured out the 4bpp support yet. I think I basically
>understand it: 3 pixels are packed into each 2 bytes you read out of
>the port, the grey coding is the same as the strange 4bpp coding used
>in the unidirectional mode.
>
>But I'm getting weird results. Scan line 0 is just fine, the top row.
>Scan line 1 is (almost*) entirely useless, though, and scan line 2 is
>also useless. Then scan line 3 is picture data again, and represents
>what'd you'd expect to see on scan line 1. Ie: only every third row is
>valid. To see the effect, compare

	Based upon analogies with fax formats, I speculate that you
might need to reset your pixel-unpacker at the beginning of each scan
line, ie, each new scan line might need to start in a new two-byte 
frame.  This is just a guess.

					Craig Milo Rogers

• What should I get?
• From: Ben Sinclair <ben@netins.net>

• Decoding in bidirectional mode: 4bpp?
• From: Nelson Minar <nelson@santafe.edu>

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