Re: b and w mjpeg prob (new cornell)

Jason Williams (streak@ccwf.cc.utexas.edu)
Wed, 20 May 1998 01:14:39 -0500 (CDT)


On Tue, 19 May 1998, ike relucio wrote:
> i think you completely missed the point here Jason.
>
> the question was why is it that in WP 3.x, you can use the MJPEG video codec
> to send B&W video from the camera while the new cornell returns an
> unsupported video capture setting. Both the new cornell and WP 3.x use the
> same PMJPEG.DLL codec file do they not ?

I believe it has nothing to do with the codec itself, but rather how White
Pine uses ActiveMovie. As I understand it, ActiveMovie allows for greater
flexibility between formats and was one of the reasons White Pine moved to
it (so their software could be compatible with more capture cards (ie:
DirectDraw ones)). If you notice, quickcam users can't send grayscale
with the 2.X versions from WP either (which didn't use ActiveMovie).

In looking at Paradigm Matrix's web page on the codec, all I've come
across is the following:
? Release 11/1/96 1.00

* tuned 16-bit color conversion tables for better color accuracy on
16 bit and 15 bit deep displays"
... and:
" * The 0.92 release incorrectly fixed the problem with end of line
pixels. On 24/32 bit color depth output, the right most pixel on
all lines was incorrectly colored. On 16/15 bit color depth, this
did not happen. This has been fixed on 32/24/16/15 bit output."
... and:
" * The YCrCb to RGB conversion would memory fault if the last pixel
in an image wasn't aligned on a 32-bit boundary and the following
memory was invalid. For 32-bit RGB formats, this was never the
case. For 24-bit and 16/15-bit formats, this was sometimes the
case. We now use byte access instructions for the last pixel on a
scan line, instead of a masked 32-bit transfer."

This was all at http://www.pmatrix.com/goodies.htm
It makes a good note:
" This codec was written to read and write data streams conforming to
the Microsoft M-JPEG codec and 11/13/95 OpenDML avi specs. As we only
deal with the compressed data block, other specifications in the
OpenDML spec relating to AVI header and segment formats, are the
domain of you video capture/editing program, not a codec. Some video
capture cards do not correctly follow these specs, so this codec may
not perform correctly."

But then, nowhere in the OpenDML specs at
http://www.matrox.com/videoweb/odmlff2.pdf does it mention this except in
section 7.0 where it mentions the difference between 8-bit and 10-bit YUV
format. All it says is that the document only addresses 8-bit 4:2:2 YUV.

> Since the new cornell and WP 3.x use the same set of drivers (the PMJPEG.DLL
> codec, and the drivers for the quickcam) shouldn't the new cornell version
> also be capable of sending B&W MJPEG video ?

Nope, you shouldn't. The ONLY versions that can use grayscale MJPEG from
a Quickcam are the 3.X versions (Cornell 0.92b2 can't, Cornell 1.0 can't,
White Pine 2.X can't). The only difference between 3.X and the others
that I know of that would affect this is the inclusion of ActiveMovie
(DirectShow).

--
streak@ccwf.cc.utexas.edu    * Jason Williams -- Austin, Tx.  |     |
streak@mail.utexas.edu       * University of Texas at Austin  | ___ |
streak@cs.utexas.edu         * BS Computer Science             \_|_/
*************** http://ccwf.cc.utexas.edu/~streak/ **************|