| Perhaps this is the right place to post this question about capturing
screens. Cross posted in OPEN3d and MultiMedia.
Thanks, Steve
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Note 1231.0 true color capture; using pseudo color default question? 1 reply
SAYER::ELMORE "Steve elmore@mail.dec.com 412-364-58" 57 lines 1-FEB-1997 15:08
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I am not quite sure where to post this question. I am trying here
first, but perhaps the X conference is better. If someone would kindly
point me to the right place, if not here, I would be grateful.
I received the following mail from a medical imaging OEM. I don't have
the expertise to help them. They are trying to mix pseudo and true
color together but capture only true color. Please read on:
> Hi.
>
> We spoke briefly in the hallway while you were at Picker MR
> a few days ago.
>
> I have a problem with a system running Dec UNIX 4.0a and X/Motif.
> (The problem is not OS or system specific, but it might make a
> difference later.)
>
> The system has a 24 bit color card and the J300 video capture card.
> We have set up our /usr/lib/X11/xdm/Xservers file to start the system
> in pseudo color mode even though it is true color capable. We then
> have some windows on the screen that use true color X visuals and
> some
> that use pseudo color. This works OK and saves memory and time when
> the windows that use the default (pseudo color) visual are moved
> around.
>
> The problem comes up when we do video capture. That routine reads
> pixels from the root window in order to capture the entire screen.
> The
> root window defaults to a pseudo color visual, so the video capture
> data is only 8 bits deep and is often the wrong value. Somehow we
> need to
> read the data from a source that has the full 24 bit pixels.
>
> Video capture works OK if we don't force the default visual to be
> pseudo color, since then the root window comes out as true color and
> the captured data looks fine. However, then we pay a price in
> performance and memory usage since all our pixmap data triples in
> size (from 8 to 24 bits). This can be 100s of megabytes in some
> cases.
>
> So, my problem is:
>
> How can I read 24 bit pixel data from the frame buffer for video
> capture when the X root window is set up with an 8 bit pseudo
> color
> visual? Is there a way to read directly from the frame buffer and
> bypass X altogether ?
>
>
> I hope this explanation makes some sense. Please let me know if you
> have any ideas about this, or other sources I might try for help.
>
> Thanks.
> Don Russell
|
| Well, I've been pointed back over here for an answer. I have searched
several conferences now and can't find specific advice. I'm appealing
again here.
Basically, this customer wants to capture a workstation's x-windows
screen. They have written a custom application using X. The root is
in psuedo-color, but there are other individual windows in true-color.
Customer is asking how to capture the screen with such a mix of
windows. They can't lose the true-color window images (this is a
medical imaging application), but they don't want the overhead of
setting the root to true-color.
Any ideas? From anyone?
Thanks,
Steve
|