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[pwc] Problems with compression in pwc module

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Subject: [pwc] Problems with compression in pwc module
From: Pablo Alvarado <>
Date: Mon, 30 Oct 2006 18:14:53 +0100 (CET)
Hello,

I'm experiencing some weird problems with a ToUCam
Camera (740) and the pwc kernel module, whenever I
activate any compression level.  I can get the images
and control the camera without any difficulties in all
available uncompressed modes, but as soon as I
activate the compression mode (any of the three
available) I get a grey image with RGB values
(128,128,128).

I've tried several programs (camstream and LTI-Lib
lti::toUCam functor) and all of them behave the same
way.  I have debugged the LTI-Lib software and all
ioctl calls return successfully when the compression
parameters are set or the image is requested.  In some
computers the kernel module with the mentioned
software works fine (with compression and everything),
but in some others I just get the grey image.  All
computers have a kernel 2.6.17-2 and the pwc module
version 10.0.12-rc1+final (installed with Debian's
module-assistant), so I don't think it is a kernel
compatibility problem.  It is not the camera because
in all tests I used the same one.

I though the grey images were generated by the
software that used the API when it detected an error,
but the grey image is directly provided by the API
interface without reporting any errors.  The size of
the returned grey images is correct.  The output in
/var/log/syslog indicates nothing special:

Oct 30 10:14:59 palvarado kernel: pwc
set_video_mode(160x120 @ 30, palette
15).
Oct 30 10:14:59 palvarado kernel: pwc decode_size = 1.
Oct 30 10:14:59 palvarado kernel: pwc Using alternate
setting 8.
Oct 30 10:15:25 palvarado kernel: pwc
set_video_mode(160x120 @ 30, palette
15).
Oct 30 10:15:25 palvarado kernel: pwc decode_size = 1.
Oct 30 10:15:25 palvarado kernel: pwc Using alternate
setting 5.

the first three lines were reported as the compression
was deactivated (and a valid image was obtained), and
the last three lines when the compression was
activated an the image turned grey.

Any hint would be very welcome,

Regards,

Pablo

--
Dr. Pablo
Alvarado                      E-Mail: 
Escuela de Ingeniería Electrónica       Tel.:   (+506)
550 2106
Instituto Tecnológico de Costa Rica     Fax.:   (+506)
591 6629
Apartado Postal 159-7050
Cartago
Costa Rica




        
                
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