turn off auto exposure on a uvc webcam

zoran119 · 10-21-2009, 05:38 AM

hi all,

i have a logitech web quickcam communicate mp/s5500 which runs with quite low frame rate (55 frames in 11 seconds). this is using the following parameters to see the video:

Code:

mplayer tv:// -tv driver=v4l2:device=/dev/video0

according to some sources on the net this is caused by auto exposure. does anyone know how to turn it off?

thanks

GazL · 10-21-2009, 06:56 AM

I had the same problem with my 9000pro. I used to use luvcview gui to turn off auto exposure, set exposure to deliver my desired framerate and then compensate for the poor lighting in my room with the contrast/brightness/saturation settings. You lose picture quality doing this, but you can usually find a compromise that doesn't look too bad.

I've not used it in quite a while but it might be worth a try.

zoran119 · 10-22-2009, 03:25 AM

i keep getting 'Set Auto Exposure off error'... any ideas?

zoran119 · 10-22-2009, 03:46 AM

and then...

Code:

$ uvcdynctrl -s 'Exposure, Auto' -- 0 
ERROR: Unable to set new control value: A Video4Linux2 API call returned an unexpected error 5. (Code: 12)

i'm not sure what the deal is but this seems interesting http://forums.quickcamteam.net/showthread.php?tid=212 but setting it to 3 didn't help.

can anyone shine some light on how to get my frame rate up?

GazL · 10-22-2009, 05:09 AM

I've just tried the 'trunk' version direct from svn.

Code:

svn checkout http://svn.quickcamteam.net/svn/luvcview/trunk

cd trunk/luvcview

wget http://svn.quickcamteam.net/svn/qct/Linux/Common/include/dynctrl-logitech.h

wget http://svn.berlios.de/svnroot/repos/linux-uvc/linux-uvc/trunk/uvc_compat.h

wget http://svn.berlios.de/svnroot/repos/linux-uvc/linux-uvc/trunk/uvcvideo.h

make

If you click on the button above the one you're clicking you should get a "Auto expose set to 1" message on stdout. This appears to turn off auto exposure, at least it does on my 9000. Clicking the button below gives an error message as you say. Once you've got the "Auto expose is set to 1" message the exposure controls appear to work normally.

Unfortunately, this program appears to be a bit of a mess and does things in a non-standard way. I think what's happened is that at some point the v4l2 kernel api or uvc driver has changed and because of the non-standard approach, a few things have broken.

I see there's now a gtk+ version called guvcview. I've not tried it, but maybe you'll have more luck with that one.

GazL · 10-22-2009, 05:32 AM

Yep, that's enlightening. Post 9, seems to explain what's going on quite well.

Try this patch to luvcview.

Code:

--- luvcview.c.old      2009-10-22 11:29:29.052116029 +0100
+++ luvcview.c  2009-10-22 11:30:17.685678188 +0100
@@ -833,7 +833,7 @@
                                        break;
                                case A_EXPOSURE_OFF:
                                        control.id    =V4L2_CID_EXPOSURE_AUTO;
-                                       control.value =8;
+                                       control.value =3;
                                        if ((value = ioctl(videoIn->fd, VIDIOC_S_CTRL, &control)) < 0)
                                                printf("Set Auto Exposure off error\n");
                                        else

zoran119 · 10-22-2009, 06:11 AM

Quote:

Originally Posted by GazL

I've just tried the 'trunk' version direct from svn.
I see there's now a gtk+ version called guvcview. I've not tried it, but maybe you'll have more luck with that one.

awesome!!! it works!!! it's a little bit weird... don't really know what i'm doing with the sliders but will get there. any idea where it stores it's config so that it can be reset to the defaults (before i started playing with the camera settings)?

thanks for your help!!!

GazL · 10-22-2009, 06:27 AM

Code:

gazl@slack:~/Projects/trunk/luvcview$ ./luvcview --help
luvcview 0.2.6

usage: uvcview [-h -d -g -f -s -i -c -o -C -S -L -l -r]
-h   print this message
-d   /dev/videoX       use videoX device
-g   use read method for grab instead mmap
-w   disable SDL hardware accel.
-f   choose video format (YUYV/yuv and MJPG/jpg are valid, MJPG is default)
-i   fps           use specified frame rate
-s   widthxheight      use specified input size
-c   enable raw frame capturing for the first frame
-C   enable raw frame stream capturing from the start
-S   enable raw stream capturing from the start
-o   avifile  create avifile, default video.avi
-L   query valid video formats
-l   query valid controls and settings
-r   read and set control settings from luvcview.cfg (save/restore with F1/F2)
gazl@slack:~/Projects/trunk/luvcview$

I've not played with it all that much, but it looks like the function keys and -r option are what you're looking for. I've not tried the gtk one at all, so I can't offer any advice on that one.

Oh, and I think one of those 4 buttons in the middle is a reset to defaults, but I can't remember which.