Thanks for the reply, I'll look out for those possible correction
commands... But the adjustment when I cover the lens already happens
in the Linux driver, so I guess it's just something internal, right?

I went back to the original driver to see if I could make the camera
usable again, and I succeeded by turning off the automatic white
balance, and changing the values of the balance by hand. There are
three values for R G and B that can be set from 0 to 127. Can gspca
support something like that? v4lctl doesn't offer anything like that
out of the box, and I couldn't find possible functions in the
code. Does that array in the setwhitebalance function (t613.c) set
these values that the win driver offers the user to set?


On Tue, Jan 26, 2010 at 12:18:01PM -0600, Theodore Kilgore wrote:
> On Tue, 26 Jan 2010, Nicolau Werneck wrote:
>> Hello. I have this very cheap webcam that I sent a patch to support on
>> gspca the other day. The specific driver is the t613.
>> I changed the lens of this camera, and now my images are all too
>> bright, what I believe is due to the much larger aperture of this new
>> lens. So I would like to try setting up a smaller exposure time on the
>> camera (I would like to do that for other reasons too).
>> The problem is there's no "exposure" option to be set when I call
>> programs such as v4lctl. Does that mean there is definitely no way for
>> me to control the exposure time? The hardware itself was not designed
>> to allow me do that? Or is there still a chance I can create some C
>> program that might do it, for example?
>> It looks like the camera has some kind of automatic exposure control. If
>> I cover the lens, and then uncover it quickly, the image is all white
>> at first, and then it gradually becomes darker. Should that give me
>> some hope of being able to control the exposure, or is it common for
>> cheaper cameras to have just an automatic exposure control that cannot
>> be overrun?
> Nicolau,
> Having had some experience with cheap cameras, I would say that they come 
> with all kinds of variations. Thus, this particular camera (with which I  
> am _not_ experienced) could either have a built-in automatic exposure  
> control, or it could require monitoring from software with periodic  
> correction of various settings. It just depends.
> Thus, one thing to do is to look carefully at some usbsnoop logs and try  
> to see if there are occasional correction sequences in between big hunks  
> of data. If there are, then the next thing is to figure out what those  
> correction sequences are doing. Then build those correction sequences 
> into the driver. An example of this kind of thing going on can be seen  
> in lots of the camera drivers in gspca, but not in all of them.
> Second thing, try to look for sensor setup commands which give initial  
> settings. If there are such, then one or more of them might control  
> exposure settings.
> Third, if there are no occurences of either of the previous items at all, 
> then either the camera does not self-adjust and can not be adjusted (i. 
> e. really, really cheap), or the adjustment mechanism is completely 
> built-in. In that case, I would say that you are probably up a tree about 
> getting the exposure reset.
> Hope this helps you.
> Theodore Kilgore

Nicolau Werneck <>          1AAB 4050 1999 BDFF 4862           4A33 D2B5 648B 4789 0327
Linux user #460716

To unsubscribe from this list: send the line "unsubscribe linux-media" in
the body of a message to
More majordomo info at

Reply via email to