Hi, On 03/29/2012 08:27 AM, Rafał Rzepecki wrote:
Hi, I've tried to reach Jean-Francois with this a week ago, but I still haven't received an answer, so I'm sending it to the mailing list. I'd appreciate a CC of any follow-ups. I've been having problems with my ID 0c45:6128 Microdia PC Camera (SN9C325 + OM6802) using driver gspca_sonixj. Specifically, launching command: $ gst-launch-0.10 v4l2src ! ffmpegcolorspace ! pngenc ! filesink \ location=/tmp/file.png gave a file that is all black. This is problematic because at least one program (odeskteam) uses a similar method to grab camshots. I thought it looked like as though the camera hasn't got enough time to initialize, and indeed, adding an msleep(30) near the end of sd_start() in sonixj.c solved the problem.
The problem is that the above method to take a snapshot is simply wrong. Many cameras need to be streaming video data for "a while" before they give a (good) picture. Many cameras need some time for things like auto-gain, auto-exposure, auto-whitebalance and auto-focus to get to their correct setting for a proper picture. A black picture probably means that the auto-gain/ auto-exposure for set camera still needs to jank up the gain and/or exposure. and you're simply not giving it time for this. My high quality HD video microsoft studio pro camera also starts out with a close to black picture when I start streaming data from it in anything but bright sunlight, and then corrects the picture in 1-5 frames. This same camera takes like .5 seconds to gets it auto focus settled so your snapshot example would likely result in a too dark, unsharp picture. Note that this is all handled by the camera itself, the UVC driver it uses has no control over this. Why do you think digital compact (still photo) cameras take so much time from you pressing the take picture button to actually taking the picture? They are in essence doing the same. The only difference with webcams is that people want more then 1 picture / second so the camera cannot do all those corrections before sending a picture, instead it does them while it is streaming data, meaning that the first second or so of data can be quite useless. Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
