Hi, On Wednesday 08 September 2010 16:14:32 Moritz Barsnick wrote: > On Wed, Sep 08, 2010 at 15:36:58 +0200, Florian Echtler wrote: > > If still image support (for still image method 2) were to be added, > > would that bring exposure control with it? (probably not?) > > Good question. I have no understanding of the UVC standard, I only know > the still image buzzword from many threads here. :) > In Message-Id: <200804162242.45541.laurent.pinch...@skynet.be>, Laurent > wrote: > > It all depends on the hardware. The UVC spec defines several method > > to capture still images. The most common one, implemented by all the > > webcams I've tested so far, is to take the next image from the video > > stream. This won't help improving image quality. > > So you're probably out of luck.
Still image capture won't bring exposure control. > > Hm, but resolutions from full HD and up in YUYV show 1/2 fps? (Don't know > > if this is actually equal to exposure time or just due to the > > bandwidth..) > > You're right, I missed that. It does say 1/2 (that's SPF, not FPS, by > the way). > > My experience - without having done _anything_ with re-adjusting > autoexposure or the likes - is that the camera will expose as much of > that interval if it needs to. But since it doesn't have an aperture, it > reduces exposure time in better lighting. One of my personal webcam > (non-UVC) installations is at constant 5 FPS, but only in the evening > does movement appear blurry in the stream. In theory, auto-exposure will modify the frame rate according to the light conditions and can lower the frame rate. It should never push the frame rate higher than the selected value. > I do _not_ know whether a constant FPS and disabled autoexposure would > lead to under-/overexposure but defined exposure time. The UVC specification isn't very clear on the subject. It states that "[...] the manual exposure control is further limited by the frame interval, which always has higher precedence." My understanding is that disabling auto-exposure and setting the exposure time manually should work when the requested exposure time is lower than the frame interval. The specificat In practice I expect most webcams not to bother about this and honor the requested exposure time. I've just tested an old Logitech camera and it seems to work that way (although the exposure time values seem broken, a lower value corresponds to a higher exposure time). > > Well, this is exactly the solution I am using right now :-) > > Ha! :-) But you have valid points there. No mechanical wear in the web > cam. (But my web cam's sensor seems to have deteriorated over the > years.) -- Regards, Laurent Pinchart _______________________________________________ Linux-uvc-devel mailing list Linux-uvc-devel@lists.berlios.de https://lists.berlios.de/mailman/listinfo/linux-uvc-devel
