Re: Camera preview, thin lines in the frames
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Shun-Yu Chang wrote:
On Thu, Nov 12, 2009 at 9:49 PM, Ryan Raasch <ryan.raasch@xxxxxxxxx <mailto:ryan.raasch@xxxxxxxxx>> wrote:Shun-Yu Chang wrote: Hello, list: I am new to v4l2. I am working on integrating a usb camera device on the beagleboard(Omap3530 dev board). Now I met a camera preview issue that is there are thin lines coming out in the frames. I still have no idea how to describe this exactly. It's like the images shows here, http://0xlab.org/~jeremy/camera_preview.html <http://0xlab.org/%7Ejeremy/camera_preview.html> I have two guesses. One is the jpeg compression ,or is it jpeg? Try saving in raw RGB or Ycbcr format and viewing with imagemagick.The raw data I got is yuyv422. I used the mmap way. I tried to convert raw data to yuv420 and jpg files both. I used ffmpeg to convert yuv420 files to jpg files and I can still see the lines.I don't know how to use imagemagick to see yuv files... Does this happen in live preview? Maybe write data from camera directly to screen to see if happening there.It happens in live preview. So I save the frames directly into files to verify.
But if you save the files, you don't know if the compression is the problem. You need to visually look on the screen with a magnifying glass or something...
The second would be the FIFO (hadn't worked with omap before) levels of the data lines to the processor in the kernel. Look at the system processor (top) usage to see how much cpu% is being used. USB has high overhead.the top command showsPID CPU% S #THR VSS RSS UID Name 1012 56% R 1 55000K 54468K root capture_test 241 40% R 1 0K 0K root pdflush [....Omit, others are 0%. .....] After grabing the first 100 frames to files, capture_test exits.
Looks pretty busy to me. Maybe you could kill the pdflush, don't save to files, and look at the display with a magnifying glass.
I don't quite understand about FIFO levels of the data lines part. Could give an instruction where I can start to look into?
It probrably has dma priorities. So if other drivers in the system (network, usb, display, etc.) use a lot of cpu time, the camera dma might be delayed.
Are you saving the files over network (nfs)?
Thanks for your reply.. Regards, -JeremyRegards, Ryan I modified capture.c sample to save the frames to picture files. So in my guess, the problem is not in userspace. And this is not happen on my laptop with the usb camera. Could anybody give me a clue ? Any one would be thankful.
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