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Re: Camera preview, thin lines in the frames

On Thu, Nov 12, 2009 at 9:49 PM, Ryan Raasch <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

> 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 shows
    PID 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.

    I don't quite understand about FIFO levels of the data lines part.
    Could give an instruction where I can start to look into?

    Thanks for your reply..


> Regards,
> 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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