uvcvideo

uvcvideo driver with still image capture support

• The base is kernel 3.2

• Picked some fixes from upstream (see list in uvc/merged-upstream-patches)

• Make it possible to build out side the kernel source tree.

• Also cand build in your Android enviroment

Background

What's still image capture in UVC?

Refer to the USB Video Class 1.1 spec, 2.4.2.4 Still Image Capture, page 14.

End user's view: it's means you can capture a still image with different size to the current preview size. e.g preview in 800x600, but you wanna still image in 1600x1200.

Technical view: it's means application don't need stream off the current video stream (preview stream), and send a trigger control command to camera, to get a still image frame via the current preview stream pipe line, after still image sent, camera will auto switch back to preview stream, and application continue to show preview stream.

Why we need still image capture mode?

• Capture still image with same size as the video/preview stream is not fit to HD camera (> 2M).

• Stream off before capture and stream on after capture may cost more than 5 seconds, because some uvc camera need a bit long time to warm up and send out first frame.

• Big size still image requires more band width and system resource, it's not wise to preview with a big size.

• Power consume (bigger size more power consumed)

Implementation

• Use a magic number to implement REQBUFS/QUERYBUF/QBUF/DQBUF/S_FMT for still image buffers management, format set..etc. While V4L2 has no special ioctl for still image, I did it this way, maybe new private ioctrl or new subdev is better approach.

• Add a new still queue for app to get still image buf with same API.

• Pares still format info in the original descriptor scan code.

• Parse still image frame in the decode_isoc start/data/end func (decode_bulk not support yet), and send out finished buffer with a frame.

Build driver

build for you pc

 cd uvc
 make
 make test

build for your android

 # Setup your android env first
 cd uvc
 make -f Makefile.android
 adb push uvcvideo.ko /data/
 adb shell rmmod uvcvideo
 adb shell insmod /data/uvcvideo.ko
#adb shell "echo 2047 > /sys/module/uvcvideo/parameters/trace"

User space tool

I also customized the famous v4l2 capture.c to do still image capture, and I've successfully captured still image on a live preview stream (I wrote a tool to convert yuv422 raw data into png, and use it to verify the captured still image).

 $> cd v4l2-capture
 $> make

FAQ

How to identify if your uvc camera support still image capture?

lsusb -v -d xxxx:xxxx

Find STILL_IMAGE_FRAME in the output, if found, it does, else not.

TODO

Implement this feature in sub device such as /dev/photo0, so that we don't need a magic number to identify if the IOCTRL is normal or for still image, the driver will more clean than the current implement.

Atuhors

• Yang Hong - Implemented still image capture
• Liu Shouyong - Tips and initial still probe/commit code

Links

• V4L2 API - http://linuxtv.org/downloads/v4l-dvb-apis/
• Linux UVC driver & tools - http://www.ideasonboard.org/uvc/
• Maillist - [email protected]
• Maillist subscribe - https://lists.sourceforge.net/lists/listinfo/linux-uvc-devel
• USB Video Class Specs - http://www.usb.org/developers/devclass_docs/USB_Video_Class_1_1_090711.zip