OpenCV

About

Wikipedia: OpenCV

OpenCV is an open source computer vision library originally developed by Intel. It is free for commercial and research use under a BSD license. The library is cross-platform, and runs on Mac OS X, Windows and Linux. It focuses mainly on real-time image processing, as such, if it finds Intel's Integrated Performance Primitives (IPP) on the system, it will use these commercial optimized routines to accelerate itself.

OpenCV's application areas include:

• Human-Computer Interface (HCI)
• Object Identification
• Segmentation and Recognition
• Face Recognition
• Gesture Recognition
• Motion Tracking
• ...

Face Recognition

Nirav Patel reports success in basic image recognition on the XO Laptop (with xo-cam) with good timings using OpenCV and xawtv.

Sources: face.py haarcascade_frontalface_alt.xml

Downloads

The source can be downloaded from sourceforge, or OpenCV can be installed from the opencv package in the Fedora repository. To use OpenCV with python, also install the opencv-python package.

$ yum install opencv opencv-python

Problems

Currently, OpenCV fails to interface with the XO's Camera. It is therefore necessary to use xawtv or Gstreamer to capture video or images, and feed the results to OpenCV.

The problem appears to rise from the interaction between OpenCV and the OV7670 driver in negotiating over what color palette to use. In theory, OpenCV should suggest fmt.pix.pixelformat values, and the driver should respond with acceptable versions of them. Somehow, OpenCV is sending values that the driver can't deal with. The temporary fix is to let the driver tell OpenCV what palette it wants by changing VIDIOC_C_FMT to VIDIOC_G_FMT. To do that to edit line 419 in otherutils/highgui/cvcap_v4l.cpp to the following

if (-1 == xioctl (capture->deviceHandle, VIDIOC_G_FMT, &capture->form))

Note that the packages required to compile OpenCV include gtk2-devel, which currently is not installable, a known bug. I got around it with the following, though your milage may vary.

yum -t --enablerepo=* install libXI-devel
yum -t --enablerepo=* install gtk2-devel

An easier but even dirtier fix is available here.

Links

• OpenCV Documentation Wiki
• OpenCV SourceForge site
• OpenCV homepage at intel