错误提示：
ubuntu opencv imshow() 报错
windows.cpp报错
the function is not implemented
If you are on Ubuntu or Debian, install libgtk2.0-dev and pkg-config, then re-run cmake or configure script in function 'cvShowImage'
原因：
opencv在ubuntu需要的一些依赖包没有安装。按照提示安装libgtk2.0-dev 和 pkg-config之后 很可能还是报这个错。
按这个教程，安装好所有依赖，然后重新安装opencv：
https://www.cnblogs.com/leoking01/p/8301724.html
sudoapt-get install build-essential libgtk2.0-dev libjpeg-dev libtiff4-dev libjasper-dev libopenexr-dev cmake python-dev python-numpy python-tk libtbb-dev libeigen3-dev yasm libfaac-dev libopencore-amrnb-dev libopencore-amrwb-dev libtheora-dev libvorbis-dev libxvidcore-dev libx264-dev libqt4-dev libqt4-opengl-dev sphinx-common texlive-latex-extra libv4l-dev libdc1394-22-dev libavcodec-dev libavformat-dev libswscale-dev default-jdk ant libvtk5-qt4-dev