cv2.imshow fail on ubuntu 18.04 anaconda

好麻煩呀，ubuntu18.04 conda python 3.8 的話，opencv 的 imshow 會 fail:

Traceback (most recent call last):
  File "testvideocap.py", line 5, in 
    cv2.imshow('dd',frame)
cv2.error: OpenCV(3.4.2) /tmp/build/80754af9/opencv-suite_1535558553474/work/modules/highgui/src/window.cpp:632: 
error: (-2:Unspecified error) The function is not implemented. Rebuild the library with Windows, GTK+ 2.x or Carbon support. 
If you are on Ubuntu or Debian, install libgtk2.0-dev and pkg-config, then re-run cmake or configure script in function 'cvShowImage'

• ref:OpenCV not working properly with python on Linux with anaconda. Getting error that cv2.imshow() is not implemented

好像是conda repo 的這個(3.4.2) 沒有人 mantain 了。
但是新的 mantainer 有做，所以換安裝新版 opencv 舊可以。

conda remove opencv
conda install -c conda-forge opencv=4.1.0

-c 是 channel 的意思，用 conda-forge 這個 channel 的 opencv4.1.0 package 來安裝。

• conda-forge

是社群貢獻的 conda package repo(?).