title: failed to install opencv-python on windows
body: <p>Ran: pip install opencv-python</p>
  <p>from windows cmd with admin.
  First time setting up python and I don't think it's using the right environment variables</p>
  <p>getting this error:</p>
  <pre><code>Collecting opencv-python
    Using cached opencv-python-4.4.0.44.tar.gz (88.9 MB)
    Installing build dependencies ... done
    Getting requirements to build wheel ... done
      Preparing wheel metadata ... done
  Processing c:\users\shub\appdata\local\pip\cache\wheels\a3\17\dd\f2dba23a35bb6008732772ccfb13d3d0e537fbc6919ce6862b\numpy-1.19.2-cp39-cp39-win_amd64.whl
  Building wheels for collected packages: opencv-python
    Building wheel for opencv-python (PEP 517) ... error
    ERROR: Command errored out with exit status 1:
     command: 'c:\users\shub\appdata\local\programs\python\python39\python.exe' 'c:\users\shub\appdata\local\programs\python\python39\lib\site-packages\pip\_vendor\pep517\_in_process.py' build_wheel 'C:\Users\Shub\AppData\Local\Temp\tmpmlx70j_s'
         cwd: C:\Users\Shub\AppData\Local\Temp\pip-install-tdd7o170\opencv-python
    Complete output (153 lines):
    Not searching for unused variables given on the command line.
    CMake Error: CMake was unable to find a build program corresponding to &quot;Ninja&quot;.  CMAKE_MAKE_PROGRAM is not set.  You probably need to select a different build tool.
    -- Configuring incomplete, errors occurred!
    See also &quot;C:/Users/Shub/AppData/Local/Temp/pip-install-tdd7o170/opencv-python/_cmake_test_compile/build/CMakeFiles/CMakeOutput.log&quot;.
    Not searching for unused variables given on the command line.
    CMake Error at CMakeLists.txt:2 (PROJECT):
      Generator
  
        Visual Studio 15 2017 Win64
  
      could not find any instance of Visual Studio.
  
  
  
    -- Configuring incomplete, errors occurred!
    See also &quot;C:/Users/Shub/AppData/Local/Temp/pip-install-tdd7o170/opencv-python/_cmake_test_compile/build/CMakeFiles/CMakeOutput.log&quot;.
    Not searching for unused variables given on the command line.
    -- The C compiler identification is unknown
    CMake Error at CMakeLists.txt:3 (ENABLE_LANGUAGE):
      The CMAKE_C_COMPILER:
  
        cl
  
      is not a full path and was not found in the PATH.
  
      To use the NMake generator with Visual C++, cmake must be run from a shell
      that can use the compiler cl from the command line.  This environment is
      unable to invoke the cl compiler.  To fix this problem, run cmake from the
      Visual Studio Command Prompt (vcvarsall.bat).
  
      Tell CMake where to find the compiler by setting either the environment
      variable &quot;CC&quot; or the CMake cache entry CMAKE_C_COMPILER to the full path to
      the compiler, or to the compiler name if it is in the PATH.
  
  
    -- Configuring incomplete, errors occurred!
    See also &quot;C:/Users/Shub/AppData/Local/Temp/pip-install-tdd7o170/opencv-python/_cmake_test_compile/build/CMakeFiles/CMakeOutput.log&quot;.
    See also &quot;C:/Users/Shub/AppData/Local/Temp/pip-install-tdd7o170/opencv-python/_cmake_test_compile/build/CMakeFiles/CMakeError.log&quot;.
    Not searching for unused variables given on the command line.
    -- The C compiler identification is unknown
    CMake Error at CMakeLists.txt:3 (ENABLE_LANGUAGE):
      The CMAKE_C_COMPILER:
  
        cl
  
      is not a full path and was not found in the PATH.
  
      To use the JOM generator with Visual C++, cmake must be run from a shell
      that can use the compiler cl from the command line.  This environment is
      unable to invoke the cl compiler.  To fix this problem, run cmake from the
      Visual Studio Command Prompt (vcvarsall.bat).
  
      Tell CMake where to find the compiler by setting either the environment
      variable &quot;CC&quot; or the CMake cache entry CMAKE_C_COMPILER to the full path to
      the compiler, or to the compiler name if it is in the PATH.
  
  
    -- Configuring incomplete, errors occurred!
    See also &quot;C:/Users/Shub/AppData/Local/Temp/pip-install-tdd7o170/opencv-python/_cmake_test_compile/build/CMakeFiles/CMakeOutput.log&quot;.
    See also &quot;C:/Users/Shub/AppData/Local/Temp/pip-install-tdd7o170/opencv-python/_cmake_test_compile/build/CMakeFiles/CMakeError.log&quot;.
  
  
    ...
  
    --------------------------------------------------------------------------------
    -- Trying &quot;NMake Makefiles JOM (Visual Studio 15 2017 Win64 v141)&quot; generator
    --------------------------------
    ---------------------------
    ----------------------
    -----------------
    ------------
    -------
    --
    --
    -------
    ------------
    -----------------
    ----------------------
    ---------------------------
    --------------------------------
    -- Trying &quot;NMake Makefiles JOM (Visual Studio 15 2017 Win64 v141)&quot; generator - failure
    --------------------------------------------------------------------------------
  
    ********************************************************************************
    scikit-build could not get a working generator for your system. Aborting build.
  
    Building windows wheels for Python 3.9 requires Microsoft Visual Studio 2017.
    Get it with &quot;Visual Studio 2017&quot;:
  
      https://visualstudio.microsoft.com/vs/
  
    ********************************************************************************
    ----------------------------------------
    ERROR: Failed building wheel for opencv-python
  Failed to build opencv-python
  ERROR: Could not build wheels for opencv-python which use PEP 517 and cannot be installed directly
  
  C:\Windows\system32&gt;
  </code></pre>
  <p>I have visual studio 2019 installed, installed c++ build tools, as well as pip and wheel but it's not able to detect visual studio for some reason. I have restarted my computer after the install as well.
  Not sure how to resolve</p>