anchor.diff:      src = fetchFromGitHub {
         owner  = "opencv";
         repo   = "opencv_3rdparty";
  -      rev    = "bdb7bb85f34a8cb0d35e40a81f58da431aa1557a";
  -      sha256 = "1ys9mshfpm8iy8h4ml792gnqrq959dsrcv26axx14niivxyjbji8";
  +      rev    = "32e315a5b106a7b89dbed51c28f8120a48b368b4";
  +      sha256 = "19w9f0r16072s59diqxsr5q6nmwyz9gnxjs49nglzhd66p3ddbkp";
       } + "/ippicv";
  -    files = let name = platform : "ippicv_2017u3_${platform}_general_20180518.tgz"; in
  +    files = let name = platform : "ippicv_2019_${platform}_general_20180723.tgz"; in
         if stdenv.hostPlatform.system == "x86_64-linux" then
  -      { ${name "lnx_intel64"} = "b7cc351267db2d34b9efa1cd22ff0572"; }
  +      { ${name "lnx_intel64"} = "c0bd78adb4156bbf552c1dfe90599607"; }
         else if stdenv.hostPlatform.system == "i686-linux" then
  -      { ${name "lnx_ia32"}    = "ea72de74dae3c604eb6348395366e78e"; }
  +      { ${name "lnx_ia32"}    = "4f38432c30bfd6423164b7a24bbc98a0"; }
         else if stdenv.hostPlatform.system == "x86_64-darwin" then
  -      { ${name "mac_intel64"} = "3ae52b9be0fe73dd45bc5e9429cd3732"; }
  +      { ${name "mac_intel64"} = "fe6b2bb75ae0e3f19ad3ae1a31dfa4a2"; }
         else
         throw "ICV is not available for this platform (or not yet supported by this package)";
       dst = ".cache/ippicv";
  
positive.code:     "-DBUILD_opencv_videoio=OFF"
    ] ++ lib.optionals enablePython [
      "-DOPENCV_SKIP_PYTHON_LOADER=ON"
    ];
  
    enableParallelBuilding = true;
  
negative.code: }:
  
  let
    version = "3.4.7";
  
    src = fetchFromGitHub {
      owner  = "opencv";
      repo   = "opencv";
      rev    = version;
      sha256 = "0r5rrcnqx2lsnr1ja5ij2chb7yk9kkamr4p0ik52sqxydwkv3z50";
    };
  
    contribSrc = fetchFromGitHub {
      owner  = "opencv";
      repo   = "opencv_contrib";
      rev    = version;
      sha256 = "1ik6acsmgrx66awf19r2y3ijqvv9xg43gaphwszbiyi0jq3r43yw";
    };
  
    # Contrib must be built in order to enable Tesseract support:
  