encoder = NetEncoder[{"Image", "ImageSize" -> {168, 168}, "ColorSpace" -> "Grayscale"}];

decoder = NetDecoder[{"Image", "ColorSpace" -> Automatic}];

Options[convolutionModule] = {"batchNorm" -> True, "downpool" -> False,
"uppool" -> False, "activationType" -> Ramp, "convolution" -> True};

convolutionModule[net_, kernelsize_, padsize_, stride_: {1, 1}, OptionsPattern[]] :=
With[{upPool = OptionValue["uppool"], activationType = OptionValue["activationType"],
convolution = OptionValue["convolution"], batchNorm = OptionValue["batchNorm"],
downpool = OptionValue@"downpool"},

Block[{nnet = net},
If[upPool,
nnet = NetAppend[nnet, DeconvolutionLayer[1, {2, 2}, "PaddingSize" -> {0, 0},
   "Stride" -> {2, 2}]];
nnet = NetAppend[nnet, BatchNormalizationLayer[]];
If[activationType === Ramp,
 nnet = NetAppend[nnet, ElementwiseLayer[activationType]]
 ];
];
If[convolution,
 nnet = NetAppend[nnet, ConvolutionLayer[1, kernelsize, "Stride" -> stride,
   "PaddingSize" -> padsize]]
];
If[batchNorm,
nnet = NetAppend[nnet, BatchNormalizationLayer[]]
];
If[activationType === Ramp,
nnet = NetAppend[nnet, ElementwiseLayer[activationType]]
];
If[downpool,
nnet = NetAppend[nnet, PoolingLayer[{2, 2}, "Function" -> Max, "Stride" -> {2, 2}]]
];
nnet]
]

CropLayer[netlayer_] := With[{p = NetExtract[netlayer, "Output"]},
PartLayer[{First@p, 1 ;; p[[2]], 1 ;; Last@p}] ];

UNET[] :=
Block[{nm, pool1, pool2, pool3, pool4, pool5, kernelsize = {3, 3},
padsize = {1, 1}, stride = {1, 1}},
nm = NetChain@
Join[{ConvolutionLayer[1, {3, 3},
   "Input" -> encoder]}, {BatchNormalizationLayer[],
  ElementwiseLayer[Ramp],
  PoolingLayer[{2, 2}, "Function" -> Max, "Stride" -> {2, 2}]}];
pool1 = nm[[-1]];
nm = convolutionModule[nm, kernelsize, padsize, stride,"downpool" -> True];
pool2 = nm[[-1]];
nm = convolutionModule[nm, kernelsize, padsize, stride,"downpool" -> True];
pool3 = nm[[-1]];
nm = convolutionModule[nm, kernelsize, padsize, stride,"downpool" -> True];
pool4 = nm[[-1]];
nm = NetAppend[nm, DropoutLayer[]];
nm = convolutionModule[nm, kernelsize, padsize, stride, "downpool" -> True];
pool5 = nm[[-1]];
nm = convolutionModule[nm, kernelsize, padsize, stride, "uppool" -> True];
nm = convolutionModule[nm, kernelsize, padsize + 1, stride, "uppool" -> True];
nm = NetAppend[nm, CropLayer@pool3];