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This folder contains the examples of image segmentation in MXNet.

Sample results

fcn-xs pasval_voc result

We have trained a simple fcn-xs model, the hyper-parameters are below:

modellr (fixed)epoch

(when using the newest mxnet, you'd better using larger learning rate, such as 1e-4, 1e-5, 1e-6 instead, because the newest mxnet will do gradient normalization in SoftmaxOutput)

The training dataset size is only 2027, and the validation dataset size is 462.

How to train fcn-xs in mxnet

Getting Started

  • Install python packageĀ Pillow (required by
[sudo] pip install Pillow
  • Assume that we are in a working directory, such as ~/train_fcn_xs, and MXNet is built as ~/mxnet. Now, copy example scripts into working directory.
cp ~/mxnet/example/fcn-xs/* .

Step1: Download the vgg16fc model and experiment data

Step2: Train fcn-xs model

  • Configure GPU/CPU for training in
# ctx = mx.cpu(0)
ctx = mx.gpu(0)
  • If you want to train the fcn-8s model, it's better for you trained the fcn-32s and fcn-16s model firstly. when training the fcn-32s model, run in shell ./, the script in it is:
python -u --model=fcn32s --prefix=VGG_FC_ILSVRC_16_layers --epoch=74 --init-type=vgg16
  • In the, you may need to change the directory root_dir, flist_name, ``fcnxs_model_prefix``` for your own data.
  • When you train fcn-16s or fcn-8s model, you should change the code in corresponding, such as when train fcn-16s, comment out the fcn32s script, then it will like this:
 python -u --model=fcn16s --prefix=FCN32s_VGG16 --epoch=31 --init-type=fcnxs
  • The output log may look like this(when training fcn-8s):
INFO:root:Start training with gpu(3)
INFO:root:Epoch[0] Batch [50]   Speed: 1.16 samples/sec Train-accuracy=0.894318
INFO:root:Epoch[0] Batch [100]  Speed: 1.11 samples/sec Train-accuracy=0.904681
INFO:root:Epoch[0] Batch [150]  Speed: 1.13 samples/sec Train-accuracy=0.908053
INFO:root:Epoch[0] Batch [200]  Speed: 1.12 samples/sec Train-accuracy=0.912219
INFO:root:Epoch[0] Batch [250]  Speed: 1.13 samples/sec Train-accuracy=0.914238
INFO:root:Epoch[0] Batch [300]  Speed: 1.13 samples/sec Train-accuracy=0.912170
INFO:root:Epoch[0] Batch [350]  Speed: 1.12 samples/sec Train-accuracy=0.912080

Using the pre-trained model for image segmentation

  • Similarly, you should first download the pre-trained model from, the symbol and model file is FCN8s_VGG16-symbol.json, FCN8s_VGG16-0019.params
  • Then put the image in your directory for segmentation, and change the img = YOUR_IMAGE_NAME in
  • At last, use to segmentation one image by running in shell python, then you will get the segmentation image like the sample results above.


  • This is the whole image size training, that is to say, we do not need resize/crop the image to the same size, so the batch_size during training is set to 1.
  • The fcn-xs model is based on vgg16 model, with some crop, deconv, element-sum layer added, so the model is quite big, moreover, the example is using whole image size training, if the input image is large(such as 700*500), then it may consume lots of memories, so I suggest you using the GPU with 12G memory.
  • If you don't have GPU with 12G memory, maybe you should change the cut_off_size to a small value when you construct your FileIter, like this:
train_dataiter = FileIter(
      root_dir             = "./VOC2012",
      flist_name           = "train.lst",
      cut_off_size         = 400,
      rgb_mean             = (123.68, 116.779, 103.939),
  • We are looking forward you to making this example more powerful, thanks.