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This code is for the paper "Linear Span Network for Object Skeleton Detection".

LSN builds on Holistically-Nested Edge Detection (HED) [1] with Liner Span Unit (LSU) under the guidance of linear span theory. LSU is used in three phases, feature linear span, resolution alignment, subspace linear span. A comparison of HED and LSN in principle is shown below. Each ellipse indicates a subspace spanned by feature maps from a convolutional layer. The union sets (the pink areas) imply the sum of the spanned subspaces. It can be seen that LSN principally spans a larger output space than HED does.

The comparision of the skeleton detection results of HED, SRN[2] and LSN on SK-LARGE dataset are shown below. From the results, it's easily to find that LSN explore more complementary features for skeleton detection and integrate them in a more effective way.


  1. Install prerequisites for Caffe (
  2. Build HED ( Supposing the root directory of HED is $HED.
  3. Copy files to $HED/example/LSN.


  1. Download the (SK-LARGE) to $HED/data/, and do data augmentation follow instructions there;
  2. Download the Pre-trained VGG [3] model (VGG19). Copy it to $HED/example/LSN/
  3. Change the dataset path in $HED/example/LSN/train_val.prototxt
  4. Run in shell (or you could use IDE like Eclipse)
cd $HED/example/LSN/


  1. Change the dataset path in $HED/example/LSN/test.ipython.
  2. run test.ipython.


We use the evaluation code of [3] to draw the PR curve. The code can be download spb-mil.

NOTE: Before evaluation, the NMS is utilized. We use the NMS code in Piotr's edges-master.


[1] S. Xie and Z. Tu. Holistically-nested edge detection. In International Conference on Computer Vision, 2015

[2] Ke, W.,Chen, J.,Jiao, J., Zhao, G., Ye, Q.: SRN: side-out residual network for object symmetry detection in the wild. In: IEEE Conference on Computer Vision and Pattern Recognition. (2017) 302-310

[3] S. Tsogkas and I. Kokkinos. Learning-based symmetry detection in natural images. In European Conference on Computer Vision