可视化每个CNN层的学习过滤器

Question

anyone please tell me how to visualize the learned filter of each CNN layer? The following answers tell me how to only visualize the learned filters of the first CNN layer, but could not visulize the other CNN layers.

1) You can just recover the filters and use Matlab's functions to display them as images. For example after loading a pretrained net from http://www.vlfeat.org/matconvnet/pretrained/ :

imshow( net.layers{1}.filters(:, :, 3, 1), [] ) ;

2) You may find the VLFeat function vl_imarraysc useful to display several filters. http://www.vlfeat.org/matlab/vl_imarraysc.html

Answer 1

For visualizing filters in intermediate layers. There are several techniques:

(1) show one or three channels as grayscale or RGB at a time. It's not very informative since they filters of ResNet and VGG are small 3x3.

(2) Turn off other units. Backpropgate only this unit to the input space. You can see a pattern that reflects what this unit cares about. There are many papers that use similar techniques. eg, Zeiler, Matthew D., and Rob Fergus. "Visualizing and understanding convolutional networks." European conference on computer vision. 2014.

(3) Find input patches that maximally activate this unit and see what they are.