What is the depth of an image in Convolutional Neural Network? I am learning cs231n Convolutional Neural Networks for Visual Recognition. The lecture notes introduce the concepts of width, height, depth. For example,


  In CIFAR-10, images are only of size 32x32x3 (32 wide, 32 high, 3
  color channels)


However, in another example,


  a volume of size [55x55x96] has 96 depth slices, each of size [55x55]


What does width 96 means? Does it mean 96 color channels? Why can we have more than 3 color channels?
It means that the number of filters (a.k.a. kernels, or  feature detector) in the previous convolutional layer is 96. You may want to watch the video of the lecture, and in particular this slide, which mentions that a filter is applied to the full depth of your previous layer: