You can extract the desired number of layers from the pretrained net and define your choice of network. Here is an small example for extracting the desired layers.
net = vgg16;
lastFeatureLayerIdx = 32;
layers = net.Layers;
middlelayers = layers(2:lastFeatureLayerIdx);
Now, you can define your choice of input layer and final layer (i.e. classification layer) and then combine them with the middle layers to get the complete network.
layers = [
inputLayer
middleLayers
finalLayers
]
Now, you can leverage this link to get an idea how to perform object detection using R-CNN:
