croplayer.py

class CropLayer(object):
    def __init__(self, params, blobs):
        # initialize our starting and ending (x, y)-coordinates of
        # the crop
        self.startX = 0
        self.startY = 0
        self.endX = 0
        self.endY = 0

    def getMemoryShapes(self, inputs):
        # the crop layer will receive two inputs -- we need to crop
        # the first input blob to match the shape of the second one,
        # keeping the batch size and number of channels
        (inputShape, targetShape) = (inputs[0], inputs[1])
        (batchSize, numChannels) = (inputShape[0], inputShape[1])
        (H, W) = (targetShape[2], targetShape[3])

        # compute the starting and ending crop coordinates
        self.startX = int((inputShape[3] - targetShape[3]) / 2)
        self.startY = int((inputShape[2] - targetShape[2]) / 2)
        self.endX = self.startX + W
        self.endY = self.startY + H

        # return the shape of the volume (we'll perform the actual
        # crop during the forward pass
        return [[batchSize, numChannels, H, W]]


    def forward(self, inputs):
        # use the derived (x, y)-coordinates to perform the crop
        return [inputs[0][:, :, self.startY:self.endY,self.startX:self.endX]]