Unable to figure out nInputPlane in SpatialConvolution in torch?
The nInputPlane is the depth or the number of the layers of the input image. In case of RGB images, this should be 3 which corresponds to the first number in the input_shape=(3, 256, 256).

The nOutputPlane is the the number of the layers of the volume that the convolution step will produce which is also the number of filters/kernels applied to the input. By convention, there is an output layer for each filter. This corresponds to the first argument of the Convolution2D function.