Conv(filter, in => out, σ = identity;
     stride = 1, pad = 0, dilation = 1, groups = 1, [bias, init])

Standard convolutional layer. filter is a tuple of integers specifying the size of the convolutional kernel; in and out specify the number of input and output channels.

Image data should be stored in WHCN order (width, height, channels, batch). In other words, a 100×100 RGB image would be a 100×100×3×1 array, and a batch of 50 would be a 100×100×3×50 array. This has N = 2 spatial dimensions, and needs a kernel size like (5,5), a 2-tuple of integers.

To take convolutions along N feature dimensions, this layer expects as input an array with ndims(x) == N+2, where size(x, N+1) == in is the number of input channels, and size(x, ndims(x)) is (as always) the number of observations in a batch. Then:

• filter should be a tuple of N integers.

• Keywords stride and dilation should each be either single integer, or a tuple with N integers.

• Keyword pad specifies the number of elements added to the borders of the data array. It can be

  • a single integer for equal padding all around,

  • a tuple of N integers, to apply the same padding at begin/end of each spatial dimension,

  • a tuple of 2*N integers, for asymmetric padding, or

  • the singleton SamePad(), to calculate padding such that size(output,d) == size(x,d) / stride (possibly rounded) for each spatial dimension.

• Keyword groups is expected to be an Int. It specifies the number of groups to divide a convolution into.

Keywords to control initialization of the layer:

• init - Function used to generate initial weights. Defaults to glorot_uniform.

• bias - The initial bias vector is all zero by default. Trainable bias can be disabled entirely by setting this to false, or another vector can be provided such as bias = randn(Float32, out).

See also ConvTranspose, DepthwiseConv, CrossCor.

Examples

			julia> xs = rand(Float32, 100, 100, 3, 50); # a batch of images

julia> layer = Conv((5,5), 3 => 7, relu; bias = false)
Conv((5, 5), 3 => 7, relu, bias=false)  # 525 parameters

julia> layer(xs) |> size
(96, 96, 7, 50)

julia> Conv((5,5), 3 => 7; stride = 2)(xs) |> size
(48, 48, 7, 50)

julia> Conv((5,5), 3 => 7; stride = 2, pad = SamePad())(xs) |> size
(50, 50, 7, 50)

julia> Conv((1,1), 3 => 7; pad = (20,10,0,0))(xs) |> size
(130, 100, 7, 50)

julia> Conv((5,5), 3 => 7; stride = 2, dilation = 4)(xs) |> size
(42, 42, 7, 50)

			Conv(weight::AbstractArray, [bias, activation; stride, pad, dilation])

Constructs a convolutional layer with the given weight and bias. Accepts the same keywords and has the same defaults as [ Conv(k::NTuple{N,Integer}, ch::Pair{<:Integer,<:Integer}, σ; ...)]( Conv).

			julia> weight = rand(3, 4, 5);

julia> bias = zeros(5);

julia> layer = Conv(weight, bias, sigmoid)  # expects 1 spatial dimension
Conv((3,), 4 => 5, σ)  # 65 parameters

julia> layer(randn(100, 4, 64)) |> size
(98, 5, 64)

julia> Flux.params(layer) |> length
2