add WarpAffine

Author: lorenzoh

Project.toml

@@ -14,6 +14,7 @@ Interpolations = "a98d9a8b-a2ab-59e6-89dd-64a1c18fca59"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 OffsetArrays = "6fe1bfb0-de20-5000-8ca7-80f57d26f881"
 Parameters = "d96e819e-fc66-5662-9728-84c9c7592b0a"
+Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 Rotations = "6038ab10-8711-5258-84ad-4b1120ba62dc"
 Setfield = "efcf1570-3423-57d1-acb7-fd33fddbac46"
 StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"

src/DataAugmentation.jl

@@ -12,6 +12,7 @@ using Interpolations
 using OffsetArrays: OffsetArray
 using LinearAlgebra: I
 using Parameters
+using Random
 using Rotations
 using Setfield
 using StaticArrays
@@ -32,6 +33,7 @@ include("./projective/bounds.jl")
 include("./projective/compose.jl")
 include("./projective/crop.jl")
 include("./projective/affine.jl")
+include("./projective/warp.jl")
 include("./preprocessing.jl")
 include("./colortransforms.jl")
 
@@ -68,6 +70,7 @@ export Item,
     OneHot,
     apply,
     Reflect,
+    WarpAffine,
     FlipX,
     FlipY,
     PinOrigin,

src/projective/warp.jl

@@ -0,0 +1,46 @@
+"""
+    WarpAffine(σ = 0.1) <: ProjectiveTransform
+
+A three-point affine warp calculated by randomly moving 3 corners
+of an item. Similar to a random translation, shear and rotation.
+"""
+struct WarpAffine <: ProjectiveTransform
+    σ
+end
+
+
+getrandstate(::WarpAffine) = abs(rand(Int))
+
+
+function getprojection(
+        tfm::WarpAffine,
+        bounds::AbstractArray{SVector{2, T}};
+        randstate = getrandstate(tfm)) where T
+    rng = Random.seed!(Random.MersenneTwister(), randstate)
+    scale = sqrt(prod(boundssize(bounds)))
+
+    srcps = shuffle(bounds)[1:3]
+    offsets = rand(SVector{2, T}, 3)
+	offsets = map(v -> (v .* (2one(T)) .- one(T)) .* convert(T, scale * tfm.σ), offsets)
+	return threepointwarpaffine(srcps, srcps .+ offsets)
+end
+
+
+# Adapted from
+"""
+    threepointwarpaffine(srcps, dstps)
+
+Calculate an affine [`CoordinateTransformations.LinearMap`](#)
+from 3 source points to 3 destination points.
+
+Adapted from  [CoordinateTransformations.jl#30](https://github.com/JuliaGeometry/CoordinateTransformations.jl/issues/30#issuecomment-610337378).
+"""
+function threepointwarpaffine(
+        srcps::T, dstps::T) where {V, T<:AbstractArray{<:SVector{2,V}}}
+	X = vcat(hcat(dstps...), ones(1,3))'
+    Y = hcat(srcps...)'
+    c = (X \ Y)'
+    A = SMatrix{2, 2, V}(c[:, 1:2])
+    b = SVector{2, V}(c[:, 3])
+    AffineMap(A, b)
+end

test/projective/warp.jl

@@ -0,0 +1,15 @@
+
+include("../imports.jl")
+
+@testset ExtendedTestSet "WarpAffine" begin
+    tfm = WarpAffine(0.1)
+    image = Image(rand(RGB, 50, 50))
+
+    @test_nowarn apply(tfm, image)
+    @test boundssize(getbounds(apply(tfm, image))) != (50, 500)
+    buf = apply(tfm, image)
+    ctfm = tfm |> CenterCrop((50, 50))
+    @test_nowarn apply(ctfm, image)
+    buf = apply(ctfm, image)
+    @test_nowarn apply!(buf, ctfm, image)
+end

test/runtests.jl

@@ -9,6 +9,7 @@ include("./imports.jl")
     include("projective/compose.jl")
     include("projective/crop.jl")
     include("projective/affine.jl")
+    include("projective/warp.jl")
     include("items/image.jl")
     include("items/keypoints.jl")
     include("items/mask.jl")