Fix imrotate for Irrational θ (#149)

Author: timholy

Project.toml

@@ -31,8 +31,9 @@ ImageIO = "82e4d734-157c-48bb-816b-45c225c6df19"
 ImageMagick = "6218d12a-5da1-5696-b52f-db25d2ecc6d1"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 ReferenceTests = "324d217c-45ce-50fc-942e-d289b448e8cf"
+Tau = "c544e3c2-d3e5-5802-ac44-44683f340e4a"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 TestImages = "5e47fb64-e119-507b-a336-dd2b206d9990"
 
 [targets]
-test = ["EndpointRanges", "ImageIO", "ImageMagick", "LinearAlgebra", "ReferenceTests", "Test", "TestImages"]
+test = ["EndpointRanges", "ImageIO", "ImageMagick", "LinearAlgebra", "ReferenceTests", "Tau", "Test", "TestImages"]

src/warp.jl

@@ -244,13 +244,19 @@ mosaicview([imgr for _ in 1:9]; nrow=3)
 """
 function imrotate(img::AbstractArray{T}, θ::Real, inds::Union{Tuple, Nothing} = nothing; kwargs...) where T
     # TODO: expose rotation center as a keyword
-    Δ = eps(θ)
-    θ = mod2pi(θ)
+    Δ = eps(float(θ))
+    θ = _mod2pi(θ)
     if abs(θ) <= Δ || abs(θ - 2π) <= Δ
         θ = zero(θ)
     end
-    tform = recenter(RotMatrix{2}(θ), center(img))
+    tform = recenter(rotmtrx2(θ), center(img))
     # Use the `nothing` trick here because moving the `autorange` as default value is not type-stable
     inds = isnothing(inds) ? autorange(img, inv(tform)) : inds
     warp(img, tform, inds; kwargs...)
 end
+_mod2pi(θ) = mod2pi(θ)
+_mod2pi(θ::Irrational{:π}) = θ
+_mod2pi(θ::Irrational) = mod2pi(float(θ))
+
+rotmtrx2(θ) = RotMatrix{2}(θ)
+rotmtrx2(θ::Irrational{:π}) = RotMatrix(@SMatrix [-1 0; 0 -1])

test/warp.jl

@@ -1,5 +1,6 @@
 using CoordinateTransformations, Rotations, TestImages, ImageCore, StaticArrays, OffsetArrays, Interpolations, LinearAlgebra
 using EndpointRanges
+using Tau
 using Test, ReferenceTests
 
 include("twoints.jl")
@@ -465,5 +466,23 @@ NaN  NaN      NaN      NaN      NaN      NaN      NaN
             @test !any(isnan, imrotate(img, π/3, axes(img); fillvalue=0.0))
             @test !any(isnan, imrotate(img, π/3, axes(img), fillvalue=0.0))
         end
+
+        @testset "Examples from #79" begin
+            @test axes(imrotate(img_camera, pi/2)) == axes(img_camera)
+            @test imrotate(imrotate(imrotate(imrotate(img_camera, pi/2), pi/2), pi/2), pi/2) ≈ img_camera
+            @test imrotate(imrotate(img_camera, pi), pi) == img_camera
+            # Also check a "generic" irrational (one that happens to be quite special)
+            ## First, check that this hits the generic code path (if we change that, pick a different irrational)
+            @test ImageTransformations._mod2pi(τ) isa Float64
+            ## Now check that it gives the expected result
+            @test imrotate(img_camera, τ) ≈ img_camera
+
+            # check special rotation degrees
+            img = rand(Gray{N0f8}, 100, 50)
+            @test size(imrotate(img, pi/2)) == (50, 100)
+            @test size(imrotate(img, pi)) == (100, 50)
+            @test size(imrotate(img, 3pi/2)) == (50, 100)
+            @test size(imrotate(img, 2pi)) == (100, 50)
+        end
     end
 end