Save Bool image with 1-bit depth (#172)

Fixes JuliaIO/FileIO.jl#232

Author: timholy

src/ImageMagick.jl

@@ -81,7 +81,11 @@ function _metadata(wand)
     # use an even # of fractional bits for depth>8 (see issue 242#issuecomment-68845157)
     evendepth = ((depth+1)>>1)<<1
     if depth <= 8
-        T = Normed{UInt8,8}     # otherwise use 8 fractional bits
+        if cs == "Gray"
+            T = getimagechanneldepth(wand, GrayChannel) == 1 ? Bool : N0f8
+        else
+            T = Normed{UInt8,8}     # otherwise use 8 fractional bits
+        end
     elseif depth <= 16
         T = Normed{UInt16,evendepth}
     else
@@ -249,15 +253,15 @@ mapIM(c::RGBA{T}) where {T<:Normed} = c
 mapIM(x::UInt8) = reinterpret(N0f8, x)
 mapIM(x::UInt16) = reinterpret(N0f16, x)
 mapIM(x::UInt32) = reinterpret(N0f32, x)
-mapIM(x::Bool) = convert(N0f8, x)
+mapIM(x::Bool) = x
 mapIM(x::AbstractFloat) = convert(N0f8, x)
 mapIM(x::Normed) = x
 
 # Make the data contiguous in memory, this is necessary for
 # imagemagick since it doesn't handle stride.
 to_contiguous(A::Array) = A
 to_contiguous(A::AbstractArray) = collect(A)
-to_contiguous(A::BitArray) = convert(Array{N0f8}, A)
+to_contiguous(A::BitArray) = convert(Array{Bool}, A)
 to_contiguous(A::ColorView) = to_contiguous(channelview(A))
 
 to_explicit(A::Array{C}) where {C<:Colorant} = to_explicit(channelview(A))
@@ -266,6 +270,7 @@ function to_explicit(A::AbstractArray)
     As .= A
     to_explicit(As)
 end
+to_explicit(A::Array{Bool}) = A
 to_explicit(A::Array{T}) where {T<:Normed} = rawview(A)
 to_explicit(A::Array{T}) where {T<:AbstractFloat} = to_explicit(convert(Array{N0f8}, A))
 

src/libmagickwand.jl

@@ -35,6 +35,7 @@ const FLOATPIXEL   = 3
 const INTEGERPIXEL = 4
 const SHORTPIXEL   = 7
 const IMStorageTypes = Union{UInt8,UInt16,UInt32,Float32,Float64}
+storagetype(::Type{Bool})    = CHARPIXEL
 storagetype(::Type{UInt8})   = CHARPIXEL
 storagetype(::Type{UInt16})  = SHORTPIXEL
 storagetype(::Type{UInt32})  = INTEGERPIXEL
@@ -208,7 +209,7 @@ bitdepth(buffer::AbstractArray{C}) where {C<:Colorant} = 8*sizeof(eltype(C))
 bitdepth(buffer::AbstractArray{T}) where {T} = 8*sizeof(T)
 
 # colorspace is included for consistency with constituteimage, but it is not used
-function exportimagepixels!(@nospecialize(buffer::AbstractArray{<:Unsigned}), wand::MagickWand,  colorspace::String, channelorder::String; x = 0, y = 0)
+function exportimagepixels!(@nospecialize(buffer::AbstractArray{<:Union{Unsigned,Bool}}), wand::MagickWand,  colorspace::String, channelorder::String; x = 0, y = 0)
     T = eltype(buffer)
     cols, rows, nimages = getsize(buffer, channelorder)
     ncolors = colorsize(buffer, channelorder)
@@ -235,11 +236,11 @@ end
 #     nothing
 # end
 
-function constituteimage(buffer::AbstractArray{T}, wand::MagickWand, colorspace::String, channelorder::String; x = 0, y = 0) where T<:Unsigned
+function constituteimage(buffer::AbstractArray{T}, wand::MagickWand, colorspace::String, channelorder::String; x = 0, y = 0) where T<:Union{Unsigned,Bool}
     cols, rows, nimages = getsize(buffer, channelorder)
     ncolors = colorsize(buffer, channelorder)
     p = pointer(buffer)
-    depth = bitdepth(buffer)
+    depth = T == Bool ? 1 : bitdepth(buffer)
     for i = 1:nimages
         status = ccall((:MagickConstituteImage, libwand), Cint, (Ptr{Cvoid}, Cssize_t, Cssize_t, Ptr{UInt8}, Cint, Ptr{Cvoid}), wand, cols, rows, channelorder, storagetype(T), p)
         status == 0 && error(wand)

test/constructed_images.jl

@@ -2,6 +2,7 @@ using ImageMagick, ColorTypes, FixedPointNumbers, IndirectArrays, FileIO, Offset
 using ImageShow       # for show(io, ::MIME, img) & ImageMeta
 using Test
 using ImageCore
+using Random, Base.CoreLogging
 
 mutable struct TestType end
 
@@ -27,24 +28,31 @@ mutable struct TestType end
         fn = joinpath(workdir, "5by5.png")
         ImageMagick.save(fn, a)
         b = ImageMagick.load(fn)
-        a8 = convert(Array{Gray{N0f8}}, a) # IM won't read back as Bool
-        @test b == a8
+        ag = convert(Array{Gray{Bool}}, a) # IM won't read back as Bool
+        @test b == ag
+        @test eltype(b) ∈ (Bool, Gray{Bool})
         aim = colorview(Gray, a)
         ImageMagick.save(fn, aim)
         b = ImageMagick.load(fn)
-        @test b == a8
+        @test b == ag
         a = bitrand(5,5)
         fn = joinpath(workdir, "5by5.png")
         ImageMagick.save(fn, a)
         b = ImageMagick.load(fn)
-        a8 = convert(Array{Gray{N0f8}}, a)
-        @test b == a8
+        ag = convert(Array{Gray{Bool}}, a)
+        @test b == ag
         aim = colorview(Gray, a)
         ImageMagick.save(fn, aim)
         b = ImageMagick.load(fn)
-        @test b == a8
+        @test b == ag
 
-        @test ImageMagick.metadata(fn) == ((5,5), Gray{N0f8})
+        @test ImageMagick.metadata(fn) == ((5,5), Gray{Bool})
+
+        # If we try to save as JPG, don't error
+        fn = joinpath(workdir, "5by5.jpg")
+        ImageMagick.save(fn, a)
+        b = ImageMagick.load(fn)
+        @test eltype(b) == Gray{N0f8}
     end
 
     @testset "Gray png" begin