Support middle on Gray

Gray is the only one with an order, so no other colorants make sense

Author: timholy

src/ColorVectorSpace.jl

@@ -28,7 +28,7 @@ import Base:      conj, sin, cos, tan, sinh, cosh, tanh,
                   gamma, lfact, frexp, modf, airy, airyai,
                   airyprime, airyaiprime, airybi, airybiprime,
                   besselj0, besselj1, bessely0, bessely1,
-                  eta, zeta, digamma, float
+                  eta, zeta, digamma, float, middle
 
 export dotc
 
@@ -202,6 +202,9 @@ for op in unaryOps
     @eval ($op)(c::AbstractGray) = $op(gray(c))
 end
 
+middle(c::AbstractGray) = base_colorant_type(c)(middle(gray(c)))
+middle(x::C, y::C) where {C<:AbstractGray} = C(middle(gray(x), gray(y)))
+
 (*)(f::Real, c::AbstractGray) = base_colorant_type(c){multype(typeof(f),eltype(c))}(f*gray(c))
 (*)(f::Real, c::TransparentGray) = base_colorant_type(c){multype(typeof(f),eltype(c))}(f*gray(c), f*alpha(c))
 (*)(c::AbstractGray, f::Real) = (*)(f, c)

test/runtests.jl

@@ -118,6 +118,8 @@ end
 
         @test typeof(float(Gray{N0f16}(0.5))) <: AbstractFloat
         @test quantile( Gray{N0f16}[0.0,0.5,1.0], 0.1) ≈ 0.10000152590218968
+        @test middle(Gray(0.2)) === Gray(0.2)
+        @test middle(Gray(0.2), Gray(0.4)) === Gray((0.2+0.4)/2)
     end
 
     @testset "Comparisons with Gray" begin