Multiplication between RGB types seems to be missing

[a-r-n-o-l-d]

julia> RGB{Float64}(1, 1, 1) * RGB{Float64}(1, 1, 1)
ERROR: MethodError: no method matching *(::RGB{Float64}, ::RGB{Float64})
Closest candidates are:
  *(::Any, ::Any, ::Any, ::Any...) at operators.jl:529
  *(::Real, ::AbstractRGB) at /home/afertin/.julia/packages/ColorVectorSpace/wI546/src/ColorVectorSpace.jl:123
  *(::AbstractRGB, ::Real) at /home/afertin/.julia/packages/ColorVectorSpace/wI546/src/ColorVectorSpace.jl:147
  ...
Stacktrace:
 [1] top-level scope at none:0

If I add:

import Base.*, ColorVectorSpace.color_rettype, ColorVectorSpace.multype
(*)(a::AbstractRGB{S}, b::AbstractRGB{T}) where {S,T} = color_rettype(a,b){multype(S,T)}(red(a)*red(b), green(a)*green(b), blue(a)*blue(b))

therefore, I can multiply two RGB images.

[timholy]

Why is channelwise the right definition of rgb1*rgb2? What if someone else thinks it should be the channelwise dot product? And someone else thinks it's the outer product,

[r1*r2 r1*g2 r1*b2;
 g1*r2 g1*g2 g1*b2;
 b1*r2 b1*g2 b1*b2]

[a-r-n-o-l-d]

OK I understand the ambiguity here. I was surprised, because channelwise product is more common in image processing libraries. Sorry about that.

[timholy]

julia> using Colors

julia> chantimes(c1, c2) = mapc(*, c1, c2)
chantimes (generic function with 1 method)

julia> c1, c2 = rand(RGB{Float32}), rand(RGB{Float32})
(RGB{Float32}(0.5848855f0,0.29970312f0,0.60462904f0), RGB{Float32}(0.57155025f0,0.32285166f0,0.91198397f0))

julia> chantimes(c1, c2)
RGB{Float32}(0.33429143f0,0.09675965f0,0.551412f0)

julia> using TestImages

julia> img = testimage("lighthouse");

julia> chantimes.(img, img)

If this is not discoverable, a democard would be wonderful!

[timholy]

Actually, it also occurs to me that we might have enough operators to distinguish this: ⋅ (\cdot), *, and ⊗ (\otimes). Assuming all these are broadcastable then perhaps we could define this operation. What do others think?

[johnnychen94]

Assuming all these are broadcastable then perhaps we could define this operation.

Great idea and I think it would be really useful! Although for me the only problem is that I can't type these symbols in vscode 😂

[timholy]

julia-vscode/julia-vscode#613 suggests you might try this extension: https://marketplace.visualstudio.com/items?itemName=GuidoTapia2.unicode-math-vscode

[timholy]

Closed by #131