Added MMMBackground estimator and tests

src/Background/Background.jl

@@ -3,7 +3,8 @@ module Background
 export estimate_background,
        Mean,
        Median,
-       Mode
+       Mode,
+       MMMBackground
 
 
 # Abstract types

src/Background/stat_estimators.jl

@@ -60,3 +60,26 @@ julia> estimate_background(Mode, data)
 struct Mode <: BackgroundEstimator end
 
 estimate_background(::Mode, data; dims = :) = mode(data)
+
+
+"""
+    MMMBackground <: BackgroundEstimator
+
+This estimator returns background using DAOPHOT MMM algorithm.
+The background is estiamated as `3*median - 2*mean`, the factors `3` and `2` can be changed by changing `median_factor` and `mean_factor`.
+
+# Example
+```jldoctest
+julia> x = ones(5,5);
+
+julia> estimate_background(MMMBackground, x)
+1.0
+
+julia> estimate_background(MMMBackground, x, dims = 1)
+1×5 Array{Float64,2}:
+ 1.0  1.0  1.0  1.0  1.0
+```
+"""
+struct MMMBackground <: BackgroundEstimator end
+
+estimate_background(::MMMBackground, data; median_factor = 3, mean_factor = 2, dims = :) = median_factor * median(data, dims = dims) - mean_factor * mean(data, dims = dims)

test/background/simple.jl

@@ -14,7 +14,7 @@ function test_zeros(estimator)
     @test estimate_background(estimator, data, dims = 2) ≈ zeros(10)
 end
 
-@testset "$E"  for E in [Mean, Median]
+@testset "$E"  for E in [Mean, Median, MMMBackground]
     @test estimate_background(E, ones(10, 10)) == estimate_background(E(), ones(10, 10))
     test_ones(E)
     test_zeros(E)