Returns the histogram of the image

Runs ImageMagick's histogram:info:- command.

Results are returned as a list of maps where each map includes keys red, blue, green, hex and count.

Examples

iex> open("test/fixtures/rbgw.png") |> histogram
[
  %{"alpha" => 255, "blue" => 255, "count" => 400, "green" => 0, "hex" => "#0000ff", "red" => 0},
  %{"alpha" => 255, "blue" => 0, "count" => 225, "green" => 255, "hex" => "#00ff00", "red" => 0},
  %{"alpha" => 255, "blue" => 0, "count" => 525, "green" => 0, "hex" => "#ff0000", "red" => 255},
  %{"alpha" => 255, "blue" => 255, "count" => 1350, "green" => 255, "hex" => "#ffffff", "red" => 255}
]