get("#348") -- bright and rgb

function getContrast(img)
  
  local w, h = img.width, img.height
  local min, max = 1, 0

  for y = 0, h-1 do
    for x = 0, w-1 do
      local b = bright(rgb(img.getInt(x, y)))
      min, max = math.min(min, b), math.max(max, b)
    end
  end

  local minp = math.floor(min*100+0.5)
  local maxp = math.floor(max*100+0.5)
  return minp, maxp, min, max
end

Began life as a copy of #371