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

function getLeftmostPoint(img, y)
  local x1 = 0
  while x1 < img.width and img.getInt(x1, y) >= 0xF00000 do
    x1 = x1+1
  end
  return x1
end

function getRightmostPoint(img, y)
  local x2 = img.width
  while x2 > 0 and img.getInt(x2-1, y) >= 0xF00000 do
    x2 = x2-1
  end
  return x2
end

function getWidth(img, y)
  local x2 = getRightmostPoint(img, y)
  local x1 = getLeftmostPoint(img, y)
  return math.max(0, x2-x1)
end

function getAverageWidth(img, y1, y2)
  local sum = 0
  for y = y1, y2-1 do
    sum = sum+getWidth(img, y)
  end
  return sum/(y2-y1)
end

function getAverageLeft(img, y1, y2)
  y1, y2 = y1 or 0, y2 or img.height -- default arguments
   
  local sum = 0
  for y = y1, y2-1 do
    sum = sum+getLeftmostPoint(img, y)
  end
  return sum/(y2-y1)
end

function getAverageLeft_debug(img, y1, y2)
  y1, y2 = y1 or 0, y2 or img.height -- default arguments
   
  local sum = 0
  for y = y1, y2-1 do
    local x = getLeftmostPoint(img, y)
    sum = sum+x
    print("y", y, "left", x)
  end
  return sum/(y2-y1)
end

function getMaxWidth(img, y1, y2)
  local max = 0
  for y = y1, y2-1 do
    max = math.max(max, getWidth(img, y))
  end
  return max
end

function upperWidth(img)
  return getAverageWidth(img, 0, math.floor(img.height/3))
end

function upperMaxWidth(img)
  return getMaxWidth(img, 0, math.floor(img.height/3))
end

function lowerWidth(img)
  return getAverageWidth(img, math.floor(img.height*2/3), img.height)
end

function lowerMaxWidth(img)
  return getMaxWidth(img, math.floor(img.height*2/3), img.height)
end

function upperToLowerWidth(img)
  return upperWidth(img) / lowerWidth(img)
end

function getCenterOfGravity(img)
  local sumx, sumy, sumdensity = 0, 0, 0
  for y=0, img.height-1 do
    for x=0, img.width-1 do
      local density = 1-bright(rgb(img.getInt(x,y)))
      sumdensity = sumdensity+density
      sumx = sumx+density*x
      sumy = sumy+density*y
    end
  end
  return sumx/sumdensity, sumy/sumdensity
end

Similar to #343, but with "img" argument