get("#348") -- rgb functions
get("#346") -- getcrop
get("#337") -- map(list, f)

w, h = img.width, img.height
brightnessThreshold = 0.95

function averageBrightness(img, x1, y1, x2, y2)
  local b = 0
  for y=y1, y2-1 do
    for x=x1, x2-1 do 
      b = b+bright(rgb(img.getInt(x, y)))
    end
  end
  return b/((x2-x1)*(y2-y1))
end

function isEmpty(x)
  return averageBrightness(img, x, 0, x+1, h) > brightnessThreshold
end

lastEmpty = true
segments = {}

for x=0, w-1 do
  empty = isEmpty(x)
  if empty and not lastEmpty then
    table.insert(segments, {start, x})
  elseif not empty and lastEmpty then
    start = x
  end
  lastEmpty = empty
end

if not lastEmpty then
  table.insert(segments, {start, w})
end

if #segments <= 1 then -- don't bother with only 1 segment
  return
end

result = {}
for _, seg in ipairs(segments) do
  local sx1, sx2 = unpack(seg)
  
  local cropped = {
    width = sx2-sx1,
    height = img.height,
    getInt = function(x, y)
      return img.getInt(x+sx1, y)
    end
  }
  local x1, y1, x2, y2 = getcrop(cropped)
  table.insert(result, (x1+sx1)..", "..y1..", "..(x2+sx1)..", "..y2)
end

return "Parts: "..table.concat(result, "|")

Began life as a copy of #345