get("#348") -- rgb functions

get("#479") -- getcrop2

get("#337") -- map(list, f)

get("#388") -- rectangle functions

brightnessThreshold = 0.9

function horizontalsplit(img)

  local function isEmpty(x)

    for y=0, img.height-1 do

      if bright(rgb(img.getInt(x, y))) <= brightnessThreshold then

        return false

      end

    end

    return true

  end

  local lastEmpty, start = true, nil

  local segments = {}

  for x=0, img.width-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, img.width})

  end

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

    return {}

  end

  local 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 = getcrop2(cropped)

    table.insert(result, newRectangle(x1+sx1, y1, x2-x1, y2-y1))

  end

  return result

end