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

maxLen = 20 -- maximum sensible length of signature

-- from Java class "SegmentCounter"

function countSegments(y, flip)
  local lastPix = 1
  local segments = 0
  for x = 0, (flip and h or w)-1 do
    local pix = bright(rgb(flip and img.getInt(y, x) or img.getInt(x, y)))
    if pix >= brightnessThreshold and lastPix < brightnessThreshold then
      segments = segments+1
    end
    lastPix = pix
  end
  if lastPix < brightnessThreshold then segments = segments+1 end
  return segments
end

function getSegmentCount(flip)
  local s = ""
  
  local lastN = 0
  for y = 0, (flip and w or h)-1 do
    local n = math.min(countSegments(y, flip), 9)
    if n ~= lastN then
      s = s..n
      if #s > maxLen then return end
    end
    lastN = n
  end
  if lastN == 0 and #s > 0 then
    return s:sub(1, #s-1)
  else
    return s
  end
end

w, h = img.width, img.height
brightnessThreshold = 0.9

s = getSegmentCount(true)
if s then
  return "Horizontal signature: "..s
end

See also: #334