       do callback
       return
 
+    c.params.step = defaultStep unless c.params.step
     ctx = canvas.getContext '2d'
     imageData = ctx.getImageData 0, 0, canvas.width, canvas.height
     result =

noflo = require 'noflo'
d3 = require 'd3-color'
# @runtime noflo-nodejs

zero = (a) ->
  for i in [0...a.length]


  c.inPorts.add 'canvas',
    datatype: 'object'
  c.inPorts.add 'step',
    datatype: 'number'
  c.outPorts.add 'histogram',
    datatype: 'object'
  c.outPorts.add 'error',
