Hello! I'm trying to implement Otsu's method of image thresholding on an incoming raster, using the PythonCaller transformer. I have the following code block in the PythonCaller parameters, although my Python isn't great, so there may well be issues with it:
import fme
import fmeobjects
import numpy as np
class OtsuThreshold(object):
def __init__(self):
pass
def input(self, feature):
#implement Otsu thresholding in native Python with numpy
#get the image from the feature
image = feature.getAttribute('image')
#compute the histogram of the image, then find the peak of the histogram
hist = np.histogram(image, bins=256, range=(0, 256))
maxVal = np.max(hist[0])
maxLoc = np.argmax(hist[0])
#perform Otsu thresholding
T = maxLoc
thresh = np.where(image > T, 255, 0)
#set the attribute value
feature.setAttribute('image', thresh)
#pass the feature on to the next transformer
self.pyoutput(feature)I am getting this error, seemingly within histograms.py within numpy itself:
Python Exception <TypeError>: '>=' not supported between instances of 'NoneType' and 'int'A little digging hints that this may indicate that the raster is being read as None values, which I can seemingly confirm by inserting the following before the "hist" array:
if image is None or len(image) == 0:
# handle empty image
# for example, you could return an empty feature
returnThis is where I hit a dead end though.
Ideally I would like to return the actual Otsu threshold pixel value itself as an attribute, although I don't think my script it currently capable of that.
Thank you!
