Filtering blobs when only one blob is detected

[dschaele]

Hey, I noticed that when I apply filters to the list of detected blobs and only one blob is in the list, this blob will not be returned even though it is within the filter criteria. I am not sure if that behavior is intended, but for my applications at least it's unfortunate.

Consider this minimal example:

from machinevisiontoolbox import Image
from matplotlib import pyplot as plt

img = Image.Zeros(1000, dtype="uint8")
img.A[300:400, 200:300] = 255
#img.A[100:105, 100:105] = 255
img.disp(block=False)

blobs=img.blobs()
print(blobs)
print('Blob_0 area:')
print(blobs[0].area)
blobs.plot_box(color='g')
blobs.plot_centroid(label=True)
plt.show(block=True)

blobs_filtered = blobs.filter(area=100)
print("Filtered blobs:")
print(blobs_filtered)

The terminal output is:

So even though the blob has an area > 100 it is not returned from the filtering. When applying the same filter with two detected blobs, everything works fine.

A potential fix is in ImageBlobs.py, Line 482 to flatten the mask variable m: return self[m] -> return self[m.flatten()]