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Properly fix moments for OpenCV single-pixel / single-line segments #10

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Properly fix moments for OpenCV single-pixel / single-line segments #10

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35 changes: 31 additions & 4 deletions machinevisiontoolbox/ImageBlobs.py
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Original file line number Diff line number Diff line change
Expand Up @@ -237,10 +237,37 @@ def __init__(self, image=None, **kwargs):

blob.contourpoint = blob.perimeter[:, 0]

## For a single set pixel OpenCV returns all moments as zero, skip such blobs
## TODO handle this situation by setting m00=1, m10=x, m01=y etc.
if blob.moments["m00"] != 0:
self.data.append(blob)
## For a single set pixel OpenCV returns non-sense, let's fix it
if blob.moments["m00"] == 0:
# Raw moments
for uv in contour:
for p, q in [(0, 0), (1, 0), (0, 1), (2, 0), (1, 1), (0, 2), (3, 0), (2, 1), (1, 2), (0, 3)]:
u = uv[0]
v = uv[1]
blob.moments[f"m{p}{q}"] += u ** p * v ** q

# Central moments
blob.moments["mu10"] = blob.moments["mu01"] = 0
blob.moments["mu20"] = blob.moments["m20"] - blob.moments["m10"] ** 2 / blob.moments["m00"]
blob.moments["mu02"] = blob.moments["m02"] - blob.moments["m01"] ** 2 / blob.moments["m00"]
blob.moments["mu11"] = blob.moments["m11"] - blob.moments["m10"] * blob.moments["m01"] / blob.moments["m00"]

# Third-order central moments
blob.moments["mu30"] = blob.moments["m30"] - 3 * blob.moments["m20"] * blob.moments["m10"] / blob.moments["m00"] + 2 * (blob.moments["m10"] ** 3) / (blob.moments["m00"] ** 2)
blob.moments["mu03"] = blob.moments["m03"] - 3 * blob.moments["m02"] * blob.moments["m01"] / blob.moments["m00"] + 2 * (blob.moments["m01"] ** 3) / (blob.moments["m00"] ** 2)
blob.moments["mu21"] = blob.moments["m21"] - 2 * blob.moments["m11"] * blob.moments["m10"] / blob.moments["m00"] - blob.moments["m20"] * blob.moments["m01"] / blob.moments["m00"] + 2 * (blob.moments["m10"] ** 2 * blob.moments["m01"]) / (blob.moments["m00"] ** 2)
blob.moments["mu12"] = blob.moments["m12"] - 2 * blob.moments["m11"] * blob.moments["m01"] / blob.moments["m00"] - blob.moments["m02"] * blob.moments["m10"] / blob.moments["m00"] + 2 * (blob.moments["m01"] ** 2 * blob.moments["m10"]) / (blob.moments["m00"] ** 2)

# Normalised central moments
blob.moments["nu20"] = blob.moments["mu20"] / (blob.moments["m00"] ** (1 + (2 / 2)))
blob.moments["nu02"] = blob.moments["mu02"] / (blob.moments["m00"] ** (1 + (2 / 2)))
blob.moments["nu11"] = blob.moments["mu11"] / (blob.moments["m00"] ** (1 + (2 / 2)))

# Third-order normalised moments
blob.moments["nu30"] = blob.moments["mu30"] / (blob.moments["m00"] ** (1 + (3 / 2)))
blob.moments["nu03"] = blob.moments["mu03"] / (blob.moments["m00"] ** (1 + (3 / 2)))
blob.moments["nu21"] = blob.moments["mu21"] / (blob.moments["m00"] ** (1 + (3 / 2)))
blob.moments["nu12"] = blob.moments["mu12"] / (blob.moments["m00"] ** (1 + (3 / 2)))

## second pass: equivalent ellipse

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