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Advanced

Emphasizing gradients

Sobel filter - Activate Sobel-filter to work on a differentiated image

Morphology and smoothing

[e=erode, d=dilate] - Erode (remove) or dilate (add) the found blob area
- Example : e2d2 - erode two pixels before dilating 2 pixels
Smooth factor - smoothing of the blob contour - used to correct the result contour length and to measure circularity

Bounding box and axes calculation

Defines the blob axes and accompanying bounding box calculations:

1. Blob Axes - the blob shape is used to calculate a set of axes; the bounding box follows these axes, and will normally not be the smallest possible.

In this mode, the tool does not calculate a true (minimum) bounding box. The blob axes (and hence the "bounding box") are calculated using different order moments of the surrounding polygon and an eigenvalue analysis of a matrix containing the moments of inertia.
The major/minor axes are sound results in some respects, but using the true minimum bounding box gives more understandable results.

2. Minimum Bounding Box - the smallest possible bounding box is found; the blob axes are defined by this box
- This method is legacy - only kept for backward compatibility - best practice replacement is 4. Minimum Area
3. Bounding Box - the smallest bounding box without rotation
- This mode will align the bounding box with the axis in the incoming reference system.
4. Minimum Area - defined by the smallest surrounding area with rotation - default

Blob center definition

This sets how the blob center results are computed

1. Bounding Box Center

2. Blob Center of Gravity - default

Rotation of child reference

When checked, the reference system delivered by Blob4 also includes an angle. When unchecked, only the best blob position is reflected.

Blob angle limit

Restrict blob angles to nominal value +/- 90 deg - useful when a "positive" blob direction is known and needed

Sort results by

This sets the order of the reported blobs:

Contour area - (default) sort results by contour area
- Ascending area - smallest first
Strictly by X position
Strictly by Y position
Grid: X then Y position
Grid: Y then X position
- Ascending X
- Ascending Y
Grid distance - used to cluster positions into row and columns

Hole filter

Blob holes can be filtered out based on size:

Ignore holes smaller than
Ignore holes larger than

Noise filter

Blobs can be filtered out based on probability when the average blob intensity is close to a threshold.

Eliminate noise blobs - turn on to filter noise blobs close to a threshold
Std - assumed standard deviation of pixel noise in image

String Results (Python tuples)

All centers string - all blob centers
Convex hull strings - first 32 blob convex hulls (disabled if Use blob axes are used [above])

Bounding box strings - first 32 bounding boxes (as polygons)

Contour/holes strings - first 32 blob contour polygons with two largest holes, if any

Simplify - creates a smaller polygon by eliminating redundant points
Tol. (pix) - redundancy threshold

Note: turn off to save processing time

Decimation (disabled if Sobel filter is active)

Decimate - decimate image before analysis for a huge speed boost. Some accuracy is lost
Decimation factor - decimate by keeping only every factor pixel in x and y directions

Intensity calculation

Calculate blob intensity/std (disabling will increase processing speed) - another option to speed up processing

Note: Constraints/Feature classification involving will break if this is turned off.

Cluster blobs (after constraints)

After constraints have been applied to the blobs found, they may be clustered. Clustering is done by grouping neighbour blobs and calculating the convex hull surrounding the group. As a safety measure, a maximum time allowed for the clustering can be given.

Cluster blobs closer than - turns clustering on/off
Distance - distance between the blobs. See options below for the interpretation of this

Max clustering time - turn on or off max time allowed for clustering

Seconds - max clustering time in seconds

Replace clustered blobs - default behaviour: remove any blobs belonging to a cluster
Add to results - retain all blobs even when they are members of a cluster
Cluster by center distance - Normally, the distance between blobs is measured as the smallest distance between the blob contour polygons, which can be a time-consuming operation. If this option is checked, distance between blobs is defined as the center distance. Useful if the blob sizes are similar. You should also increase the Distance setting some.
Eliminate blobs by center position - when Replace clustered blobs is selected, any blobs completely within the cluster hulls are removed. You can gain a little speed by only testing if the blob centers are within the hulls instead.