The MV Blob Counter filter counts all blobs (objects or contours) within an image. The filter contains two filters for blobs. One filter excludes all blobs outside a minimum and maximum size. The second filter excludes all blobs whose seven "hu invariants" are outside a minimum and maximum value. Hu invariants are proved to be invariants to the image scale, rotation, and reflection except the seventh one, whose sign is changed by reflection. Use the invariants to detect objects within a video stream.

New interfaces (IMVBlobCounter2 and IMVBlobCounter3) extend the filter to provide detailed information about the recognized blobs, including size, position, angle, bounding rectangle and average blob color.

This MontiVision DirectShow Filter is used in combination with the MontiVision Smart Control in the BlobCounter and FindObject Sample Applications.

File:	blobcounter.ax
CLSID:	CLSID_MVBlobCounter

Supported Interfaces

Supported COM Events

The filter supports following events through the IMVFilterEvents interface. Look at the filter events page for more information.

Event	Value	Description
MV_ALGORITHM_START_EVENT	0	A filter starts processing a video frame or sample.
MV_ALGORITHM_END_EVENT	1	A filter finishes processing a video frame or sample.

Supported I/O Pins

I/O Pin	Corresponding method	Discription
Count [int 32]	IMVBlobCounter::get_BlobCount	Blob count from the current image.
Threshold [uint8]	IMVBlobPreProcessing::put_SegmentationThreshold	Segmentation threshold.

MV Blob Counter Property Pages

Uses the IMVBlobCounter configuration interface.

MontiVision Blob Counter DirectShow Filter Property Page
Blob counter filter property page

External	Use only external contours. All contours (blobs) within an other blob are ignored.
List	All blobs are arranged in on list.
Two level	The blobs are arranged into a two level list. All external blobs are in the first level. All other blobs are in the second level. The filter counts all first level blobs.
Tree	Same as Two level option, but internal all blobs are arranged in a tree.
Draw Contour	Draw blob contour into the output image.
use convex hull	Use the convex hull.
use approximate contour	Use an approximation algorithm to reduce the contour complexity.
accurency	Accuracy value for the approximation algorithm.
Draw	Draw count result into the output image.
x	X-position for the output text.
y	Y-position for the output text
Evaluate blob contour properties	Enables the calculation of the blob contour properties provided by the IMVBlobFinder2 interface.
Calculate Average Color	Calculates the average color value for every blob.
Redraw Blobs	Redraws the blobs using their average color.

MontiVision Blob Counter DirectShow Filter Contour Filter Property Page

enable contour filter	Enable the contour filter
contour size	Enable size contour filter
width	Minimum and maximum value for the contour width.
height	Minimum and maximum value for the contour height.
hu invariants	Enable hu invariants contour filter.
hu 1 to hu 7	Minimum and maximum value for the seven hu invariants.

MontiVision Blob Counter DirectShow Filter Pre-Processing Property Page

Segmentation Threshold	Threashold value for image segmentation.
Draw Segmentation	The output image cotains the result after segmentation and edge detection.
Edge Detection	Select the algorithm for edge detection.
Blob Type	Find dark or bright blobs.