"Blobs" are connected regions that stand out from their surroundings, usually in terms of pixel intensity. Such regions, once found, are marked in the output image with sequential numeric labels. Pixels belonging to the first detected blob have a value of one. Zero means background.
The Blob Detection Tool has two modes of operation. The mode is selected by setting the
Threshold Type parameter to either static or dynamic thresholding mode.
In the static mode you can set an absolute threshold which the intensity of each pixel in the object must exceed. If the
Invert flag is
false, the qualified pixels are brighter than the threshold. Setting the flag to
true reverses the logic. In the example below, the threshold is set such that pixels with an intensity of 200 or higher are qualified. Notice that in the labels in the lower image have different colors because the image is displayed with a "light colors" color map.
In the dynamic mode the tool decides the threshold automatically and separately for each blob. You can set the sensitivity with which the tool tries to identify prominent objects. The smaller the sensitivity, the sharper the edge of a region must be in order to qualify as a detected blob. in the example below, the sensitivity is set to a value which qualifies both high and low contrast pills.
You can also set the minimum and maximum sizes of the regions which will be qualified as blobs. Blob sizes are calculated in world units using an approximate scaling factor for each blob. If the image has bad perspective distortion, the limits may not be accurate.