OpenCV: cv::SimpleBlobDetector Class Reference

| OpenCV 3.4.2 Open Source Computer Vision

Classes | Public Member Functions | Static Public Member Functions | List of all members
cv::SimpleBlobDetector Class Reference
2D Features Framework » Feature Detection and Description

Class for extracting blobs from an image. : More...

`#include "features2d.hpp"`

Inheritance diagram for cv::SimpleBlobDetector:

## Classes
struct | Params

## Public Member Functions
virtual String | getDefaultName () const CV_OVERRIDE
Public Member Functions inherited from cv::Feature2D
virtual | ~Feature2D ()
virtual void | compute (InputArray image, std::vector< KeyPoint > &keypoints, OutputArray descriptors)
| Computes the descriptors for a set of keypoints detected in an image (first variant) or image set (second variant). More...
virtual void | compute (InputArrayOfArrays images, std::vector< std::vector< KeyPoint > > &keypoints, OutputArrayOfArrays descriptors)
virtual int | defaultNorm () const
virtual int | descriptorSize () const
virtual int | descriptorType () const
virtual void | detect (InputArray image, std::vector< KeyPoint > &keypoints, InputArray mask=noArray())
| Detects keypoints in an image (first variant) or image set (second variant). More...
virtual void | detect (InputArrayOfArrays images, std::vector< std::vector< KeyPoint > > &keypoints, InputArrayOfArrays masks=noArray())
virtual void | detectAndCompute (InputArray image, InputArray mask, std::vector< KeyPoint > &keypoints, OutputArray descriptors, bool useProvidedKeypoints=false)
virtual bool | empty () const CV_OVERRIDE
| Return true if detector object is empty. More...
void | read (const String &fileName)
virtual void | read (const FileNode &) CV_OVERRIDE
| Reads algorithm parameters from a file storage. More...
void | write (const String &fileName) const
virtual void | write (FileStorage &) const CV_OVERRIDE
| Stores algorithm parameters in a file storage. More...
void | write (const Ptr< FileStorage > &fs, const String &name=String()) const
Public Member Functions inherited from cv::Algorithm
| Algorithm ()
virtual | ~Algorithm ()
virtual void | clear ()
| Clears the algorithm state. More...
virtual void | save (const String &filename) const
void | write (const Ptr< FileStorage > &fs, const String &name=String()) const
| simplified API for language bindings This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. More...

## Static Public Member Functions
static Ptr< SimpleBlobDetector > | create (const SimpleBlobDetector::Params &parameters=SimpleBlobDetector::Params())
Static Public Member Functions inherited from cv::Algorithm
template<typename _Tp >
static Ptr< _Tp > | load (const String &filename, const String &objname=String())
| Loads algorithm from the file. More...
template<typename _Tp >
static Ptr< _Tp > | loadFromString (const String &strModel, const String &objname=String())
| Loads algorithm from a String. More...
template<typename _Tp >
static Ptr< _Tp > | read (const FileNode &fn)
| Reads algorithm from the file node. More...

## Additional Inherited Members
Protected Member Functions inherited from cv::Algorithm
void | writeFormat (FileStorage &fs) const

## Detailed Description

Class for extracting blobs from an image. :

The class implements a simple algorithm for extracting blobs from an image:

1. Convert the source image to binary images by applying thresholding with several thresholds from minThreshold (inclusive) to maxThreshold (exclusive) with distance thresholdStep between neighboring thresholds.
2. Extract connected components from every binary image by findContours and calculate their centers.
3. Group centers from several binary images by their coordinates. Close centers form one group that corresponds to one blob, which is controlled by the minDistBetweenBlobs parameter.
4. From the groups, estimate final centers of blobs and their radiuses and return as locations and sizes of keypoints.

This class performs several filtrations of returned blobs. You should set filterBy* to true/false to turn on/off corresponding filtration. Available filtrations:

- By color. This filter compares the intensity of a binary image at the center of a blob to blobColor. If they differ, the blob is filtered out. Use blobColor = 0 to extract dark blobs and blobColor = 255 to extract light blobs.
- By area. Extracted blobs have an area between minArea (inclusive) and maxArea (exclusive).
- By circularity. Extracted blobs have circularity ( \(\frac{4*\pi*Area}{perimeter * perimeter}\)) between minCircularity (inclusive) and maxCircularity (exclusive).
- By ratio of the minimum inertia to maximum inertia. Extracted blobs have this ratio between minInertiaRatio (inclusive) and maxInertiaRatio (exclusive).
- By convexity. Extracted blobs have convexity (area / area of blob convex hull) between minConvexity (inclusive) and maxConvexity (exclusive).

Default values of parameters are tuned to extract dark circular blobs.

## Member Function Documentation

## ◆ create()

static Ptr<SimpleBlobDetector> cv::SimpleBlobDetector::create | ( | const SimpleBlobDetector::Params & | parameters = `SimpleBlobDetector::Params()` | ) |
| static

## ◆ getDefaultName()

virtual String cv::SimpleBlobDetector::getDefaultName | ( |  | ) | const
| virtual

Returns the algorithm string identifier. This string is used as top level xml/yml node tag when the object is saved to a file or string.

Reimplemented from cv::Feature2D.

The documentation for this class was generated from the following file:

- features2d/include/opencv2/features2d.hpp