Module imagingbook.common

Package imagingbook.common.image

Class LocalMinMaxFinder

java.lang.Object

imagingbook.common.image.LocalMinMaxFinder

public class LocalMinMaxFinder
extends Object

Provides methods for detecting local maxima or minima in images or 2D data arrays. A local maximum (minimum) is defined as a pixel position whose value is larger (smaller) than all its eight neighboring values. The detection is controlled by a 'threshold' parameter specifying the minimum difference between the center value and the surrounding values. There is also a 'borderWidth' parameter specifying the outer image margins to be ignored. This implementation deliberately provides separate methods getMaxima(int) and getMinima(int) for detecting maxima and minim, respectively. An alternative would be to have only one method and invert the data to obtain the other, but inversion of float-data is not well defined and we wanted the original data values preserved with the returned point sets. (This may change eventually.)

Note that this form of local extremum detection is simple but may fail on ridge points or locally flat spots. See MaximumFinder for a more robust (but also more complicated) implementation.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	LocalMinMaxFinder.ExtremalPoint	A 2D point with integer coordinates and a score value (LocalMinMaxFinder.ExtremalPoint.q) attached.

Constructor Summary

Constructors

Constructor	Description
LocalMinMaxFinder(float[][] fpixels, double threshold, int borderWidth)	Constructor accepting a 2D data array of type float.
LocalMinMaxFinder(ImageProcessor ip)	Constructor accepting an ImageProcessor instance using default parameters.
LocalMinMaxFinder(ImageProcessor ip, double threshold, int borderWidth)	Constructor accepting an ImageProcessor instance.

Method Summary

Modifier and Type	Method	Description
LocalMinMaxFinder.ExtremalPoint[]	getMaxima(int maxCount)	Returns the detected local maxima as an array of type LocalMinMaxFinder.ExtremalPoint.
LocalMinMaxFinder.ExtremalPoint[]	getMinima(int maxCount)	Returns the detected local minima as an array of type LocalMinMaxFinder.ExtremalPoint.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

LocalMinMaxFinder

public LocalMinMaxFinder(float[][] fpixels,
 double threshold,
 int borderWidth)

Constructor accepting a 2D data array of type float.

Parameters:

fpixels - the 2D data array

threshold - the minimum difference between a center value and its 8 surrounding values to be accepted as a local extremum

borderWidth - width of border margin to be ignored (> 0)

LocalMinMaxFinder

public LocalMinMaxFinder(ImageProcessor ip,
 double threshold,
 int borderWidth)

Constructor accepting an ImageProcessor instance. Color images are converted to scalar float values for extremum detection.

Parameters:

ip - the input image

threshold - the minimum difference between a center value and its 8 surrounding values to be accepted as a local extremum

borderWidth - width of border margin to be ignored

LocalMinMaxFinder

public LocalMinMaxFinder(ImageProcessor ip)

Constructor accepting an ImageProcessor instance using default parameters.

Parameters:

ip - the input image

Method Details

getMaxima

public LocalMinMaxFinder.ExtremalPoint[] getMaxima(int maxCount)

Returns the detected local maxima as an array of type LocalMinMaxFinder.ExtremalPoint. The resulting array is sorted such that the position with the maximum score value (LocalMinMaxFinder.ExtremalPoint.q) comes first. The array is never larger than the specified count.

Parameters:

maxCount - the maximum number of extrema to search for

Returns:

a sorted array of LocalMinMaxFinder.ExtremalPoint instances

getMinima

public LocalMinMaxFinder.ExtremalPoint[] getMinima(int maxCount)

Returns the detected local minima as an array of type LocalMinMaxFinder.ExtremalPoint. The resulting array is sorted such that the position with the minimum score value (LocalMinMaxFinder.ExtremalPoint.q) comes first. The array is never larger than the specified count.

Parameters:

maxCount - the maximum number of extrema to search for

Returns:

a sorted array of LocalMinMaxFinder.ExtremalPoint instances