imagingbook.pub.hough

Class HoughTransformLines

java.lang.Object

imagingbook.pub.hough.HoughTransformLines

public class HoughTransformLines
extends Object

This class implements the Hough Transform for straight lines. This version fixes the problem with vertical lines (theta = 0). TODO: merge the two implementations, add bias correction

Version:

2015/11/13

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	HoughTransformLines.HoughLine This class represents a straight line in Hessian normal form, i.e., x * cos(angle) + y * sin(angle) = radius.
static class	HoughTransformLines.Parameters

Constructor Summary

Constructors

Constructor and Description
HoughTransformLines(ij.process.ImageProcessor I, HoughTransformLines.Parameters params) Creates a new Hough transform from the image I.
HoughTransformLines(Point2D[] points, int M, int N, HoughTransformLines.Parameters params) Creates a new Hough transform from a sequence of 2D points.

Method Summary

Modifier and Type	Method and Description
double	angleFromIndex(int ai) Calculates the actual angle (in radians) for angle index ai
ij.process.FloatProcessor	getAccumulatorImage() Creates and returns an image of the 2D accumulator array.
ij.process.FloatProcessor	getAccumulatorImageExtended() Creates and returns an image of the extended 2D accumulator array, produced by adding a vertically mirrored copy of the accumulator to its right end.
ij.process.FloatProcessor	getAccumulatorMaxImage() Creates and returns an image of the local maxima of the 2D accumulator array.
HoughTransformLines.HoughLine[]	getLines(int amin, int maxLines) Finds and returns the parameters of the strongest lines with a specified min.
Point2D	getReferencePoint()
double	radiusFromIndex(int ri) Calculates the actual radius for radius index ri.

Methods inherited from class java.lang.Object

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

Constructor Detail

HoughTransformLines

public HoughTransformLines(ij.process.ImageProcessor I,
                           HoughTransformLines.Parameters params)

Creates a new Hough transform from the image I.

Parameters:

I - input image, relevant (edge) points have pixel values greater 0.

params - parameter object.

HoughTransformLines

public HoughTransformLines(Point2D[] points,
                           int M,
                           int N,
                           HoughTransformLines.Parameters params)

Creates a new Hough transform from a sequence of 2D points. Parameters M, N are only used to specify the reference point (usually at the center of the image). Use this constructor if the relevant image points are collected separately.

Parameters:

points - an array of 2D points.

M - width of the corresponding image plane.

N - height of the corresponding image plane.

params - parameter object.

Method Detail

getLines

public HoughTransformLines.HoughLine[] getLines(int amin,
                                                int maxLines)

Finds and returns the parameters of the strongest lines with a specified min. pixel count. All objects in the returned array are valid, but the array may be empty. Note: Could perhaps be implemented more efficiently with insert-sort.

Parameters:

amin - the minimum accumulator value for each line.

maxLines - maximum number of (strongest) lines to extract.

Returns:

a possibly empty array of HoughTransformLines.HoughLine objects.

getReferencePoint

public Point2D getReferencePoint()

Returns:

The reference point used by this Hough transform.

angleFromIndex

public double angleFromIndex(int ai)

Calculates the actual angle (in radians) for angle index ai

Parameters:

ai - angle index [0,...,nAng-1]

Returns:

Angle [0,...,PI] for angle index ai

radiusFromIndex

public double radiusFromIndex(int ri)

Calculates the actual radius for radius index ri.

Parameters:

ri - radius index [0,...,nRad-1].

Returns:

Radius [-maxRad,...,maxRad] with respect to reference point (xc, yc).

getAccumulatorImage

public ij.process.FloatProcessor getAccumulatorImage()

Creates and returns an image of the 2D accumulator array.

Returns:

A FloatProcessor (since accumulator values may be large).

getAccumulatorImageExtended

public ij.process.FloatProcessor getAccumulatorImageExtended()

Creates and returns an image of the extended 2D accumulator array, produced by adding a vertically mirrored copy of the accumulator to its right end.

Returns:

A FloatProcessor (since accumulator values may be large).

getAccumulatorMaxImage

public ij.process.FloatProcessor getAccumulatorMaxImage()

Creates and returns an image of the local maxima of the 2D accumulator array.

Returns:

A FloatProcessor (since accumulator values may be large).