boofcv.alg.feature.orientation

Class OrientationHistogramSift<Deriv extends boofcv.struct.image.ImageGray>

java.lang.Object

boofcv.alg.feature.orientation.OrientationHistogramSift<Deriv>

public class OrientationHistogramSift<Deriv extends boofcv.struct.image.ImageGray>
extends java.lang.Object

Computes the orientation of a region around a point in scale-space as specified in the SIFT [1] paper. A histogram of angles is computed using a weighted sum of image derivatives. The size of the region is specified by the scale function parameter. Every pixel inside the sample region is read and contributes to the angle estimation. If the image border is encountered the sample return is truncated.

To get the orientation for the largest peak invoke getPeakOrientation(). Other

Differences from paper:

• The angle in each bin is set to the atan2(y,x) of the weighted sum of image derivative
• Interpolation is done using a 2nd degree polynomial instead of a parabola.

[1] Lowe, D. "Distinctive image features from scale-invariant keypoints". International Journal of Computer Vision, 60, 2 (2004), pp.91--110.

Constructor Summary

Constructors

Constructor and Description
OrientationHistogramSift(int histogramSize, double sigmaEnlarge, java.lang.Class<Deriv> derivType) Configures orientation estimation

Method Summary

Modifier and Type	Method and Description
org.ddogleg.struct.GrowQueue_F64	getOrientations() A list of found orientations
double	getPeakOrientation() Orientation of the largest peak
void	process(double c_x, double c_y, double sigma) Estimates the orientation(s) of a region at the specified location and scale
void	setImageGradient(Deriv derivX, Deriv derivY) Specify the input image

Methods inherited from class java.lang.Object

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

Constructor Detail

OrientationHistogramSift

public OrientationHistogramSift(int histogramSize,
                                double sigmaEnlarge,
                                java.lang.Class<Deriv> derivType)

Configures orientation estimation

Parameters:

histogramSize - Number of elements in the histogram. Standard is 36

sigmaEnlarge - How much the scale is enlarged by. Standard is 1.5

Method Detail

setImageGradient

public void setImageGradient(Deriv derivX,
                             Deriv derivY)

Specify the input image

process

public void process(double c_x,
                    double c_y,
                    double sigma)

Estimates the orientation(s) of a region at the specified location and scale

Parameters:

c_x - Location x-axis

c_y - Location y-axis

sigma - blur standard deviations of detected feature. Also referred to as scale.

getOrientations

public org.ddogleg.struct.GrowQueue_F64 getOrientations()

A list of found orientations

Returns:

orientations

getPeakOrientation

public double getPeakOrientation()

Orientation of the largest peak