vec_math
Class ImageMoments

java.lang.Object
  vec_math.ImageMoments

All Implemented Interfaces:

Serializable

public class ImageMoments
extends Object
implements Serializable

Similar to one-dimension power sums or CentralMoments this class calculates image moments meaning statistic properties in a two-dimensional image. Suppose you have an array of pixel values I_ij = I(x,y) Sampled at integer x/y pixel values, thus representable as a two-dimensional double array ADU[y][x] like returned from astro.fits.FitsTools#getAsArray (note the counter-intuitive indexing within the array; this stems from the FITS standard. Passing this to the constructor of this class immediately calculates I_0, x_c and y_c via the formulars:

   I_0=ΣADU_ij,

   xc=Σ(x_ij·ADU_ij)/I_0,
   
   yc=Σ(y_ij·ADU_ij)/I_0.
   

Further calls to #getImageMoment first check, if the moment to n,k has already been cached, otherwise it is calculated according to M_nk=Σ(x_ij-xc)n(y_ij-yc)k/I_0

See Also:

Serialized Form

Nested Class Summary

private static class	ImageMoments.DualIndex Helper class that combines to integer indices, both hermitian, to a single key.
static class	ImageMoments.Focus This class reads an fits image and calculates the requested image moment.

Field Summary

private double[][]	adu This is the image array, innner index is y!.
private double	bias If a bias is set, only adus above this are considered.
private Map<ImageMoments.DualIndex,Double>	cache Cache is updated at each call to #getImageMoment with no hit.
private double	high The multiplicator to the RN for maximum ADU still considered BG.
private double	low The multiplicator to the RN for minimum ADU still considered BG.
private double	readnoise The standard deviation estimate for background rejection.
private double	sum0 Once the image is set, this is the ADU-sum.
private double	xc Once the image is set, this is the center-of-gravity, x coordinate.
private double	yc Once the image is set, this is the center-of-gravity, y coordinate.

Constructor Summary

ImageMoments(double[][] image)
Takes an image array and readily calculates the count sum plus the center of gravity.

ImageMoments(double[][] image, double bias, double rn)
Takes an image array and readily calculates the count sum plus the center of gravity.

ImageMoments(double[][] image, double bias, double rn, double hi, double lo)
Takes an image array and readily calculates the count sum plus the center of gravity.

Method Summary

private double	calculateMnk(int n, int m)
Point2D	getCenter() Returns xc yc as a Point2D object.
double	getMoment(int x0, int y0) If the queried moment has not been calculated, we evaluate it by M_nk=Σ(x_ij-xc)n(y_ij-yc)k/I_0.
void	setImage(double[][] image, double bs, double rn, double hisig, double losig) Sets a new pixel array, erasing the cache, but immediately calculating the new count sum plus center of gravity.

Methods inherited from class java.lang.Object

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

Field Detail

adu

private double[][] adu

This is the image array, innner index is y!.

bias

private double bias

If a bias is set, only adus above this are considered.

readnoise

private double readnoise

The standard deviation estimate for background rejection.

high

private double high

The multiplicator to the RN for maximum ADU still considered BG.

low

private double low

The multiplicator to the RN for minimum ADU still considered BG.

sum0

private double sum0

Once the image is set, this is the ADU-sum.

xc

private double xc

Once the image is set, this is the center-of-gravity, x coordinate.

yc

private double yc

Once the image is set, this is the center-of-gravity, y coordinate.

cache

private Map<ImageMoments.DualIndex,Double> cache

Cache is updated at each call to #getImageMoment with no hit.

Constructor Detail

ImageMoments

public ImageMoments(double[][] image)

Takes an image array and readily calculates the count sum plus the center of gravity.

ImageMoments

public ImageMoments(double[][] image,
                    double bias,
                    double rn)

Takes an image array and readily calculates the count sum plus the center of gravity.

ImageMoments

public ImageMoments(double[][] image,
                    double bias,
                    double rn,
                    double hi,
                    double lo)

Takes an image array and readily calculates the count sum plus the center of gravity.

Method Detail

setImage

public void setImage(double[][] image,
                     double bs,
                     double rn,
                     double hisig,
                     double losig)

Sets a new pixel array, erasing the cache, but immediately calculating the new count sum plus center of gravity.

getMoment

public double getMoment(int x0,
                        int y0)

If the queried moment has not been calculated, we evaluate it by M_nk=Σ(x_ij-xc)n(y_ij-yc)k/I_0. The moment is also cached for further queries. The special case with x0=y0=0 returns the ADU-sum, I_0, while queries with x0=1,y0=0 or x0=0,y0=1 return the center of gravity coordinate.

Parameters:

x0 - The leading index in M_nk

y0 - The trailing index in M_nk

getCenter

public Point2D getCenter()

Returns xc yc as a Point2D object.

calculateMnk

private double calculateMnk(int n,
                            int m)