SobelKernel1D.java

package edu.stanford.rsl.tutorial.motion.estimation;

import edu.stanford.rsl.conrad.data.numeric.Grid1D;
import edu.stanford.rsl.conrad.data.numeric.Grid1DComplex;
import edu.stanford.rsl.conrad.data.numeric.Grid2D;
import edu.stanford.rsl.conrad.data.numeric.Grid3D;
import edu.stanford.rsl.conrad.utils.FFTUtil;
import edu.stanford.rsl.conrad.utils.VisualizationUtil;
import edu.stanford.rsl.tutorial.filters.GridKernel;
/**
 * This class implements the 1-D version of the Sobel Kernel (-2 0 2)
 * @author Marco Boegel
 *
 */
public class SobelKernel1D extends Grid1DComplex implements GridKernel {
	private int width=0;
	public SobelKernel1D(final int size, int width) {
		super(FFTUtil.getNextPowerOfTwo(size));
		this.width = width;
		final int paddedSize = getSize()[0];

		for (int i = 0; i < paddedSize / 2; ++i) {
				setAtIndex(i, 0 );
		}
		for (int i = paddedSize / 2; i < paddedSize ; ++i) {
				setAtIndex(i, 0);
		}
		setAtIndex(0, -2);
		setAtIndex(1, 0);
		setAtIndex(paddedSize-1, 2);
		transformForward();
	}
	
	public Grid1D paddGrid(Grid1D input, int width) {
		Grid1D out = new Grid1D(input.getSize()[0]+width);
		int size = input.getSize()[0];
		for(int i = 0 ; i < width/2; i++) {
			out.setAtIndex(i, input.getAtIndex(0));
		}
		for(int i = width/2; i < width/2+size; i++) {
			out.setAtIndex(i, input.getAtIndex(i-width/2));
		}
		for(int i = width/2+size; i<size+width; i++) {
			out.setAtIndex(i, input.getAtIndex(size-1));
		}
		
		return out;
	}
	
	/**
	 * This method implements the Convolution in Fourier Space for a 1-D Grid.
	 * @param input 1-D Image
	 */
	public void applyToGrid(Grid1D input) {

		Grid1D paddedInput = paddGrid(input, width);
		Grid1DComplex subGrid = new Grid1DComplex(paddedInput);
		int size = subGrid.getSize()[0];
		subGrid.transformForward();
		for (int idx = 0; idx < size; ++idx) {
			subGrid.multiplyAtIndex(idx, getRealAtIndex(idx),
					getImagAtIndex(idx));
		}
		subGrid.transformInverse();

		Grid1D filteredSinoSub = subGrid.getRealSubGrid(width/2, input.getSize()[0]);
		for(int i = 0 ; i < input.getSize()[0]; i++) {			
			input.setAtIndex(i, filteredSinoSub.getAtIndex(i));
		}

	}
	
	/**
	 * This method implements the Convolution with a 2-D Image by applying the Filter to each 1-D subgrid.
	 * @param input 2-D Image
	 */
	public void applyToGrid(Grid2D input) {
		
		int iter = input.getSize()[1];
		
		for(int i = 0; i < iter; i++) {
			applyToGrid(input.getSubGrid(i));
		}
	}
	
	/**
	 * This method implements the Convolution with a 3-D Image by applying the Filter recursively to each 2-D subgrid.
	 * @param input 3-D Image
	 */
	public void applyToGrid(Grid3D input) {
		
		int iter = input.getSize()[2];
			
		for(int i = 0; i < iter; i++) {
			applyToGrid(input.getSubGrid(i));
		}
	}

	public final static void main(String[] args) {
		final int size = 200;
		SobelKernel1D r = new SobelKernel1D(size,9);
		Grid1D in = new Grid1D(new float[size]);
		
		for(int i= 0 ; i < size; i++) in.setAtIndex(i, 0);
		int k = 30;
		for(int i = 3*size/8; i< size/2; i++) {
			in.setAtIndex(i, k);
		}
		for(int i = size/2; i < 5*size/8; i++) {
			in.setAtIndex(i, k);
		}
		VisualizationUtil.createPlot("before",in.getBuffer()).show();
		VisualizationUtil.createPlot("Filter",r.getSubGrid(0, FFTUtil.getNextPowerOfTwo(size)).getBuffer()).show();
		r.applyToGrid(in);
		VisualizationUtil.createPlot("after",in.getBuffer()).show();
		
	}

}
/*
 * Copyright (C) 2010-2014 Marco B�gel
 * CONRAD is developed as an Open Source project under the GNU General Public License (GPL).
*/