SkeletonFilter.java

/*
Copyright 2006 Jerry Huxtable

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package com.jhlabs.image;

import java.awt.Rectangle;

/**
 * A filter which reduces a binary image to a skeleton.
 *
 * Based on an algorithm by Zhang and Suen (CACM, March 1984, 236-239).
 */
public class SkeletonFilter extends BinaryFilter {

	private final static byte[] skeletonTable = {
		0, 0, 0, 1, 0, 0, 1, 3, 0, 0, 3, 1, 1, 0, 1, 3, 
		0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 2, 0, 3, 0, 3, 3,
		0, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 
		2, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 3, 0, 2, 2,
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
		2, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 
		3, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 3, 0, 2, 0,
		0, 1, 3, 1, 0, 0, 1, 3, 0, 0, 0, 0, 0, 0, 0, 1, 
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
		3, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
		2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
		2, 3, 1, 3, 0, 0, 1, 3, 0, 0, 0, 0, 0, 0, 0, 1, 
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
		2, 3, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 
		3, 3, 0, 1, 0, 0, 0, 0, 2, 2, 0, 0, 2, 0, 0, 0
	};
	
	public SkeletonFilter() {
		newColor = 0xffffffff;
	}

        @Override
	protected int[] filterPixels( int width, int height, int[] inPixels, Rectangle transformedSpace ) {
		int[] outPixels = new int[width * height];

		int count = 0;
		int black = 0xff000000;
		int white = 0xffffffff;
		for (int i = 0; i < iterations; i++) {
			count = 0;
			for (int pass = 0; pass < 2; pass++) {
				for (int y = 1; y < height-1; y++) {
					int offset = y*width+1;
					for (int x = 1; x < width-1; x++) {
						int pixel = inPixels[offset];
						if (pixel == black) {
							int tableIndex = 0;

							if (inPixels[offset-width-1] == black) {
                                                            tableIndex |= 1;
                                                        }
							if (inPixels[offset-width] == black) {
                                                            tableIndex |= 2;
                                                        }
							if (inPixels[offset-width+1] == black) {
                                                            tableIndex |= 4;
                                                        }
							if (inPixels[offset+1] == black) {
                                                            tableIndex |= 8;
                                                        }
							if (inPixels[offset+width+1] == black) {
                                                            tableIndex |= 16;
                                                        }
							if (inPixels[offset+width] == black) {
                                                            tableIndex |= 32;
                                                        }
							if (inPixels[offset+width-1] == black) {
                                                            tableIndex |= 64;
                                                        }
							if (inPixels[offset-1] == black) {
                                                            tableIndex |= 128;
                                                        }
							int code = skeletonTable[tableIndex];
							if (pass == 1) {
								if (code == 2 || code == 3) {
									if (colormap != null) {
                                                                            pixel = colormap.getColor((float)i/iterations);
                                                                        } else {
                                                                            pixel = newColor;
                                                                        }
									count++;
								}
							} else {
								if (code == 1 || code == 3) {
									if (colormap != null) {
                                                                            pixel = colormap.getColor((float)i/iterations);
                                                                        } else {
                                                                            pixel = newColor;
                                                                        }
									count++;
								}
							}
						}
						outPixels[offset++] = pixel;
					}
				}
				if (pass == 0) {
					inPixels = outPixels;
					outPixels = new int[width * height];
				}
			}
			if (count == 0) {
                            break;
                        }
		}
		return outPixels;
	}

        @Override
	public String toString() {
		return "Binary/Skeletonize...";
	}

    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone(); //To change body of generated methods, choose Tools | Templates.
    }

}