圖像處理中的倒角距離變換(Chamfer Distance Transform)在對(duì)象匹配識(shí)別中經(jīng)常用到，算法基本上是基于3x3的窗口來(lái)生成每個(gè)像素的距離值，分為兩步完成距離變換，第一步從左上角開(kāi)始，從左向右、從上到下移動(dòng)窗口掃描每個(gè)像素，檢測(cè)在中心像素x的周圍0、1、2、3四個(gè)像素，保存最小距離與位置作為結(jié)果，圖示如下：
第二步從底向上、從右向左，對(duì)每個(gè)像素，檢測(cè)相鄰像素4、5、6、7保存最小距離與位置作為結(jié)果，如圖示所：
完成這兩步以后，得到的結(jié)果輸出即為倒角距離變換的結(jié)果。完整的圖像倒角距離變換代碼實(shí)現(xiàn)可以分為如下幾步：
1.對(duì)像素?cái)?shù)組進(jìn)行初始化，所有背景顏色像素點(diǎn)初始距離為無(wú)窮大，前景像素點(diǎn)距離為0
2.開(kāi)始倒角距離變換中的第一步，并保存結(jié)果
3.基于第一步結(jié)果完成倒角距離變換中的第二步
4.根據(jù)距離變換結(jié)果顯示所有不同灰度值，形成圖像
最終結(jié)果顯示如下(左邊表示原圖、右邊表示CDT之后結(jié)果)
完整的二值圖像倒角距離變換的源代碼如下：
package com.gloomyfish.image.transform; import java.awt.Color; import java.awt.image.BufferedImage; import java.util.Arrays; import com.gloomyfish.filter.study.AbstractBufferedImageOp; public class CDTFilter extends AbstractBufferedImageOp { private float[] dis; // nn-distances private int[] pos; // nn-positions, 32 bit index private Color bakcgroundColor; public CDTFilter(Color bgColor) { this.bakcgroundColor = bgColor; } @Override public BufferedImage filter(BufferedImage src, BufferedImage dest) { int width = src.getWidth(); int height = src.getHeight(); if (dest == null) dest = createCompatibleDestImage(src, null); int[] inPixels = new int[width * height]; pos = new int[width * height]; dis = new float[width * height]; src.getRGB(0, 0, width, height, inPixels, 0, width); // 隨機(jī)生成距離變換點(diǎn) int index = 0; Arrays.fill(dis, Float.MAX_VALUE); int numOfFC = 0; for (int row = 0; row < height; row++) { for (int col = 0; col < width; col++) { index = row * width + col; if (inPixels[index] != bakcgroundColor.getRGB()) { dis[index] = 0; pos[index] = index; numOfFC++; } } } final float d1 = 1; final float d2 = (float) Math.sqrt(d1 * d1 + d1 * d1); System.out.println(numOfFC); float nd, nd_tmp; int i, in, cols, rows, nearestPixel; // 1 2 3 // 0 i 4 // 7 6 5 // first pass: forward -> L->R, T-B for (rows = 1; rows < height - 1; rows++) { for (cols = 1; cols < width - 1; cols++) { i = rows * width + cols; nd = dis[i]; nearestPixel = pos[i]; if (nd != 0) { // skip background pixels in = i; in += -1; // 0 if ((nd_tmp = d1 + dis[in]) < nd) { nd = nd_tmp; nearestPixel = pos[in]; } in += -width; // 1 if ((nd_tmp = d2 + dis[in]) < nd) { nd = nd_tmp; nearestPixel = pos[in]; } in += +1; // 2 if ((nd_tmp = d1 + dis[in]) < nd) { nd = nd_tmp; nearestPixel = pos[in]; } in += +1; // 3 if ((nd_tmp = d2 + dis[in]) < nd) { nd = nd_tmp; nearestPixel = pos[in]; } dis[i] = nd; pos[i] = nearestPixel; } } } // second pass: backwards -> R->L, B-T // exactly same as first pass, just in the reverse direction for (rows = height - 2; rows >= 1; rows--) { for (cols = width - 2; cols >= 1; cols--) { i = rows * width + cols; nd = dis[i]; nearestPixel = pos[i]; if (nd != 0) { in = i; in += +1; // 4 if ((nd_tmp = d1 + dis[in]) < nd) { nd = nd_tmp; nearestPixel = pos[in]; } in += +width; // 5 if ((nd_tmp = d2 + dis[in]) < nd) { nd = nd_tmp; nearestPixel = pos[in]; } in += -1; // 6 if ((nd_tmp = d1 + dis[in]) < nd) { nd = nd_tmp; nearestPixel = pos[in]; } in += -1; // 7 if ((nd_tmp = d2 + dis[in]) < nd) { nd = nd_tmp; nearestPixel = pos[in]; } dis[i] = nd; pos[i] = nearestPixel; } } } for (int row = 0; row < height; row++) { for (int col = 0; col < width; col++) { index = row * width + col; if (Float.MAX_VALUE != dis[index]) { int gray = clamp((int) (dis[index])); inPixels[index] = (255 << 24) | (gray << 16) | (gray << 8) | gray; } } } setRGB(dest, 0, 0, width, height, inPixels); return dest; } private int clamp(int i) { return i > 255 ? 255 : (i < 0 ? 0 : i); } } 以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持VeVb武林網(wǎng)。
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