图像处理之Lanczos采样放缩算法

一:什么是Lanczos采样

参见这里:http://en.wikipedia.org/wiki/Lanczos_resampling

二:大致算法流程

三:算法运行结果

1.向下采样, 生成缩略图, 左边为原图,右边为缩略图

向上采样,生成放大图像时效果:

算法源代码:

package com.gloomyfish.zoom.study;     import java.awt.p_w_picpath.BufferedImage; import java.awt.p_w_picpath.ColorModel;     import com.gloomyfish.filter.study.AbstractBufferedImageOp;     public class LanczosScaleFilter extends AbstractBufferedImageOp {     // lanczos_size     private float lanczosSize;     private float destWidth;             public LanczosScaleFilter()     {         lanczosSize = 3;         destWidth = 100;     }         public LanczosScaleFilter(float lobes, int width) {         this.lanczosSize = lobes;         this.destWidth = width;     }         public void setLanczosSize(float size) {         this.lanczosSize = size;     }         public void setDestWidth(float destWidth) {         this.destWidth = destWidth;     }         @Override     public BufferedImage filter(BufferedImage src, BufferedImage dest) {         int width = src.getWidth();         int height = src.getHeight();         float ratio = width / this.destWidth;         float rcp_ratio = 2.0f / ratio;         float range2 = (float) Math.ceil(ratio * lanczosSize / 2);                     // destination p_w_picpath         int dh = (int)(height * (this.destWidth/width));         int dw = (int)this.destWidth;             if (dest == null) {             ColorModel cMD = src.getColorModel();             dest = new BufferedImage(src.getColorModel(), cMD.createCompatibleWritableRaster(dw, dh), cMD.isAlphaPremultiplied(), null);         }             int[] inPixels = new int[width * height];         int[] outPixels = new int[dw * dh];                     getRGB(src, 0, 0, width, height, inPixels);         int index = 0;         float fcy = 0, icy = 0, fcx = 0, icx = 0;         for (int row = 0; row < dh; row++) {             int ta = 0, tr = 0, tg = 0, tb = 0;             fcy = (row + 0.5f) * ratio;             icy = (float) Math.floor(fcy);             for (int col = 0; col < dw; col++) {                 fcx = (col + 0.5f) * ratio;                 icx = (float) Math.floor(fcx);                     float sumred = 0, sumgreen = 0, sumblue = 0;                 float totalWeight = 0;                 for (int subcol = (int) (icx - range2); subcol <= icx + range2; subcol++) {                     if (subcol < 0 || subcol >= width)                         continue;                     int ncol = (int) Math.floor(1000 * Math.abs(subcol - fcx));                         for (int subrow = (int) (icy - range2); subrow <= icy + range2; subrow++) {                         if (subrow < 0 || subrow >= height)                             continue;                         int nrow = (int) Math.floor(1000 * Math.abs(subrow - fcy));                         float weight = (float) getLanczosFactor(Math.sqrt(Math.pow(ncol * rcp_ratio, 2)                                 + Math.pow(nrow * rcp_ratio, 2)) / 1000);                         if (weight > 0) {                             index = (subrow * width + subcol);                             tr = (inPixels[index] >> 16) & 0xff;                             tg = (inPixels[index] >> 8) & 0xff;                             tb = inPixels[index] & 0xff;                             totalWeight += weight;                             sumred += weight * tr;                             sumgreen += weight * tg;                             sumblue += weight * tb;                         }                     }                 }                 index = row * dw + col;                 tr = (int) (sumred / totalWeight);                 tg = (int) (sumgreen / totalWeight);                 tb = (int) (sumblue / totalWeight);                 outPixels[index] = (255 << 24) | (clamp(tr) << 16) | (clamp(tg) << 8) | clamp(tb);                                     // clear for next pixel                 sumred = 0;                 sumgreen = 0;                 sumblue = 0;                 totalWeight = 0;                 }         }         setRGB(dest, 0, 0, dw, dh, outPixels);         return dest;     }             public static int clamp(int v)     {         return v > 255 ? 255 : (v < 0 ? 0 : v);     }         private double getLanczosFactor(double distance) {         if (distance > lanczosSize)             return 0;         distance *= Math.PI;         if (Math.abs(distance) < 1e-16)             return 1;         double xx = distance / lanczosSize;         return Math.sin(distance) * Math.sin(xx) / distance / xx;     }     }

五:窗口大小对结果的影响

如果是向下采样生成缩略图的话, 窗口大小设置为3就已经非常清楚了

如果向上采样要放大图像的话, 窗口大小设置要大于6才能获得较好结果,推荐使用窗口

大小为8.