图片缩放应用比较多，我们看看imageFilters提供的ScaleFilter怎么完成这项工作。
首先了解怎么调用过滤器，实例代码如下：
public void imageScale(String fromPath, String toPath, int width, int height)throws IOException {// 定义“缩放过滤器”ScaleFilter scaleFilter = new ScaleFilter(width, height);BufferedImage fromImage = ImageIO.read(new File(fromPath));//BufferedImage toImage = new BufferedImage(width, height,BufferedImage.TYPE_INT_RGB);// 缩放处理scaleFilter.filter(fromImage, toImage);// 写回指定目标文件ImageIO.write(toImage, "jpg", new File(toPath));}
效果如下所示：
原图：
处理后：
这里没有做等比例缩放，要想实现这个功能——在图片长宽做相应处理即可！
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来了解下ScaleFilter内部怎么处理的！
public BufferedImage filter( BufferedImage src, BufferedImage dst ) {if ( dst == null ) {ColorModel dstCM = src.getColorModel();dst = new BufferedImage(dstCM, dstCM.createCompatibleWritableRaster( width, height ), dstCM.isAlphaPremultiplied(), null);}Image scaleImage = src.getScaledInstance( width, height, Image.SCALE_AREA_AVERAGING );Graphics2D g = dst.createGraphics();g.drawImage( scaleImage, 0, 0, width, height, null );g.dispose();return dst;}
关键类：
- BufferedImage
- Image
- Graphics2D
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图片黑白处理（去颜色）
public void gray(String fromPath, String toPath) throws IOException {// 定义过滤器GrayscaleFilter filter = new GrayscaleFilter();BufferedImage fromImage = ImageIO.read(new File(fromPath));int width = fromImage.getWidth();int height = fromImage.getHeight();BufferedImage toImage = new BufferedImage(width, height,BufferedImage.TYPE_INT_RGB);//for (int i = 0; i < width; i++) {for (int j = 0; j < height; j++) {int rgb = fromImage.getRGB(i, j);// 过滤int grayValue = filter.filterRGB(i, j, rgb);toImage.setRGB(i, j, grayValue);}}//ImageIO.write(toImage, "jpg", new File(toPath));}
效果：
内部实现原理：
public int filterRGB(int x, int y, int rgb) {int a = rgb & 0xff000000;int r = (rgb >> 16) & 0xff;int g = (rgb >> 8) & 0xff;int b = rgb & 0xff;
// rgb = (r + g + b) / 3; // simple averagergb = (r * 77 + g * 151 + b * 28) >> 8; // NTSC lumareturn a | (rgb << 16) | (rgb << 8) | rgb;}
注意点：还有一个过滤器是GrayFilter，注意和这里的GrayscaleFilter予以区别。
