java image filters[02]-过滤器初探
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 average rgb = (r * 77 + g * 151 + b * 28) >> 8; // NTSC luma return 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。
