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：

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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！

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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）

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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：

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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。