android图片压缩

andriod提供了一些方法如下：
压缩图片质量:  
bitmap.compress(Bitmap.CompressFormat.JPEG, quality, fos);  
其中的quality为0~100, 可以压缩图片质量, 不过对于大图必须对图片resize  

这个是等比例缩放:
bitmap = Bitmap.createScaledBitmap(bitmap, width, height, false);

这个是截取图片某部分:

bitmap = Bitmap.createBitmap(bitmap, x, y, width, height);

这几个方法都是针对Bitmap的, 不过鉴于Bitmap可以从file中读取, 也可以写入file

这段代码很多网站都有转载，在这里是为了注释：较大的图片文件上传到服务器一般都需要压缩调整，保证数据通信的效率是最主要的。

//对图片进行压缩
           BitmapFactory.Options options = new BitmapFactory.Options();
           options.inJustDecodeBounds = true;  

           //获取这个图片的宽和高
           Bitmap bitmap = BitmapFactory.decodeFile("/sdcard/dcim/Camera/hello.jpg",options);//此时返回bm为空
           options.inJustDecodeBounds =false;
           //计算缩放比
           int be = (int)(options.outHeight / (float)200);
           if(be <= 0)
                be =1;
           options.inSampleSize =be;
           //重新读入图片，注意这次要把options.inJustDecodeBounds设为false哦
           bitmap = BitmapFactory.decodeFile("/sdcard/dcim/Camera/hello.jpg",options);
           int w = bitmap.getWidth();
           int h=bitmap.getHeight();
           System.out.println(w+" "+h);
           myImageView.setImageBitmap(bitmap);  

           //保存入sdCard
           File file2= new File("/sdcard/dcim/Camera/test.jpg");
           try {
            FileOutputStream out = new FileOutputStream(file2);
            if(bitmap.compress(Bitmap.CompressFormat.JPEG, 100, out)){
                out.flush();
                out.close();
            }
        } catch (Exception e) {
            // TODO: handle exception
        }  

        //读取sd卡
           File file =new File("/sdcard/dcim/Camera/test.jpg");
           int maxBufferSize = 16 * 1024;  

            int len = 0;
            ByteArrayOutputStream outStream = new ByteArrayOutputStream();
             BufferedInputStream bufferedInputStream;
            try {
                bufferedInputStream = new BufferedInputStream(new FileInputStream(file));
                int bytesAvailable = bufferedInputStream.available();
                int bufferSize = Math.min(bytesAvailable, maxBufferSize);
                byte[] buffer = new byte[bufferSize];
                while ((len = bufferedInputStream.read(buffer)) != -1)
                {
                    outStream.write(buffer, 0, bufferSize);
                }
                 data = outStream.toByteArray();
                outStream.close();
                bufferedInputStream.close();  

            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }