学步园

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();  
            }