Bitmap bitmap =null;
//通过工厂类，解释路径，获得图片
bitmap = BitmapFactory.decodeFile(filePath); 
//get width & height  
      int width = bitmap.getWidth(); 
      int height = bitmap.getHeight(); 
Bitmap destBitmap = null;
//destination height & width
      float destH = height;
      float destW = width;
      //Scale new/old
      float temp1 =  0; 
      float temp2 =  0; 
      
      //compress height below 1024
      if (height > 1024) {
        destH = 1024;
        temp1 =  ((float) destH) / ((float) height); 
        destW = width * temp1;
         if (destW > 1024) {
           temp1 =  ((float) 1024) / ((float) destW); 
           destW = 1024;
           destH = destH * temp1;
      }
    }else{
      if (width > 1024) {
        destW = 1024;
        temp2 =  ((float) destW) / ((float) width);
        destH = height * temp2;
        
      }
    }

        try {
//Creates a new bitmap, scaled from an existing bitmap, when possible
          destBitmap = Bitmap.createScaledBitmap(bitmap, (int) destW, (int)destH, true);
          destBitmap = switchColor(destBitmap);
//save new bitmap
          OutputStream outStream = null;
          outStream = new FileOutputStream(new File(filePath));
//Write a compressed version of the bitmap to the specified outputstream.
          destBitmap.compress(Bitmap.CompressFormat.JPEG, 100, outStream);
    } catch (FileNotFoundException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }