BitmapFactory.Options options = new BitmapFactory.Options();

        options.inPreferredConfig = Bitmap.Config.ARGB_8888; // 默认是Bitmap.Config.ARGB_8888

        // 下面两个字段需要组合使用

        options.inPurgeable = true;

        options.inInputShareable = true;
 

         options.inJustDecodeBounds = true;//true和false之间获得长宽和缩放比例

         BitmapFactory.decodeFile(filepath, options);

         int wRatio = (int) Math.ceil(options.outWidth /(unit_width * PtsPerUnitPic));

         int hRatio = (int) Math.ceil(options.outHeight /( unit_height * PtsPerUnitPic));

         // 如果超出指定大小，则缩小相应的比例

         if (wRatio > 1 && hRatio > 1) {

         if (wRatio > hRatio) {

         options.inSampleSize = wRatio;

         System.out.println(wRatio);

         } else {

         options.inSampleSize = hRatio;

         System.err.println(hRatio);

         }

         }else {

            return;

        }         

         options.inJustDecodeBounds = false;

        temp_unit_bitmap = BitmapFactory.decodeFile(filepath, options);