//進行大小縮放來達到壓縮的目的
 BitmapFactory.Options options = new BitmapFactory.Options();
 options.inJustDecodeBounds = true;
 BitmapFactory.decodeFile(srcImagePath, options);
 //根據原始圖片的寬高比和期望的輸出圖片的寬高比計算最終輸出的圖片的寬和高

 float srcWidth = options.outWidth;
 float srcHeight = options.outHeight;
 float maxWidth = outWidth;
 float maxHeight = outHeight;
 float srcRatio = srcWidth / srcHeight; //原始圖片寬高比
 float outRatio = maxWidth / maxHeight; //目標圖片寬高比
 float actualOutWidth = srcWidth;
 float actualOutHeight = srcHeight;
  if (srcWidth > maxWidth || srcHeight > maxHeight) {
   if(srcRatio>outRatio){ //原始寬高比大于目標寬高比
     actualOutWidth = maxWidth;
     actualOutHeight = actualOutWidth / srcRatio;
   }else if(srcRatio<outRatio){ //原始寬高比小于目標寬高比
     actualOutHeight = maxHeight;
     actualOutWidth = actualOutHeight * srcRatio;
   }
 }else{
   actualOutWidth = maxWidth;
   actualOutHeight = maxHeight;
 }

 options.inSampleSize = computSampleSize(options, actualOutWidth, actualOutHeight);
 options.inJustDecodeBounds = false;
 Bitmap scaledBitmap = null;
 try {
   scaledBitmap = BitmapFactory.decodeFile(srcImagePath, options);
 } catch (OutOfMemoryError e) {
   e.printStackTrace();
 }
 if (scaledBitmap == null) {
   return null;
 }

  //生成最終輸出的bitmap
 Bitmap actualOutBitmap = Bitmap.createScaledBitmap(scaledBitmap, (int) actualOutWidth, (int) actualOutHeight, true);

 //釋放原始位圖資源
 if(scaledBitmap!=actualOutBitmap){ //判斷目標位圖是否和原始位圖指向棧目標相同
   scaledBitmap.recycle();
   scaledBitmap = null;
 }

  //處理圖片旋轉問題
 ExifInterface exif = null;
 try {
   exif = new ExifInterface(srcImagePath);
   int orientation = exif.getAttributeInt(
       ExifInterface.TAG_ORIENTATION, 0);
   Matrix matrix = new Matrix();
   if (orientation == ExifInterface.ORIENTATION_ROTATE_90) {
     matrix.postRotate(90);
   } else if (orientation == ExifInterface.ORIENTATION_ROTATE_180) {
     matrix.postRotate(180);
   } else if (orientation == ExifInterface.ORIENTATION_ROTATE_270) {
     matrix.postRotate(270);
   }
   actualOutBitmap = Bitmap.createBitmap(actualOutBitmap, 0, 0,
       actualOutBitmap.getWidth(), actualOutBitmap.getHeight(), matrix, true);
 } catch (IOException e) {
   e.printStackTrace();
   return null;
 }

  //進行有損壓縮
 ByteArrayOutputStream baos = new ByteArrayOutputStream();
 int options_ = 100;
 actualOutBitmap.compress(Bitmap.CompressFormat.JPEG, options_, baos);//質量壓縮方法，把壓縮后的數據存放到baos中 (100表示不壓縮，0表示壓縮到最小)

 int baosLength = baos.toByteArray().length;

 while (baosLength / 1024 > maxFileSize) {//循環判斷如果壓縮后圖片是否大于maxMemmorrySize,大于繼續壓縮
   baos.reset();//重置baos即讓下一次的寫入覆蓋之前的內容
   options_ = Math.max(0, options_ - 10);//圖片質量每次減少10
   actualOutBitmap.compress(Bitmap.CompressFormat.JPEG, options_, baos);//將壓縮后的圖片保存到baos中
   baosLength = baos.toByteArray().length;
   if (options_ == 0)//如果圖片的質量已降到最低則，不再進行壓縮
     break;
 }
 actualOutBitmap.recycle();

 //將bitmap保存到指定路徑
 FileOutputStream fos = null;
 String filePath = getOutputFileName(srcImagePath);
 try {
   fos = new FileOutputStream(filePath);
   //包裝緩沖流,提高寫入速度
   BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fos);
   bufferedOutputStream.write(baos.toByteArray());
   bufferedOutputStream.flush();
 } catch (FileNotFoundException e) {
   return null;
 } catch (IOException e) {
   return null;
 } finally {
   if (baos != null) {
     try {
       baos.close();
     } catch (IOException e) {
       e.printStackTrace();
     }
   }
   if (fos != null) {
     try {
       fos.close();
     } catch (IOException e) {
       e.printStackTrace();
     }
   }
 }

 //獲取位圖縮放比例
 private int computSampleSize(BitmapFactory.Options options, float reqWidth, float reqHeight) {
   float srcWidth = options.outWidth;//20
   float srcHeight = options.outHeight;//10
   int sampleSize = 1;
   if (srcWidth > reqWidth || srcHeight > reqHeight) {
     int withRatio = Math.round(srcWidth / reqWidth);
     int heightRatio = Math.round(srcHeight / reqHeight);
     sampleSize = Math.min(withRatio, heightRatio);
   }
   return sampleSize;
 }

float srcWidth = options.outWidth;
float srcHeight = options.outHeight;
float widthScale = outWidth / srcWidth;//目標/原始 寬比例
float heightScale = outHeight / srcHeight; //目標原始 高比
//對比寬高比選擇較大的一種比例
float scale = widthScale > heightScale ? widthScale : heightScale;
float actualOutWidth = srcWidth;
float actualOutHeight = srcHeight;
if (scale < 1) {
  actualOutWidth = srcWidth * scale;
  actualOutHeight = srcHeight * scale;
}

  Matrix matrix1 = new Matrix();
  matrix1.postScale(scale, scale);// 放大縮小比例
  //生成最終輸出的bitmap
  Bitmap actualOutBitmap = Bitmap.createBitmap(scaledBitmap, 0, 0, scaledBitmap.getWidth(), scaledBitmap.getHeight(), matrix1, true);

  if (actualOutBitmap != scaledBitmap) {
    scaledBitmap.recycle();
    scaledBitmap = null;
    System.gc();
  }