//进行大小缩放来达到压缩的目的
 BitmapFactory.Options options = new BitmapFactory.Options();
 options.inJustDecodeBounds = true;
 BitmapFactory.decodeFile(srcImagePath, options);
 //根据原始图片的宽高比和期望的输出图片的宽高比计算最终输出的图片的宽和高

 float srcWidth = options.outWidth;
 float srcHeight = options.outHeight;
 float maxWidth = outWidth;
 float maxHeight = outHeight;
 float srcRatio = srcWidth / srcHeight; //原始图片宽高比
 float outRatio = maxWidth / maxHeight; //目标图片宽高比
 float actualOutWidth = srcWidth;
 float actualOutHeight = srcHeight;
  if (srcWidth > maxWidth || srcHeight > maxHeight) {
   if(srcRatio>outRatio){ //原始宽高比大于目标宽高比
     actualOutWidth = maxWidth;
     actualOutHeight = actualOutWidth / srcRatio;
   }else if(srcRatio maxFileSize) {//循环判断如果压缩后图片是否大于maxMemmorrySize,大于继续压缩
   baos.reset();//重置baos即让下一次的写入覆盖之前的内容
   options_ = Math.max(0, options_ - 10);//图片质量每次减少10
   actualOutBitmap.compress(Bitmap.CompressFormat.JPEG, options_, baos);//将压缩后的图片保存到baos中
   baosLength = baos.toByteArray().length;
   if (options_ == 0)//如果图片的质量已降到最低则，不再进行压缩
     break;
 }
 actualOutBitmap.recycle();

 //将bitmap保存到指定路径
 FileOutputStream fos = null;
 String filePath = getOutputFileName(srcImagePath);
 try {
   fos = new FileOutputStream(filePath);
   //包装缓冲流,提高写入速度
   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();
     }
   }
 }

 //获取位图缩放比例
 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;//目标/原始 宽比例
float heightScale = outHeight / srcHeight; //目标原始 高比
//对比宽高比选择较大的一种比例
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);// 放大缩小比例
  //生成最终输出的bitmap
  Bitmap actualOutBitmap = Bitmap.createBitmap(scaledBitmap, 0, 0, scaledBitmap.getWidth(), scaledBitmap.getHeight(), matrix1, true);

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