android bitmap compress（图片压缩）

android bitmap compress

android的照相功能随着手机硬件的发展，变得越来越强大，能够找出很高分辨率的图片。

有些场景中，需要照相并且上传到服务，但是由于图片的大小太大，那么就上传就会很慢(在有些网络情况下)，而且很耗流量，要想速度快，那么就需要减小图片的大小。减少图片的大小有两种方法，1. 照小图片； 2. 压缩大图片。 照相时获取小图片一般不太符合要求，因为，图片的清晰度会很差，但是这种情况有个好处就是应用速度会快些； 压缩图片，就是把大图片压缩小，降低图片的质量，在一定范围内，降低图片的大小，并且满足需求（图片仍就清晰）。下面组要是介绍图片的压缩：

1. 照相请查看http://blog.csdn.net/luhuajcdd/article/details/8826587 -> 想要保存图片到制定目录，启动Camera应用时，需要指定文件

2. 压缩过程：

    2.1 从图片路径中读取图片(图片很大，不能全部加在到内存中处理，要是全部加载到内存中会内存溢出)

 final BitmapFactory.Options options = new BitmapFactory.Options();
     options.inJustDecodeBounds = true;
     BitmapFactory.decodeFile(filePath, options);

     // Calculate inSampleSize
     options.inSampleSize = calculateInSampleSize(options, 480, 800);

     // Decode bitmap with inSampleSize set
     options.inJustDecodeBounds = false;

     Bitmap bm = BitmapFactory.decodeFile(filePath, options);

    2.2 处理图片旋转    

 int degree = readPictureDegree(filePath);
         bm = rotateBitmap(bm,degree) ;

 private static int readPictureDegree(String path) {
            int degree  = 0;
            try {
                    ExifInterface exifInterface = new ExifInterface(path);
                    int orientation = exifInterface.getAttributeInt(ExifInterface.TAG_ORIENTATION, ExifInterface.ORIENTATION_NORMAL);
                    switch (orientation) {
                    case ExifInterface.ORIENTATION_ROTATE_90:
                            degree = 90;
                            break;
                    case ExifInterface.ORIENTATION_ROTATE_180:
                            degree = 180;
                            break;
                    case ExifInterface.ORIENTATION_ROTATE_270:
                            degree = 270;
                            break;
                    }
            } catch (IOException e) {
                    e.printStackTrace();
            }
            return degree;
        }

 private static Bitmap rotateBitmap(Bitmap bitmap, int rotate){
         if(bitmap == null)
             return null ;

         int w = bitmap.getWidth();
         int h = bitmap.getHeight();

         // Setting post rotate to 90
         Matrix mtx = new Matrix();
         mtx.postRotate(rotate);
         return Bitmap.createBitmap(bitmap, 0, 0, w, h, mtx, true);
     }

    2.3压缩图片         

 bm.compress(Bitmap.CompressFormat.JPEG, 30, baos);//30 是压缩率，表示压缩70%; 如果不压缩是100，表示压缩率为0

完整的方法代码：

 public static Bitmap getSmallBitmap(String filePath) {

         final BitmapFactory.Options options = new BitmapFactory.Options();
         options.inJustDecodeBounds = true;
         BitmapFactory.decodeFile(filePath, options);

         // Calculate inSampleSize
         options.inSampleSize = calculateInSampleSize(options, 480, 800);

         // Decode bitmap with inSampleSize set
         options.inJustDecodeBounds = false;

         Bitmap bm = BitmapFactory.decodeFile(filePath, options);
         if(bm == null){
             return  null;
         }
         int degree = readPictureDegree(filePath);
         bm = rotateBitmap(bm,degree) ;
         ByteArrayOutputStream baos = null ;
         try{
             baos = new ByteArrayOutputStream();
             bm.compress(Bitmap.CompressFormat.JPEG, 30, baos);

         }finally{
             try {
                 if(baos != null)
                     baos.close() ;
             } catch (IOException e) {
                 e.printStackTrace();
             }
         }
         return bm ;

     }

 private static int calculateInSampleSize(BitmapFactory.Options options,
             int reqWidth, int reqHeight) {
         // Raw height and width of image
         final int height = options.outHeight;
         final int width = options.outWidth;
         int inSampleSize = 1;

         if (height > reqHeight || width > reqWidth) {

             // Calculate ratios of height and width to requested height and
             // width
             final int heightRatio = Math.round((float) height
                     / (float) reqHeight);
             final int widthRatio = Math.round((float) width / (float) reqWidth);

             // Choose the smallest ratio as inSampleSize value, this will
             // guarantee
             // a final image with both dimensions larger than or equal to the
             // requested height and width.
             inSampleSize = heightRatio < widthRatio ? widthRatio : heightRatio;
         }

         return inSampleSize;
     }

转自： http://blog.csdn.net/luhuajcdd/article/details/8948261