android bitmap compress（圖片壓縮）

android bitmap compress
android的照相功能隨著手機硬體的發展，變得越來越強大，能夠找出很高解析度的圖片。
有些情境中，需要照相併且上傳到服務，但是由於圖片的大小太大，那麼就上傳就會很慢(在有些網路情況下)，而且很耗流量，要想速度快，那麼就需要減小圖片的大小。減少圖片的大小有兩種方法，1. 照小圖片； 2. 壓縮大圖片。 照相時擷取小圖片一般不太符合要求，因為，圖片的清晰度會很差，但是這種情況有個好處就是應用速度會快些； 壓縮圖片，就是把大圖片壓縮小，降低圖片的品質，在一定範圍內，降低圖片的大小，並且滿足需求（圖片仍就清晰）。下面組要是介紹圖片的壓縮：

1. 照相請查看http://blog.csdn.net/luhuajcdd/article/details/8826587 ->想要儲存圖片到制定目錄，啟動Camera應用時，需要指定檔案
2. 壓縮過程：
    2.1 從圖片路徑中讀取圖片(圖片很大，不能全部加在到記憶體中處理，要是全部載入到記憶體中會記憶體溢出)
[java]  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); 

 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 處理圖片旋轉  
[java]  int degree = readPictureDegree(filePath); 
        bm = rotateBitmap(bm,degree) ; 

int degree = readPictureDegree(filePath);
  bm = rotateBitmap(bm,degree) ;[java] view plaincopyprint?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 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; 
    } [java] view plaincopyprint?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); 
    } 

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壓縮圖片       
[java]  bm.compress(Bitmap.CompressFormat.JPEG, 30, baos);//30 是壓縮率，表示壓縮70%; 如果不壓縮是100，表示壓縮率為0 

bm.compress(Bitmap.CompressFormat.JPEG, 30, baos);//30 是壓縮率，表示壓縮70%; 如果不壓縮是100，表示壓縮率為0

 

完整的方法代碼：
[java] 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 ; 
 
    } 

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 ;

 }[java] view plaincopyprint?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; 
    } 

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;
 }