android bitmap compress

android的照相功能隨着手機硬件的發展，變得愈來愈強大，可以找出很高分辨率的圖片。

有些場景中，須要照相而且上傳到服務，可是因爲圖片的大小太大，那麼就上傳就會很慢(在有些網絡狀況下)，並且很耗流量，要想速度快，那麼就須要減少圖片的大小。減小圖片的大小有兩種方法，1. 照小圖片； 2. 壓縮大圖片。 照相時獲取小圖片通常不太符合要求，由於，圖片的清晰度會不好，可是這種狀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，下降圖片的質量，在必定範圍內，下降圖片的大小，而且知足需求（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 -> 想要保存圖片到制定目錄，啓動Camera應用時，須要指定文件

2. 壓縮過程：

    2.1 從圖片路徑中讀取圖片(圖片很大，不能所有加在到內存中處理，要是所有加載到內存中會內存溢出)

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 處理圖片旋轉   

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壓縮圖片        

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

 

完整的方法代碼：

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;
    }