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;
    }