bitmap生产缩略图

Android BitMap数据源生产缩略图 
/**
 * 生成缩略图
 * 缩略图是将原图等比压缩，压缩后宽、高中较小的一个等于198像素
 */
private Bitmap getThumb(Bitmap bm){
    ByteArrayOutputStream stream = new ByteArrayOutputStream();
        bm .compress(Bitmap.CompressFormat.PNG, 100, stream);
        byte[] bitmapByte = stream.toByteArray();

    final BitmapFactory.Options options = new BitmapFactory.Options();
    int reqWidth, reqHeight, width = bm.getWidth(), height = bm.getHeight();
    if (width > height){
        reqWidth = 240;
        reqHeight = (reqWidth * height)/width;
    }else{
        reqHeight = 160;
        reqWidth = (width * reqHeight)/height;
    }
    int inSampleSize = 1;
    if (height > reqHeight || width > reqWidth) {
        final int halfHeight = height / 2;
        final int halfWidth = width / 2;
        while ((halfHeight / inSampleSize) > reqHeight
                && (halfWidth / inSampleSize) > reqWidth) {
            inSampleSize *= 2;
        }
    }
    options.inSampleSize = inSampleSize;
    options.inJustDecodeBounds = false;
    Matrix mat = new Matrix();
    Log.d(TAG, "data.length========"+bitmapByte.length);
    Bitmap bitmap = BitmapFactory.decodeByteArray(bitmapByte, 0, bitmapByte.length, options);
    Log.d(TAG, "klx====bitmap.getWidth()===="+bitmap);
    return Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), mat, true);
}