public int[] getRange(){
        if (mRange != null){
            return mRange;
        }
        mRange = new int[2];
        boolean isFirst = true;
        for (Map.Entry<Integer, Integer> entry : mHistorgram.entrySet()) {
            if (isFirst) {
                isFirst = false;
                mRange[0] = mRange[1] = entry.getKey();
            } else {
                mRange[0] = mRange[0] < entry.getKey() ?
                        mRange[0] :
                        entry.getKey();
                mRange[1] = mRange[1] > entry.getKey() ?
                        mRange[1] :
                        entry.getKey();
            }
        }
        return mRange;
    }