Android: 轉換 Immutable Bitmap into Mutable

BitmapFactory.Options options = new BitmapFactory.Options();
options.inMutable = true;  //加上這個選項!!!! (API level 11以上)

Bitmap bm = BitmapFactory.decodeByteArray(data, 0, data.length, options);
Canvas canvas = new Canvas(bm);  // 不然會有錯誤產生！
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