Print on pos printer (Datecs DPP-450)

HI,

I have Windows Phone 8 and wanna to print directly on datecs dpp-450 pos printer. When I print some text, everything is ok, but when print picture i got only dots.

First, I send command for graphical data (ESC *) , after that I convert picture to BitArray and send bits to printer. But I got dots, not a picture.

Where i am wrong?