A new approach for lossless compression of DNA microarray images is proposed in this work. First DNA image spots are automatically detected and extracted. Then employing a new scanning technique called spiral path, 2D spots are converted into 1D sequences. Linear interpolation method is used in the prediction coding of the 1D sequence. Finally the prediction residual sequence is divided into spot and background parts and Huffman coded. Two stages of local optimization result in excellent compression which not only outperforms ordinary compression engines, but also previous works in this area.