Two-dimensional (2-D) Otsu algorithm is analyzed. It is shown that when a 2-D histogram is segmented by 2-D Otsu threshold method, the within-class means is easily far from the main diagonal, so that the algorithm isn't robust enough to noises. This paper proposes a new algorithm. The new algorithm establishes a line intercept histogram directly from the 2-D information of images based on the line threshold segmentation concept. Then, it uses the Otsu criterion to find the best intercept threshold from the histogram. Furthermore, the 2-D information of images and the intercept threshold are adopted to implement the image segmentation. Compared the new algorithm with the 2-D Otsu algorithm, it demonstrates that the new algorithm can avoid both disadvantages of 2-D Otsu algorithm. Firstly,it improves the anti-noise ability. When the noise variance is more than 0.003 or stepup, it shows robustness to noises. Secondly, the processing speed of the new algorithm is faster than the fast Otsu algorithms based on 2-D histogram by two orders of magnitude, and it takes up more less memory. In conclusion, the proposed algorithm is robust anti-noise, more accurate segmentation and is suitable for applications in real time.