Zero-crossings extracted from LoG filtering are widely used for pattern recognition and computer vision. Recursive filtering techniques have been applied to reduce the computational complexity of LoG filtering. However, extracting zero-crossings remains a time-consuming task and usually requires a second scanning process after filtering. This paper presents an algorithm using a line buffer to extract zero-crossings along with LoG filtering hence avoiding the need for an additional convolution and extra memory units. Because we know where the sign of two pixels crosses zero, the exact location of each zero-crossing can be calculated down to sub-pixel level by linear interpolation. The line buffer can be implemented easily in hardware, and real-time processing can be achieved.