Fig. 3.

The synchronizing scheme for the strips. A $y$ translation stage cycle consists of two mechanical movements that produce two image strips: the “forward scan” $P_0$ to $P_3$, and the “return scan” $P_3$ to $P_0$. The velocity profiles are depicted in red for the forward movement, and blue for the return. The image is acquired within the constant velocity portion (d), between $P_1$ and $P_2$, of the scans. This avoids distortion of the mosaic due to compression or elongation of pixels. Therefore, we choose a scan distance (D) for the $y$ translation stage such that the region of constant velocity (d) is larger than the size of the tissue sample. After the forward scan is initiated and the stage reaches $P_1$, the “position trigger” signal is asserted to arm the counter that monitors horizontal synchronization pulses (HSYNC) from the asynchronous optical scanner. When the HSYNC counter receives the next HSYNC pulse, the data acquisition begins. When the stage reaches $P_2$, the HSYNC counter resets and the acquisition continues until the last line is complete in the strip image. Then the stage decelerates and stops at $P_3$. Once the $x$ translation stage moves in the $x$ direction to a predetermined position that sets the width of the strip and the overlap between adjacent strips, the return scan is initiated from $P_3$ to $P_0$. It follows a similar mechanism to the forward scan. This cyclical process, forward scan and return scan, is repeated until the entire tissue is imaged.