The part of the slide which has more number of metaphases is covered by a cover slip. The aim of the cover slip scan is to find the edges of the cover slip so that it can start looking for the metaphases inside the area contained by the cover-slip. For this, the stage is first moved to the top middle of the slide and starts taking images along a straight line down the slide moving in steps of 900 microns, looking for the first edge of the cover slip. Image processing algorithm used to find the edge of the cover slip is MatLab mfile BordertestF.m. It measures the thickness, the straightness and the length of the objects in the image. If an object satisfies certain criteria in all of these three categories it is assumed to be a cover slip boundary.
Once the first cover slip edge is detected the stage is moved by a distance of 19000 microns along the same straight line. This is due to the fact that the cover slip is around 20000 microns (2 cms) in width. Images are now processed to find the other cover slip edge. In case the other cover slip edge is not detected by the algorithm after moving more than 25000 microns (2.5 cms) distance from the first cover slip edge, then the algorithm assumes it to be at a distance of 20000 microns (2 cms) from the first cover slip edge.
Once the cover slip scan is complete, the locations of edges of cover slip on the slide can be obtained, and the area to look for metaphases can be derived. It takes around 17 to 25 Images and 50 to 80 seconds to complete the cover slip scan. Image processing algorithm to find the edges of the cover slip in an image takes around 2 to 3 seconds