Abstract
A new method to detect contour lines by the Marr-Hildreth filter was developed for the particle image. First, tuning of the filter parameter was studied to detect separate contour lines for a picture of two isolated particles. The correct contour lines can be obtained for both particles when the filter parameter σ is chosen so that the off-area radius of the filter is smaller than a certain value. This value is a linear function of the distance between the two particles, edge width and radius of the particle. second, the average value of the first derivative of the density on the contour line can be used for judging whether a particle image is in focus or not. These methods enable accurate detection of contour lines for the particle image in focus.
