Hi Noboru, The Laplacian filter is a second derivative filter and it is normal that it gives positive and negative values -- basically doing edge detection. You would only use that with Chimera fitting routines to fit one Laplacian filtered map into another Laplacian filtered map. I have no experience whether that is a useful technique. I have heard it can be used to match boundaries. It is not a routine fitting approach and you'll need to do extra work to use it and it may not work well at all. So be careful. Tom

Hello, This is my first time trying to apply the Laplacian filter to a cryo-EM map in Chimera before I perform the global search to fit my crystal structure. However, the resulting map looks like the original map blown up into million pieces with positive and negative density showing. I get the same effect even after I "smooth" the map with the Gaussian filter first. Could someone advise me on how I could use this Laplacian filtered map information to better fit my molecule into the original EM map? Thanks for your help in advance. Noboru