I do not see that in my postscript previewer - this is usually a result of the antialias settings of your viewer. There are no such lines in the PostScript file.
I tried three outputs (ps, png, and pdf) and all gave these fake grids. Is this error a result of windows settings? I use GSview for ps files.
Not sure, this is a recurring thread… In fact (on macOS) my PDF shows the lines because I cannot (easily) control its antialias settings, but gv with PS and making a PNG gives no lines.
Perhaps @Joaquim has comments on the Windows side settings.
Thank you for your response. I will check my system settings.
Thank you so much for your response.

