[Chimera-users] streaks in Chimera image of virus electron density map

Hello, I've been using Chimera to generate beautiful images of entire virus particle from an O-style map file. However, most of the images that I capture have a few black streaks in the image. The streaks appear as thin, parallel lines, like someone dragged a pen across a painting before it dried. Does anyone know how I can remove these streaks without having to resort to Photoshop? I can provide sample images too. Thanks in advance! -Lu Gan