How to reduce noise via a median filter, effective for retaining feature borders while blurring at varying levels on images from microscopes and other sources. Median filtering is especially important when using tonal differences to segment for quantitation, quantification, image analysis, etc.
How to Median Filter in GIMP
Follow method in video except that Median filter is found under Filter > Enhance > Despeckle.
Set Black to 0 and White to 255 and Radius to 1. Repeat if more filtering is desired.
How to Median Filter in Image J
Under Process > Filter, choose Median.