Image Processing Reference
The image noise.png after applying the Selective Gaussian Blur filter
When you smooth an image, you always lose some sharpness. You can
apply the Unsharp Mask filter ( Filters > Enhance > Unsharp Mask ) to sharpen
You can then apply the Clone tool to eliminate any remaining pixel noise.
You can also try to use a different method. Try this: The remaining noise pixels
are blue. Use the Zoom tool to zoom into a section of the image with visible
noise. Choose the Select by Color tool (keep the tool settings in mind) and
select several different blue pixels. Then reduce the saturation of the selected
pixels down to grayscale and darken them with the Hue/Saturation tool ( Colors
> Hue/Saturation ).