Image Processing Reference
Although the picture doesn't depict any noise contamination, there
are still visible signs from raster printing. We will smoothen the raster with a
blurring filter, using the Selective Gaussian Blur filter ( Filters > Blur > Selective
Gaussian Blur ).
In this case, we will choose a Blur radius value of 5 pixels and a Max. delta
value of 20. With considerably higher values, you could smoothen a noise-
contaminated picture as shown earlier.
Nevertheless, smoothing an image always causes a loss of sharpness.
Therefore, you should sharpen your image after you apply a smoothening
effect—for example, with the Unsharp Mask filter ( Filters > Enhance > Unsharp
Mask ). If we had applied a sharpening filter beforehand, we would have
sharpened the printing screen too.
The Selective Gaussian Blur filter can also be used to remove blemishes
from dust and scratches in images from scanned slides. However, you should
be especially cautious with the filter settings. The filter could easily change
your image into an oversimplified, artificial-looking picture. This also applies
to the Despeckle filter.
The picture after