Smoothing and Sharpening

Digital images can be improved or altered for a special purpose by many processes including by smoothing or sharpening which seems contradictory.


Within any picture a few of the pixels will be“wrong”. There will be errors in the recording. For example this blue pixel is darker than the others around it. We can reduce these by smoothing.

The software examines the code of each pixel and makes each an average of those immediately around, like this:




Pixel code before smoothing

Pixel code after smoothing

Smoothing reduces these odd errors but will also remove other information from the image. Note that the edge between the blue and the head is softened and blurred.

Edges are smoother with no "odd" pixels



Sharpening does the opposite to smoothing, enhancing the differences between adjacent pixels and increasing the contrast at boundaries between colours.

Edges are more defined


If you would like to learn more about digital signal processing there are some notes sheets in PDF format which you can download here:

There are two other notes pages here: