Contrast and sharpening are related, but they are not the same.

Contrast changes tonal separation across the image or a larger region. Increasing contrast makes bright tones brighter and dark tones darker, reducing the number of midtones. This affects the overall look of the photo.

Sharpening is more local: it increases contrast mainly along edges, where one tone or detail meets another. A sharpening filter typically brightens the light side of an edge and darkens the dark side, which makes details appear crisper without necessarily changing the overall contrast of the whole image.

A simple example: imagine a blurry transition from dark gray to light gray.

• Increasing contrast changes the tones across the broader image.
• Sharpening targets that transition itself, making the edge look steeper and more defined.

Sharpening is often used to counter blur or softness, but it can also make noise more visible if the settings are too strong or the threshold is too low, because noise may be mistaken for fine detail.

So in short:

• contrast = global or broad tonal difference
• sharpening = edge contrast, used to make detail look clearer