How to apply sharpening to your images.
Description with a slight slant for photoshop:
0. resize to appropriate size for web/publish
1. make a copy of the image as a new layer (CTRL-J)
2. zoom to 100% (CTRL-ALT-0 <- That is a ZERO, not an ‘Oh’-char).
3. Select “Filter > Other > High pass” from the menu.
4. Adjust the Radius so that just slight contours can be seen in the image shown at 100%.
5. Click OK
6. Select any of the blending modes: Overlay or ” <something> Light”
7. Adjust opacity to reduce the effect, if you find the need.
NOTE: If you cannot find a nice setting, throw away the layer and try again with a lesser radius.
8. Select “Layer > Flatten Image” and then
9+10 “Image > Mode > …” RGB and 8bit to be able to save as JPG
This is possible in Gimp too, given that you find the High pass filter first (separate download).