Digital sharpening isn't real sharpening. In fact, it's increasing contrast between pixels. If this enhancement follows a certain line or pattern, it gives the impression of sharpening.

The main problem with standard sharpening is that the increase of contrast happens everywhere in your image. Because the algorithm ( =math behind the scene ) doesn't "know" what is on the image, it increases contrast everywhere it was designed to do so. For jpegs for example, this can be dramatic as all the artefacts are increased. Artefacts that are most visible where there are no smooth but abrupt transitions.

Which is why the sharpening should be limited to where you want it, meaning the use of masks and more specific: edge-masks. This is the method I use and prefer:

1/ duplicate your image. ( Image>Duplicate ). This frees us from all concern. You can work on this copy without worrying about your original.

2/ Image > Adjustments > Channel Mixer. Set to Monochrome (bottom-left) and drag the three sliders untill you get an image that has sufficient contrast without losing detail. If the sum of your changes adds up to more than 100% your image will lighten, if it adds up to less, it will darken. Limit both of these. Stay around 100% in total.

3/ Filter > Stylize > Find Edges . We're looking for edges, so why not use the existing command?

4/ Image > Adjusr > Invert . Because for a mask we need the pixels we want to select be white ot at least light, we need to invert the result.

5/ Filter > Noise > Median . The Median filter works in steps, always taking the median value of the pixels it works with.I t's  good to remove noise in some specific cases.  When you apply it here it'll make the edges better for the next steps. Use a value of around 2.

6/  Filter > Other > Maximum . Maximum expands the white parts of images, so here it'll thicken the line that has been prepared by  the Median filter. Use a Radius of around 4. The result is now very stair-stepped and ugly.

7/ Filter Blur > Gaussian Blur . Set to the same value as you did for the radius in Maximum, meaning around 4.

This is your mask. Save it, so you can, if needed, adjust a bit more.

8/ Now press Ctrl+A to select all, Ctrl+C to copy all  (Cmd on the mac)

9/ Go back to your original work. Copy your image to a new layer and add a layer mask.

10/ Alt+click on the icon of your layer mask in the layers panel. Your image will turn white as there is presently no mask there.

11/ Ctrl+V to paste the mask you created in there. Eventually, deselect with Ctrl+D .

12/ Now apply Unsharp Mask with a radius of some 2 and the maximium percentage ( around 500% ). Even jpg's won't suffer much.

It looks more complicated than it is. And the result if really visibly better than most, if not all, other methods. It may look like overkill, but if you don't respect your own work enough to put some time in it to make it really the best possible quality, you may as well have your images printed in the local supermarket. Nothing wrong with that, but you have to accept their standards, not yours.

There are no Borg. All resistance is fertile.