There are multiple ways to sharpen your photo in Photoshop. It can help you to repair a photo or bring out the details, but it can create (unwanted) noise too. That is why I use a technique where the (sharpened) details are separated from the photo, so I can control where I want the photo to be sharper and where not. This allows me to control and minimize the amount of noise too.
The technique I am about to explain is called the “Frequency Separation Technique“. Here, the lines and details of the photo are stored in a separate monochrome layer, that is blended in the original photo. With a brush, you can control where the details need to pop out and where not.
(In the example I also used the “Intensify” technique to create a nice dark background. You can read about this technique in this article)
STEP 1. Duplicate the photo to create a new layer on top.
Use CTRL+J or right-click the layer en click “Duplicate Layer”
STEP 2. Select the new top layer and go to “Filter >> Other >> High Pass”
STEP 3. You see that the layer is turned into a grey object, where you can see very small lines through the gray. Increase the “Radius” to increase the separation. It depends on the type and size of the photo how high the radius has to be. Try not to go beyond the point where colours are showing through. Usually, a lower radius is better than a higher radius.
Click “OK” when you are done.
STEP 4. Select the new (grey) details layer and change the blend mode to “Hard Light”. The grey will disappear and only the details are visible. You can decrease the opacity of the layer to adjust the level of detail.
STEP 5. Select the new details layer and create a new Layer Mask by clicking on the Layer Mask button. A white rectangle will appear behind the details layer.
STEP 6. Click on the new layer mask (the white rectangle) and use a soft brush to paint on the details layer. Use black to remove details and use white to undo the removal.