Take control over the sharpening tools in photoshop to get the best results for your image. This simple little technique is quite old and known only to the pros in the industry, can be done in photoshop elements also. So lets see how to get the most out of the 'unsharp mask' filter.
First of all lets see what IS sharpening in photoshop. When you apply any sharpening filter, it looks for the pixels of greater contrast in your image. It identifies those pixels and....this is intresting......it puts a lighten pixel on one side of it and a darken pixel on the other side to increase the contrast between them. This inturn gives you sharpening. Keep this logic in mind and read on....
Ok, as we all know by now, always make a duplicate layer of the main image you want to work on.
Now with the new layer selected, go to Filter>Sharpen>Unsharp Mask. You can use any other sharpening filter like smart sharpen or sharpen more, but, the best control is with the 'unsharp mask' filter. Always zoom in the image to actual pixels while applying this filter. That is the best way to judge the amount of sharpening.
Sharpening settings depend a lot on the file size of the image. For a large sized image, say of a 22 megapixel camera, will have a different sharpening setting compared to a 6 megapixel camera. Hence there is no standard sharpening setting which works best. The above setting works best for a 16 megapixel file, and for an 8 megapixel file, an ideal setting would be Amount:100, Radius:0.8, Threshold:0(i always keep it nil). My advice is not to follow numbers....this is just a guideline. Go with your instincts. Let it be very slightly oversharpened as we can dial it down later. Press Ok when done, and change the layer mode to 'darken' as shown below.
What you are seeing now, are only the darken pixels that the sharpening filter put. Now, duplicate this sharpened layer(right click/command click on the layer and select duplicate layer), and set the layer mode to lighten as shown below.
So now we have the same effect as of the original sharpened layer set to normal, but only difference is that we have split it into two parts. One having all the lighten pixels and the other having all darker pixels. Imagine the amount of control you have now. With the opacity of each layer, you can get the exact amount of lighten and darken pixels for that perfect sharpened look. In our image, we need to dial the lighten pixels a little first.
Now select the layer with the darken pixels and dial the opacity down so that the image looks crisp with very little 'sharpening halo'. For this image opacity between 50-70% of the darken layer did the trick.
So there you have it... the Secrets of sharpening revealed. Have fun experimenting!