I must say my web sharpening method (and taste) have evolved a bit over the last few years, but I'm happy with where I'm at now.
I usually use Unsharp Mask, and that's what I'll be discussing here. To get the best value out of this post, I strongly recommend you read my thorough explanation of USM here, and my overview of web image practices here, if you haven't already.
So, I edit my image, I save the master file, blah blah blah. Then, when I'm ready to prepare a web-size proof, I flatten the layers, then resize to the appropriate pixel dimensions. Remember, your sharpening will be for naught if you don't get the size exactly right beforehand. To resize I use either the Crop Tool, the Image Size dialog, or Fit Image, depending on the circumstances. I use plain ol' Bicubic method for interpolation, but that's because I'm lazy! You should experiment with the Bicubic Sharper method to see if you like it better.
Then I open the Unsharp Mask filter (it's F10 on my keyboard, for ease).
I want to say at this point that I'm not fond of oversharpened images. I don't go for "crunchy". So my approach is to start subtle, and only push it as far as I dare. I want my sharpening to look like fantastic focus, not obvious post-processing.
I begin with the values of 500, 0.2, 0. 0.2 is the smallest effective radius, and about half the time, it's too small. But I start there. I toggle the Preview to have a look at the effect.
If it's too strong, I just reduce the Amount from 500 down to 400, or 300, or whatever. Easy. (I almost never have to adjust the Threshold setting while the Radius is at 0.2.) I get it down to a satisfactory point, smile a contented little smile, and press Ok.
If it's too weak, then I have to move into Phase 2. I change the values to 150, 0.3, 0. 0.3 is as high as I ever go with the Radius for web sharpening. You might think that three tenths of one pixel is an outrageously small value, but trust me, anything wider looks awful.
So, I toggle the Preview again. If it's too strong now, I reduce the Amount from 150 down to 120, or 100. One of those values usually does the trick. (Again, it's extremely rare to have to increase the Threshold from 0 in this circumstance.)
If it's still too weak, it's time to start raising the Amount. I might try 180, or 200, or even as high as 250. An Amount of 250 with a Radius of 0.3 is almost always too strong for my personal taste, but you might love it for your images :)
Finally, this is where the Threshold slider starts to come into play. Once you take the Amount above 150 (while the Radius is 0.3), you might begin to encounter some noise when you sharpen. Well, maybe not noise, exactly, but exaggeration of fine detail (eg skin creases) to which you'd rather not draw attention. If this is the case, you'll need to increase the Threshold from 0 to 1, and if that's not enough, even to 2 or 3. (If you have to take it over 3, it means that your Amount is too high, so bring it down a bit instead). Threshold is the least understood of all the sharpening sliders, but it's very important, so don't neglect it.
Finally, when I can toggle the Preview and see that the sharpening is to my satisfaction, I press Ok, then continue on to watermark (if necessary) and save.
Ok, that might all seem a bit long-winded, so I'll summarise:
- USM 500, 0.2, 0
- If too strong, reduce Amount; if too weak, continue to next step
- USM 150, 0.3, 0
- If too strong, reduce Amount; if too weak, increase Amount then adjust Threshold as necessary
One more thing to discuss - the need for masking. I rarely find it necessary to selectively sharpen, but sometimes "busy" parts of the photo such as trees or patterned clothing grab too much sharpening, and the subject's eyes don't seem sharp enough by comparison. If I see this occurring when I toggle the preview, I take a mental note of the USM settings I've established, then cancel, and duplicate the layer, then apply the sharpening to that. Then I add a layer mask and mask away the problem areas, either fully or partially. No sweat.