Is there an easy way to see whether an image needs "amount" or "radius" values adjusted, in Photoshop's "Unsharpen Mask"?

Question

I'm touching up photos for analysis, so they need to be as true to the original as possible (including when zoomed), but sharpened (anything from slightly to greatly) to bring out whatever textures, features and edges are possible. The originals might be faded, in poor lighting, soft focused, or lower-resolution so there's any number of causes.

If I use the unsharpen tools in a heavy-handed manner and sharpen them too much, the tool will create the appearance of textures and features that weren't actually present in the original subject matter of the photo. So there's a delicate balance.

My problem is that as I'm using the tool, I'm constantly trying to figure whether a photo would benefit from more of (or has too much of) "amount" and/or "radius". I can easily see if sharpening is overdone or not done enough, but when it comes to adjusting it, I'm spending ages experimenting with each slider in turn, trying to adjust one, then see if adjusting the other improves it, and so on.

I think that a big part of the problem is that I don't have much of a sense what the specific symptoms/differences would be, to distinguish over/underdoing "amount" vs. over/underdoing "radius". So I can't look at the photo and immediately work out which of the two settings it is, that's likely to be more mis-set, to get the sharpness closer to how I would like it.

Does anyone have any hints about the difference between how the two settings affect photos, and how I can approach this more methodically, or what to look for as guidance/symptoms, to figure out quicker which of the two settings for the tool is more relevant to an under/over sharpened picture, so I can cut down my trial and error attempts, or approach sharpening a poor photo in a more effective way?

Thanks for any help on this, it comes up a lot!

Answer 1

Have you tried converting the image to a Smart Object (for Smart Filters), before applying the filter? At least that way, if you go too far, or don't apply enough, you can change the amount of sharpening afterwards. Applying filters to Smart Objects is a useful way of applying filters non-destructively.

Although this doesn't solve the problem of how much sharpening to add in the first instance, it should make the process of adjusting it less painful.

I think it's safe to say that the result of applying sharpening on a photo will depend very much on the photograph itself, and also on the orignal resolution of the image. It's really difficult to estimate the resulting effect on a photo until you've actually tried it. Also over sharpening can look terrible at 1:1 zoom, but perfectly acceptable when you zoom out, or have the image printed. In fact, for printing, slight over sharpening is often desirable.

Generally speaking, with the unsharp mask filter, I have found that making the radius quite large has more the effect of increasing the local contrast, which is especially useful for faded/low contrast images, whereas keeping the radius low will help with slight blurriness/lack of detail. The Amount slider generally controls the power of the effect, and so the final look will depend on what radius you have chosen, and of course the radius you choose will also depend on the resolution (pixel dimensions) of the image.

If a photograph is both faded and blurry, you might benefit from making a Levels Adjustment layer, to address the fading/low contrast issue, then unsharp mask, with the radius set quite low, to address the blurring/lack of detail.

There's a useful guide to the unsharp mask here which goes into much more detail. Here the author describes how the threshold setting can be used to prevent undesirable sharpening of any noise, and how to avoid halos and other such undesirable effects of over sharpening.