Introduction

This tutorial covers the basics of sharpening digital images. I explain what exactly sharpening is, show some examples where it helps, explain how to choose the right parameters, and warn about some problems that can cause it to degrade your pictures. Sharpening is a large topic, so I've broken it up into two separate tutorials. A second tutorial covers some more advanced material, in particular how to get finer control and apply more sharpening exactly where required without making a mess where it is not.

I would be remiss if I didn't start out by mentioning Dan Margulis' work, in particular his book "Professional Photoshop". I learned nearly everything I know about this topic from this book, in particular from Chapter 4: "Sharpening with a Stiletto" and from taking Dan's course. You should view this tutorial as at best a vast oversimplification of Dan's work. I've reread this chapter 4 times carefully, and each time I get more out of it. I cannot stress this too strongly: Anyone who is serious about getting the most from his or her photographs in digital post processing needs to have a copy of Professional Photoshop and make an extended study of it.

What is Sharpening and what can it do

Sharpening can make your images look a lot, well, sharper. Here are a couple of before and after examples:





In the demolition derby shot, look in particular at the door handle, ant the mesh seen through the back window, and at the dirt under the care. Look at the rooster's comb, his eye the feathers just to the right of his wing, and the ground directly beneath his feet. The difference is subtle, but makes a large difference in the overall perceived clarity of the images.

Sharpening is a very old technique for making the outlines of things look more distinct. It is so old that it predates photography by many hundreds of years. Maybe the all time most famous practitioner of sharpening of is the Spanish painter El Greco (1541-1614). Here is a painting of his called The spoliation, Christ Stripped of His Garments, completed in 1579:



Here is a detail from Christ's hand:



See how El Greco has outlined the fingers with dark lines? See how this makes them stand out against Christ's robe in the full painting? This is an example of sharpening. Pretty good for a guy who couldn't afford Photoshop.

Sharpening enhances the perceived sharpness of images by emphasizing the transitions between light and dark areas with halos. Just as El Greco drew a black halo around Christ's hand, sharpening draws halos at the points of transition. Actually, it draws two kinds of halos, a light and a dark halo. It both outlines dark areas with light halos and light areas with dark halos.

Let me illustrate with another image. In this case, I have deliberately over sharpened to make my point.



The difference between these two images looks like the difference between a cheap lens and one that cost a bundle, but really they are exactly the same except for one application of the basic Photoshop sharpening tool, USM. To see how this illusion has been created, let's take a look at a very close crop, before and after:



This is the bottom left of the "B" in "Believe". In the original the transition between blue and gray wasn't completely sharp. It shades from gray to blue over a couple of pixels. Dan says this is caused by, "the real life line of transition being narrower than ... even ... film ... can resolve." The after image shows clearly how the USM magic trick works. The dark blue area has been surrounded with a light colored halo in the gray area. And the lighter gray area has been surrounded with a darker colored halo in the blue area.

What sharpening can't do

Understanding how sharpening works leads to an understanding of its limitations. When I first heard about it, I thought, "Just what I need, a way to correct fuzzy out-of-focus shots." But sharpening cannot help where transitions aren't fairly crisp. It works by looking for transitions finner than some threshold (more about this soon.) If there are now such transitions, it does nothing and thus has no effect. Sharpening also can't help images without sharp transitions. Skin for example, is usually lacking in such transitions, and the ones that it does have are things we don't want to emphasize (wrinkles, pimples, etc.) On the other hand, portraits usually have things we do want to sharpen, eyes, hair, clothing, and things we really don't, skin for example. This is often true and a large part of the second tutorial is devoted to fine tuning so that sharpening does what we want and doesn't do what we don't want.

When to sharpen

Sharpen last after, any color correction, cropping, black and white conversion, not to mention composting and edits involving masks, brushes or cloning. Steepen curves after sharpening and you effectively change the amount parameter with unpredictable results. Sharpen before masking, extraction, composting, or cloning and you make you job all the harder and will likely end up with unnatural looking results. Once you become proficient at sharpening in post processing, you will want to disable in camera sharpening because you will want to sharpen yourself after other edits. Sharpening twice is generally a bad idea. Users of raw conversion software also will want to disable sharpening during conversion. Users of ACR should disable such automatic sharpening by following the arrow to the right of "Settings Selected Image" to the preferences menu. Option "Apply sharpening to preview images only".

Prepress professionals preparing images for publication sharpen with knowledge of the actual size of the reproduction, but that's probably to much to ask under most circumstances. If you are very prefectionistic, though, and want huge prints, it is a good idea to sharpen separately for them.

Unsharp mask recipe

The examples I gave above illustrate one of the frustrating things about sharpening. There is no pat formula that you can apply to all your photographs; each image requires some work to determine the correct sharpening parameters. It's actually worse than that. The correct sharpening parameters are also a function of the size the image will be reproduced. Large prints require a very light hand with the sharpening parameters. Images for posting on the Internet may require quite a bit of sharpening before the effect is noticeable and in many cases this poses insurmountable problems. The amount of sharpening required to make a visible difference is often so much that at least some parts of the image are over sharpened. Thus I usually take the approach of sharpening for largish sized prints and letting it go at that. In the cases where it matters most, this helps images posted on the web. It never make a mess. And it makes prints look great. The demolition derby and rooster pictures illustrate this. At dgrin L size, the effect of sharpening is subtle. In prints, it would be dramatic. The "Believe" picture is over sharpened for the sake of illustration. Here the difference is dramatic, even at this small size. A print of the sharpened version has visible halos that are very unattractive and distracting.

Take heart, though, there is a simple 9 step procedure that produces good results for many shots. I'll outline the steps first and go through in detail with illustrations.

1. Work in the LAB color space. If the image is not already in LAB mode, use Image->Mode->LAB to get it there. Select the L channel by clicking on it and then click the box to the left of the composite LAB channel in order to make all the channels visible at once.
2. Work with 100% magnification. Select some important part of your image, eyes and hair for example. If you care more about how your picture will look posted on the web, work at lower magnification. If you care more about very large prints work at higher magnification. Dan taught me that 100% was a good compromise, and I have found this to be true.
3. Bring up the USM dialog box with Filters->Sharpen->Unsharp Mask.
4. Set the "Amount" slider to it's highest setting, 500.
5. Set the "Radius" slider to 5. The slider actually goes much higher, but trust me, this is a very high setting.
6. Tune the "Threshold" slider so that noise isn't being sharpened. With the slider at 0, you will see lots of ugly noise in areas that should be solid. Increase the threshold until only features that you actually want sharpened are affected. I often find that values between 10 and 30 work well. (Use the "preview" check box in this step and future steps to compare the unsharpened image with your current parameters.)
7. Tune the "Radius" parameter so that the halos are not so large as to obscure fine detail. Large halos can extend into neighboring areas and make a real mess. The correct values for this parameter are very dependent on the resolution of the image. For 8MP images, I find the right value is often somewhere between 1 and 3.
8. Tune the "Amount" parameter until the image actually looks good at 100%. This means turning it down until the halos are not quite visible but their effect is. Use the "preview" check box often here to compare with the original. The sharpened image should look sharper, but the halos should not be obvious. You may need to iterate a few times between steps 7. and 8. to fine tune a bit more.
9. Apply the filter and zoom to fit the image to your screen. Use undo/redo to compare the image before and after.

Now I'll revisit some of these steps to provide further explanation and details.

Work in LAB, sharpen the L channel

Nuts & bolts: The channels palette should look like this:



Theory: Sharpening the L channel only prevents it from introducing colored halos and restricts it to lightening and darkening the colors that are already there. Here is a crop from the same part of the "Believe" shot, this time sharpened all the channels of RGB:



See how USM has added some red in the blue halos? This is because it works on each channel individually and sometimes the interactions produce these color shifts. (Exactly why is left as homework for the aspiring color theorist.) I'll paraphrase Dan Margulis here. Unless you actually want to introduce unexpected color shift during sharpening, and you shouldn't, sharpen only the L channel. In the second tutorial, I'll give at least one example where this is not the best thing; but, you should break this rule only if you have a good reason and understand what you are doing.

Walk through

Steps 4 and 5 set up USM to extreme parameters. The idea behind this is to make the effects of sharpening painfully obvious. This will allow you easily to see what is going on. Here is the USM dialog after steps 4 and 5:



I'm going to use the demolition derby shot above as an example. Here is what the 100% crop looks like the threshold set to 0:



Pretty ugly, eh. But remember, we are just starting to tune. We are at step 6 of our recipe, tuning the threshold value in the USM dialog. Threshold controls how large a transition is required between light and dark before sharpening notices it and works on it. Increase the threshold amount and subtle transitions are ignored in favor of more distinct ones. In this case, we can see how USM can introduce a lot of noise if it doesn't ignore the small transitions. So turn up the threshold amount just until the last of the unwanted noise is quited. In this case, this happened with threshold set to 20:



We are now at step 7, ready to tune the Radius amount. This controls how wide the halos are. The image above uses a radius value of 4.3, clearly too much. The light halos are very large, large enough to obscure detail in the driver's face and the pattern of cracks on the window and on the window wiper, among other places. The black halos in the chain clearly overlap the light halos from the other sides of the links. So turn down the radius amount until the halos are small enough to make the image look sharper instead of more blurry. Here, I arrived at a value of 1.7:



We can still see the halos, but they no longer overpower the detail. Unlike the choice of threshold amount, there is some judgment involved in this step. With experience, it will come more naturally. For now, make liberal use of the preview check box to compare with the unsharpened image. Be a little conservative. Remember, sharpening is a magic trick. The goal is to create the maximum illusion without being detected. But if the mechanisms behind the trick are visible, the illusion is ruined.

Now we have arrived at step 8, and it is time to finish making the image actually look good by tuning the amount parameter. This controls how light the light halos are and how dark the dark halos are. At the end of step 7, the halos are still clearly visible, and the illusion is still unrealistic. Turn down the amount until the halos are no longer obvious but the illusion still works:



I found this point with amount set to 220. If you look very hard (or magnify more), can still see the halos. But mostly compared to the original, this just looks sharper compared to the original. Once we step back to look at the entire image, we can judge our success a little better (see the comparison at the top.)

Here is the USM dialog with the final settings for this image:

Thanks for the work, 2nd or 3rd time I've read it helps everytime. I think I might be getting it
Have been working in lab since 1st reading one of your tut's.

Outstanding!

Rutt, your posts are fabulous! Man I love seeing this stuff.

Sharpening is actually a factor in returned prints, the current topic that consumes me. I know photographers live in fear of oversharpening and halos, but I must say that in nearly a million prints shipped, I don't have a record of any being returned for oversharpening (although I've been expecting them in the case of people with shiny skin and on-board flash).

In cricital portraits, my experience is you can go soft on the sharpening on the skin but the customer expects the eyes and lips to be sharp. Dan Margulis shows a lot of examples of sharpening the hair yet keeping the skin soft (personally, I thought his examples of sharpened hair were over the top and made the hair look lacquered).

We've received roughly 1,000 returned prints from too little sharpening and the customer always concludes our printers aren't good. That means another 9,000 prints were disappointing in terms of sharpness, but the customer didn't complain.

Originally Posted by Baldy Rutt, your posts are fabulous! Man I love seeing this stuff.

Thanks.

Originally Posted by Baldy Sharpening is actually a factor in returned prints, the current topic that consumes me. I know photographers live in fear of oversharpening and halos, but I must say that in nearly a million prints shipped, I don't have a record of any being returned for oversharpening (although I've been expecting them in the case of people with shiny skin and on-board flash). ... We've received roughly 1,000 returned prints from too little sharpening and the customer always concludes our printers aren't good. That means another 9,000 prints were disappointing in terms of sharpness, but the customer didn't complain.

I strongly suspect that people who sharpen themselves think they know what they are doing. If they oversharpen, they blame themselves, not you. I'll bet 98% of the prints that people hassle you about have no sharpening or in camera sharpening.

Originally Posted by baldy In cricital portraits, my experience is you can go soft on the sharpening on the skin but the customer expects the eyes and lips to be sharp. Dan Margulis shows a lot of examples of sharpening the hair yet keeping the skin soft (personally, I thought his examples of sharpened hair were over the top and made the hair look lacquered).

I plan on covering that and other stuff in part 2, and post by next weekend. In Dan's defense, I found when I wrote this post that it is quite difficult to sharpen for the computer screen in a way that makes it clear. I had to over sharpen the "Believe" shot quite a bit before it worked to make my point. I think Dan was showing just how much he could sharpen the hair &etc without hitting the face.

Here is my current outline for the part 2:

1. Sharpening other channels, especially for portraits
2. Separate control over light and dark halos
3. Sharpening with the sharpen tool
4. Using layer masks to apply different sharpening parameters to different parts of the image
5. FM sharpening and other(?) plugins

OK, I do have a question. I read alot of your tutorial today and plan to print it out. I think I did find out what a "halo" was. I am not sure I would recognize it anywhere except in your car situation, though.

As an aside, one thing I will not do is sharpen a photo with any grain at all.

My question is: how can you tell a photo is oversharpened? What aspects of a photo make you think "over sharpened"?

I think of this as such a small question, but I don't have a problem with wanting more sharpening, as long as the photo is not a disaster of blur, and, as you pointed out, sharpening will not do much with that, I have used high pass, just to see, and it has helped, however.

I am trying very hard not to show any photos that have obvious flaws, are OOF, blown, etc. on the forum threads.
I did have a problem with the highlight/shadow when Andy said I should clean up my masking. I hadn't used a mask, but had used the highlight shadow, and he said it was that.

What am I looking for so I can "NOT" do it, or at least not present it on a thread.

What signs do I look for to see if a photograph is over sharpened?

Halos? I am not quite sure what a halo is?
What else?

If I know it looks oversharpened I can back up and fix it, before I show it to people. Right now I am having a lot of luck by "not using the USM much at all."

However I do use the highlight/shadow feature and the saturation feature, I am beginning to think that can mimic oversharpening, but I am not sure how to detect it when it does.

ginger

I just woke up, realized I wanted to ask this and threw the question together. There may have been a better way to ask it.

Originally Posted by ginger_55 OK, I do have a question. I read alot of your tutorial today and plan to print it out. I think I did find out what a "halo" was. I am not sure I would recognize it anywhere except in your car situation, though.

A halo is an outline that sharply delineates an area of the image. Go back to the El Greco detail. See his clear black outline of the hand. Go back to the detai from the "Believe" picture. See the light and black lines on either side of the line where the blue and grey meet? Those are the light and dark halos that USM introduced. Maybe "outline" would be a better word, but "halo" is the term of art. Does that help? If not, play with PS and one of your own images. Go through the recipe. After you adjust the threshold amount, the halos will be very evident. A good place to find them will be around tree branches, but they'll be visible everywhere with Amount = 500, Radius=5.

And that leads to the answer to your second question. How do you know when a picture is oversharpened? I suppose the simplest answer is, when it looks worse than before you sharpened it. I know this is flip, so I'll try again. You don't want to be able to see the halos without looking very closely, probably not even then. USM is a magic trick, and it is spoiled if the audience sees the trap door. When it is done right, the image looks sharper, but it isn't obvious why. When it is overdone, the halos are visible, the audience sees the lady fall through the trap door, and the illusion is spoiled.

Lots of time oversharpening is evident in the trees and bushes and grass. Usually there is a lot of fine detail here. Often I sharpen to get the effect we want in the foreground, perhaps a person's face or an animal. Then I step back and see those really ugly bushes that just look wrong.

Here's an example. I posted this shot this morning. I had sharpening on the brain, so I took pains to get it right.

Carefully sharpened:



Oversharpened (by a lot):



See

Ginger, an even better example might be the "Believe" picture. I said it was oversharpened. Look at the grain of the tombstone. Does that look right to you? Look at the grass. This image is oversharpened because the radius is too wide and the halos are "bumping into each other" and obscuring the detail. I made the radius very large in this case so that they would be apparent in the detai I show later on. While you are looking at these two versions, notice how much clearer the text on the banner looks in the sharpened shot. There isn't a lot of detail there, so the wider radius value works OK.

Originally Posted by rutt A halo is an outline that sharply delineates an area of the image.

I, too, didn't know what halos were until I saw them appear during a demonstration to illustrate the fact. I'm not sure, exactly, why digital images require sharpening. I'm also not quite sure why (it seems) that the more pixels your camera has the more sharpening you want to do. What bothers me most is how subjective sharpening is, and that there is no universal formula for sharpening. "Do this and you are sharp". Oh well.

I'll be very interested in your review of the FM plug-in. I have the 20D version. I'm intrigued by the "halo-less" option, not sure how they do that, or how effective it is. I'm intrigued by the possibility to sharpen in a generic manner that can be batched.

I have found that I'm using the extreme sharpening method outlined here on DGrin recently that used a high-pass filter to sharpen slightly out of focus images. I'm using it in my racing pictures. They are well-focused, but due to fast motion with relatively long shutter speeds (compared to the motion) results in images that look a touch out of focus. And the extreme sharpening does wonders there. Best of all, I've found I can use it blindly on all my racing images, and the action runs very quickly. I refuse to manually sharpen 700-1500 images, especially when I don't know which ones will sell.

Sharpening is rather religious. Some swear by sharpening in multiple steps. Once at RAW conversion, once again before printing. Some swear by USM, some swear at it. Some love Genuine Fractals. I think, basically, it depends on the type of image, and personal preference, which is why there is no single way to do it.

Originally Posted by mercphoto I'm not sure, exactly, why digital images require sharpening.

Film shots also benefit from sharpening, but it is harder to do in the analog world. Ever wonder where the name "unsharp mask" comes from. It's an old darkroom technique. A slightly out of focus mask (very high contrast, no grey) was made of the image and the superimposed over it. The result was to create halos. An early application was for astronomy photography, where it made stars visible that were otherwise to faint to see.

Originally Posted by mercphoto I'm also not quite sure why (it seems) that the more pixels your camera has the more sharpening you want to do.

I think you are asking why you want to use a larger radius with higer resolution images. Think about the exact same picture in lower and higer resolutions but reproduced the same size. In the lower res picture, a 3 pixel wide line will actually be much bigger, because there are fewer pixels per inch.

Originally Posted by mercphoto What bothers me most is how subjective sharpening is, and that there is no universal formula for sharpening. "Do this and you are sharp". Oh well.

It's frustrating, I know. I don't think it's actually subjective, just image dependent. The "Believe" picture illustrates this. The words on the tombstone dont' have a lot of fine detail and look good with fairly large radius halos. But the granite itself looks wrong and so does the grass.

Originally Posted by mercphoto I'll be very interested in your review of the FM plug-in. I have the 20D version. I'm intrigued by the "halo-less" option, not sure how they do that, or how effective it is. I'm intrigued by the possibility to sharpen in a generic manner that can be batched.

We both signed agreements not to try to reverse engineer the FM sharpening plug-in when we bought it. So I won't. I've learned a good place for it in my workflow, though. I think it works really well about 80% of the time for images that are going to be posted on the WEB. The other 20% of the time, it's not effective. I find I can very often improve on it for prints. So, it's a fine thing to use if you are going to post stuff and have dgrin print for your customers. If you are going to make a limited edition, print yourself, and sign, you should fuss over each image, including sharpening carefully for the specific reproduction size.

Originally Posted by rutt We both signed agreements not to try to reverse engineer the FM sharpening plug-in when we bought it.

Agreed. My comment was meant to be rhetorical, but I can see how I was not clear about that.

I've learned a good place for it in my workflow, though. I think it works really well about 80% of the time for images that are going to be posted on the WEB. The other 20% of the time, it's not effective. I find I can very often improve on it for prints. So, it's a fine thing to use if you are going to post stuff and have dgrin print for your customers.

I'd love a more in-depth explanation of your experiences. Do you go halo-less? Which amount of sharpening do you use? Do you noise redue with the plug-in?

Lastly, if I said I've found that I should add any text layers after sharpening, or take care to not include any text layer in the sharpening process, would you agree? I've found that any text can halo very quickly. So, any copyright notices or credits or other text goes on last.

Originally Posted by mercphoto I'd love a more in-depth explanation of your experiences. Do you go halo-less? Which amount of sharpening do you use? Do you noise redue with the plug-in? Lastly, if I said I've found that I should add any text layers after sharpening, or take care to not include any text layer in the sharpening process, would you agree? I've found that any text can halo very quickly. So, any copyright notices or credits or other text goes on last.

I have no experience with text, but there is no reason to sharpen it since it will have perfectly sharp edges.

As to to the FM plugin, I don't use halo-less. I find it's noise reduction doesn't work. I mostly use the defaults, but I do tell it to sharpen fine details. It's important to specify low/high iso correctly. If I have to tweak it, I'd rather use something I actually understand, so when it makes a mess, I bail and roll my own. The only exception is that I'll sometimes sharpen a duplicate and then copy into a layer or two and play with opacity and blending options. But only if I'm pretty sure where I'm going.

Unfortunately the universal substitute for thought and understanding has not yet been invented.

This is the best explanation of and tutorial on USM I have come across yet. I feel that I have a much better understanding now of what USM does and how to use the 3 basic parameters to achieve the best results for my particular purpose.

Thanks so much, Rutt.

Rutt,
many thanks for that, it will definately give some method to my fiddling with USM.

Have you done any work on USM for printing?

Anecdotally the method is different depending on whether you intend on printing or view on screen.
I suppose this really applies to printing on a local printer rather than at a print shop. To qualify that last comment:-I'll resize an image , then sharpen for printing locally.

Hi Rutt,

Been away from Dgrin for a while and have come back to see this. Superb tutorial, and I know a number of people who'll really benefit from this.

Well done for taking the time to write it up.

Yvonne

Really appreciate all your work on this tute, I've read several others on USM and understood some of the basics but this really brought it home. The step by step begining with cranking the parameters is an excellent method.

Hi Rutt,

I was so excited this evening, in following to the letter your tutorial!

I followed step by step through this Great! tutorial and actually for the first time, really internalized the basics...as before I was winging the sharpening process, from here on in, I will be sharpening (pun intended) my sharpening skills, all because of this absolutely fabulous tutorial...

had a few hiccup's along the way (my stumbles, but in the end got through all 9 steps and was tickled to do so).
..must review with a few more test photographs to drill it into my head...but from here on in, I definitely have acquired a solid foundation, regarding this mysterious Adobe sharpening technique!

my original re-sized (only)



my lvld/unshrp masked masterpiece



Okay, wait a minute! ...looks like I have to go back to the drawing board as I see little difference with my untrained eye...

..what do you folks see between the two? Anything?

As my first test, I simply used the tutorial parameters...(as I quickly realized that I still need to develop my eye, in fine tuning those halo's)
-amount 220
-radius 1.7
-threshold 20

...no matter what my initial outcome has produced, with a little more practice, I will be submitting much sharper photo's from here on in!

Thanks Again, Rutt!

and each run through with USM, turns out something like this...Blahh...Mmm?




original (no USM)



-perhaps my original is not sharp enough (out of camera) to begin with?

Great stuff! Does all this apply to Elements 3 as well as CS? I am searching about the differences, afraid to justify the full version ($) when I may get by with some success with elements for the first year os so.

Also - how about the raw converter that ships with Canon cameras? I watch their tutorial on their website and it looks pretty good.

BTW: For what its worth, I am enjoying the tutorials that Canon has on thier web site (www.canonusa.com) They have camera specific and digital darkroom tutorials that for the rank beginner are really good.

Z

rank beginner..hey! that's me.

I will definately check out the Canon tutorials!

regards,