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- View Offline
- Understanding grayscale values and channels
- Evaluating and correcting images with histograms
- Saving to different file formats
- Managing color
- Cleaning the scanner and images
- Reproducing versus assigning colors
- Recognizing contone versus dot pattern images
- Understanding bit depth
- Scanning logos and line art
- Scanning transparent film, positive or negative
- Capturing high dynamic range (HDR) scans
Skill Level Intermediate
One of the most common adjustments you'll make to a scanned image or for digital photographic image for that matter is sharpening, and the reason for this is the very process of capturing your image with a scanner or digital camera, process of digitizing, that is converting your images into pixels softens your image. This makes perfect sense conceptually, because you're taking a not completely infinite resolution image, like a scene or a photograph, but a very, very high fine-grained image, and you're converting it into pixels, which has definite structure at a much lower resolution than the original image.
The very process softens your image. So you'll want to sharpen nearly every one of your digital images that you capture with a scanner or digital camera, the question becomes how much and when you want to apply the sharpening? And along the way, we'll talk about some things to avoid. Here we have the same image, this is the Kodiak Tundra image, but the left hand one has no sharpening applied to it. So I've labeled this a Nosharp image. The right hand one has already had some sharpening applied to it. Let's start with the left-hand one. First, I want to show you that I have actually assigned two color sampler points here.
sampler point #1 is right on the edge of the leaf and it's a critical white highlight area near the edge of the leaf, and sampler point #2 is a critical shadow area down here where we want to maintain shadow detail. We are going to zoom in and focus visually on the edge of the leaf and the highlight point, and then we'll monitor the values of the shadow point over here. Notice, currently, the highlight point is about 228, and it's a good highlight value. it's not right at 5% white highlight, which is what we shoot for in a pure white highlight. You'll notice that our starting value along that highlight edge is 228, which is certainly plenty good value in terms of not being too light.
The shadow value is at 13. we don't want to go too far below that. A shadow value of 12 is about as low as I will ever want to go, because if we go below that, that's 95% shadow in the percentage scale, then our shadows tend to fill in. On the highlight end, we don't want to go any lighter than 242. So we're okay in terms of the image and how it's exposed right now. Let's zoom in a little bit, I am going to move this over and we are going to zoom in on the highlight edge, and we are going to bring up a common sharpening tool.
This one is called Unsharp Mask. This other good sharpening tool, that's your smart sharpen, but they all work pretty much the same way. We create focus, we enhance the focus or sharpness of an image when we apply sharpening tool by increasing the contrast, and particularly along high contrast edges. Notice here, in this Unsharp Mask tool, we are going to focus first on addressing the amount or changing the amount of sharpening and the amount is a percentage as you see here, and we have 50% sharpening. That means that the increase in contrast between two adjacent pixels is going to increase by 50%.
Let's zoom way in right on the edge here, and let's turn the Preview checkbox off and on, and you can see how the contrast between adjacent pixels is being increased when we apply sharpening in the preview. That's how we create focus. lighter pixels get lighter, darker pixels get darker. Move over to the Info panel here and see what's going on at the same time. Remember, our starting values is 228. when we apply 50% sharpening, our highlight value goes to 242. That's right at 5% white highlight, and notice the shadow stays at about 13, which means, there probably isn't a lot of difference in contrast in the shadow area, which is okay, but we certainly wouldn't want to go too much higher along this edge than 242.
Notice what happens when we increase the Sharpness amount to 100%. Visually, you can see the pixels get much higher contrast and over here numerically, we see these white highlight edge gets blown out to 255. Now granted that's just one pixel, but notice that a lot of the edge pixels are getting very, very light, and let's back off in our view just a little bit and come up one. there we go, and I am going to take this all the way up to 200% on this image, and you can see that the whole image gets very grainy.
The other thing that happens is you see these white halos that start to form along that edge? That's a very common phenomenon of oversharpening. My point is a little bitter of sharpening goes a long way and it's easy to oversharpen an image. Point that I want to make is to really get the best visual representation of what sharpening is going to do to your image, you'll always want to work ultimately at 100%. You want to take a look at that 100% view of your image and when we turn the Preview off and on, you can see at 100 %, the whole image gets a little bit grainy actually, and you do start to get that white halo along the edge.
So for this particular image, we can see that at 200%, this whole image gets very, very grainy and we get a very distinctive white halo along the edge. So 200% would be way too much for this image. Say, nothing of the fact that our edge has certainly blown out and our shadow has dropped down to a numeric value of 8. For this image, probably 50% sharpening for the amount of sharpening would be good for this image, because this was a pretty darn sharp image to begin with. Notice, when we turn the Preview off and on, you can visually see the increase in overall sharpness of the image, but you don't get a lot of graininess in your image.
These other two values that we typically adjust when we do a high-quality sharpening is Radius and Threshold. Again, I'd like to zoom in on the edge of our image to show you the impact of those. The Radius controls the width over which the sharpening is going to be applied. Watch this edge right here where my cursor is, when I go to a Radius of 2. Do you see how everything thickens up a little bit? On a Radius of 3 it gets really thick, rarely, if ever do I go above a Radius of 1 on a continuous tone image. For some line art images, I'd go higher, but not for continuous tone images.
And then a more subtle control is something called Threshold, and various sharpening tools do this in different ways. What Thresholds allows you to control is where the sharpening is going to be applied to an image. For instance, a Threshold of 0 means sharpening is going to be applied across the entire image and notice there's equal graininess across the whole image when we have a Threshold of 0. When I apply a Threshold of 3 to this image, you'll notice that the interior of these leaves get a little bit softer. The edges are still sharp and pretty much the same, but the interior has softened.
Let me just go back to 0 and watch this area right in here, and then go to a Threshold of 3. Notice the high contrast edge details are still sharpened, but the interior portions, which are a little bit lower contrast, are protected a little bit from that sharpening. This is a very important tool when you're sharpening people's faces, for instance, where you want the eyebrows and the teeth and the hair to be sharpened more than say the skin tones. Or on this particular image, if you wanted the interior of the leaf to be a little bit smoother than the edges, then you can apply a small amount of Threshold in the 1 to 3 category.
This would be a little good sharpening amount for this image. Amount of 50, a Radius of 1 and maybe a Threshold of 2 or 3 or for this image and in a lot of night landscape images I'll use a Threshold of 0, I want everything sharpened. But something in this range here would give us good quality amount of sharpening in our image. And notice, we end up with the RGB value of 245 for our highlight area and an RGB value of 11, which just falls below the 12 Threshold. And if you want to apply a little bit more sharpening than what the two highlight and shadow details will allow, you can always fine-tune your highlight and shadow details afterwards and I've done that quite a bit, and particularly if you use adjustment layers in Photoshop, it gives you that freedom without damaging your images.
So that's pretty good sharpening on that particular image, and if we take that to, again, 100% view and return that Sharpening off and on, you can see that it's enhanced the quality of that image. Let's move over to the pre-sharpened image and the point that I want to make here, I think, you probably have already figured out where I am going to go with this, but let's just go there anyway. Is this image is already sharpened, you can tell by looking at the nice sharp edges here. Look at our value 242 and 12. The point I want to make is if I come back in and I apply sharpening to this image, just the 50% we did before, notice the edge values go to 255, the shadow value is dropped way too low down to 9, and the image is getting too grainy.
You don't want to over sharpen your image, you sharpened it completely twice. This very commonly happens, because the automatic mode on most scanners and for that matter on a lot of digital cameras is set to sharpen your image. My suggestion is and particularly if you intend to edit your image in Photoshop after you scan your image, don't apply sharpening during the scan. If you go apply sharpening during the scan and afterwards in Photoshop, you are going to over sharpen your image. Another thing to consider is if you do want to work in your image, you want to edge your image in Photoshop, notice that sharpening not only increases contrast along these edges giving us better focus, but it also decreases the overall tonality of your image.
That is the amount of tones in your image decreases, because we are increasing contrast between adjacent pixels everywhere. If you want to edit your image, and you want to have all the tonal values to work with, you don't want to be editing your sharpen image. So my suggestion is finish your editing and then apply sharpening. So if you are going to go to Photoshop, wait, don't apply it during the scan. And in fact, as a general rule, I don't sharpen any of my images during the scan. I always like to have a fully color corrected, but not sharpened image that I can always go back to, if I decide to apply some editing later on.
So there's how to apply sharpening and how sharpening works and some things to worry about. One final thing that we want to talk about is there are some kinds of images that are really dangerous to apply sharpening to, and it is a kind of an image that we talked about already, and this is a JPEG image, particularly one that has had a lot of JPEG compression applied to it. I mentioned that sharpening really has its greatest impact along high contrast edges. Let's zoom in on this image and this is the JPEG compressed image we talked about a little bit earlier in the class. Well, this is how the JPEG compression amount of 4 applied to it.
When you zoom in, you see these boxes of compressed pixels that have been created. When we come in and just apply a modest amount of sharpening to this image, say, 50% of sharpening to this image, watch what happens to all those JPEG compression boxes that we see in the image. The impact of the compression is actually exacerbated by the application of sharpening. It makes it actually worse, because the edges of all those groups and pixels are high contrast edges and the sharpening tool doesn't know what they are. they are just season this high contrast edges.
If you were to apply something like 100% sharpening, oh, my gosh! that impact of the JPEG compression becomes worse and worse and worse. This is one more reason why you really don't want to save your high-quality images out as JPEG, because when you apply sharpening to them, the impact of the JPEG compression just is exacerbated.