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Sharpening by its nature emphasizes the contrast found along edges of objects in the image. When an image contains relatively smooth textures that you want to keep smooth, it can be beneficial to take steps that ensure the sharpening effect will only be visible along the edges of objects in the photo. In this lesson I'll show you a method for accomplishing this. Here, for example, I have a photograph of some flowers and there's some relatively fine detail found within the flour but I don't want to sharped the detail along the petals themselves. The petals are relatively smooth but they do have some striations and other texture that I do not want to emphasize by sharpening.
So I want the sharpening to only affect the highest contrast edges within the image. We can do this by creating a mask based on one of the channels in the image. And in fact there's several ways you could approach this, sometimes even using the overall image as the basis of a mask, but I generally use the green channel. We'll go ahead and go to the channels panel so that we can take a look at the individual channels that make up this image. You can see that I have a red channel which indicates how much red light will be visible in specific areas of the image, a green channel for green light and a blue channel for blue light. In most cases you'll find that the green channel contains the most information, the highest level of detail within the image.
As a result, the green channel is also generally the best place to start when we want to create a layer mask that will identify just the edges within the image. That's certainly the case here. So I'm going to make a copy of my green channel by dragging the thumbnail for the green channel down to the Create New Channel button, the blank sheet of paper icon down at the bottom of the Channels panel. This will create a green copy, and so I can manipulate this green copy without worrying about altering the appearance or other qualities of my image.
The first thing I want to do is to locate the actually edges. The highest contrast edges within this green channel copy. So I'm going to choose filter from the menu and then choose stylize and find edges. There aren't any options associated with Find Edges. Once you choose this command, it will be executed on the image, and as you can see, we get something of a sketch-effect in the image. I'd like to get better seperation between the areas that are versus are not edges, and so I want to enhance the contrast of this green copy channel.
So I'll choose image, adjustments, and then levels, from the menu. I'll then bring in my black point to darken up more of the dark areas, to make more areas black. And I'll bring in the white point so that the areas that are not edges will become white. I want to maximize contrast. I want to have a very high contrast image here, but I only want the true edges, the areas that I want to be sharpened, to appear as black. I might allow some sharpening of details that are not exactly edges but still important to the image.
But I can fine tune as I see fit. Keeping in mind that in this case the areas that are black are those that I will eventually want to sharpen, and those that are white are those that I do not want to sharpen, at least at the moment. So I think somewhere around there looks to be pretty good in this particular case. I will be emphasizing just the most important details in the image. Without of course resulting in sharpening for areas that should remain relatively smooth. So I'll go ahead and click OK in order to apply that change. Now I'm going to use this as the basis of a layer mass, and that being the case.
This is actually the opposite of what I need. Ultimately, I want the white areas to be the areas that will be sharpened, and the black areas to be areas that will be blocked from that sharpening effect. So I'm going to choose image, adjustments, and then invert from the menu in order to inverse this so that white represents the areas I want sharpened and black represents areas that I do not want sharpened. I'm going to zoom into a 100% scale here, so that we can get a better sense of the mask we've created so far. And you can see there's relatively crisp edges along those transitions from black to white.
I'd like to keep the transition relatively smooth, so that the areas being sharpened versus the areas not being sharpened have a gradual transition between them. So I will go ahead and choose Filter > Blur and then Gaussian Blur, in order to bring up the Gaussian Blur dialog. Now I don't need much of a blur, I just need a little bit of a transition so that we don't have an odd appearance in the final image. An abrupt transition between sharpened versus not sharpened pixels. So that looks to be pretty good, just a slight softening of the image.
I'll go ahead and click okay. And now we have the basis of our layer mask. I'll go ahead and click the Load Channel As selection button, the dashed circle button at the bottom of the channels panel, and this will create a selection. More areas that are white are selected. Areas that are black are not selected. And areas that are a shade of gray are partially selected. I can then switch to my full color image. I'll roll up on the channels panel and click the thumbnail for the RGB tile. And then I can go back to my layers panel, and in this case, I'm going to create a copy of my background image later to work on just to maximize my flexibility.
I'll go ahead and drag the thumbnail for the background image layer down to the create new layer button. The blank sheet of paper icon at the bottom of the layer's panel. And this will create a background copy. Then with my selection active, I'll add a layer mask by clicking on the add layer mask button. The circle inside of a square icon at the bottom of the layer's panel. And this will add a layer mask based on that selection. You can see from the thumbnail that that layer mask matches the appearance of what I had created previously with my green copy channel. Now I can click on the thumbnail for my background copy layer to make sure that that is the active layer and then I can sharpen this layer. I'll go ahead and choose filter, sharpen, and then smart sharpen. And I'll exaggerate the sharpening here just for a moment, so that we can get a better sense of exactly what's happening.
I'll increase the radius dramatically and I'll also take the amount up to very high level. And you can see in the preview for smart sharpen we're seeing the sharpening as it effects the layer that we're currently working on. In other words the mask is not really taking effect in the preview for smart sharpen, but if you look out into the image you'll see that the layer mask is restricting that sharpening to only the areas we identified with the mask we created. So, for example, I get the edge of the petals, and some of the stronger details within the petals sharpened. But most of the face of the petals remains smooth. Now of course, I can push my sharpening a little bit more, since I'm focusing it only on the edges.
But I still want to keep it at a reasonable level. So I'll bring my radius value back down to a more appropriate level. In this case, maybe somewhere around one pixel, and also want to reduce the amount setting to a more reasonable level here. I can go a little bit stronger than typical but I dont want to go to far so probably somewhere in the 150 to 200 range will produce a good result. And I can turn off the preview to get a sense of the effect in the actual image. In this case, I'll make it a little bit stronger I think. Maybe somewhere around there and that looks to be pretty good. So now I'm applying a reasonably strong sharpening effect, but it is only effecting the areas I've identified with my layer mask. I'll go ahead and click okay in the smart sharpen dialog and the effect is finalized.
Of course I could always reduce the opacity of my background copy layer since I have my original background layer which is unsharpened and I could also modify the layer mask if I needed to, for example if I wanted to block the sharpening from certain areas I could paint with black on that layer mask. And if I wanted to reveal the sharpening in additional areas, I could paint with wipe on that layer mask. By creating a layer mask that defines the true edges withing the image, you can apply a sharpening effect that only enhances those edges while keeping other areas of the image relatively smooth.
This technique obviously requires a little bit of additional effort, but that effort can really pay off with a better final result than could be achieved with a typical approach to sharpening.
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