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Transcript for High Pass Sharpening Video -- Part I

Narration by Ron Bigelow

Photoshop CS4 Used in this Tutorial

Welcome to the Ron Bigelow Photography High Pass Sharpening tutorial. High pass sharpening is just one of many sharpening techniques that are available to digital photographers. With so many sharpening methods available, you might be tempted to ask why you would want to use high pass sharpening. The answer is that high pass sharpening uses the High Pass filter. This filter isolates the edges in images. Consequently, High Pass sharpening applies sharpening mainly to the edges where it is needed and protects smoother areas from the sharpening. The issue here is that noise is most noticeable in the smoother areas. Since high pass sharpening protects the smoother areas from sharpening, high pass sharpening has less of a tendency to sharpen noise than some of the other sharpening techniques.

Now, it’s time to actually sharpen an image using the high pass technique, so let’s get started.

This image is a close up of a leaf that has many little veins that create fine detail. This will provide a good test for the high pass technique. Now, the first thing that we should notice is that this image is not a Smart Object. How can we tell? The only layer in this image is missing the Smart Object symbol in the lower right corner of the layer icon. Now, I prefer to work with Smart Objects due to the quality and flexibility advantages that they provide. So, the first thing we need to do is to convert this image into a Smart Object. There are a number of ways to initiate the conversion. One way is to choose Layer/Smart Objects/Convert to Smart Object. We can now see the Smart Object symbol on the layer, so we know that our image is now a Smart Object. Let’s rename this layer as the Original layer.

Since we now have a Smart Object, many of you might be tempted to apply the sharpening directly to this layer. After all, applying filters, including the High Pass filter, to a Smart Object is nondestructive, so why not apply the sharpening to this layer. For most sharpening methods, this might be acceptable. However, as you will see shortly, this will not work for the High Pass technique. So, we need to duplicate this layer. To do this, we just drag the Smart Object to the Create New Layer Icon at the bottom of the Layers panel. Let’s rename this new layer as High Pass.

Now, if we apply the high pass filter to a color layer, we might end up with some color shifts. This is very undesirable. Luckily, we can avoid this by changing the blend mode of this Smart object to Luminosity. The Luminosity Blend Mode lets the tonal information, but not the color information, through. We can easily change the High Pass Smart Object Blend Mode to Luminosity by choosing the Luminosity Blend Mode from the Blend Mode pop-up menu.

Now, when we carry out the sharpening, it is best if we can see a close up of the detail so that we can better understand how the sharpening is affecting the image detail. Thus, we need to move in to the 100% view on the monitor. This is easily achieved by pressing Control-Alt-0 on a PC or Command-Option-0 on a Mac. Now, using the navigator, we can move to the area that we want.

Next, we apply the high pass filter by choosing Filter/Other/High Pass. Okay, our image has suddenly become rather strange looking. That is because we have not yet applied the proper Blend Mode for this High Pass filter. Let’s take care of that right now by closing this dialogue box. Then, we can later come back to the High Pass Filter.

At this point, we can see that we now have the High Pass filter below the High Pass Smart Object. We can now change the Blend Mode for the filter by double clicking the Blending Options icon on the filter. This brings up the Blending Options dialogue box. We need to change the Blend Mode to Overlay. Notice that our image now looks more like what we would expect.

We are now at the point where we can understand why we didn’t apply the High Pass filter directly to the Original layer. The problem was that we actually needed to apply two different Blend Modes. First, we needed to apply the Luminosity Blend Mode to ensure that we did not create any color shifts with the sharpening. Then, we needed to apply the Overlay Blend Mode to get the proper effect with the High Pass filter. Since we can not apply two different Blend Modes to a single filter, we needed to create a separate Smart Object. Thus, we were able to apply the Luminosity Blend Mode to the High Pass Smart Object and the Overlay Blend Mode to the High Pass Filter.

Next, let’s reopen the High Pass filter dialogue box by double clicking the High Pass filter. Now, it is a good idea to understand a couple of things before we start sharpening. First, we should understand what the high pass filter does. The high pass filter retains the edge detail that is within the radius setting that we choose. The rest of the detail does not get through. In other words, when correctly set, the high pass filter only lets the edge detail get sharpened. It functions like a filter or mask that lets us sharpen only the major edges without sharpening the rest of the image. This is important because the high pass filter helps to prevent the noise and minor detail from being oversharpened. Second, we should understand what the Overlay Blend Mode does. The Overlay blend mode darkens the dark tones and lightens the light tones. In other words, the Overlay Blend Mode will make the dark sides of the edge detail darker and the light sides of the edge detail lighter. Thus, the Overlay Blend Mode increases the contrast of the edges, and that is what sharpening is all about.

Notice, that at this time, the radius in the High Pass dialogue box is set to its lowest setting of 0.1 pixels. Also, looking at the image, we can see that there is little, if any, sharpening effect. Now, watch as the radius is increased by moving the slider to the right. You can see detail start to sharpen in the image. At first, it might appear that the larger we make the radius, the sharper the image becomes. So, why don’t we just make the radius really large and maximize the sharpening.

Well, up to a point, the image detail improves as we increase the radius. However, at some point, the image detail starts to degrade. Watch as I deliberately increase the radius way too much. The fine detail has been degraded. Thus, by increasing the radius too much, the image detail is actually destroyed. This clearly demonstrates that the proper radius setting on the high pass filter is critical. Too small of a radius and we do not get much sharpening. Too large of a radius and we destroy image detail.

Now that we know that the radius affects the sharpening, the next step is to set the radius value. This is most likely the most challenging part of the high pass sharpening technique. So, this brings us to the big question, “how do we determine the best radius for high pass sharpening?” The reality is that there is no one best radius for all images. The best radius setting varies from image to image. The way that I recommend that you determine the best radius setting is to start the radius at its lowest setting and gradually increase the radius up to the point where you begin to notice that the detail is just starting to degrade. Then, decrease the radius setting a bit. This will produce the most sharpening without degrading the image detail.

Let’s try this with this image. Starting at a radius of 0.1, there is no noticeable sharpening. Now, I will slowly increase the radius by typing in different radius values. I can see the sharpening improve up to about a radius of 6. However, near a radius of 10 or so, I begin to notice a loss of some image detail. This might be a little difficult to see in this video, but on a large monitor it is fairly obvious. If you are having a hard time figuring out the best radius, you might want to look at the detail at 200%. Also, clicking the preview box off and on will help you see the effect of the sharpening. If you are not sure, it is better to go with a smaller radius as too large of a radius will degrade detail. For this image, I will settle on a radius of 6.0. Using the preview box, we can see the effect of the sharpening.

Okay, that wasn’t bad for a first pass. However, we can fine tune this sharpening. In fact, we have three ways to tune the sharpening. What’s that I hear? You want to know more about fine tuning High Pass Sharpening. Well, for that, you’ll just have to watch the next video.