Sharpen your images using the HIGH PASS filter

Image Sharpening
It really has nothing to do with “sharpening” at all. How does it work? Basically, when you “sharpen” an image in photoshop, you can use various methods or techniques to increase the contrast along the edges of objects within an image. When the contrast is increased along these edges (making the light side appear lighter, and the dark side appear darker) the resulting effect is a “sharper” looking image.

High Pass Filter
So why should we use it? Well, the High Pass filter was actually designed for edge detection. Since all we’re actually doing when sharpening an image is increasing the contrast between edges, the high pass filter is a great technique to use. When applying the high pass filter to an image, it’s edge detection properties will specifically locate and highlight the edges within an image, while all other areas are ignored. They key to the sharpening effect is the high pass filters ability to strictly increase the contrast along these highlighted edges without effecting any other parts of the image.

Steps
1. Duplicate Your Background Layer
While in school for photography, I was taught to always duplicate the background layer. It became the first thing I did as soon as I started editing an image, and has remained an important, initial step in my workflow. By leaving the locked background layer and producing a duplicate, you’ll always have an untouched, unchanged original image layer. It’s like the “back-up” copy.

Right click your background layer, and select “Duplicate Layer”.
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You will now have a copy of your background layer (Named Layer 1 by default).
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2. Convert the Duplicated Layer Into a Smart Object
Right click the duplicated layer (in this case, “Layer 1”), and convert it into a smart object.
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Your duplicated layer (layer 1) will now have a small symbol in the bottom right corner of it’s thumbnail, indicating it is now a smart object.
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Why convert it to a smart object?
By converting your duplicated layer into a smart object, you’ll be able to apply the high pass as an editable, smart filter. This allows us to apply the effect separately from the image itself, producing non-destructive editing by avoiding permanent changes to the layer itself.


3. Apply The High Pass Filter

On the top menu, go to filter > other > and click High Pass…

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Once you click High Pass, the filter’s dialogue box will appear. It contains a preview window, as well as a Radius slider.

The dialogue box will look like this (Radius Slider at it’s lowest point: 0.1 Pixels).
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What is the RADIUS SLIDER?
The radius slider is measured in pixels. What will happen when you set the radius slider to your chosen pixel amount, is Photoshop will determine how many pixels on each side of the edge it should include as part of that edge. If this is a little confusing, think of it like this. If you set the radius slider to 4.0, it will apply 4 pixels to each side of the edges it has detected (4 pixels on the light side, 4 pixels on the dark side). In other words, it is extending the width of the edges by 4 pixels on either side.

To illustrate an example, lets begin to slide the radius slider to the right (increasing pixel amount) and compare two different options to compare the results.

A) Radius Slider at 4.0 
This is what the preview in the dialogue box looks like when you set the radius to 4.0. You can begin to see the highlighting of the edges, with a width of 4.0 pixels on either side.
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When you click OK, here’s what the image will look like.
The edges are faint, but visible.
Image at 4.0.png

B) Radius Slider at 10.0
In example B, the radius is set to 10.0, and you can see a very noticeable difference in the highlighting and in the width of the edges.
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When you click OK, here’s what the image will look like.
Again, you are able to notice a large difference between the two examples.
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What you need to be aware of, is not to set the radius slider amount too high. This will result in an undesirable effect, and will not give you the “sharpening” effect you are looking for. For example, if we set the radius slider to 50 pixels, Photoshop will extend the width of the edge on each side, by that amount. By doing this, a large portion of your image will be considered an “edge”.

This is how it looks when the radius slider is set to 50 pixels. You are able to clearly see from this example, how the width of the edges can effect the results.
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*Generally, an approximate amount of 1.0 pixels to 5.0 pixels works best on most images.

4) Change The Blending Mode to “Overlay”
You are probably wondering why the images above are still grey. Well, here is how we put it all together.

Your final step in “sharpening” your image using the high pass filter is to change the layer’s blending mode to “Overlay”. By doing this, we are combining and blending both the results of the high pass filter and the highlights we created (which increases contrast), with our original image. This will cause the “grey” to be no longer visible in your image.

To do this, double click the “blending options” icon, shown below.
DoubleClick Layer Modes

This will bring up your blending options dialogue box. Click the Mode drop down menu, and choose “Overlay”.
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5) Your Image Will Now Have the “
Sharpening” Effect

Lets compare the results from our 2 examples with our original image.
The differences are most evident at one of the main focus points of the image, where the texture of the shoe is visible.

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Use the slider below to see each image individually.

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