The High Pass Filter
If you have ever opened a photograph and wondered why its a little softer than you expected, then read on.
Digital Cameras produce images that have a slight softness to them. This is because they contain an anti-aliasing filter. I won't go into the technicalities of anti-aliasing, but in a nut-shell the filter attempts to reduce the distortion in patterns and edges of an image. Whilst great, it also softens the image overall, details can become muddy, and in some cases some they can almost disappear.
I use various techniques for sharpening depending on whats in my image, but my most used technique is the much talked about High Pass Filter. I have provided a step by step tutorial below on how to do this, enjoy!
Step 1: Pick an image
I have picked the above image of a graffiti wall, but you can pick any subject, the technique works on anything from landscape, portrait and even product photography.
Step 2: Duplicate the layer
With your image selected, hit the drop down menu button and select "Duplicate Layer" (Ctrl J shortcut)
Step 3: Hard Light
Next step is to select the Duplicated top layer, then head up to the layer styles and select "Hard Light or Overlay"
You should see a contrast increase on your image but you can ignore that for now.
Step 4: High-Pass Filter
With the top layer now set to Hard Light, go to the top menu of Photoshop, hit "Filter", then scroll down to "Other" then select High-Pass. A little dialogue box with a grey version of you image should appear.
Step 4: Comparing Pixel Radius
At the bottom of the Grey image you should see a slider to control the Pixel Radius. The more you increase the Pixel Radius the greater the effect of sharpening will become. Its not a good idea to go over the top with this, subtle is always best.
Results will vary depending on the pixel density of your image, for example I tend to use different sharpening amounts for my Canon 6D and my 5DS which is 50 megapixel camera.
I usually find 1-3 is a decent amount for my Canon 6D which outputs images at 5472 x 3648 pixels.
Step 4: Let's Compare
For the purpose of this tutorial I have exaggerated the effect, and as you can see there's quite a big difference between the two images. I do urge subtlety in practice though, especially with portraits.
An important step here is to ensure you view your image at 100% as well as viewing the image overall to ensure it's to your liking.
Step 4: Work Around
The downside to the High Pass filter is that it can enhance and create noise, especially if the image in use already contains quite a bit. I have listed a few ways to tweak the effect below, but most importantly experiment, every image is different.
Too strong! Reduce the opacity of the High Pass Layer, a quick cheap way of knocking the effect back
Enhanced Blemishes! Use a layer mask and brush out some of the areas where you don't want sharpening. This can be useful when editing portraits, such as keeping the eyes sharp whilst leaving hair and skin looking natural.
- Weird Highlights! Luminosity masks can be used to remove issues created in the highlights by the High Pass. I'll post a tutorial on this soon.
If used properly the High Pass Filter can be a really powerful tool to add a little "pop" to your photographs and enhance those little details. I use it alongside a few other sharpening techniques across all of my Architectural and Interior photography. It can be incredibly useful when photographing spaces with lots of different finishes and texture.
Do experiment, but remember subtlety is key, enjoy!