Most people who have experimented in Photoshop, especially those who shoot in raw, will have some experience of trying to sharpen an image. Sharpening increases the contrast between neighbouring pixels resulting in the visual effect of a crisper image. It is typically the last processing step that should be performed on an image and is often used to enhance already well-focussed images or in desperation to try and rescue elements of a photograph that weren’t captured in-focus when the shutter was pressed.
There are numerous ways to sharpen images in Photoshop, so much so that there is a whole sub-menu of filters dedicated to sharpening, each offering a different amount of control and different levels of success. However, one of the most overlooked filters that can help you achieve better results with more control isn’t found in the Sharpen sub-menu, but is in fact found in the, usefully named, Filter -> Other menu: the high pass filter.
I’ll take you through a step-by-step guide to using high pass filter and hopefully show you how simple and effective image sharpening can be.
Start by opening the image that you want to sharpen – ideally, the image will have come from a raw file so not to over-sharpen an ‘out-of-camera JPEG’. Make sure that you have completed all other processing steps that you wish to perform. Here I’ll use this image of a fox to illustrate the process (feathers and fur often react well to a bit of sharpening).
In the layers palette, right click the Background layer, select Duplicate and click OK. This creates a copy of the original layer and is a key step for the application of the high pass filter.
With the duplicate layer selected, select Filter -> Other -> High Pass
This will bring up a high pass window with a small preview of the results and a Radius control. If you can see the whole image behind this window, you will notice that the Duplicate layer has turned grey – don’t panic, it’s supposed to.
Set the Radius value and click OK. The higher the Radius, the more sharpening will be applied to the image. If you play around with the Radius slider, you will notice that at low values, e.g. 1.0 pixels, only high-contrast edges are visible in the grey layer, whereas if you move the Radius slider up to 10 pixels, you will notice that more edges within the image will be highlighted.
The precise Radius value that will result in optimal sharpening will be image dependant, but somewhere in the range 1.0 to 5.0 pixels will suffice. Generally, 5.0 pixels will be too much, but given that we are performing this action on a duplicate layer gives us the flexibility to be heavy handed with the high pass filter, I’ll explain more shortly.
In the layers palette, set the blending mode of the duplicate layer to Overlay.
The Overlay mode ‘multiplies’ the blacks and ‘screens’ the whites of the layer below – that is, makes the dark areas darker, and the light areas lighter. Up on application of the high pass filter, our image was turned grey (neutral grey in fact), and when setting the Radius value, edges were picked out in light/darker shades of grey. Therefore, when the blending mode is set to Overlay, the neutral grey areas of the image have no effect, yet the lighter/darker edges screen/multiply the edges of the layer below, increasing the contrast, resulting in a sharper image.
Change the Opacity of the duplicate layer to achieve the desired sharpness. I mentioned that you can be heavy handed with the high pass filter – that is because you can tone back any over sharpening using the Opacity slider. It is often a good idea to set the Opacity to zero and work your way up to an acceptable level of sharpness so not to over sharpen and introduce artefacts.
It is advisable to try and print off a section of your image, at the same scale as you intend to print the full photograph, to get a feel for how much sharpening an individual image requires and adjust the Opacity slider as appropriate.
And that’s it, image sharpened!
The benefit of using this method to sharpen your images is that the sharpening effect is applied in a non-destructive fashion, on a duplicate layer, with a very simple to understand parameter (in the Radius value) that controls the magnitude of the sharpening, as well as giving you the ability to fine tune the final effect using the Opacity slider.
In addition, given that the sharpening is entirely controlled by the duplicate layer, you can have further control for where the sharpening is applied within the image by applying a layer mask to the duplicate layer.
So there you have it, a quick yet effective method for sharpening your images that gives you full control.