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This is a very simple tutorial which demonstrates using Photoshop\'s high pass filter to sharpen an image.
This tutorial is most likely to be of interest to people using digital cameras. or to webdesigners and artists wishing to sharpen images.
Why do images need sharpening?
Many digital photographs can appear to be slightly out of focus, either on screen or printed.
Photoshop\'s sharpening tools can usually do a good job when provided with good quality images. They do this by enhancing the contrast on the edges of images - no extra digital information is added to the image (in fact, some information is lost) but images with sharper edges appear to "jump out of the page".
In this tutorial, we are demonstrating using the high pass filter to sharpen images.
Always make a duplicate of your original image
When working with images in Photoshop, we always recommend "non destructive" methods of enhancement. This means creating a duplicate layer of the original image, and applying any effects to that layer.
If the worst happens and the photopshop file is saved, and you later wish to go back and edit or undo any changes, you have the original image to work on - stored as a layer.
Method
Firstly, we will duplicate the layer. This can be done by selecting the original image and pressing "CTRL + A" to select its entire contents. Then pressing "CTRL + J" will create a duplicate layer.
We then set the blend mode of the duplicate layer to "overlay".
The overlay blend mode effectively enhances the contrast of the darker and lighter regions of the image.
Regions of exactly 50% brightness are unaffected. Brightness below this point effectively has the Multiply blend applied; Brightness above 50% has the Screen blend mode applied.
With the original layer duplicated and set to Overlay mode, the on screen result looks like the contrast has been boosted (like the layer curves have been set to an S curve).
Applying the Filter > Other > High pass will show a dialog box, and a preview image (set to grayscale).
The slider adjusting the radius of the High pass filter can be adjusted until the preview window only contains the edges of objects in the image. This effect will, when applied, serve to visually sharpen the edges of objects visible.
We recommend using as low a value as possible, to avoid introducing "Halo" effects into our completed image.
Excessive sharpening
Halo effects become visible with excessive sharpening, as light "blooms" around dark edges in the image.
If the image looks good on screen, its ideal for our purposes.
Sharpening an image for printing
If the image is intended for printing, it is worth doing a test run - some images may look sharp on screen, but when printed the end result is still not sharp.
This depends on the image size, and the specific printer and paper type. It may be that additional sharpening is required for printing purposes.
