Sharpen your images – Part 1

Unsharp Mask FilterWhy would you need to apply any sharpening to your images? Haven’t you spent hundreds if not thousand of pounds or dollars on the digital camera? Shouldn’t the images be sharp? You focused correctly when taking images, so why sharpen?

Or maybe you’re thinking that if you didn’t focus properly, you could use the software to improve the sharpeness of your images?

Let’s get it straight – if  your images haven’t been focused properly, you can’t refocus them using software. If your image is not in focus, no software will bring it back in focus.

So what does sharpening do?

Sharpening is a solution to what happens with a digital capture – digital image converts image to coloured pixels and it can’t render straight lines and natural forms. With millions of pixels image looks very good, but if you get very close, you will see the complex mosaic of pixels:


As you can see on the image here, the edges between the pixels look like a staircase. To get around it the camera manufacturers use filter over the sensor to blur the image just a bit – it’s known as anti-aliasing. This creates a compromise as the image does look a bit better on the edges but at the same time the image looks a bit softer. Anti-aliasing filter adds a bit of fuzziness to the image.

Sharpening with Photoshop

Different methods of sharpening in Photoshop (and other applications) don’t really sharpen images. They increase the contrast on the edges between the pixels. Increased contrast on the edges gives images increase in sharpness (apparent sharpness).

The oldest and a very good method of sharpening images in Photoshop is by using the Unsharp Mask Filter:

Unsharp Mask filter sounds misleading for many users as they’re thinking that it’s going to “unsharp” images (blur them). It’s not the case as the filter actually accentuates contrast on the edges which results in sharper looking image. The name of the filter comes from an old photography technique where a blurred image was placed directly above the original, and when they were placed together under the enlarger, the edges in the print were given extra definition.

Remember that sharpening should be the last process when you work with the image, so do any image or colour manipulations first.

Unsharp Mask Filter

Here’s what the sliders in the Unsharp Mask Filter in Photoshop do:

Amount – defines how much contrast you’re adding to the edges. The more you increase the Amount, the lighter the light pixels get and the darker the dark pixels get.

Radius – defines the size of the edge you’re increasing contrast on. Lower settings (less then 2 pixels) enhance finer details in the image.

Threshold – defines how different tones have to be in brightness before they get sharpened. Setting of 0 sharpens all tones.

In the next part of the article, next week, I’m going to show you the second method of using High Pass filter.

Till then, enjoy!

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