Sharpening is about Luminosity

I’m not shouting here, just pointing that sharpening in any digital imaging program, is based on Luminosity. This is vital to understanding the sharpening process in both Photoshop and Lightroom.

Put simply, sharpening is about brightening pixels, or creating contrast between pixels. This process fools the eye in to believing a image to be sharper, than it was pre-sharpening.

When we sharpen an image we are in fact creating a greyscale mask of the original, and applying a gaussian blur to this mask.

Below is the original.

Before sharpening

Before sharpening

When we come to sharpen the image, we are creating a blurred greyscale mask, which is overlaid on the original. The blurred version extends outside the original image bounds.

Gaussian Mask applied

This is the image with Gaussian mask overlaid on the image.

When the original image is subtracted, we now see what sharpening is all about, as the sharpening process will be working on this edge. Of course, we have sliders that control the sharpening process.

The basic principle is we are actually working on this mask, minus the original image.

Sharpening final

This is what sharpening is actually working on – the white border

The Sharpening Process in Lightroom.

Before we go any further, there are three things I should point out:

  1. To get the most from the four sliders in the Detail panel, you must keep the Alt/Option key pressed, whilst moving the sliders. This will show you the greyscale mask.
  2. Always sharpen at 1:1 view, 100 pct view. You need to see the full effect of the sharpening.
  3. Sharpening is a two part process. You sharpen for the screen first in the Detail Panel. But, you should always sharpen on Output from Lightroom. Either in the Export Dialogue Box, (standard is fine). Or, by going to into Photoshop to make use of, frankly, better sharpening tools.

The ‘Amount’ slider

This slider ranges from 0 to 150.

Don’t worry about the 150 figure here.

The Amount Slider  is like an edge detection tool, the more you move the slider to the right the more pixel edges you are going to bring into the sharpening process.

The adjustment locates pixels that differ from surrounding pixels.

With an obvious edge, like a building, that will be picked up quite quickly  as you move the slider right. The more you move the slider right, the more edges it will bring into the sharpening process.

It’s very hard to show you example of the amount slider in action, but these two extreme examples will help.

Below is no sharpening whatsoever. The other sliders have no effect.

No sharpening whatsoever

No sharpening whatsoever

This is an over sharpened image, with the slider at 150. Here, the three other sliders come in to play. You can see the classic, worm cast effect here.

Over Sharpened.

The Amount slider at it’s maximum of 150.

The ‘Radius’ Slider

This slider ranges from 0 to 3.

It controls the width of the luminosity border around the pixels. The higher the setting, the wider the contrast there is between pixels.

A high setting is fine for hard edged objects. A low setting is best for finer details.

It’s almost impossible to show this visually here, as you need to have the Alt/Option key pressed whilst you are moving the slider to see the effect properly. That makes it very difficult to grab a screenshot.

The ‘Detail’ Slider

This slider ranges from 0 to 100

This slider is about High Frequency detail, which is fine detail, textures etc.

To be honest I dislike this slider as I believe it’s not needed on most images.

If you need to emphasise textures, it’s fine.

Use it with care!

The ‘Masking’ Slider

This slider ranges from 0 to 100

I love this slider, but you must keep the Alt/Option key pressed on whilst you move this slider for you to see it’s true power.

The Masking slider is like the Amount slider in reverse. As you move the slider to the right the fewer edges it finds. Until only the very defined edges are left behind.

As I said you have to keep the Alt/Option key pressed whilst you’re using the slider, as this shows the greyscale mask.

The basic principle is this:

  • The whiter it is, the more it will be affected by the sharpening process.
  • The darker it is, the less likely it is to be affected by the sharpening process.

I often use the Masking slider first to choose the areas of the image I want to work on in advance. If I’m sharpening a Landscape, I mask out the finer details first, That way I push the Amount and Radius sliders more, without affecting the finer details in the image.

I’ll cover Noise Reduction in another post. Remember though that the Luminance slider will remove your sharpening the farther you move the slider to the right. You can pull back some of the lost sharpening with the Detail, or Contrast sliders. But, try not to get the Detail panel to work against the Noise Reduction panel, or vice-versa.

Finally, every raw image benefits from some sharpening, as you’ll notice on raw files the detail sliders are set by default as follows. This is not the case for any other formats.

Default raw Setting

Default raw Setting

And don’t forget Output Sharpening on Export from Lightroom. Apply some sharpening again. ‘Standard’ will be fine.

Always sharpen on Export

Always sharpen on Export.