'Sharpening Edges, Gently'

Clive R. Haynes FRPS

Sharpening is frequently essential, however it can cause a variety of problems.
Sometimes the sharpening is simply overdone and the image appears unnatural by virtue of its over sharp definition. At other times the sharpening process also enhances (sharpens) unwanted areas and sections such as 'noise', 'film grain' and skin texture (exaggerating blemishes and being generally unflattering).

Something can be done to 'fine tune' our sharpening technique by applying sharpening to the 'edges' of objects and areas rather as a 'blanket' to the whole image.

Described below is a method that will enable you to control how much sharpening you apply and address principally 'edges'.
We'll be using the 'Find Edges' filter in combination with the 'Unsharp Mask' filter.

Above: This image of the ruined Abbey of Maillezais will be our example

The Method

Open the picture as a Background Layer

Make a copy of this layer, placing it on the layer above

Click on the Adjustment Layer icon.......... at the bottom of the Layers Palette and from the drop-down Adjustment Layer menu choose Channel Mixer.

In the Channel Mixer dialogue box, click 'Monochrome'

Adjust contrast to suit the image by the Red, Green and Blue 'sliders'. When you're happy, click 'OK'.
Don't forget - this is an Adjustment Layer so when you wish, you may return to it again to refine the adjustment made

(Above: the Channel Mixer dialogue box - the slider settings are just as a 'for instance' - adjust yours for best contrast)

Make the Channel Mixer as a 'Clipping Group' with the layer beneath
(do this by holding down the Alt key whilst passing the cursor between the two layers in the Layers Palette, when you see the two overlapping circles appear, left (or right) click and the upper and lower layers will be 'clipped' together. This is represented by a downward arrow shown in the upper layer. NB If this is not done, the Channel Mixer setting will affect all layers beneath and not just the one you wish to alter).

Activate the copy layer

Go to Filter > Stylise > Find Edges







(Above: Section of image showing 'Find Edges)

Filter > Gaussian Blur > 1 to 2 pixels

Image > Adjust > Invert to make a 'negative' version. (Quick Key: Ctrl + I)







(Above: Section of image showing inverted & blurred 'Find Edges')
Should you wish to be selective about what you sharpen at this stage, use black to paint-out areas not required for sharpening

Go to the Channels Palette

Click on the 'Load Channel as a Selection' icon

'Marching Ants' appear - see below







(Above: Section of image showing 'Marching Ants')

Go to the 'Select' menu - choose 'Save Selection' and name it (so you can find it again should you need it)

Return to / activate the (original) Background layer - This is the layer to which the sharpening is going to be applied. The work on the (copy) layer above has been to 'find' the edges, separating it from the noise or grain.

Switch off (click on the eye) the upper, copy image, layer - you don't wish to 'see' it - it's done its job!

Hide the 'Marching Ants' by Ctrl + H

Go to Filter > Sharpen > Unsharp Mask > adjust to suit

That's it - only the edges will have been sharpened, leaving grain & noise unsharpened

The saved selection is available for further use.

Above: Detail showing final stage - sharpening complete








Related Topics
Sharpening in Luminosity
Selective Sharpening
Sharpening Texture with 'Emboss'
High Pass Sharpening
Know-How Contents
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