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How to sharpen without halos (super-simple method)

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One of the banes of sharpening, especially in landscapes, is that light lines appear around horizons, trees and so on, forcing you to scale back your sharpening efforts. This can be a nuisance when everythings' great, apart from those darned halos!


A very simple solution:


1. Duplicate the pixel layer.


2. Sharpen away. Use Unsharp Mask and turn up the radius as far as you like. Ignore the light halos around things.


3. Here's the magic: Blend mode: Darken.


Ole! The halos disappear!


So what's happening? For those who are not saying 'but that's obvious': 


Sharpening finds edges and makes one side lighter and the other side darker to trick the eye into taking greater notice of the edge.


In Darken blend mode, Affinity compares pixels in both the duplicate and original images and shows the darker pixel (not the lighter one). Any pixels which have been darkened will be in the sharpened, duplicated layer along edges, and will be shown. Any which have been lightened (on the other side of the sharpened line) will not be shown as the darker pixels from the original layer will be used. Any pixels not affected by the sharpening will be the same, so the blend has no colour-changing effect.


Just like that.


If there are parts of the picture where you want to keep the light edges in the sharpening, then of course all you need to do is add a white mask to the original layer (or between the original and duplicate) and paint black over the areas to keep this light edging.


Note: You can use Difference blend mode to see the sharpened area and guide any masking. Add a temporary Invert layer at the top to make this easier to see, if you like.


Corollary: If you blend with Lighten mode, you can probably use this one-sided sharpening to create a glow around things.

Dave Straker

Cameras: Sony A7R2, RX100V

Computers: Win10: Chillblast i9 Custom + Philips 40in 4K & Benq 23in; Surface Pro 4 i5; iPad Pro 11"

Favourite word: Aha. For me and for others.

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