Removing Sharpening Halos in Photoshop
Digital images are inherently soft and when sharpened often show white or light toned halos particularly on high contrast edges. The same effect may be seen when increasing the contrast of the image, which is effectively how sharpening works, but more selectively.
Removing these halos is both a straightforward and fast process and does not require a high degree of precision. Removing them is essential as they are extremely detrimental to the finished image.
The image shown below of sea stacks in Iceland is a typical example of sharpening halos which surround all the high contrast edges as shown in the enlarged crops which follow.
Sea Stacks Snaefellsnes, Iceland
|Sharpening Halos||Enlarged view of Sharpening Halos|
The process involves cloning some darker pixels from right next to the halo over the lighter pixels adjacent to the high contrast edge.
Open the image and either flatten it or preferably Merge Visible to a new image layer at the top of the Layer stack. To Merge Visible select the Layer at the top of the stack and while holding down the Alt key Left click and hold on the icon in the top right hand corner of the Layers palette.
Run the mouse pointer down the list which opens to Merge Visible and release the mouse button. The new Layer is a flattened version of the image. With this Layer open select the Clone Stamp Tool, choose a small soft edged brush and set the opacity and flow to 100%. From the Mode drop down list select Darken mode and check Aligned Sample.
|Clone Stamp Tool Toolbar|
Enlarge the image to, say, 500-600%, sample close to the edge of the halo and then clone over the halo – depending on the outline of the halo it may be necessary to resample frequently. This is not a delicate process as the cloning will only overwrite the lighter pixels and the darker pixels will not be affected. NOTE - Unlike Normal cloning the process does not work when cloning to a blank layer – it must be done on a full image layer.
|Clone Tool Sample & Deposit points||Halo Cloned|
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