Removing halos at sky boundary

[jsachs]

Here is a trick I recently discovered for removing the annoying light and dark halos that sometimes show up in landscapes between the sky and the rest of the image, especially if the image is over-sharpened.

This is a 600% enlargement of a cell phone JPEG that was sharpened.

To remove light halos, clone over the white halo from just above it, with Mode set to Darken Only. This will overwrite the halo with sky but not disturb the darker mountain below it.

To remove dark halos, clone over the dark halo from just below it, with Mode set to Lighten Only.

Finally, touch up as necessary.

[tomczak]

I tried to automate reducing halos in already oversharpened images for which there are no unsharpened originals using this technique:

viewtopic.php?f=5&t=513&p=4754&hilit=halos#p4754

In summary: Composite, in Soft Light (or reduced-amount Hard Light) mode, the Input image with the Inverted High Pass filtered version of it.

For halos that can be localized (as in trees/sky boundary), a crude mask can be helpful to prevent creating artifacts elsewhere in the image.

[jsachs]

I tried playing with this a little, but it seems to soften the rest of the images as it removes the halos. You could probably fix this by applying a curve that leaves bright and dark parts of the inverted high pass image alone by changed everything else to mid-level gray.

[tomczak]

The technique indeed seems to soften the image where it shouldn't sometimes. Making small details in inverted High Pass dissolve into 50% gray while leaving the oversharpened edges intact should work the magic, but I'm having a hard time automating it (tried curves, tried texture mask, edge filter, and a few others). So far mild Denoise with a relatively large radius seems the most promising...

I've attached the workspace (ZIP) that I'm playing with - maybe there is a better way of doing it. Jonathan, would you mind trying it on your mountain phone shot to see how it does?

[jsachs]

I ran into similar problems trying to modify the inverse high pass image.

Maybe it would be more useful to make a new tool that lets you automatically de-halo by painting on the image with a brush, so the effects are localized.