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- Adobe made great improvements to the old recovery slider and in most cases I find the highlights/shadows sliders produce pleasing results. I would suggest turning on the clipping warnings if you need a visual guide to the normal effect. Click the triangle icon (top-left or right on histogram) when using either slider. Clipping is shown in the image with a red or blue warning.
- The halo is often seen in hdr tone mapping, as the tonal range is compressed. Some people like the effect for a grungy look. The masking aims to reduce this. When pushed to extremes, halos will be apparent on close inspection but generally it is well disguised, subject to sensor exposure, even when sliders are pushed fully to the right/left.
Thank you for your time and valuable information.
Further, do you know how the mask come about and how it works, or the principle and the algorithm behind these two sliders(Highlights & Shadows)?
As I understand it, in that explanation "normal" means to say that a particular amount of lightening or darkening is applied to a given pixel, solely based on its starting tonal value.
And "halo mask" means to say that LR further considers whether a pixel of that same starting value, happens to be sitting within a generally light or a generally dark part of the photo. So different things will then happen either way.
IOW this has to do with "local contrast": when a consideration of what something is next to, comes into how it gets shown.