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I have a Pentax K-S2 and whenever I use the A-HDR (advanced HDR) mode, the pictures come out with this strange halo around the edges of objects. Is this normal?

sample 1.

sample 2

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2 Answers 2

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Is it normal? Yes… and no.

It depends on the ability/quality of the HDR routine and its ability to recognise & correctly handle edges where the overall light level changes rapidly.

A low-ability algorithm will leave this halo to a greater or lesser extent - it's pretty much the trademark of poor HDR. This is an area where modern phones are beating regular cameras hands-down. They can form very well-defined masks to separate these contrast edges & the results are getting close to invisible.

For a DSLR etc, the best way to do this is actually in post, in Photoshop or a dedicated HDR app such as Aurora HDR [which I just learned is discontinued - the functionality has now been folded into Luminar Neo]

Some examples [chosen not by its inspiring subject matter but just because I rarely take photos that include sky;)… The processing was done on a small jpg not the original file, to make the results worse.

Click for full size
Original
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Photoshop, with the borders set intentionally high and overall settings to emphasise the bad edges. Clear halo. [Photoshop can do a lot better than this, but is not as good as dedicated software]
enter image description here

Aurora, at default settings, very slight halo
enter image description here

Aurora with intentionally aggressive settings, reasonably acceptable halo for the settings
enter image description here

AI-based algorithms will tend to improve on these results as they are developed further. My versions of Photoshop & Aurora are pre-AI. Newer software is likely to be better still.

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The Halo effect you are seeing is the result of Unsharp masking (USM) imo. It seems likely your camera's A-HDR mode runs the photo through a faily intense USM. Many devices try to emulate HDR images using post-processing filters like this, however as you can see the results often have noticable drawbacks.

On a side note: If you want the highest dynamic range you're better off getting your cameras exposure and white-balance well adjusted for the scene and editing the RAW image manually.

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  • No, these artifacts have nothing to do with USM.
    – jarnbjo
    Aug 8 at 19:01
  • @jarnbjo many HDR are generated using various Tone-Mapping algos which are very closely related to Unsharp Masking, in fact some do just run a large-radius unsharp mask.
    – Jordy Toke
    Aug 9 at 0:12

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