OPOD - New Zealand Halos - To enhance or not to enhance?

Now we are in the realm of processing purely to reveal halos and with little regard for aesthetics.

Levels were less kindly adjusted. The right (bright levels) slider was moved leftwards to brighten the area of interest above the 22 degree halo. The area around the sun becomes unpleasantly over-saturated and loses all information. The middle slider (gamma) was then adjusted to increase the halo contrast. There is little to be gained by going further with levels.

Next, the image was unsharp masked [filter -> sharpen -> unsharp mask]. Again, do this on a duplicate layer. Leave the middle 'radius' slider at about 1 pixel. Move the top slider (amount) all the way to the right. Then carefully increase 'radius' watching what happens. Faint details become more evident - and so do cloud streaks and artifacts! Strike a balance between halo visibility and unwanted details/artifacts. Then decrease 'amount' until halos are still visible but the scene is less extreme. Less is more.

There is a a clear extended upper tangent arc fragment and above it a suncave Parry arc. But look between the 22 degree halo and the UTA - Is that a trace of an upper Lowitz arc?

This bit is disliked by some halo experts because it can introduce misleading artifacts.

The unsharp masked image has been embossed [filter -> stylize -> emboss]. Start with the 'amount' slider in mid position and the height at ~20%. Then swivel the 'angle' to attempt to show up faint arcs. The ones at left had the angle pointer at 2pm to highlight any Lowitz arc.

The emboss is revealing. The upper Lowitz arc is seen leaving the 22 degree halo at 2pm and curving outwards to join the Parry arc. Even more, there is a hint of the upper Lowitz arc curving in from the sundog to become tangent with the 22 degree halo. With the eye of faith one might even discern a faint trace of a middle Lowitz arc beneath the sundog.

All this is tenuous unless confirmed by other photographs. The lower image, similarly processed, hints also at an upper Lowitz arc but not as clearly.

New Zealand Halos ~ 21st April
Stefan Krivan saw this ice halo display at Manawatu, New Zealand. It contained some everyday halos, a rare one and a very rare one but they had to be searched for!
©Stefan Krivan, shown with permission.

To Enhance or not to Enhance?
The topmost image is straight from the camera.
The streaky cirrus shows tantalizing halo fragments, part of the everyday 22° halo and a right-hand sundog. The parhelic circle links the sun to its dog. Something is above the 22 degree halo and it is always worth searching this area for an upper tangent arc or the more rare Parry arc.

Would image ‘enhancement’ tell more?

Image manipulation can be to render the image more akin to what was seen by eye or to modify its aesthetics. A third reason is to try to reveal fainter halos.

Here is a gentle manipulation for presentation purposes. It still preserves the truth but you would have to have been there to say whether it resembles the appearance and mood of the actual scene.

Levels were changed in PhotoShop. First, create a duplicate layer - never, ever, destroy or save over the original image! The right (bright levels) slider was eased leftwards watching the histogram display and taking care not to clip or over saturate important highlights. Then the middle (gamma) slider was moved slightly rightwards to change contrast.

Other changes are a matter of personal taste. But overdone they can give an unreal and even unpleasant looking image. Less is more.

There appear to be two halos above the 22 degree circle, an upper tangent arc and Parry arc.