Halos

[reheat module]

I really enjoy looking through the landscape forum and marvel at the skill of the people on there.
Sometimes, comments include the use of "Halos", often noticeable along the horizon.
I'm seeking some clarification into what a halo is, what causes it, does it always extend along the horizon, is it specific to a horizon, is it prominent in HDR or RAW/jpeg conversion, how it can be minimised or even eliminated.
Are there any settings in Photoshop elements that can minimise it?
Lots of points there, but I'm keen to learn about any improvement in my photography.

 

[Nawty]

It happens between areas of contrast and happens because of overuse of clarity or over excessive tone mapping (HDR). Refrain from this and all will be fine.

It can also happen if you post a large(stitched) panorama on the forum as the forum software can't seem to cope.

 

[Kodiak Qc]

seeking some clarification into what a halo is, what causes it?

•

Paul, since I am a guilty one often complaining about those, I will try
to answer you question.

A halo may be positive (brighter) or negative (darker) than the areas it
is in-between of.

I will not talk here of halos consequent to
— compression, as I never experienced them nor
— sharpening, as I never use sharpening

The only left source of haloing I am aware of (every week my students
supply plenty of examples) are PP related.

Say one wants to darken the sky, everything is fine until the brush
(even a soft one) reaches the horizon line

— if you go too close, you may create a darker horizon or con-
tact line (like on the head of the ape and the butterfly in the pic-
ture on the home page of TP
— if you stay away, you will get a lighter line above the horizon
— if you enlarge say at 400% and use a much smaller brush and
go meticulously say around trees, it will take an eternity and the
results may not be pleasing either
— using a gradient layer may be a solution (as a ND filter is) only
if the horizon is quite flat like on the see. Otherwise ~​

One way to go around halos is using, in a pixel editor, a healing brush in
darken more in case of a positive halos or lighten mode for negative ones.

The method I use and teach is called "tonal separation". It offers the better
results in the most difficult cases using colour editors.

 

[juggler]

It happens between areas of contrast and happens because of overuse of clarity or over excessive tone mapping (HDR). Refrain from this and all will be fine.

It can also happen if you post a large(stitched) panorama on the forum as the forum software can't seem to cope.

Lots of the tools in Color Efex Pro and Silver Efex Pro can cause it too.

Here's a good example and one way of fixing it - but it's best not to have to fix it in the first place. If you do want to boost the local contrast or sharpen then apply it selectively rather than to the whole image.

 

[Nod]

Fairly often a problem made worse by letting Flickr resize and resharpen shots. When I use Flickr to post shots here, I upload them to there at the size I want to post here after sharpening to suit (the final step after cropping etc..)

 

[ancient_mariner]

Some software is especially prone to produce halos: the Nik Efex software suite (now free from google) does it when the structure control is sometimes used. It can also happen in Lightroom, where excessive use is made of highlights & shadows, the black & white point controls to extend tonal range. It may bee seen as a gentle lightening/darkening around where light & dark areas meet, or sometimes appears as a much narrower line when an image is over-sharpened. Under some circumstances it even seems to appear in the raw file, though this is unusual.