Halo removing in digital processing

Hi folks,

I´m about to ask, in your workflow/processing, what´s the method you´re using for halos removal in photoshop, can you share some technique in PS for this matter?
I guess this is an important thing, as for my method, I just try to balance all "manually" controlling light, when I got this kind of situation.
Thanks for your time

If I understand your question, then the secret to removing halos is not to create them in the first place.

Most "halos" are a side-effect of oversharpening an image in Photoshop. There are other ways you can create them; by over-feathering a selection, for example. But the most common reasons involve bad sharpening technique.

There are several articles in the NPN library on sharpening; mine is pretty basic but might give you a starting point.

I agree with Jim. Halos are a product of post processing, most likely over-sharpening. The way to deal with halos is not to create them in the first place. I've found PhotoShop's smart sharpening to be pretty good in avoiding halos. Its sliders are intuitive. I haven't used unsharp mask since I discovered smart sharpen. But when I did use unsharp mask, I applied it in small increments, usually two to six times as needed. If a halo appeared, I'd back off until it looked okay. I don't remember my settings, but they were fairly light.

Just a little more info on what Buck said....unsharp mask (USM) type sharpening works by increasse the transition at edges between colors or from light to dark. Using it too much can actually increase the contrast around edges so much that the pixels near the edge go lighter or darker than the pixels a little further from the edge - resulting in halos.

Smart sharpen mostly avoids this because it uses "pinning" (not sure what the real term is, but that's what I've heard). This means it looks further away from the edge to determine max and min values for the pixels near the edge, so that they don't go beyond values that provide proper transitions across edges. That's why Smart Sharpen (which is still a form of USM) avoids halos so well.

Good explanations here. I switched back to using "Unsharp" a couple weeks ago - seemed to me to be a bit sharper end-product - but several comments mentioneed hal in the new submissions. .
I'll go back to smart Sharpen at once.
Sandy r

Try using unsharp mask immediately followed by fade - this will do a nice job on halos. Or sharpen using the high pass filter. The sharpening method you select and the strength required will depend on the image.

Thanks Helio for asking this question. It is something I have been wondering about. I have a shot of a blackbird with a very distinct halo, went back to the original sharpened with Smart Sharp instead of unsharpe filter and there was no halo! Thanks also to everyone for responding, this is an example IMO why NPN is such a good group to be a member of.

Thanks for the input
So, it´s all a matter of sharpening...? My method for web presenting is using Sharpen Filter 2 ou 3 times on the doubled size of the final image, example: my image will have 720pix. for NPN posting - I resize it to 1440 and apply sharpen twice most times (or even three times depending on the image). And then, when really over-sharpened, resize to final 720pix.

I thought this halos matter could be also due to localized contrast processing.

"I thought this halos matter could be also due to localized contrast processing. "

This is quite true, and is what Jim is referring to about over-feathering a selection and then adjusting brigthenss/contrast or color of the selected area. Halos will also occur if you make a selection, say, of a sky, and then invert the selection to, say, encompass the foreground. The resulting halos can be very difficult and time consuming to eliminate.

I've tried various ways to get rid of such halos; the clone tool, heailing brush, or spot healing tool. It is no fun. If anyone has a more workable method, I wuld love to hear it!

--P

I resize it to 1440 and apply sharpen twice most times (or even three times depending on the image). And then, when really over-sharpened, resize to final 720pix.

This trick works best if you multiply your target size by 1.6667 and not 2.0. I'm a little fuzzy (sorry) on why, but it has to do with the algorithm Photoshop uses for resizing photos. Marc Adamus explained it to me back when I wrote the article linked in my previous post, but the explanation didn't stick. Fading the luminosity after the Smart Sharpen step definitely helps as well (Edit -> Fade Smart Sharpen -> Luminosity).

Preston has done a much better job of explaining what I called over-feathering. If I buy CS5, it will be because it reportedly has improved those kind of edge effects...

duplicate layer
invert
desaturate
switch blend mode to soft light
high pass filter on a radius size that is similar to halo size (get this right or it won't work right)
adjust opacity so halo is diminished
merge all visible layers shift-command-option-e
switch blend mode to darken
delete highpass layer (background copy), no longer needed. should be the layer right below
mask off the layer you put on darken, brush into the areas that need help.
Use the layer blend if commands if it contaminates wanted highlight and shadow areas.

Thanks for the great explanations.
@Jim, nice trick. I´ll try it out, and post some feedback on how it worked for me.
@Matt, great! Must see this on action ;)
@Preston, you bet! What a headache, I also tried all that stuff. Too much work, and not so good results...

HC, vai por mim, dica destas nao aparecem todos os dias. lol. Se fores ao meu blog e seguires as instruçoes vais ver que halos sao coisas do passado. E simples e muito eficaz. Novas imagens para breve

Hélio, my recommendation is to find out where the halos are coming from first. (There is no need to fight sharpening if that's not the problem!) Check each step in your processing closely, and note when the halos develop; this will let you attack them more effectively. While sharpening can be a problem, I suspect shadow/highlight adjustments, inappropriate masks, etc., are a much more common source. There are many options to play with when reducing halos, and what works best will depend on each individual situation. The three most common techniques I use are to blur my masks aggressively, painting masks to remove the offending adjustment from where it shows (almost always on the lighter side of where dark meets light), and to fade the blurs that I apply to masks.