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05/02/2005 09:57:53 PM · #1
This has been bugging me for some time. But now I'm afraid that I won't get a print approved because of it. I've seen it in others challenge entries so I know it's not just me with these issues.

In my last Free Study entry:
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only one commentor mentioned the halo around the left side of the building which really surprised me as detail oriented as many of you are in your comments. At this resolution, it's really not all that noticible, but at full size it looks like this:
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and like this on the right side:
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but on the dome itself it's hardly noticeable at all...
' . substr('//images.dpchallenge.com/images_portfolio/9906/thumb/173377.jpg', strrpos('//images.dpchallenge.com/images_portfolio/9906/thumb/173377.jpg', '/') + 1) . '

To achieve the affect I was looking for, I first selected the building and made a mask to bring up the levels of just the building. I used the same mask to desat the building seperate from the sky. I then inversed the selection and used that as the mask to desat the sky. If I feather the selections, it exagerates the effect. I didn't save one like that but believe me it's worse... First question, what causes the halo effect. Second question, how do you avoid it?

HELP!!!
05/02/2005 10:06:13 PM · #2
Does the halo appear during editing, or is it apparent on the original? I'll take a guess it appears, or at least is greatly exaggerated, after the levels boost on the building...
05/02/2005 10:09:14 PM · #3
From a photographer's tutorial manual on istockphoto.com:

Purple fringing: Commonly a problem of digital cameras when shooting in low light settings against high contrast borders, causing a purple, (or other hue), glow around edges. The issue can also be affected by lens model & focus quality. Possible Solution: Adjust aperture settings to a higher level, (f4 and above) to balance light.

Even if it's not particularly noticeable on the original, any contrast, color, levels, etc. corrections can bring the glow out in a photo. Assuming the original photo is full color, you might possibly adjust the contrast so that it's darker rather than lighter, then convert to sepia or b&w.

Hope that helps a little.

~Savannah

Message edited by author 2005-05-02 22:09:38.
05/02/2005 10:10:13 PM · #4
If it shows on the original, which is very possible, it's too much in-camera sharpening. More likely it's an artifact of the levels boost. You can help avoid it by shrinking the selection once you've made it, by 1 or 2 pixels. You can also fix it in the edited image by reloading the selection, turning it into a 3 pixel "border" selection, and then using history brush to revert that burder part or all of the way back to the pre-levels condition.

Robt.
05/02/2005 10:13:25 PM · #5
If it shows up as chromatic aberration (as savannah suggests) in the original, then fix it on a clone of the original before making any other changes. Save-as a new file, make new layer from background, slam the levels very contrasty on that and make a selection. Discard the contrasty duplicate layer, load the selection, make it a border as previous post, and use hue/saturation to adjust the chroma to blend.

Robt.
05/02/2005 10:14:31 PM · #6
Here are the originals:
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and
' . substr('//images.dpchallenge.com/images_portfolio/9906/thumb/173386.jpg', strrpos('//images.dpchallenge.com/images_portfolio/9906/thumb/173386.jpg', '/') + 1) . '
I guess there may be a little on the left side, but I don't see any in the reflection from the skylight on the right...

Edited to add: Sharpness contrast and saturation are all set to normal in camera...

Message edited by author 2005-05-02 22:16:32.
05/02/2005 10:15:13 PM · #7
You might be able to retract the selection and then feather it 1-2 pixels less then the retraction.
05/02/2005 10:16:42 PM · #8
There's another fix that I've used in cases where it's easier to do so than to back up and reedit...
Set the clone tool to opacity 100%, mode "darken", and about 3-4x the width of the halo. Set the clone source about one brush-width into the sky area, move the tool edge near the building edge, and clone in strokes along the building edge. Only the halo will be affected, since the building is already darker than the sky (or halo). The color that the halo is replaced with will match the sky.
05/02/2005 10:17:51 PM · #9
Yup, looks like oversharpening in camera. Your levels work has exaggerated it, but I can see it alla round the contrasty areas.

If you really want to, you can fix it by hand by loading a clean selection and then using the clone tool at high magnication and small diameter to sawp down the adjacent sky. I shoot with my in-camera sharpening set at "none"; I want to control this myself in photoshop.

Robt.

I see kirbic likes the clone thingy too. I prefer to work it witht he selection in place, but otherwise we're on the same wavelength. I also experiment with different modes to get it right.

Message edited by author 2005-05-02 22:19:02.
05/02/2005 10:21:10 PM · #10
Is it the same effect on the right side (skylight)?
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05/02/2005 10:22:21 PM · #11
Yes. I can distinctly see it.

R.
05/02/2005 10:23:40 PM · #12
Originally posted by bear_music:

Yes. I can distinctly see it.

R.


I can't see it... But then again I have some color issues that may be coming into play in that section...
05/02/2005 10:39:41 PM · #13
Two more questions:
I shot this in raw mode. If I go back to the original raw file and set the sharpening to the left, resave and re-edit, will this help?

If it's a in camera sharpening issue causing the problem where should I set the sharpening for this kind of shot? I have 5 options on my camera:
-2 -1 0 +1 +2

I just got called into work so I'll have to check back later for answers...
05/02/2005 10:42:12 PM · #14
I think you might be able to fix it in RAW but I'm not sure. I'd think the elast sharpening possible is what youw ant in any case, on all your shots. It's certainly what i want. But I don't have a negative option, just a "none" option, so I can't speak to that.

Enjoy work.

R.
05/02/2005 10:52:38 PM · #15
TC: I might disagree with the in-camera sharpening thing... it looks to me like it's a masking issue. There are so many different ways to mask in Photoshop, and each of them have a use. It looks to me as if you may have painted the mask in the "quick mask" mode using a too-large diameter or too-soft brush.
05/02/2005 10:54:07 PM · #16
Alan, that's what I thought but we can see the beginnings of it in the unedited original. There's slight haloing in the dark/light junctions.

R.
05/02/2005 11:00:10 PM · #17
I don't think its oversharpenning or purple halos...

I agree with alanbataar, it seems to be a masking problem. This effect is very noticiable in my photography when I use two masks, one inverted from the other which is the situation you described yourself....

there is a small amount of feathering at the edges of a mask. On its own, this doesn't show as much, but create a second, inversed mask, and now the areas that overlap are letting a good amount of the part you don't want to get through... can't explain properly, but its the overlap of the two feathered edges that is causing this...

One solution may be not to invert your second mask, but to redraw it by hand.... OR

Go in with a a fine brush around the edges and try to paint in more around the edge on one or both of the masks (ie, less feathering or aliasing).

One of the above methods usually resolves the problem for me...
05/02/2005 11:06:30 PM · #18
Originally posted by sylandrix:

I don't think its oversharpenning or purple halos...

I agree with alanbataar, it seems to be a masking problem. This effect is very noticiable in my photography when I use two masks, one inverted from the other which is the situation you described yourself....

there is a small amount of feathering at the edges of a mask. On its own, this doesn't show as much, but create a second, inversed mask, and now the areas that overlap are letting a good amount of the part you don't want to get through... can't explain properly, but its the overlap of the two feathered edges that is causing this...

One solution may be not to invert your second mask, but to redraw it by hand.... OR

Go in with a a fine brush around the edges and try to paint in more around the edge on one or both of the masks (ie, less feathering or aliasing).

One of the above methods usually resolves the problem for me...


You guys may be right, but the originalimage shows a fairly distinct haloing in those areas, and it may be exaggerated by the levels work;

' . substr('//images.dpchallenge.com/images_portfolio/9906/thumb/173387.jpg', strrpos('//images.dpchallenge.com/images_portfolio/9906/thumb/173387.jpg', '/') + 1) . '

If it IS the masking, then these suggestions are in line with what Kirbic and i were getting at also, there's several ways to work around that problem.

R.

You can, incidentally, select the sky, no feathering, save it, invert the selection, save that, and then reload the sky and feather it slightly to basically elimninate this effect, now that I think of it.

Message edited by author 2005-05-02 23:08:48.
05/02/2005 11:09:01 PM · #19
Originally posted by sylandrix:

...there is a small amount of feathering at the edges of a mask. On its own, this doesn't show as much, but create a second, inversed mask, and now the areas that overlap are letting a good amount of the part you don't want to get through... can't explain properly, but its the overlap of the two feathered edges that is causing this...


IMO you've nailed it on the head. There's not enough halo in the original to really stick out like that given the amount of sharpening that's evident elsewhere.
In order to avoid this, I usually shrink the mask just inside the darker area before reversing it. Any halo effect is unnoticeable there.
05/02/2005 11:20:46 PM · #20
Originally posted by kirbic:

There's another fix that I've used in cases where it's easier to do so than to back up and reedit...
Set the clone tool to opacity 100%, mode "darken", and about 3-4x the width of the halo. Set the clone source about one brush-width into the sky area, move the tool edge near the building edge, and clone in strokes along the building edge. Only the halo will be affected, since the building is already darker than the sky (or halo). The color that the halo is replaced with will match the sky.


Once the halo is there this suggestion by Kirbic is the easiest way to go with one little change... Before cloning select just the sky which you may already have a selection for and you don't have to be so careful removing the halo because the building will be protected.

Just be sure the selection contains the halo, but not the building. I often use this technique for touchups on haloing and it is fast and easy.
05/02/2005 11:24:16 PM · #21
I appreciate the thoughts on this subject as I have encountered the same effect. Now I will examine my selection masks more carefully for this inherent lack of precision. Doesn't show up much in large images but can be a disaster with small and cropped images. Thanks!
05/03/2005 01:57:00 AM · #22
As I said in my oringinal post, if I feather the two opposite masks then the halo is much more pronounced... Which makes me wonder what exactly does feathering do?
05/03/2005 02:07:51 AM · #23
Originally posted by TooCool:

As I said in my oringinal post, if I feather the two opposite masks then the halo is much more pronounced... Which makes me wonder what exactly does feathering do?


Feathering gives you semi transparent pixels on the edges of your selection to smoothe the transition to whatever it is next to. Im not completely sure about it but i think on some settings feathering can give pixels that fade to white rather than to tranparent. Again not exactly sure what said settings are.

I havent read the whole thread yet but from your sample images I would say that the halo is a result of over-sharpening which adds more and more contrast to the edges until there is a pure white line against a black line.
05/03/2005 05:09:02 AM · #24
Feathering reduced the amount of affect applied progressively over that border of the selection. So, if you use the invert selection process, you're applying all your processing at roughly 50% power along some of the join: if you're working on sky and a foreground, you're probably lightening one and darkening the other (basically), and therefore pretty much not affecting that feathered area.

The clone brush is the only way I know of sorting that stuff out.

e
05/03/2005 08:43:41 PM · #25
The best way to understand how the "Feathering" command works is to make a rectangular selection, then switch into quick mask mode: you will see the mask represented by editable paint pixels.

Next, switch out of quick mask back into selection mode, then put a fairly prominent feather -- something like 30 pixels -- on your rectangular selection. Now switch back into quick mask mode: you will see a blurry rectangle. Notice that the blur expands beyond the original selected area, but the hard edge of the selected area is also eroded by the blur.

This is that "50%" thing that e301 was referring to. Technically, the feathered edge (the blur) ramps down from 100% (i.e. solid paint in quick mask) to 0% (i.e. white paint in quick mask) over the distance of the feather.

If you have a 100 px feather, each pixel in the blur drops in value 1%. If you have a 25 px feather, each pixel in the blur drops in value 4%.
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