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12-10-2010, 11:48 AM   #1
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Cutting through haze and other such environmental conditions

OK, I browsed the via the search engine here about a couple of things regarding "haze" and humidity related conditions while taking photos.
I didn't find what I am looking for.

I do a fair amount of landscape/scenery photography during the winter months (the birds are gone until next spring ... ) and I more often than not have to deal with high humidity levels, haze over the large St Lawrence River, trying to get some decent shots of the distant snowy mountains, etc ...

As you may realize, most of those shots will turn up rather "hazy" with a lack of details - which I expect because of the adverse conditions. But I would like to be able to get better, clearer shots if possible.

I am aware that "haze" filters can be used, and I did try that, but it just doesn't cut through enough.
Polarizing filters may be an answer and I haven't tried that in the winter.

Is there a way to deal with this hazy situation with some specifically designed filter or perhaps a way to PP the image in Photoshop and try to make the image somewhat sharper?

Any suggestion would be appreciated.

JP


Last edited by jpzk; 12-13-2010 at 03:02 PM. Reason: spelling
12-10-2010, 03:49 PM   #2
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I add more. With longer focal lengths and a cheap' fog' filter. (If I ever think to carry the darn filters, that. ) Then it almost looks like it looks.

Other than that, how does it go, blue scatters more? I may be backwards, there, but the built-in Jpeg effects in the digital Pentaxes can cut out various colors or render whole monochrome images from one of the RGB channels. I dunno if that'd suit, but it might give a slight advantage. (Probably better results messing with Photoshop in the same way, but easy to try) I haven't tried: I usually want the opposite.
12-10-2010, 05:19 PM   #3
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Fog is tricky, and I don't claim to have mastered it, but I have found that long exposures cut through it better. A polorizing filter not only cuts glare but allows for even slower exposures with small apatures.
When the fog is close, and I want to emphasis it, I use flash fill on a foreground object. When the scene is more distant, I've used my truck headlights to illuminate it. I stretch Suran Wrap over them as a diffuser.
12-10-2010, 11:14 PM   #4
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QuoteOriginally posted by jpzk Quote

Is there a way to dela with this hazy situation with some specifically designed filter or perhaps a way to PP the image in Photoshop and try to make the image somewhat sharper?

Any suggestion would be appreciated.

JP
I would usually deal with it using processing. The hazy areas lack contrast, so adding local contrast to the areas that need it is the solution for a cleaner look.

There are different ways to add contrast but one that I have seen and used is using an unsharp mask. Set the amount=10-30%, radius=30-80 pixels, threashold=0. Mess around with the values a little bit to fine tune if you need to. In the middle of those ranges is a good place usually.

Use a mask to apply the effect where needed if the whole photo isn't hazy. Use google and you can find some other suggestions or suggestions on using unsharp mask to remove haze.

12-11-2010, 12:22 AM   #5
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Not sure about digital, but on film haze is harder to combat shooting in colour and easier with b&w. Using a #25 red filter with b&w film cuts UV light and haze quite a lot. You also get some nice dark skies.

Phil.
12-11-2010, 04:29 AM   #6
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One major effect of haze is to add scattered light to the image. This scattered light decreases contrast and renders blacks as grays.

It is easy to subtract a constant brightness from an image; after doing so, contrast will still be low, but can be easily restored. Here's an example using ImageJ (freeware):

"Curves" operations can do the same thing in many photo editors.

Here's another example showing extensive haze, the average haze brightness is about 40% of the overall brightness:


Better correction can be made if attention is paid to each color channel. Here's the above example separating haze into red, green, and blue channels:

Notice how much more haze is in the blue channel. Using a red filter on the camera would decrease the blue haze, but would also reduce any blue detail.

Here's the re-assembled, de-hazed RGB image:


Notice that there is still haze in the background of the image because haze builds with distance. This could be corrected by working on areas of the photo.

Another effect of haze is to de-sharpen an image (a point is rendered as a fuzzy disk); this can also be corrected with software....I use Focus Magic to recover focus (no sharpening was applied in the examples above.)

Dave

Last edited by newarts; 12-11-2010 at 05:09 AM.
12-11-2010, 04:58 AM - 1 Like   #7
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Here's another method of Haze reduction using local contrast enhancement (it automatically applies what I described earlier to local regions of a photo):


One region had Paint Shop Pro's "clarify" function applied with default parameters. It helped quite a bit I think.

The same kind of local contrast enhancement exists in other photo editors, but I don't know what proprietary names are used to identify them. (If anybody out there knows, please tell us!)

Dave

PS pay no attention to the overall image quality of these examples, they are low resolution images snagged with a screen-grabber.
12-13-2010, 03:07 PM   #8
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QuoteOriginally posted by Ratmagiclady Quote
I add more. With longer focal lengths and a cheap' fog' filter. (If I ever think to carry the darn filters, that. ) Then it almost looks like it looks.

Other than that, how does it go, blue scatters more? I may be backwards, there, but the built-in Jpeg effects in the digital Pentaxes can cut out various colors or render whole monochrome images from one of the RGB channels. I dunno if that'd suit, but it might give a slight advantage. (Probably better results messing with Photoshop in the same way, but easy to try) I haven't tried: I usually want the opposite.
Adding more, really?

I did try with one single such filter this past weekend and it didn't much at all. So, by adding more ... filters? Not sure if you meant it that way.

JP

12-13-2010, 03:10 PM   #9
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QuoteOriginally posted by Ron Kruger Quote
Fog is tricky, and I don't claim to have mastered it, but I have found that long exposures cut through it better. A polorizing filter not only cuts glare but allows for even slower exposures with small apatures.
When the fog is close, and I want to emphasis it, I use flash fill on a foreground object. When the scene is more distant, I've used my truck headlights to illuminate it. I stretch Suran Wrap over them as a diffuser.
Thanks Ron,

The fact is that we are not really dealing with fog here, but simple "haze" caused by high humidity over large bodies of water, especially.

But you have a good point and I will give it a go as you suggest: longer exposure time and a polarizing filter.

JP
12-13-2010, 03:13 PM   #10
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QuoteOriginally posted by lowspark86 Quote
I would usually deal with it using processing. The hazy areas lack contrast, so adding local contrast to the areas that need it is the solution for a cleaner look.

There are different ways to add contrast but one that I have seen and used is using an unsharp mask. Set the amount=10-30%, radius=30-80 pixels, threashold=0. Mess around with the values a little bit to fine tune if you need to. In the middle of those ranges is a good place usually.

Use a mask to apply the effect where needed if the whole photo isn't hazy. Use google and you can find some other suggestions or suggestions on using unsharp mask to remove haze.
Thanks!!

I never thought of this and that makes sense.

I'll dig out a hazy image (no problem, I have tons of them) and start doing some PP.

Cheers!

JP

Edit: I tried your suggestion and it does make a difference! and I also found that using ACR (opening the DNF file in ACR that is) and doing a bit of "Clarify" does also make a subtle difference.

Last edited by jpzk; 12-13-2010 at 04:43 PM.
12-13-2010, 04:47 PM   #11
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QuoteOriginally posted by newarts Quote
Here's another method of Haze reduction using local contrast enhancement (it automatically applies what I described earlier to local regions of a photo):


One region had Paint Shop Pro's "clarify" function applied with default parameters. It helped quite a bit I think.

The same kind of local contrast enhancement exists in other photo editors, but I don't know what proprietary names are used to identify them. (If anybody out there knows, please tell us!)

Dave

PS pay no attention to the overall image quality of these examples, they are low resolution images snagged with a screen-grabber.
That is quite a post, Dave! Thanks!

This freeware seems to be the easy way out, and it does indeed thake the haze away.
When you say "local contrast enhancement", do you mean that only a part of the image is PP'd (like with your amples in your first post) or does it still apply to the entire image?
I am not quite sure I understand the concept; sorry ... my own inadequacy at anything too technical.

JP

Edit:OK, I think I got this concept:
Such as you'd find when using the Unsharp Mask: the amount (low) of "unsharping", the Radius (high) and the Threshold (none) are rather the opposite to what one would like to achieve if "sharpening" was needed?
And this is probably what this freeware can do, right?

Last edited by jpzk; 12-13-2010 at 04:54 PM.
12-13-2010, 06:40 PM   #12
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QuoteOriginally posted by jpzk Quote
.....
When you say "local contrast enhancement", do you mean that only a part of the image is PP'd (like with your amples in your first post) or does it still apply to the entire image?....
For "local contrast enhancement" an approach similar to that I used with ImageJ is applied automatically to small regions of the photo such that no boundaries between regions are apparent. Imagine dividing the photo into hundreds of small regions then subtracting haze and increasing contrast for each region making sure the edges between regions don't show.

I think the logic is very similar to that used for "tone mapping" which is done when for HDR photography; ie contrast is brought out in shadows and highlights.

Dave
12-13-2010, 08:17 PM   #13
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QuoteOriginally posted by newarts Quote
For "local contrast enhancement" an approach similar to that I used with ImageJ is applied automatically to small regions of the photo such that no boundaries between regions are apparent. Imagine dividing the photo into hundreds of small regions then subtracting haze and increasing contrast for each region making sure the edges between regions don't show.

I think the logic is very similar to that used for "tone mapping" which is done when for HDR photography; ie contrast is brought out in shadows and highlights.

Dave
Got that, Dave.

Thanks for the clarification.

JP
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