Haze isn’t always a bad thing. In fact, there are many times I quite like it in a shot. But haze obscures detail and washes out colors. So it's often considered a photographer's enemy.
The latest version of Lightroom now has a dedicated tool to cut through haze. It's available in Lightroom CC 2015, which is the latest version available through a Creative Cloud subscription. If you have the standalone version, Lightroom 6.1, the slider is there but greyed out. It is, however, possible to enable the dehaze functionality by creating a develop preset. Here's how.
Bringing detail out of haze is something that can be tackled to some extent with a combination of the clarity slider and black levels, as well as other methods using levels and curves, but Lightroom's dehaze slider works a bit differently and is designed as a one-step package of what would otherwise be multiple different steps.
It works basically like a local contrast tool with added saturation. It's similar in some ways to the clarity slider, but it does work much better for recovering detail from hazy or foggy images.
How to Use Lightroom's Dehaze Filter
The slider is at the bottom of the effects panel in the Lightroom's develop module.
The slider goes from -100 to +100, with a default setting of 0. Sliding to the left, towards -100, will simulate adding haze. Sliding it to the other direction, to the right towards +100, works to cut through the haze and restore detail and color.
Examples of Lightroom's Dehaze Filter
At certain times of the year, Istanbul can get covered with a thick, soupy haze that lasts all day. This shot of a container ship navigating the Bosphorus Straight in the early morning shows it clearly, with the lighthouse at left giving some indication of how thick the haze is.
Using the dehaze slider at +100 certainly recovers detail and largely eliminates the haze, but it also introduces some rather unsettling saturation and contrast.
I prefer a much more subtle effect of +40, which you can see in this set of slides. The haze is still prominent, but it brings out slightly the buildings and structures on the far bank in Kadıköy.
Like Istanbul, Hanoi can be covered in thick haze and smog. In these shots from West Lake, I like the effect of the thick haze almost obscuring the far bank. The combination with the glassy waters of the lake create a very high key effect naturally.
I've included here two photos with this along with the versions using the dehaze filter at +100. In both instances I prefer the original and wouldn't use the dehaze slider at all, but by cranking them up to maximum it provides a good illustration of what the dehaze filter is doing. Because the filter is mostly an implementation of local contrast, you can end up with a halo effect. In many instances, it can be quite subtle, but in these it isn't. If you look around the shadowed areas of the boats in the first photo and around the fisherman in the second you can see very pronounced halo areas. There are also some rather ugly splodges on a smaller scale in areas of the foreground water in bottom left where the tones aren't entirely uniform.
In the second example, with the fisherman, you can see a very obvious halo around the man and his reflection.
In this example of two zebras wandering across the dry floor of Lake Manyara in Tanzania, I've again deliberately exaggerated the effect to illustrate a different point: that the dehaze filter can also introduce some pretty dramatic color shifts. This is something to be particularly aware of when people are in the photo because skin tones can get pretty odd.
The result in this case is actually interesting in kind of cross-processed way. The resulting colors are pretty unnatural, but now that we're all more conditioned to the look of Instagram filters, it's not as immediately objectionable as it once might have been.
That said, I again prefer a much more subtle application, and in the second variation I've used the dehaze filter at +22 (although I'd again stick with the original for this shot).
Here's an example of what I mean by the dehaze filter making optical flaws much worse. In this shot of mountain ridges on a hazy early morning in Temecula, the lens's vignetting becomes overbearing when +100 dehaze is applied. And while chromatic aberration isn't visible in the original, some has become clearly visible along the top ridge line with the dehaze turned up. This one is also a good example of how the filter can darken the overall image. The end result is a good cautionary tale about over using the dehaze filter.
But the second variation is also a good example of how the dehaze filter can be put to good use if used with care. With the same original image I've used dehaze at +30 as well as lightened up the exposure a bit and fixed the chromatic aberration. I prefer this version over the original because it is less washed out, adds more color, but still preserves the sense of hazy.
Here's another shot from Temecula, with hot air balloons going for an early-morning flight, where the dehaze filter can be very effective. In this case, using +100 isn't horrible, although it does exaggerate the lens vignetting in the top left and top right of the image. The rest of the image, though, actually benefits quite a lot from the dehaze filter at +100. For this shot, I'd do some more fixing for a final version--especially to fix the top corners--but the dehaze filter actually gives a great start on its own.
Here's another example where the dehaze filter helps. In this shot of the Citadel's massive flag in Hue, Vietnam, the late-afternoon haze makes the mountains in the distance almost invisible.
Using dehaze at +100 isn't much good, but in the second variation I've used it at +48 for a much more subtle effect that keeps the overall hazy look but shows the mountains in the distance better and adds a little definition in the foreground.
Not Just for Haze
Haze is basically just light being scattered. But there are other ways that that happens too, creating glare. And the dehaze slider can be used in situations that aren't strictly haze.
Here's an example not with haze or smog but with rain. It was raining heavily when I took this shot of Galata Tower from across the other side of the Golden Horn at Topkapi Palace. And while I like the high key original, the dehaze +100 version has character too. The detail is not as sharp as it would be without any rain, and it now has a kind of misty-eyed look, but it's remarkable how much detail has been recovered. This one still requires a bit more work, especially in fixing the vignetting in the sky on both sides, but the dehaze filter has done a really nice job here.
The dehaze filter isn't exactly like true polarizing, but there are some similarities. Here's an example with a shot of a chinstrap penguin "flying." In this case there's no haze in sight--Antarctica has exceptionally dry and clear air, and the shot is close--but the dehaze filter can still be effective in combating some of the glare coming off the water. There's nothing wrong, per se, with the original, but I like how the dehaze filter darkens the background to make the penguin stand out a bit along with the splashed water drops. There are other ways to get a similar effect, but the dehaze filter does a nice job of it.
When Not to Use the Dehaze Filter
It can definitely be overdone, especially if you ramp it up too much. It tends to darken the overall exposure quite a bit, often in a kind of muddy way, so when I use it I often find myself nudging up the exposure slider to compensate.
It can also accentuate optical flaws, often in a very ugly way. It makes lens vignetting more pronounced by increasing the contrast. It makes chromatic aberration more obvious by ramping up the saturation. And it can bring dust spots from dirt on the sensor out of hiding (which can also be a positive—see below).
But used with care, there are times it can improve an image in ways that would take a lot more processing steps otherwise.
One of the lovely things about nondestructive editing like Lightroom does is that you can't easily mess up your originals. So you can safely experiment away and zero out the dehaze slider, use the undo feature, or even revert to your original if you need to. But there are at least two places that the dehaze filter can do more harm than good.
Flesh tones. of them is with flesh tones. The extra contrast and the color shift can do some pretty strange things to skin tones, so it's definitely something to use with caution in people shots.
Timelapse Images. other is when processing images for timelapse. Because the dehaze filter involves calculations made on an image by image basis, even the slightest difference between images can result in different effects. There's also subtle halo effects which can be essentially invisible in an individual image. But these variations are magnified when compiling timelapse video. If you're using LRTimelapse 4, there's a new feature built into that software to factor in the dehaze filter, but even then it's worth experimenting before you run that massive export job on a deadline.