Lightroom has a great set of tools for editing your images. However, if you are not careful while processing many of the adjustments can create halos in your images. These halos can occur in any image but are more likely to be an issue in pictures which have hard edges set against an area of smooth tones. For example, a mountain or a building set against a bright sky is an ideal situation for generating halos. Files which need to be pushed harder in post-processing are also more likely to show halos.
Figure 1. Halos are visible on this photograph of a church. They can be most easily seen along the right edge of the tower and along the roof line.
Figure 2. Halos are not limited to hard edge subjects and can be seen on this photograph of a pelican. See the area by the pelicans chest and feet.
The main culprits are the adjustments for
- highlights & shadows
- clarity & texture
I’ll go over each of these in turn and then discuss some techniques for avoiding halos. Even if you don’t use Lightroom, most programs for photo processing have similar controls so even if the exact same slider is not present, there’s probably something comparable in your editor of choice that can also cause halos.
Hightlight Recovery (and Shadows)
To make it easier to see how the highlight and shadow sliders generate halos, I’m going to be demonstrating on the following test image (which is designed to be similar to a typical landscape photo with a dark foreground and brighter sky):
Figure 3. Test image for highlight recovery, no Lightroom adjustments.
If we drop the highlights to -100 in Lightroom, it darkens the sky region as we would expect, but it also creates a halo on the sky-land boundary.
Figure 4. Test image with -100 highlights applied in Lightroom.
To make the halos a bit more obvious, I brightened the image with a simple curves adjustment by moving the white point (this does not cause halos by itself). There are two halos on either side of the sky-land boundary: a white fringe on the sky (bright) side and a black fringe on the land (dark) side.
Figure 5. Test image with -100 highlights and white point adjusted to brighten entire image.
The shadow slider can create halos in a similar fashion to highlights. However, because the shadows are darker they tend to be much less noticeable and are usually not a problem.
Clarity & Texture
The clarity and texture sliders are another source of halos. Let’s go back to our mountain example, except this time I made the test image with a darker sky a bit to make the halos more noticeable.
Figure 6. Test image for clarity, no Lightroom adjustments.
If we add positive clarity (+100) we see a white halo on the sky side of the sky-land boundary. If I use my cursor and the information panel, I can tell there is a corresponding dark halo on the land side but it is not noticeable because it’s hard for our eyes to tell slight differences in luminance in shadow regions.
Figure 7. Test image with +100 clarity applied in Lightroom.
Sometimes it can be desireable to add negative clarity to soften and smooth out the textures in an image. The image below shows the result of adding -100 clarity. We can see a dark halo with a wider radius around the sky-land border.
Figure 8. Test image with -100 clarity applied in Lightroom.
Texture can have a similar effect as clarity, although it is usually less pronounced. I have found dehaze to be fairly resistance to generating halos.
HSL Luminance Adjustments
I often use the HSL controls to adjust specific colors in my images. However, these controls, especially the luminance adjustment, can create halos in our images. For example, in the cityscape below, I turned the luminance slider for blue in the HSL panel to -100 and it shows clear halos around the opening between the buildings. Now an adjustment of -100 is a much stronger than I would apply in practice, but I choose it to help demonstrate the issue.
Figure 9. The HSL panel can create halos. Left: original image, right: -100 luminance applied to the blue channel.
Sharpening almost by definition is adding halos to our images. Normally this is a good thing as it makes the image appear, well, sharper. Edges appear more crisp and we can make out more details. So halos from sharpening is not a problem per se, they are however an issue when the halos are too large and obvious.
Figure 12. Our mountain example (fig. 6) with too much sharpening applied (amount = 150, radius = 3) resulting in strong halos around the sky-land border.
The main cause of sharpening halos is using too high an amount or too large a radius. In general, I recommend radius < 1 and small amounts of sharpening. Remember that it is always possible to add more sharpening later, but adding too much early on is impossible to fix.
Figure 13. Halos are much less noticeable with a smaller sharpening radius (amount = 150, radius = 0.5).
How to Avoid Halos
Although you can fix halos after the fact, it’s usually easier to not create them in the first place. If you see halos being generated, you can backoff a bit from your adjustment and they may dissappear. However sometimes it’s not possible to reduce your adjustments enough and still achieve the processing effect you want. In these cases, you should be able to use alternate controls (which do not generate halos) to get the desired result.
For example, say the goal is to darken the sky in a landscape photo without unduly affecting the land. The easiest way is to use the highlights slider with negative values but this can generate halos as discussed. But here are some alternative methods that won’t create halos:
Exposure slider with a range mask
Starting with the example in figure 3, we can darken the sky area using a local adjustment. Here I selected the graduated filter and placed it off to the side so that it would affect the entire image. Setting the exposure to -3 would normally darken both the sky and foreground, however we can restrict the adjustment to just the brighter parts of the image (i.e. the sky) using the range mask feature in Lightroom. Set the range sliders to cover the brighter tones in the sky and then adjust the smoothness slider if the halo is still visible until it disappears.
Another way to darken the sky without causing halos is with the curves tool. Use control points to keep the dark tones in the image unchanged and then gradually taper the brightness of the sky. In general, as long as the curve is smooth and doesn’t have crazy hairpin turns it should not create halos (technically the curve should be monotonic which means that the curve is always increasing as we go left to right).
The main drawback of using curves in Lightroom is that you can only set one curve for the entire image and I like to use my curve at the end of my editing to tweak the image’s overall brightness and contrast. So if I want to use curves to darken the sky, I will bring the image into Photoshop where multiple curves can be applied in separate adjustment layers.
Similar to the range mask tool in Lightroom, in Photoshop you can use luminosity masks or blend-if to limit changes to the sky/brighter regions and leave the foreground untouched.
Pixel Perfect Sky Mask
In Photoshop, it’s possible to make a pixel perfect mask to affect just the sky. With this mask, you can bring down the bright sky without affecting other areas of the image. There are several ways to make the mask: I usually start with the quick mask tool and then hit the “Select and Mask” button to refine the selection. Another option is to use the Select » Sky menu option. The selection tools will typically get you close to the necessary mask, but you may need to do some manual touch ups.
Shown below is an example with both man-made and natural edges (the buildings and vegetation) with an overly bright sky.
Figure 16. Test image with overly bright sky that needs to be darkened.
Figure 17. A pixel perfect mask generated by the quick mask tool and then refined with “Select and Mask” in PS.
Figure 18. The result of darkening the sky with a curves adjustment and the mask in the previous figure.
In theory you could make a similar mask in Lightroom using the auto-mask option and careful brushing. But in practice I find it far more difficult to do without artifacts and hence bring my image into Photoshop instead.
Lightroom has a number of powerful sliders that make editing our images much easier. However, under some circumstances, these sliders can result in halos around edges. I think the best strategy for avoiding halos is to simply not create them in the first place. One can do this by easing off on the sliders known to be problematic (e.g. highlights, clarity, HSL, sharpening, etc.) and to use alternate controls that are less susceptible to haloing, often in conjunction with masks, to achieve the same effect.
In rare circumstances, when I think this will be easier, I will let the halos develop in my editing and then remove them with a clone stamp layer at the very end of processing.