Why do bright night lights show blue/white smearing at the edges?
Asked 4/3/2016
162 views
2 answers
0
When shooting a city scene at night, some bright point light sources show blue/white fringes or smeared edges in the photo. Adjusting exposure in the RAW file does not remove it. What causes this effect, and is there a way to reduce it when shooting?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
4
- The reason of those flares to appear is optical diffusion and internal refraction which is almost fine with normally observed objects but is obvious if the object is a bright spot light source - it affects all objects equally but it is only visible on high contrast transitions.
- The reason of them being asymmetrical is coma.
- The reason of them being coloured is longtitudinal chromatic aberration which results from dispersion.
- The reason for them to look so terrible is aggressive profiling which needs to be done to bring the image data recorded by camera closer to the reality (the bad form of colour sensing to be specific), and it's imperfection is exceptionally obvious with saturated objects. This is very apparent in photos of recent Canon DSLRs because they tend to require strong profiling.
Here are two verions from same file, one from Adobe Camera RAW and one from RawTherapee with custom weaker (less saturated) colour profile.
There is a way of making saturated bright sources look good - give tonal curve a wide shoulder and it will look natural. (your tonal curve will be different from the one displayed, experiment to find the one which you need)
Originally by user49477. Source · Licensed CC BY-SA 4.0
user49477
10y ago
0
Generated from our catalog & community — verify before relying on it.
This is mainly a lens aberration issue, especially coma, which becomes very visible on bright point light sources at night. Coma can make lights look asymmetrical or smeared toward the edges of the frame.
The blue/white color fringing can also come from chromatic aberration and internal reflections/diffusion in the lens. These problems affect the whole image, but you usually only notice them at high-contrast transitions like small bright lights against a dark background.
RAW exposure adjustments usually won’t fix it, because the effect is created optically before the image is recorded. In some cases, camera color profiling/rendering can make the color edges look worse.
To reduce it:
- stop the lens down a couple of stops from wide open
- avoid placing critical bright lights near the frame edges
- use a lens known for better coma control
For night and astro scenes, stopping down is often the simplest fix, though it trades away some light-gathering ability.
Recommended products
UniqueBot
AI10y ago
Your Answer
Related Questions
What causes red/blue fringes along object edges on a white background?
How do I prevent illuminated building signs from blowing out in night city photos?
Why do city lights look different colors in photos, and can I correct them?
Does a circular polarizer change starburst effects from streetlights at night?
What causes the rainbow grid flare around bright lights in an out-of-focus photo?