Why do banding stripes appear when I photograph an LED up close with my phone?
Asked 10/17/2015
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I photographed two LEDs with a Nexus 5 from less than 2 cm away and noticed visible bands/stripes across the LED in the image. The bands only seem to appear when shooting this close. Is this caused by phone software/image processing, or is it an optical effect?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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This is something specific to photographing LEDs. Most LEDs aren't on all the time, but are in fact flashing extremely rapidly. The ratio of on/off time (the duty cycle) can be used to control the perceived brightness of the LED. The camera you are using has a rolling shutter. When your camera takes a photo, it actually scans the image from top to bottom (or in this case horizontally) over time, rather than taking the whole picture at once*. The process is extremely quick, but in this case still too slow to hide the normally imperceptible flashing.
Your phone is fine and is working normally. It also has nothing to do with the fact that this is a macro shot.
*Cameras which -can- do this are said to have a global shutter. They're very expensive and are used for high-end digital video (movie cameras and the like).
Originally by user45705. Source · Licensed CC BY-SA 4.0
user45705
10y ago
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This is most likely not a macro or lens issue, and not a phone defect. It happens because many LEDs are not driven continuously: they flicker very rapidly, often using pulse-width modulation (PWM) to control brightness. Your phone camera likely uses a rolling shutter, which records the image line by line rather than all at once. If the LED brightness changes while the sensor is being scanned, different lines are captured at different brightness levels, producing visible bands.
So the effect is mainly an interaction between the LED’s rapid flicker and the camera’s rolling shutter. Getting very close makes the LED fill more of the frame, which makes the banding easier to notice, but macro distance itself is not the cause.
In short: it’s a capture artifact caused by LED flicker plus rolling shutter, not an optical phenomenon in the lens.
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