How should I handle hot pixels in long-exposure night photos?
Asked 7/24/2015
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I’m seeing red, blue, and white pixels in long-exposure night shots, and they also appear when I make a dark frame with the lens cap on. At fast shutter speeds I don’t notice them, but as the exposure gets longer, more of them appear. My normal exported images don’t seem to show obvious problems, possibly because RAW conversion is already correcting them.
Is this normal behavior for long exposures, or a sign that my camera has a bigger issue? Should I worry about warranty service, or is it better to handle this in-camera or in post-processing?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
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For exposures longer than 1 second, you can enable Long Exposure Noise Reduction (LENR). This is Canon's nomenclature for in-camera dark frame subtraction. When you take a photo the camera will expose the image normally and then use the same settings to create a dark frame with the shutter left closed. The readings for each pixel in the dark frame will be subtracted from the reading for each pixel in the first frame before sending the raw data to your memory card.
Be aware that the time required for a dark frame is the same as the time required for the initial exposure - so if you shoot a 30 second exposure you will then have to wait an additional 30 seconds before you can take another shot!
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
11y ago
0
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What you’re describing is typical of hot pixels becoming more visible as exposure time increases. If they’re not showing up in your normal processed images, it usually isn’t something to panic about.
A standard in-camera fix is Long Exposure Noise Reduction (LENR), which on Canon uses dark-frame subtraction. After the main exposure, the camera makes a second exposure of equal length with the shutter closed, then subtracts that pixel noise pattern from the image data.
So if you shoot a 30-second exposure, the camera will spend another 30 seconds making the dark frame before it finishes the file. That’s the main downside: it works, but it doubles the time before you can take the next shot.
Since the issue appears mainly in long exposures and not in your normal final images, it does not by itself suggest a serious camera fault. If needed, using LENR is the practical solution.
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