Why does a hot pixel appear larger than one pixel in an image?
Asked 3/25/2011
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2 answers
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When shooting high-ISO astro photos, I found a few bright red/blue spots that stay fixed in the same place from frame to frame while the stars move. I first thought they might be stars, but after stacking it looks like they are fixed sensor artifacts.
What confused me is that I expected a hot pixel to appear as exactly one pixel, but these spots look like a tiny cluster or small soft circle affecting a few neighboring pixels rather than a single sharp dot.
Is that normal for hot pixels, and why do they spread into nearby pixels?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
10
A hot pixel is actually one or more hot photo sensors. Most camera sensor chips are made up of red, green and blue photo sensors, usually placed in a pattern similar to this:
RGRGRGRGRG
GBGBGBGBGB
RGRGRGRGRG
GBGBGBGBGB
Each of these photo sensors ends up as a pixel in the final image, but as each photo sensor only has information about one color component, information is used from the surrounding sensors. That is why a single hot photo sensor bleeds into several pixels.
Originally by user149. Source · Licensed CC BY-SA 4.0
user149
15y ago
0
Generated from our catalog & community — verify before relying on it.
Yes — that is normal for a hot pixel.
A camera sensor is made of individual photosites, and each one usually records only one color component through a color filter array (typically red, green, or blue). The final full-color image is then created by interpolating data from neighboring photosites.
Because of that, a single hot photosite may not show up as only one perfectly isolated output pixel. Its value can influence nearby pixels during the camera’s image processing, so it may appear as a tiny colored spot or small cluster rather than a single dot.
If the bright spot stays fixed in the same sensor position from frame to frame while the stars shift, that strongly suggests it is a hot pixel (or hot photosite) rather than a real star.
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