Why does a hot pixel appear as a small square/checker pattern in long-exposure night photos?
Asked 3/23/2016
3 views
2 answers
0
In long-exposure night-sky shots, I’m seeing the same bright squarish/checker-like mark in the exact same spot in every image. I understand that hot pixels can show up brighter during long exposures, but this looks larger than a single pixel. Why does it appear this way, and is it still just a hot pixel?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
8
It is a hot pixel.
The reason it makes that little checkerboard shaped mark is because of the way digital cameras use single luminance values for each pixel to create color information by filtering some pixels for red, some for blue, and some for green and then doing a process known as demosaicing to assign a luminance value for each of those three color channels to each pixel. The way demosaicing works is that the luminance value of adjacent pixels with different colored filters as well as nearby pixels with the same colored pixels are compared to determine how much of each color component the light is composed of that is striking each pixel well.
If a pixel is hot enough and the surrounding pixels are very dark, the value of the single pixel is enough to influence the value of some of the surrounding pixels.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
10y ago
0
Generated from our catalog & community — verify before relying on it.
Yes — it’s still a hot pixel. In long exposures, a hot pixel can become bright enough that the camera’s color processing makes it appear larger than one pixel.
Most digital sensors use a color filter array, where each pixel records only one color component. The camera then uses demosaicing to estimate full color at each pixel by comparing neighboring pixels. If one pixel is much brighter than the dark pixels around it, that value can influence nearby reconstructed color values, producing a small square, cross, or checker-like pattern instead of a single point.
The fact that it appears in the same place in every long exposure is consistent with a hot pixel.
Recommended products
UniqueBot
AI10y ago
Your Answer
Related Questions
Why do the same red or white pixels appear in every photo from my Canon Rebel T2i?
How can I prevent or remove hot pixels in long night exposures on a Canon T3i/600D?
Why do bright colored pixels appear in every photo from my Olympus OM-D E-M10?
Can downsampling or pixel binning improve low-light image quality?
What causes fixed colored speckles in long-exposure night photos—hot pixels or lens reflections?