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Settings of the image: ISO 320 f/8 15s at 70mm. Shot RAW Large. Nikon z6. The image below is zoomed in to show the stuck pixel.
I noticed this blue dot and found out it is known as a stuck pixel. I found a white one in another image - a panning shot. In this image attached there are a couple more blue stuck pixels.
This is very worrying and frustrating, I have no idea what to do. Please advise me.
The simplest way is to use Lightroom. Select the healing tool, resize it using the scroll wheel of your trackball or mouse, and click on the hot pixel. Lightroom will automatically detect where suitable pixels exist to replace those missing when the hot-pixel is removed.
I can't tell if they are hot or stuck pixels (see: Hot, stuck, or dead pixels. What's the difference?). Stuck and dead pixels are completely normal, they happen. As a matter of fact, there are almost certainly more stuck pixels in your camera than you even know about. The camera maintains a "pixel map" of known hot pixels, and automatically filters them out before the sensor data is ever written to storage cards, even in raw files (.nef, in the case of Nikons).
Also, tools such as Lightroom and Photoshop / Adobe Camera Raw will automatically eliminate hot, stuck, and dead pixels when importing raw files. So if you shoot raw (and I generally highly suggest you do), check if your post-processing software will handle them for you so you never have to worry about it.
You can make the camera update its pixel map by performing two back-to-back sensor cleaning cycles — "Clean image sensor" in the Setup menu. It will find stuck and dead pixels, and save the pixel remapping.
To reduce hot pixels in long-exposure photographs, you can enable "Long exposure noise reduction" (LENR), which will take your photo, then immediately take a "dark frame" image of the same duration. It will then subtract the dark frame (which is just averaged noise + hot pixels) from the captured long exposure image, and produce a single photo. The downside of LENR is that it takes twice as long as your shutter speed to take the image. So a 30-second long-exposure shot will actually take 60 seconds to capture and process, before the camera is ready to take another shot.
See also:
Scottbb's answer tells you why it's there, and what you can do and what you can expect in the future, but as for the image you already have: Paint over it! I would use a "clone" tool, to paint over the bright spot by cloning some of the surrounding texture.
Do two back-to-back sensor cleaning cycles from the setup menu. That will run Nikon's hot-pixel remapping logic, which should remove these pixels. This worked for Z7 owners, along with most of Nikon's recent DSLR models. Source: https://www.dpreview.com/forums/post/61945064
