I recently took a couple long exposure night shots that I later realized have a ton of red, green, and blue pixels all throughout the image. In looking into this online, I've learned they are likely "hot pixels", as they only show up in the images that were particularly, long exposure. See example below, with bad pixels in both the trees and star trails:
In reading online, I have seen that Lightroom should automatically remove hot/dead pixels, but it's not doing so in this case, possibly because there are so many. Is there any way for me to automatically remove these?
You have enough hot pixels that it may be confusing to the auto-removing algorithm so that it thinks they are data, maybe?
In the Develop module, Details panel, Noise Reduction, "color" slider, see if a setting of 15 helps you out. Experiment as necessary, but too high may affect the star trails.
Thanks for the reply! The Color slider was already on 25, and changing it to be more or less didn't seem to have any effect on the dots.
Even though that is not the purpose of the Color slider, I thought it might be worth a try.
In this case something like what Nikon calls "long exposure noise reduction" might help you, if your camera has it, where a dark image of the same exposure time is subtracted from the original image to remove the stuck pixels and heat blooms, etc. However, that might also leave some gaps in your star trails.
The red, green and blue you see in your image, is digital color noise produced by an electrical disturbance which occurs in any electrical process. With high ISO images the camera's sensor is more sensitive and records more electrical disturbance. With long shutter speed more there is more time to capture the electrical disturbance. Most of the time the red, green and blue is in the darkest areas of the image. In the Detail panel Magnify the image to 4:1 or 8:1 so you can see the colors better. Take the Color noise effect slider to the right and you should see the color noise start to disappear. Add some luminance noise reduction and more should disappear. Finally, sharpen the image and then mask it in the sharpening section of the Detail panel. Hope this helps.
You don't want to mess with the color noise reduction sliders too much as it will desaturate the actual star trails if you do this. The "hot pixels" are actually caused by cosmic radiation hitting your sensor not by them being stuck somehow. Lightroom is supposed to be able to automatically find them and get rid of them but it does not do a very good job and even if it did, a lot of night photographers would cry foul and accuse Adobe of "eating their stars" just like they are doing with Sony whose firmware does an extremely mild form of this. The only solution to this that doesn't affect the star trails you really want is to use dedicated star photography software or to use photoshop to clone them out.
LR Noise Reduction algorithm removes single hot pixels automatically. I suspect the ones you are seeing have two or more adjacent hot pixels, which LR interprets as subject matter (star, spotlight, etc.). You can use the in-camera Long Exposure Noise Reduction setting (if available). The overall exposure time is 2X so not very convenient with long exposures like this one (30 min.).