Hot Pixels will generally appear when shooting long exposures. The hot pixels are bright spots that may show up in your image when taking a long exposure shot, especially at higher ISO values. If only a few appear in your image, you can clone them out quickly. However, if you get a lot of spots, going in and cloning the spots out can be a tedious and time-consuming process.
There are a few ways to deal with hot pixels:
- Dark Frame Subtraction: This method minimizes image noise by subtracting a second exposure captured with the sensor in the dark (with the lens cap on for example). The position of the hot pixels would be fixed between the two frames. This method takes more time in the field, and you have to remember to do it.
- Adjust settings: Lowering ISO or decreasing exposure time could minimize the number of hot pixels that appear in an image. However, this may not give you the desired final result.
- Post Processing Techniques: This is what I will go over in this blog. This technique requires Photoshop.
Open your image in Photoshop. The image I am using was taken in October 2018. It was relatively warm for a fall night in the Rockies. This shot is my foreground image. A second image was taken for the sky at a shorter exposure to capture Orion and minimize star trails.
Duplicate the background layer, Command/Ctrl+J. You can rename it however you want.
Select Filter -> Noise -> Dust & Scratches
The value chosen for Radius should be small, as the noise we want to remove is minimal. I have decided on 2 with a threshold of 5. You can play around with the values and converge on parameters that eliminate all the noise but minimize any effect on the rest of the image.
Once you apply the Dust & Scratches filter, go to the layer panel and change the blending mode of the layer to Darken. The darken mode will compare the pixels between the background layer and the copy and replace the lighter colours with darker colours.