Hot pixels are defects commonly found in digital cameras. You can determine if they are hot pixels because they will show in the same location in every frame — they do not move. They will look extra sharp because they are just one pixel. Below, I’ll discuss what they are and talk about three ways to remove them.
What are hot pixels?
Hot pixels are caused by electrical charges which leak into the sensor wells. You usually begin noticing them when you go home and look at your images more closely during post-processing.
Hot pixels can become more visible at high ISOs. They can also become more visible when the sensor becomes hot. This can occur when you are photographing during a hot day or evening. They tend to be more visible in dark areas of your image. They tend to show up far more often in long exposure images. And of course, this includes dark night photography images!
Above, I used the Dust& Scratches filter in Photoshop to remove hot pixels. This is viewing the image at 200% zoom.
A pixel by any other name …
For the purposes of this article, I am not going to differentiate between hot pixels, dead pixels (a pixel that is no longer receiving any information) or a stuck pixel (pixels that receive erroneous information, often showing up as red, blue or green). I’m simply going to refer to them as hot pixels for the sake of expediency.
Three ways to get rid of wayward pixels
1. Pixel mapping
We’ll start straight at your source: Your camera. Your camera may include pixel mapping features in its firmware. The general idea is that your camera takes a black reference frame and then eliminates the detected stuck pixels. Easy. Pentax and Olympus have pixel mapping features.
2. Removing noise
I’ll use Photoshop as an example, mostly because, well, that’s what I use. If you don’t use Photoshop, look for a similar feature on your photo editor.
Photoshop already has an excellent method of getting rid of hot pixels without resorting to third party plug-ins. It’s quite easy.
Go to Filter > Noise > Dust & Scratches. This will open a dialog box.
Set the pixel radius to 1-2 pixels. Set the threshold based on how much you wish to eliminate the offending pixels.
What if the Dust & Scratches Filter messes up other parts of my image?
If this occurs, do one of the following:
Paint out the pixels with Layer Masks
Create a Layer Mask (Layer > Layer Mask > Reveal All). This should create a white mask in the Layers Window. Then click that white mask, select a brush with the color black and paint out all the areas where you feel the image has been adversely affected.
Use luminosity masks
Since offending pixels are far more visible in dark, shadowy or unexposed areas, you may target these in those areas with a luminosity mask. Create a luminosity mask where only the darker areas of the image are targeted. The pixels should be gone. If there are other pixels visible, you can paint those out on the mask itself with a white brush, brushing on more of the effect.
3. Dark frame subtraction
There are two ways of doing dark frame subtraction — long exposure noise reduction and dark frame subtraction.
Long exposure noise reduction
You can turn on long exposure noise reduction (LENR) in your camera’s settings.
Remember, though, that this will result in your long exposure taking twice as long. For example, if you do a 3-minute exposure, your camera will then employ LENR for an additional three minutes, so your wait time will be six minutes total. Because of this, you also should not have LENR on if you are doing stacking of any kind. For these reasons, I rarely use LENR.
Dark frame subtraction in post-processing
This is how I prefer to do dark frame subtraction. While you are out in the field taking long exposure photos, take a dark exposure image.
Set up your camera with the settings you are using. However, keep the lens cap on. This may get puzzled looks from your family if they are not photographers. Take the photo.
Remove the lens cap and go ahead and take the long exposure.
When you do your post-processing, open the dark frame subtraction image and your regular image. Put the dark image as the top layer. Change the Blend Mode to Subtract. Boom! That gets rid of whatever errant pixels you may have had.
It’s easy to deal with hot pixels
As I mentioned earlier, this mostly occurs with long exposure photos, especially in the dark areas. This unfortunately makes them particularly noticeable, especially when viewed on a large screen. Thankfully, there are numerous ways to address taking them out. And most of them are easy.
There are other methods of removing them as well. You could use either the Spot Healing Brush or the Clone Stamp tool to remove them. However, you would need to generally remove them individually. I tend to use the Spot Healing Brush for removing sensor dust more so than hot pixels.
You might also be able to use a noise reduction program such as Topaz Labs DeNoise AI.
Do you have a preferred method of removing hot pixels? If so, please tell me in the comments!