Roll mouse over image to see 200% enlargement of box on right.
Hot pixels are individual pixels which look much brighter than they should. They are also called sparkles.
Most cameras have a few of these at higher ISOs. It's normal. They come and go over time. Almost every camera I own has a couple. They aren't a problem unless they are dead smack in the center and appear every time.
They are usually invisible unless you go looking for them at 100%. I had to enlarge the example above to 200% to make them visible.
WHAT DO THEY LOOK LIKE?
They appear as one or a few unnaturally bright individual pixels.
They will be at exactly the same single-pixel location in every frame. They do not move. They literally are locked in stone on the sensor. They will be one pixel, and therefore much sharper than anything else in the image.
They are the two tiny green crosses in the example above, when you roll your mouse over the image.
Because camera sensors used color-striped sensors, hot pixels are usually colored red or green or blue.
They are not spots. They are not evenly distributed. They do not look like noise.
WHAT CAUSES THEM?
Image sensors are analog!
Sensors collect photons in microscopic wells, called pixels. Sensors do their magic by assigning electric charges to these photons. These charges are read as analog voltages. These voltages are sampled and quantized to make them into digital values. These digital values go through much more digital processing before we get to see them.
Leakage currents are electric charges which leak into sensor wells. These excess electric charges increase the voltage at the well (pixel) and make it look brighter than it should.
Manufacturing variations will cause some pixels to have much more leakage current than others. It's these few pixels on each sensor which are called "hot."
WHAT MAKES THEM WORSE?
Leakage currents increase with temperature, so a hot sensor will show more hot pixels.
They are much more visible at high ISOs.
They are tiny, so they are more visible at high magnification.
They stay in the same place. If you are a worrier, you'll learn where they are and always see them. It's like any other minor cosmetic defect on anything. No one else will notice them.
HOW TO GET RID OF THEM
I ignore them. If they bug you, they clean up easily in Photoshop. It's easy for Photoshop to identify and repair them because they stand out so sharply on a pixel-by-pixel basis.
I find the Spot Healing Brush the easiest and most efficient. Use a small brush and they're gone.
Every camera does this.
Even if it's OK today, your camera may start doing it tomorrow.
Don't worry about it. If you look hard enough you'll always find them.
DON'T return a camera because of hot pixels. The replacement will, too, over time.
Likewise, don't bother hand-picking a camera. I used to do this, and even the ones I picked as clean eventually picked up some hotties.
Sensors are analog, and as you analog circuit designers know, everything matters. Over time hot pixels will come and go. They won't move, but their intensity will vary.
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Thanks for reading!