Dead Pixel
A photosite that records no signal at all, appearing as a permanently black point in every image.
Measured in
count
In depth
Dead pixels result from manufacturing defects or damage and, unlike hot pixels, do not depend on exposure length or temperature. Cameras maintain a defect map and interpolate over known dead sites from their neighbours, so a small number are invisible in practice and are within every manufacturer's tolerance.
Examples in practice
A single dead photosite is filled from surrounding pixels and never appears in the final file.