They're not returning too-high values (such as all blue) they're turning no values at all (which results in a pitch black spot). A "dead pixel" in a digital image is the result of a set of non-functioning photodiodes. The actual stuck pixel is a fixed location but as the camera processes the raw input from the CMOS sensor using a demosaicing process and Bayer filter the single point of failure in the sensor ends up taking on this spot-like appearance.Ī stuck pixel is distinct from other common artifacts and imperfections found in a digital image. If you're curious why the blue spot appears to bleed out like ink on paper, it's a side effect of the JPEG processing algorithm in the camera. The right side shows a 3000 percent crop (with the Photoshop pixel grid overlaid).
The left side shows two stuck pixels (one bright blue and one bright white) as seen at 100 percent crop in a JPEG image captured off a Nikon D80 camera. Here's an example of a stuck pixel in the wild. This stuck pixel can therefore be bright blue, green, or red if only some of the photodiodes are stuck or pure white if all the diodes for that particular pixel are stuck at their maximum value. The most obvious malfunction is known as a "stuck pixel." In the case of a stuck pixel some or all of the photodiodes that make up the RGB component that comprise a single pixel in your image become stuck at their maximum value.
When things start to malfunction, however, suddenly one (or many) of the little guys take center stage in your photos. When everything works well, you don't give much thought to those microscopic photodiodes.
Just like your monitor uses millions of pixels combined with backlighting to create an image you can view, the CMOS sensor has millions of pixels that capture light combined with a processing algorithm to create an image you can view. The sensor is a tiny array of photodiodes arranged in a grid just like your computer monitor is a large array of pixels. Inside your digital camera is a CMOS sensor and that's the source of the pixel errors we're interested in.
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