A pixel (a contraction of “picture element”) is the smallest discrete unit of a digital image, a single colored point in a two-dimensional grid that, multiplied by millions of others, forms the full picture. Each pixel stores numerical values that encode color and brightness. In an 8-bit per channel RGB image, every pixel holds three numbers between 0 and 255, one each for red, green, and blue. In 16-bit images, the range expands to 0 through 65,535 per channel, providing much finer tonal gradation.
It is worth distinguishing the pixel as a unit of the displayed or stored image from the photosite as a unit of the physical sensor. A photosite is a single light-collecting well on the sensor, typically covered by a red, green, or blue filter in a Bayer pattern. Demosaicing software reconstructs full RGB pixel values for each photosite by interpolating from its neighbors, which is why a 24-megapixel Bayer sensor produces a 24-megapixel image even though no single photosite directly records all three colors. Monochrome sensors skip this step because they have no color filter array.
Image resolution is expressed in pixel dimensions (6000 by 4000 pixels) or as a megapixel count (24 megapixels) by multiplying the two. File size scales with both pixel count and bit depth: a 24-megapixel 16-bit per channel TIFF occupies roughly 138 megabytes uncompressed, while the same image as an 8-bit JPEG at moderate quality might be 6 megabytes. Detail recovery, print size at high quality, and crop latitude all scale directly with pixel count, which is why high-resolution sensors remain valuable despite the storage and processing cost.
Pixel density on a display, measured in pixels per inch (PPI), determines how sharp an image appears at a given size. A modern 5K monitor packs around 218 PPI; a high-end smartphone display reaches 460 PPI or more, dense enough that individual pixels are invisible to the naked eye at typical viewing distance. DPI versus PPI confusion is common: DPI refers to dots of ink per inch in printing, PPI to image samples per inch on screen, and the two are not interchangeable despite frequent loose usage.
Pixel-peeping describes the habit of inspecting images at 100 percent magnification on screen, where each image pixel maps to one display pixel. This view reveals noise, artifacts, chromatic aberration, and softness that are invisible at fit-to-screen view, and it tempts photographers into chasing differences that will never appear in print or on web at typical sizes. Disciplined practitioners pixel-peep only when a specific question (focus accuracy, noise at high ISO) requires that level of inspection.
Dead pixels (always black), hot pixels (always bright), and stuck pixels (locked to a fixed color) are defects that emerge over time, particularly during long exposures or at high ISO. Most cameras include a pixel-mapping function that detects and masks these defects automatically. The number of dead or hot pixels in a sensor’s lifetime is generally small relative to the millions present, and modern processing handles them invisibly.