What is Pixel?

Pixel: Simple Definition

A pixel (picture element) is the smallest individual point in a digital image. Every digital photo, video frame, and screen display is made up of millions of tiny colored pixels arranged in a grid.

Each pixel stores color information as RGB values - red, green, and blue values from 0-255 that combine to create any color in the spectrum. Your smartphone screen has millions of pixels packed so tightly together they appear as one smooth image.

Color Depth

How many colors a pixel can express depends on its bit depth. The common 24-bit color allocates 8 bits each to red, green and blue, giving 256 levels per channel and about 16.7 million possible colors.^[2] Many formats add a fourth alpha channel to record transparency, so each pixel may store four values rather than three.^[1] Higher bit depths (10 or 12 bits per channel) give smoother gradients and underpin HDR, while lower depths like the 256-color palette of GIF save space at the cost of color accuracy.

Pixels and File Size

Because an image is a grid of pixels, its raw size grows with the total pixel count: a 4000 by 3000 photo holds 12 million pixels, and at 3 bytes each that is 36 megabytes uncompressed. This is exactly why image formats compress, and why resolution drives file size so directly. It also explains the value of resizing: shrinking an image's pixel dimensions to the size it will actually be displayed at removes data that would otherwise be wasted, often cutting file size dramatically before any compression is applied.

Device Pixels versus CSS Pixels

On the web a "pixel" is not always a physical dot. A CSS pixel is an abstract unit, and on high-density displays several physical device pixels render a single CSS pixel; the devicePixelRatio property reports this multiplier.^[1] This distinction lets layouts stay a consistent visual size across screens of widely different sharpness.^[1] It is also why images for the web are often provided at two or more pixel densities, so a "retina" screen can show extra detail while ordinary screens download a smaller file.

Subpixels and Rendering

Each on-screen pixel is physically built from smaller red, green and blue subpixels, and their arrangement varies between display technologies.^[2] Some text-rendering techniques exploit these subpixels to sharpen edges, treating a single pixel as three independently addressable color stripes.^[2]

How Pixels Work

When you take a 12-megapixel photo, your camera captures 12 million individual pixels. Each pixel records the exact color and brightness at that point in the scene. Zoom in far enough on any photo and you will see the individual colored squares.

The concept of pixels is important for image editing because it determines image quality limits. You cannot add detail by enlarging a low-resolution image - you just make the existing pixels bigger, creating a blurry, “pixelated” result.

Examples of Pixel

Frequently Asked Questions