What Is a Digital Image?

← Back to Digital Image Processing Basics

A digital image is a discrete, two-dimensional representation of a continuous scene, stored as a rectangular array of numerical values called pixels (picture elements).

Formally, a grayscale image is a function:

\[f: \{0, 1, \ldots, M-1\} \times \{0, 1, \ldots, N-1\} \to \{0, 1, \ldots, L-1\}\]

where \(M \times N\) is the spatial resolution (height × width) and \(L\) is the number of discrete intensity levels (e.g., \(L = 256\) for 8-bit images).

Key Concepts

Resolution

The number of pixels in each spatial dimension. Higher resolution captures finer detail but requires more storage and computation. Common resolutions in microscopy range from 512×512 to 4096×4096.

Bit Depth

The number of bits used to represent each pixel value. Common depths:

  • 8-bit: 256 levels (0–255), standard for display.

  • 16-bit: 65 536 levels, common in scientific microscopy for preserving dynamic range.

  • 32-bit float: used after processing operations that may produce fractional values.

Color Spaces

  • Grayscale: single channel; most scientific microscopy images.

  • RGB: three channels (red, green, blue); standard for color images.

  • HSV / HSL: hue–saturation–value/lightness; useful for color-based segmentation.

  • Lab: perceptually uniform; useful for color-difference metrics.

See also