Colour depth refers to the number of distinct colours that a digital imaging device, such as a scanner or camera, can capture or display. Measured in bits per channel, a 24-bit colour depth provides 8 bits each for red, green, and blue, allowing over 16 million possible colours. Modern scanners and cameras may offer 30-bit or 36-bit colour depth, capturing billions of colours for even finer tonal gradations. In practice, the human eye finds it difficult to distinguish differences beyond 24-bit, but higher colour depths can be useful for high-end imaging, post-processing, and professional photography workflows where subtle colour transitions and precision are critical.