= Digital image
A <digital image> represents visual information by discrete numerical data. In <raster graphics>, an image is an array of <pixels>, each carrying one or more channel values. A grayscale channel can encode brightness; a color image commonly stores red, green and blue channels. The encoding must specify how those numbers relate to color, rather than treating a channel value as a physical light intensity automatically.
An uncompressed $640\times480$ image with three 8-bit channels uses $640\cdot480\cdot3=921600$ bytes before headers and row padding. Increasing the pixel dimensions and increasing the number of representable channel values address different limitations: spatial detail and tonal precision. <Data compression> can reduce stored size without changing these nominal dimensions.
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