What is the fundamental unit of a raster image?

The fundamental unit of a raster image is a pixel. A raster image, also known as a bitmap image, is composed of a grid of these individual pixels, each of which represents a specific color. When these pixels are arranged in a two-dimensional array, they collectively form the complete image.

The resolution of a raster image is determined by the number of pixels it contains; more pixels generally translate to higher image quality and detail. If you think of a mosaic made of tiny colored tiles, each tile corresponds to a pixel in the context of digital images. This pixel-based structure is what allows for the detailed representation of images, but it is also what limits scalability because enlarging a raster image can lead to pixelation, where individual pixels become visible.

While paths and vectors are fundamental to vector images, which are composed of mathematical equations creating shapes, they do not apply to raster images. Metadata, though essential for providing information about the image, such as its dimensions, color depth, and creation date, isn't part of the image itself. Instead, it's additional information that accompanies the pixel data. Thus, pixels are indeed the basic building blocks of raster images, making them the correct answer.