Learn in the textbookData Representation Methods for Still Images
DefinitionRaster data (ラスターデータ) divides an image into a grid of pixels arranged in rows and columns and records a color value for each pixel.
ExplanationMore pixels (higher resolution) give finer detail, but there are more values to store, so the data grows larger. When the image is enlarged, each pixel stretches and the edges of diagonal lines and curves show stair-step jaggies. Raster data suits images like photographs, where color and shading change finely from spot to spot.
AnalogyIt is like a mosaic made of small colored tiles. From a distance you see a picture, but up close you can see the seams between each tile.
Memory hookThe word raster comes from the Latin for rake. Picture the parallel lines a rake leaves, packed side by side, as rows of pixels stacked one on another.