Simplify the following text for a Grade 7 native English-speaking person.
Original: In computer graphics , a raster graphics image or bitmap is a data structure representing a generally rectangular grid of pixels , or points of color , viewable via a monitor , paper , or other display medium . Raster images are stored in image files with varying formats ( see Comparison of graphics file formats ) .
Simplified: Raster graphics ( or bitmap graphics ) is one of two kinds of computer graphics .