raster
noun [ C ] computing specialized uk/ˈræs.tər/ us/ˈræs.tɚ/
（电视机或电脑屏幕的）光栅
a rectangular pattern of lines that an electron beam follows on a television or computer screen
The characters can be exposed line by line using a raster scan. 使用光栅扫描可以逐行暴露字符。
光栅图像
a type of computer image that is based on a rectangular grid (= pattern of lines and columns) of pixels (= small dots)
PNG is a graphics file format for raster images. PNG是光栅图像的一种图形文件格式。