What are Pixels?
They are the building blocks of an image. When we view an image the individual pixels are not distinguishable to us. They together place themselves beside each other to form the image. It is the smallest unit of a picture.
Here is an example. The small circle is actually made up of several small sruares of different shades of yellow.
Vector images are smaller in size(not dimension). The image information is represented by formula.
In raster graphics the image is represend by the pixels unlike mathematical formula as in vectors.Fille formats like .bmp, .jpg, .tiff are raster formats.