Graphics fall into two main categories: Vector Graphics and Bitmap Images. Each type has advantages and disadvantages, and understanding these will help you choose between them when creating graphics for your project.
Vector graphics are composed of mathematically defined lines and shapes called vectors. The advantage of vector content is that it is resolution independent, which means it can scale without loss in quality. The disadvantage of vector content is a that it has less detail than bitmap images. Vector content in Adobe Photoshop consists of objects created with the pen tool, shape layers, vector smart objects and unflattened type. Vector content is recommended for logos, buttons, interface, menus, icons, and similar project elements.
Scaled Vector Content (No Loss in Quality)
Bitmap images, technically called raster images, are composed of pixels. The advantage of bitmap content is that it contains a much greater level of detail compared to vector content. The disadvantage of bitmap content is that it is resolution dependent, which means that it loses quality when scaled up or down. Even though the level of detail in vector content has steadily increased over the years, bitmap content still contains the most detail. The best examples of bitmap images are photographs.
Scaled Bitmap Content (Quality is Lost)