480I is an interlaced signal that will have artifacts due to using this form of signal compression. It displays 60 fields per second yielding 30 frames per second.
480I is the original native scan rate of our NTSC broadcast television system. It comes in two versions. The first is the television system which uses composite video. Composite video is where the color and b/w signal have been put together into one requiring separation in your TV which degrades the image. Another variation is S-Video or separate video which means the color and b/w signals are already separated greatly enhancing picture quality depending on the source. For DVD the 480I component video system is used which has three wires or connections labeled as green, red and blue. One is the b/w signal and the other two represent the red and blue color difference signals. Component video is used as a form of analog compression to reduce storage space.
For more information go to, Scan rate.