Video compression picture types

In the field of video compression a video frame is compressed using different algorithms with different advantages and disadvantages, centered mainly around amount of data compression. These different algorithms for video frames are called picture types or frame types. The three major picture types used in the different video algorithms are I, P and B. They are different in the following characteristics:

• I‑frames are the least compressible but don't require other video frames to decode.
• P‑frames can use data from previous frames to decompress and are more compressible than I‑frames.
• B‑frames can use both previous and forward frames for data reference to get the highest amount of data compression.

Summary

There are three types of pictures (or frames) used in video compression: I‑frames, P‑frames, and B‑frames.

An I‑frame is an 'Intra-coded picture', in effect a fully-specified picture, like a conventional static image file. P‑frames and B‑frames hold only part of the image information, so they need less space to store than an I‑frame, and thus improve video compression rates.

A P‑frame ('Predicted picture') holds only the changes in the image from the previous frame. For example, in a scene where a car moves across a stationary background, only the car's movements need to be encoded. The encoder does not need to store the unchanging background pixels in the P‑frame, thus saving space. P‑frames are also known as delta‑frames.

A......
Read More