Video compression is the process of reducing the amount of data that is needed to represent a video signal. Video compression is performed by analyzing the information contained within images sequences and removing redundancies.

Spatial Compression (Image compression) - Spatial compression is the removing of redundant information within each image. Spatial compression can use processes such as JPEG which use blocks of images to approximate portions of information. This can reduce the amount of data by a factor of 20:1 or more depending on the underlying complexity of the image (solid images compress much better).

Temporal Compression (Sequence compression - Temporal compression is the removal of redundant information between each image. Temporal compression can use processes such as difference coding to identify objects that repeatedly appear in sequences of images.

This figure shows how video compression may use spatial and temporal compression to reduce the amount of data needed to represent a video sequence. Video data is greater than 300,000 pixels per frame and each pixel also has color information. Inevitably, the compression process introduces loss of detail and distortion artifacts. In order to deliver the compression factors that are required, similar areas of video are treated as one, resulting in loss of detail. This diagram shows that a frame in a video sequence may use spatial compression by representing the graphic elements within the frame with objects or codes. The first frame of this example shows that a picture of a bird that is flying in the sky can be compressed by separating the bird image from the blue background and making the bird an object (group of pixels) and representing the blue background as a box. The next sequence of images only needs to move the bird on the background and record the difference in the group of pixels from the previous frame (temporal - time compression).