Video quality

Video quality can be measured with formal metrics like PSNR or with subjective video quality using expert observation.
The subjective video quality of a video processing system is evaluated as follows:

• Choose the video sequences (the SRC) to use for testing.
• Choose the settings of the system to evaluate (the HRC).
• Choose a test method for how to present video sequences to experts and to collect their ratings.
• Invite a sufficient number of experts, preferably not fewer than 15.
• Carry out testing.
• Calculate the average marks for each HRC based on the experts' ratings.

Many subjective video quality methods are described in the ITU-T recommendation BT.500. One of the standardized method is the Double Stimulus Impairment Scale (DSIS). In DSIS, each expert views an unimpaired reference video followed by an impaired version of the same video. The expert then rates the impaired video using a scale ranging from "impairments are imperceptible" to "impairments are very annoying".

Video compression method (digital only)

Main article: Video compression

Uncompressed video delivers maximum quality, but with a very high data rate. A variety of methods are used to compress video streams, with the most effective ones using a Group Of Pictures (GOP) to reduce spatial and temporal redundancy. Broadly speaking, spatial redundancy is reduced by registering differences between parts of a single frame; this task is known as intraframe compression and is closely related to image compression. Likewise, temporal redundancy can be reduced by registering differences between frames; this task is known as interframe compression, including motion compensation and other techniques. The most common modern standards are MPEG-2, used for DVD, Blu-ray and satellite television, and MPEG-4, used for AVCHD, Mobile phones (3GP) and Internet.