**2. Human visual system**

Visual perception is very important to human. We are constantly receiving information and processing it, in order to interact with the environment that surrounds us. That justifies the big interest existed in video and measurement of its quality, because there is a big necessity of receiving that information in our visual system as faithful as it appears in nature.

The evolution of technologies in codification has made video compression more efficient with the reduction of introduced artifacts. But the accuracy in developed vision models and quality metrics has increased when in consequence of the video content transfer from analogue to digital. The vision models are based on human perception, moving closer to the final consumer.

The human visual system is extremely complex, but analyzing its behavior, characterizing the operation of the eye. The eye is a human body organ which is sensitive to a wide range of wavelengths from the radio-electric spectrum, from 400 to 780nm approximately. A large part of our neurological resources are used in visual perception.

For all these reasons, optimizing the performance of digital imaging systems with respect to the capture, display, storage and transmission of visual information is one of the most important challenges in this domain.

Video compression schemes should reduce the visibility of the introduced artifacts, creating more effective systems to reproduce video an image: Additionally printers should use the best half-toning patterns, and so on. In all these applications, the limitations of the human visual system (HVS) can be exploited to maximize the visual quality of the output. To do this, it is necessary to build computational models of the HVS and integrate them in tools for perceptual quality assessment.
