Lossy compressionIn information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size for storing, handling, and transmitting content. The different versions of the photo of the cat on this page show how higher degrees of approximation create coarser images as more details are removed. This is opposed to lossless data compression (reversible data compression) which does not degrade the data.
Subjective video qualitySubjective video quality is video quality as experienced by humans. It is concerned with how video is perceived by a viewer (also called "observer" or "subject") and designates their opinion on a particular video sequence. It is related to the field of Quality of Experience. Measuring subjective video quality is necessary because objective quality assessment algorithms such as PSNR have been shown to correlate poorly with subjective ratings. Subjective ratings may also be used as ground truth to develop new algorithms.
Compression de donnéesLa compression de données ou codage de source est l'opération informatique consistant à transformer une suite de bits A en une suite de bits B plus courte pouvant restituer les mêmes informations, ou des informations voisines, en utilisant un algorithme de décompression. C'est une opération de codage qui raccourcit la taille (de transmission, de stockage) des données au prix d'un travail de compression. Celle-ci est l'opération inverse de la décompression.
Compression artifactA compression artifact (or artefact) is a noticeable distortion of media (including , audio, and video) caused by the application of lossy compression. Lossy data compression involves discarding some of the media's data so that it becomes small enough to be stored within the desired or transmitted (streamed) within the available bandwidth (known as the data rate or bit rate). If the compressor cannot store enough data in the compressed version, the result is a loss of quality, or introduction of artifacts.
Video qualityVideo quality is a characteristic of a video passed through a video transmission or processing system that describes perceived video degradation (typically, compared to the original video). Video processing systems may introduce some amount of distortion or artifacts in the video signal that negatively impacts the user's perception of a system. For many stakeholders in video production and distribution, assurance of video quality is an important task. Video quality evaluation is performed to describe the quality of a set of video sequences under study.
Métrique (logiciel)Une métrique logicielle est une compilation de mesures issues des propriétés techniques ou fonctionnelles d'un logiciel. Il est possible de classer les métriques logicielles en trois catégories : Maintenance applicative Qualité applicative Respect des processus de développement Elles peuvent être simples ou plus complexes. Elles se composent toujours de mesures dites « de base », par exemple le nombre de lignes de code, la complexité cyclomatique, le nombre de commentaires.
Video coding formatA video coding format (or sometimes video compression format) is a content representation format for storage or transmission of digital video content (such as in a data file or bitstream). It typically uses a standardized video compression algorithm, most commonly based on discrete cosine transform (DCT) coding and motion compensation. A specific software, firmware, or hardware implementation capable of compression or decompression to/from a specific video coding format is called a video codec.
Transformée en cosinus discrèteLa transformée en cosinus discrète ou TCD (de l'anglais : DCT ou Discrete Cosine Transform) est une transformation proche de la transformée de Fourier discrète (DFT). Le noyau de projection est un cosinus et crée donc des coefficients réels, contrairement à la DFT, dont le noyau est une exponentielle complexe et qui crée donc des coefficients complexes. On peut cependant exprimer la DCT en fonction de la DFT, qui est alors appliquée sur le signal symétrisé.
Visiocasquethumb|Le casque de réalité virtuelle Oculus Rift. Un visiocasque est un dispositif d'affichage, porté sur la tête ou dans un casque, qui a un petit écran d'affichage en face d'un œil (visiocasque monoculaire) ou de chaque œil (visiocasque binoculaire). Le visiocasque est parfois appelé casque de visualisation, casque immersif, casque-écran ou casque HMD (où HMD signifie head-mounted display), voire simplement .
Video compression picture typesIn 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.
