{"id":178539,"date":"2011-02-03T18:40:00","date_gmt":"2011-02-03T17:40:00","guid":{"rendered":"https:\/\/cms.galaxiemedia.fr\/tomshardware\/2011\/02\/03\/retina-distance-et-definition-expliquons\/"},"modified":"2023-06-22T17:49:22","modified_gmt":"2023-06-22T15:49:22","slug":"retina-distance-et-definition-expliquons","status":"publish","type":"post","link":"https:\/\/www.tomshardware.fr\/retina-distance-et-definition-expliquons\/","title":{"rendered":"Retina, distance et d\u00e9finition : expliquons"},"content":{"rendered":"
\n
Retina et r\u00e9trocompatibilit\u00e9<\/h5>\n

Retina est aussi li\u00e9 \u00e0 un point : la r\u00e9trocompatibilit\u00e9. Apple, en passant en 960 x 640, a multipli\u00e9 la d\u00e9finition horizontale et la d\u00e9finition verticale par deux. L’avantage est un redimensionnement plus efficace des anciennes applications : il suffit d’utiliser quatre pixels au lieu d’un pour un affichage \u00ab propre \u00bb. Sans cette petite astuce, des calculs de redimensionnement sont n\u00e9cessaires, ce qui induit des calculs et un effet de flou qui n’est ici pas visible gr\u00e2ce \u00e0 la diagonale qui reste fixe.<\/p>\n<\/div>\n

\"Image<\/span><\/span><\/h4>\n<\/p>\n

Alors que l’iPad 2G est attendu dans les prochaines semaines, revenons sur un point : l’\u00e9cran \u00ab Retina \u00bb. Avec l’iPhone 4, Apple a introduit un terme marketing, le Retina<\/em>. La soci\u00e9t\u00e9 explique qu’avec le Retina<\/em>, on atteint les limites de l’oeil humain, avec l’impossibilit\u00e9 de diff\u00e9rencier deux pixels de couleurs proches sur l’\u00e9cran de l’iPhone 4. Comme l’appareil a un \u00e9cran de 3,5 pouces dot\u00e9 d’une r\u00e9solution de 330 ppp (960 x 540), beaucoup en ont conclu qu’un iPad Retina<\/em> devait travailler en 2 048 x 1 536, mais ce n’est absolument pas le cas. Expliquons.<\/p>\n<\/p>\n

Retina, c’est quoi ?<\/h4>\n<\/p>\n

Retina<\/em> est bas\u00e9 sur le fait que l’oeil humain a une limite physique. Typiquement, on consid\u00e8re qu’une personne avec une vue parfaite (20\/20) arrive \u00e0 diff\u00e9rencier deux pixels de couleurs proches s’ils sont distants d’un angle de plus d’un soixanti\u00e8me de degr\u00e9 (une minute). La notion d’angle est importante : si on prend la taille du pixel comme base pour un triangle isoc\u00e8le, l’angle oppos\u00e9 ne doit donc pas d\u00e9passer 0,016\u00b0. On en d\u00e9duit rapidement que la taille du pixel n\u00e9cessaire pour indiquer que l’\u00e9cran est Retina<\/em> est donc d\u00e9pendante de la distance entre l’oeil et ce pixel. Pour l’iPhone 4, Apple indique que l’\u00e9cran est Retina<\/em> avec une distance de 12 pouces (30 centim\u00e8tres) : \u00e0 partir de cette distance, il est donc impossible de diff\u00e9rencier deux pixels de couleurs proches. La nuance est importante, car si l’oeil n’arrive pas \u00e0 s\u00e9parer deux pixels dont les couleurs sont proches \u00e0 cette distance, il y arrivera si le contraste est \u00e9lev\u00e9. Un pixel blanc sur un fond noir restera visible.<\/p>\n<\/p>\n

Un iPad Retina ?<\/h4>\n<\/p>\n

Pour un iPad Retina<\/em>, pas besoin d’atteindre 300 ppp, donc : la distance entre l’oeil de l’utilisateur et l’appareil est plus grande qu’avec un t\u00e9l\u00e9phone. Empiriquement, on peut estimer que la distance pratique d’utilisation d’une tablette en g\u00e9n\u00e9ral est de 45 cm. \u00c0 cette distance, un \u00e9cran est Retina<\/em> d\u00e8s 205 ppp. Pour un iPad, dot\u00e9 d’un \u00e9cran de 9,7 pouces en format 4\/3, il faut travailler en 1 600 x 1 200 pour atteindre cette limite. Pour une tablette 10 pouces en 16\/9, le 1080p est un bon compromis, alors qu’un \u00e9cran de 7 pouces comme celui de beaucoup de tablettes est Retina<\/em> d\u00e8s le 720p.\u00a0<\/p>\n<\/p>\n

En faisant le calcul \u2014 nous vous passons les d\u00e9tails \u2014 on peut aussi calculer que la diff\u00e9rence entre un t\u00e9l\u00e9viseur dot\u00e9 d’une dalle HD Ready (720p) et un autre dot\u00e9 d’une dalle Full HD (1080p) se voit \u00e0 partir d’une diagonale de 32 pouces avec un recul de 2 m\u00e8tres. Au del\u00e0 de 2 m\u00e8tres ou en dessous de 32 pouces, la diff\u00e9rence n’est pas visible. <\/p>\n<\/p>\n

Notons aussi que la limite de l’oeil humain varie fortement entre les personnes. La minute d’arc est la valeur pour une personne \u00e0 la vue parfaite, dans la pratique c’est rarement le cas.\u00a0<\/p>\n<\/p>\n

Terminons avec un mot sur les smartphones Android : si la majorit\u00e9 des mod\u00e8les actuels ont un \u00e9cran de 4 pouces en 800 x 480, un passage en 1 024 x 576 serait id\u00e9al pour que la trame devienne invisible.<\/p>\n","protected":false},"excerpt":{"rendered":"

Alors que l'iPad 2G est attendu dans les prochaines semaines, revenons sur un point : l'\u00e9cran \u00ab Retina \u00bb. Avec l'iPhone 4, Apple a introduit un terme marketing, le Retina.<\/p>","protected":false},"author":36,"featured_media":178540,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"ep_exclude_from_search":false,"footnotes":""},"categories":[487,4080,4079],"tags":[],"hubs":[],"acf":{"post_show_excerpt":false,"post_source":{"title":"Tom's Hardware FR","url":"http:\/\/www.presence-pc.com\/","target":""}},"yoast_head":"\nRetina, distance et d\u00e9finition : expliquons<\/title>\n<meta name=\"description\" content=\"Alors que l'iPad 2G est attendu dans les prochaines semaines, revenons sur un point : l'\u00e9cran \u00ab Retina \u00bb. 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