JPEG Network Graphics
Un article de Wikipédia, l'encyclopédie libre.
| JPEG Network Graphic | |
.jng |
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image/x-png |
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Développé par : |
W3C |
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Type de format : |
format d'image matriciel Compression de données avec perte |
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Conteneur de fichiers : |
PNG |
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Extension du : |
MNG |
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Spécification : |
Format ouvert |
JPEG Network Graphics (JNG) est un format d'images numériques ouvert basé sur le PNG et utilisant la compression JPEG.
en cours de traduction depuis en.wikipedia.org
JNG a été comme une partie du format d'images animées MNG, mais il peut être utilisé comme un format a part entière. Comme le format PNG le format JNG peu comporter une couche de transparence (couche alpha). contrairement au PNG qui utilise une compression sans perte, le JNG utilise la compression JPEG avec perte.
JNG files embed an 8-bit or 12-bit JPEG datastream in order to store color data, and may embed another datastream (1, 2, 4, 8, 16 bit PNG, or 8 bit JPEG grayscale image) for transparency information. Actually, a JNG may contain two separate JPEG datastreams for color information (one eight-bit and one twelve-bit) to permit decoders that are unable to (or do not wish to) handle twelve-bit datastreams to display the eight-bit datastream instead, if one is present.
La spécification du format JNG version 1.0 est sortie le 31 janvier 2001 (initialement comme une part de la spécification du format MNG). Usually, all the applications supporting the MNG file format can handle JNG files, too. E.g., Konqueror has native MNG/JNG support, and MNG/JNG plugins are available for Opera, Internet Explorer, and Mozilla Firefox. The Mozilla Application Suite (and hence Netscape) originally supported MNG/JNG, but native support was removed in Mozilla 1.5a by developers and Mozilla has not supported the format since, despite requests from its users. Safari does not support MNG/JNG.
JNG enhances the capabilities of the JFIF format (the usual JPEG file format), by supporting transparency, two consecutive color streams (one 8 bit and the other 12 bit), and other useful PNG features like color correction, gamma correction, embedded color profiles, PNG style metadata, checksums, etc. The transparency information inside a JNG file (as an alpha channel) can be saved either in lossless PNG format, or in lossy JPEG format. This way, users can benefit from the power of JPEG compression while preserving lossless (PNG compressed) transparency information.
The chunk based structure of JNG files is essentially the same as that of PNG files, differing only in the slightly different signature and the use of different chunks.
| Name | Signature | |
|---|---|---|
| hexadécimal | ASCII + C0, C1 | |
| PNG | 89 50 4E 47 0D 0A 1A 0A | HTJ "PNG" CR LF SUB LF |
| MNG | 8A 4D 4E 47 0D 0A 1A 0A | VTS "MNG" CR LF SUB LF |
| JNG | 8B 4A 4E 47 0D 0A 1A 0A | PLD "JNG" CR LF SUB LF |
JNG n'a pas de type MIME enregistré, mais image/x-jng peut être utilisé.
