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''It is very helpful to adopt a convention for the display of images transferred via the FITS format. Many of the current image processing systems have converged upon such a convention. Therefore, we recommend that FITS writers order the pixels so that the first pixel in the FITS file (for each image plane) be the one that would be displayed in the lower-left corner (with the first axis increasing to the right and the second axis increasing upwards) by the imaging system of the FITS writer. This convention is clearly helpful in the absence of a description of the world coordinates. It does not preclude a program from looking at the axis descriptions and overriding this convention, or preclude the user from requesting a different display. This convention also does not excuse FITS writers from providing complete and correct descriptions of the image coordinates, allowing the user to determine the meaning of the image. The ordering of the image for display is simply a convention of convenience, whereas the coordinates of the pixels are part of the physics of the observation.'' | ''It is very helpful to adopt a convention for the display of images transferred via the FITS format. Many of the current image processing systems have converged upon such a convention. Therefore, we recommend that FITS writers order the pixels so that the first pixel in the FITS file (for each image plane) be the one that would be displayed in the lower-left corner (with the first axis increasing to the right and the second axis increasing upwards) by the imaging system of the FITS writer. This convention is clearly helpful in the absence of a description of the world coordinates. It does not preclude a program from looking at the axis descriptions and overriding this convention, or preclude the user from requesting a different display. This convention also does not excuse FITS writers from providing complete and correct descriptions of the image coordinates, allowing the user to determine the meaning of the image. The ordering of the image for display is simply a convention of convenience, whereas the coordinates of the pixels are part of the physics of the observation.'' | ||
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==Logiciels utilisant ce mot clé== | ==Logiciels utilisant ce mot clé== | ||
* Siril (depuis la version 1.0.0) | * Siril (depuis la version 1.0.0) | ||
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* FireCapture (depuis la version 2.7) | * FireCapture (depuis la version 2.7) | ||
* N.I.N.A (depuis la version 1.10) | * N.I.N.A (depuis la version 1.10) | ||
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Revision as of 19:13, 17 July 2020
Orientation des images FITS
La norme FITS est un conteneur qui décrit comment stocker les données et métadonnées de l'image. Des outils professionnels, dès les débuts du format FITS, comme ds9 (Harvard Smithsonian Center for Astrophysics), fv ( FITS viewer de la NASA), stockent les images de bas en haut. On pourrait être tenté de dire que cela n'a pas vraiment d'importance, mais lorsque le dématriçage ou l'astrométrie sont impliqués, des problèmes surviennent. Par exemple, le motif Bayer RGGB habituel devient GBRG si l'image est à l'envers.
De nos jours, malgré cela, la plupart des pilotes de caméra écrivent des données dans l'ordre descendant (de haut en bas) et nous devons y faire face.
Pour ces raisons, nous avons récemment introduit, avec P. Chevalley de CCDCiel, un nouveau mot clé FITS. Nous encourageons tous les producteurs de données, les développeurs INDI et ASCOM, à l'utiliser afin de faciliter les choses pour tout le monde.
Ce mot clé est ROWORDER de type TSTRING. Il peut prendre deux valeurs : BOTTOM-UP et TOP-DOWN.
Siril lira et affichera toujours les images dans l'ordre ascendant (de bas en haut), mais si l'information top-down est spécifiée dans le mot-clé, alors Siril dématricera l'image avec le motif de Bayer correspondant.
Pourquoi les logiciels écrivent d'ils les images de façon descendante ? La raison est la suivante : la logique mathématique.
Aussi, les spécifications du format FITS disent, en anglais :
5.1. Image display conventions It is very helpful to adopt a convention for the display of images transferred via the FITS format. Many of the current image processing systems have converged upon such a convention. Therefore, we recommend that FITS writers order the pixels so that the first pixel in the FITS file (for each image plane) be the one that would be displayed in the lower-left corner (with the first axis increasing to the right and the second axis increasing upwards) by the imaging system of the FITS writer. This convention is clearly helpful in the absence of a description of the world coordinates. It does not preclude a program from looking at the axis descriptions and overriding this convention, or preclude the user from requesting a different display. This convention also does not excuse FITS writers from providing complete and correct descriptions of the image coordinates, allowing the user to determine the meaning of the image. The ordering of the image for display is simply a convention of convenience, whereas the coordinates of the pixels are part of the physics of the observation.
Logiciels utilisant ce mot clé
- Siril (depuis la version 1.0.0)
- CCDCiel (depuis la version 0.9.72)
- Indi (depuis 2020)
- SharpCap (depuis la version 3.3)
- FireCapture (depuis la version 2.7)
- N.I.N.A (depuis la version 1.10)