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Recueil cinématographique

10 bit, HDTV - 16/9 | 31 octobre 2009

10 bit, HDTV (...

1024 niveaux.

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10 bits (...

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10.2 Gbits/s (...

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10-BIT Lin (Conversion Analogique-Numérique)

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Anglais :

A type of digital sampling of analog images that creates 10-bit (210, 1024 possible levels) numbers to describe the post gamma corrected analog brightness levels of an image. Lin, short for ‘linear’ means the levels are assigned equally to the levels of the post gamma corrected analog signal they describe. So an LSB change describes the same change in level if it is in a bright area or a dark area of the picture. Most professional HD and some SD television is sampled this way according to ITU-R BT.601 and 709. 10-bit lin sampling allows good quality to be maintained through TV production and post production where the processes can make particular demands outside the range of normal viewing, and so produce good results for viewers. However if color grading is required then the useful wide dynamic range that can be described by 10-bit log would be preferable.

10-BIT Log (...

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Anglais :

This usually refers to a 10-bit sampling system that maps analog values logarithmically rather than linearly. It is widely used when scanning film images which are themselves a logarithmic representation of the film’s exposure. This form of sampling is now available directly from some digital cinematography cameras.

The 10-bit data can describe 210 or 1024 discrete numbers, or levels: 0-1023 for each of the red, blue and green (RGB) planes of an image. However, as all electronic light sensors have a linear response and so produce an output directly proportional to the light they see, when scanning film they represent the transmittance of the film. Usually it is negative film that is scanned and this means a large portion of the numbers generated describe the scene’s black and dark areas (representing bright areas of the original scene), and too few are left for the light areas (dark scene) where ‘banding’ could be a problem – especially after digital processing such as grading and color correction. Transforming the numbers into log (by use of a LUT) gives a better distribution of the digital detail between dark and light areas and, being better matched to the eyes’ response, offers good rendition over the whole brightness range without having to use more bits. A minimum of 13-bits linear sampling converted to 10-bit log sampling means sufficient detail in the pictures is stored to allow headroom for downstream grading that is common in film production.

10-bit log is the basis for sampling in the Cineon and SMPTE DPX formats that are widely used in the post production and DI industries.

12 bit, Cinéma (Cinéma - Mode)

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13,5MHz (Codage vidéo Numérique - SD)

Fréquence d'échantillonnage utilisée pour le codage numérique 601 de la vidéo SD.

Cette valeur étant un multiple des fréquences des systèmes de télévision à 525 et 625 lignes,
elle permet un certain niveau de compatibilité entre les systèmes numériques.

La vitesse d'échantillonnage est telle que les informations de luminance les plus détaillées présentes dans les images en SD sont fidèlement reproduites, même à la fréquence la plus élevée (5,5 MHz).

Pour la plupart des normes HD, l'échantillonnage numérique de la luminance s'effectue à 74,25 MHz,
soit 13,5 MHz multipliés par 5,5.

Anglais :

This is the sampling frequency of luminance in SD digital television. It is represented by the 4 in 4:2:2. The use of the number 4 is pure nostalgia as 13.5 MHz is in the region of 14.3 MHz, the sampling rate of 4 x NTSC color subcarrier (3.58 MHz), used at the very genesis of digital television equipment.

Reasons for the choice of 13.5 MHz belong to politics, physics and legacy. Politically it had to be global and work for both 525/60 (NTSC) and 625/50 (PAL) systems. The physics is the easy part; it had to be significantly above the Nyquist frequency so that the highest luminance frequency, 5.5 MHz for 625-line PAL systems, could be faithfully reproduced from the sampled digits – i.e. sampling in excess of 11 MHz - but not so high as to produce unnecessary, wasteful amounts of data. Some math is required to understand the legacy.

The sampling frequency had to produce a static pattern on both 525 and 625-line standards, otherwise it would be very complicated to handle and, possibly, restrictive in use. In other words, the frequency must be a whole multiple of the lines speeds of both standards.

The line frequency of the 625/50 system is simply 625 x 25 = 15,625 Hz

(NB 50 fields/s makes 25 frames/s)

So line length is 1/15,625 = 0.000064 or 64μs

The line frequency of the 525/60 NTSC system is complicated by the need to offset it by a factor of 1000/1001 to avoid interference when transmitted. The line frequency is 525 x 30 x 1000/1001 = 15,734.265 Hz. This makes line length 1/15,734.265 = 63.5555μs

The difference between the two line lengths is 64 – 63.55555 = 0.4444μs

This time divides into 64μs exactly 144 times, and into 63.5555μs exactly 143 times. This means the lowest common frequency that would create a static pattern on both standards is 1/0.4444 MHz, or 2.25 MHz.

Now, back to the physics. The sampling frequency has to be well above 11 MHz, so 11.25 MHz (5 x 2.25) is not enough. 6 x 2.25 gives the sampling frequency that has been adopted – 13.5 MHz.

Similar arguments have been applied to the derivation of sampling for HD. Here 74.25 MHz (33 x 2.25) is used.

14:9 (Format d'image vidéo)

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Anglais :

A picture aspect ratio that has been used as a preferred way to present 16:9 images on 4:3 screens. It avoids showing larger areas of black above and below letterboxed pictures but does include more of the 16:9 image than 4:3. It is commonly used for analog transmissions that are derived from 16:9 digital services.

15:1s (Informatique – compression)

Résolution Avid (Off Line) Non diffusable "s" = simple trame (1 image/2)

16 bits (Numérique - Son - Résolution)

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16 mm (Format cinéma – pellicule)

Format cinéma de pellicule : largeur 16mm.

Encore très présent chez les réalisateurs amateurs,
il tombe en désuétude dans le milieu professionnel.

16/9 (Vidéo - format)

Ce format, plus large que le traditionnel 4/3, se rapproche du CinémaScope.

16/9 = 1.77

Chaque ligne d'un signal vidéo 16/9 transmet une plus grande quantité d'informations visuelles.

Le téléviseur 16/9 reconnaît automatiquement l'émission d'un tel signal et commute en conséquence.

720x432 (Letterbox)
960x576 (SD Pal)
1280x720 (HD)1920x1080 (HD)

Anglais :

Picture aspect ratio used for HDTV and some SDTV (usually digital).