The controversial and confusing topic of the pixel aspect ratio , discussed earlier in this blog, seems to keep to complicated.
In the new version of After Effects CS4, Adobe has changed the proportions of some of its settings in composition, since the sizes used during the nine previous versions of After Effects seems, according to Adobe's own admission, they were "slightly inaccurate" .
Now, if we work on PAL square pixels, we set the compositions in the following frame sizes:
- 4:3 square pixels (PAL D1/DV): 788 × 576 (formerly 768 × 576)
- 16:9 square pixels (PAL D1/DV): 1050 × 576 (previously 1024 x 576)
These proportions go to recalculate the dimensions of the box and reinterpret PAL analog to digital, taking into account the so-called "clean aperture", which is the name given to the overall size of the box counting PAL analog lines that do not carry picture information. According to recommendations of the BBC, which are those that have led to Adobe tiing a bit more with the theme, the calculations to arrive at these sizes would be:
- , aplicando una regla de tres lo deducimos: (576×4)/3=768 There is a measure which is always unchanged: an image 576 pixels PAL is always horizontal (digital equivalent of the 625 analog) 576 horizontal pixels in a 4:3 ratio, providing 768 vertical pixels by applying a rule of thumb we deduce: (576 × 4) / 3 = 768
- The TV pixels are not square but rectangular in PAR ratio of 1:1094, therefore: 768 / 1.094 = 702. That is, an image is actually analog PAL 702 × 576 rectangular pixels. ¿?
- Where are los18 missing pixels to 720 × 576 which we all use?. These 18 pixels are equivalent to the two side black bars (of 9 pixels each) that we always observed that digitized PAL video. This is called "clean aperture", ie including the full PAL image signal lines that carry picture information. , es decir exclusivamente las líneas que llevan información de imagen. Within this "clean aperture" or fully open, is the proportion of 702 × 576 pixels of which we spoke earlier, that is called "production aperture", ie only the lines that carry picture information. But digital should be used fully open and all its pixels, watching these 18 pixels as safety margins, or 720 pixels (702 +18) rectangular.
- One more thing, if those 18 pixels are rectangular what if they are converted to square pixels? Let's see them doing the reverse: 18 × 1.094 = 20. 20 square pixels, 768 pixels added to the square of which we set equal to 788 × 576. Here are the new dimensions that proposes Adobe After Effects.
- : (18 x 4)/ 3 = 24 pixels rectangulares que equivalen a 24 x 1,094 = 26 cuadrados . In a ratio of 16:9, those 18 pixels rectangular pixels are converted into 26 squares (18 x 4) / 3 = 24 equivalent rectangular pixels to 24 x 1.094 = 26 square. They added 26 pixels to 1024 pixels which had previously assumed PAL 16:9 gives us: 1024 +26 = 1050 × 576 square pixels, which are the correct dimensions to compose a digital image in 16:9 PAL square pixels! !
But many laps and marearnos with these conversions, it is true that we have to assume that the new box sizes proposed Adobe, taught by the BBC, are correct and in theory we should use so that the proportions of graphs and images appear properly when converting PAL.
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