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Topic: Which Movies Have Been Released in 4K?
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Bobby Henderson
"Ask me about Trajan."
Posts: 10973
From: Lawton, OK, USA
Registered: Apr 2001
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posted 06-13-2008 10:20 PM
I don't know where you're drawing that conclusion. You might want to check this passage on Page 6 of that document which points out a major disadvantage of digital cameras versus film:
quote:
In that case, though, the test rasters should flow not only horizontally and vertically, but also diagonally, and, ideally, circularly. The pixel alignment on the digital camera sensor (bayer pattern) is rectangular in rows and columns. This allows good reproduction of details which lie in the exact same direction, but not of diagonal structures, or other details which deviate from the vertical or horizontal. This plays no role in film, because the “sensor elements” – film grain – are distributed randomly and react equally well or badly in all directions.
Arri showed performance examples of how film recorded test patterns and then how well those patterns were reproduced in various resolutions.
Aliasing is a major problem with low resolution scans of imagery with repeating patterns and patterns that progressively tighten (what Arri calls a "frequency sweep"). They show pretty well how a 3K native scan has more problems with aliasing than a scan originally done at 6K.
Anyone doing graphics work with film or flatbed scanners deals with similar problems on occasion. Someone will bring in a photo from a printed article because that's the only piece of art he has for the job. You can't just scan something like that in a typical manner otherwise your image gets infected with moiré patterns. The printing halftone screens in the image wind up clashing with the pixel grid and create unwanted patterns. You have to scan at much higher resolutions. If you can't do that then you have to use tricks like rotating the image on the scanning glass in 15 degree increments. Anyway, this is all getting off topic from the original point of the thread. There's no debating the higher quality merits of using 4K work flow than the usual 2K thing.
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Bobby Henderson
"Ask me about Trajan."
Posts: 10973
From: Lawton, OK, USA
Registered: Apr 2001
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posted 06-13-2008 11:51 PM
That's taking into account the usual case scenario where generational loss occurs in the 35mm release print making process. The same article offered this passage:
quote:
“An analog copy is always worse than the original.” This is an often-repeated assertation. But it is true only to a certain extent in the classical postproduction process; there are in fact quality-determining parameters that, if controlled carefully enough, can ensure that the level of quality is maintained: when photometric requirements are upheld throughout the chain of image capture, creating the intermediates and printing, the desired brightness and color information can be preserved for all intents and purposes.
The topics of generational loss on print making are irrelevant when considering the 2K versus 4K question on digital cinema. The argument narrows down to whether 2K is good enough to show the detail of a 35mm image, even something shot in Super35.
Arri's paper claims to see 4153 X 3112 pixels of worth spatial detail from a test pattern on a Super35 frame. General rule of thumb is to scan 150% above that as a hedge against aliasing. 6K scan and reductions to 4K for digital intermediate would seem worthwhile. The visual examples they provide on the following pages seem to back up the point pretty well.
I also found this passage on page 19 interesting:
quote:
The MTF of a 35 mm negative scanned with 4k contains only little more than 56 lp/mm (the equivalent of 3k with the image width of Super 35 mm) usable modulation.
The resolution limit is defined by the spatial frequency which is still transferred with 10% modulation. This result computes from the multiplication of the modulation of the scanner and of the film material for 57 lp/mm:
MTF_4k_scanner (57 lp/mm) × MTF_exposed_film (57 lp/mm) =
MTF_in_4k_scan (57 lp/mm)
36% × 28% = 10.08%
By the way – the same goes for a digital camera with a 4k chip: There, a low pass filter (actually a deliberate defocussing) must take care of pushing down modulation at half of the sampling frequency (80 lp/mm) to 0, because otherwise aliasing artefacts would show up.
Ultimately : neither a 4k scan nor a (3-chip) 4k camera sensor can really transfer resolution up to 4k.
This is a not an easily digestible paradigm. It basically means that 4k data only contains 4k information if they were created pixel by pixel on a computer – without creating an optical image beforehand.
Of course, this cannot be the solution, since we would then in the future have to make do with animation movies only. A scenario where actors and their affairs could only be created on the computer. A tragic loss, not just for the yellow press!
Kinda shoots a hole through the merits of 4K digital video cameras being equal to that of 35mm. Maybe 6K ought to be the real target for all digital based movie making.
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