Originally Posted by Joe Bloggs
Thanks trbarry & John. It can get quite complicated some of this.
Also, the fact that they usually scan film at 2K - does that mean we don't usually get the full 1920x1080 resolution (ie. all the frequencies) even if the way they filmed it would allow maximum res, and that to get the full 1920x1080 +all frequencies you'd have to scan at at least 2x that width & height (eg. 4K) because of Nquist?
Seems to me, for 1920X1080 you're always getting the full format resolution. It's just that for 'artistically' camera-filtered and selectively focused productions the higher frequencies/resolutions lack enough contrast to be clearly resolved; they merge into shades of gray (for luma or B&W). The Nyquist limitations of sampled signals (cameras, telecines/scans) limit this resolvability, too. By contrast, non-sampled signals, like 1920X1080 test patterns (computers, generators) do provide full resolvability; (discussed here
in more detail).
Downconversion to 1920X1080 from 2k or 4k tends to make images appear sharper because the contrast of lower and mid-range frequencies/resolutions are boosted. Pictures can thus appear sharp without offering significant fine detail. Figure 8 in an Arri pdf paper
contrasts the resolution-vs-contrast graphs of higher-resolution and 'sharper' camera images. Fig. 22 in this Arri paper shows how even with a 10k film scan, multiple stages of processing greatly reduces the final resolution (multiplication of the various MTFs).
Determining what resolutions survive onto home screens with 4k transfers/downconversions to Blu-ray , such as King Kong, seems to require spectrum analysis to distinguish between sharpness from boosted mid-range and perhaps slightly higher frequencies. For example, does it 'jump' from, say a 800--1000-line guesstimate for typical Blu-rays to only 1200? As the film-camera photos (Fig. 6) in the Arri paper show, sharpness created by the boosted contrast of coarse details can easily be misinterpreted as higher resolution. The author (below Fig. 6) draws an interesting evolution comparison involving monkeys. -- John