Blu ray resolution and 4K or 8K transfers

[Canada]

Being in this site for a long time I should know better so please forgive my ignorance. Why do Blu ray's taken from a 4 or 8K master look better than say taking it from a 2K one, when the max resolution of a Blu ray is 1920 x 1080?

PS: Mods feel free to move this post if it should be in another area.

[42041]

Originally Posted by Canada

Being in this site for a long time I should know better so please forgive my ignorance. Why do Blu ray's taken from a 4 or 8K master look better than say taking it from a 2K one, when the max resolution of a Blu ray is 1920 x 1080?

PS: Mods feel free to move this post if it should be in another area.

http://en.wikipedia.org/wiki/Oversampling
http://en.wikipedia.org/wiki/Nyquist...mpling_theorem

basically, to accurately convert analog to digital you need to sample at at least twice the frequency of your signal.

[Canada]

Originally Posted by 42041

http://en.wikipedia.org/wiki/Oversampling
http://en.wikipedia.org/wiki/Nyquist...mpling_theorem

basically, to accurately convert analog to digital you need to sample at at least twice the frequency of your signal.

For once I wish I had taken advanced algebra.

[KubrickFan]

Originally Posted by Canada

Being in this site for a long time I should know better so please forgive my ignorance. Why do Blu ray's taken from a 4 or 8K master look better than say taking it from a 2K one, when the max resolution of a Blu ray is 1920 x 1080?

PS: Mods feel free to move this post if it should be in another area.

You can really tell whether a Blu-ray is sourced from a 2K or 4K source? Just curious.

[Canada]

Originally Posted by KubrickFan

You can really tell whether a Blu-ray is sourced from a 2K or 4K source? Just curious.

No I can't but almost every one on the forum will agree with me the IMAX sequences in The Dark Knight look better than than the ones shot on regular film stock, and Baraka is one of the best looking Blu ray's out, it was the first Blu ray to be sourced from an 8k negative.

[KubrickFan]

Those were also shot on large stock film, I think the difference in quality has more to do with that than anything else.

[42041]

Originally Posted by Canada

No I can't but almost every one on the forum will agree with me the IMAX sequences in The Dark Knight look better than than the ones shot on regular film stock, and Baraka is one of the best looking Blu ray's out, it was the first Blu ray to be sourced from an 8k negative.

Baraka is a 70mm film, and obviously the Dark Knight IMAX sequences are IMAX film. The big negative has more to do with the quality than the scan resolution (bigger film = finer grain, more detail).
http://static.howstuffworks.com/gif/imax-film.gif

[42041]

Originally Posted by KubrickFan

You can really tell whether a Blu-ray is sourced from a 2K or 4K source? Just curious.

I rarely know what a blu-ray is sourced from. Criterion does give you such information and IMO the 4K transfers they've put out have a distinct quality advantage, though that's also indicative of better care all around.

[Penton-Man]

Originally Posted by KubrickFan

You can really tell whether a Blu-ray is sourced from a 2K or 4K source? Just curious.

Rather easily if you watch 2K vs 4K sourced Blu-ray samples in a split screen or side-by-side evaluation while seated at the proper viewing distance….with the caveat that the principal photography wasn’t out-of-focus or moderately or heavily filtered in-camera to begin with.

As those with discerning eyes will notice (even on a typical consumer-sized properly calibrated HD flat panel) that a 4K sourced Blu-ray will be sharper than a 2K sourced Blu-ray (unless the later is cropped to compensate for going 2048 ->1920). The reason being that downsampling digital filters are based on algorithms and those filters don’t do that great with tiny fractions (ratios, i.e. 2048 ->1920). Experience has shown that the best solution is to 4K scan and then down-rez directly to Blu-Ray resolution (1920) as the algorithms cope much better that way (the picture isn’t as fuzzy as going 2048 ->1920).

Also, the digital tools for color correction work much better (i.e. are more precise) at 4K rather than with 2K proxies, something which has an additive transferable visual effect downstream to the HD masters and Blu-ray.

[Anthony P]

Originally Posted by Canada

For once I wish I had taken advanced algebra.

You don't really need advanced algebra for the why. In the end the video gets compressed the hell out of it and so more data helps determine how to compress it better (i.e. get rid of the less important data while keeping the more important data).

Let me give a couple of simple examples.

1) is something that looks like "stairs" in 2k stairs or a diagonal line that was limited by resolution. If it was a diagonal line (or smaller steps in the stairs) then it is a lot less important to keep the steps as they are when compressing, on the other hand if they are the same at 4k then they are actual steps and more important to keep them correct.

2) Now let's assume there is a place where there is a straight line between two colours. since a block is an array of 8x8 pixels

OOOOOOOOOOOOOO
OOOOOOOOOOOOOO
OOOOOOOOOOOOOO

if @ 4k you get
IIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIthen it is better to treat it as 8 x red & 6 x blue and compress it as a red block
i.e.
OOOOOOOOOOOOOO
IIIIIIIIIIIIIIIIIIIIIIIIIIII
OOOOOOOOOOOOOO
and it is not any more incorrect then the 2k scan


but if it is

IIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIthen it is better to treat it as 6 x red & 8 x blue and compress it as a blue block on the left

i.e.
OOOOOOOOOOOOOO
IIIIIIIIIIIIIIIIIIIIIIIIIIII
OOOOOOOOOOOOOO

Now imagine if all you had was the 2k scan, how will you determine if it is better to go with a red block or a blue one?



And in reality it gets more complicated, such as how does the scanner work (right in the example above it assumed the combined pixel got one of the colours, but they could have ended up magenta or something.

Will the result necessarily be different? better? No, but chances are that it will be.