Blu-ray is 1080p, so why care about 4k scans?

[xxxJohnDrakexxx]

Blu-ray is 1080p. It does not support HDR. Whatever the scan used, it will still be encoded and displayed at 1080p. So if all of this is true, why is there this push for 4k scans on regular Blu-rays?

Mind you, I'm not talking about UHDs. UHDs are 4K and support HDR and wide gamut color. There the source is being encoded and displayed at 4K resolution, but a regular Blu-ray is still just 1080p, no matter how you slice it.

Is there really a difference between a clean 1080p/2k/4k source if the end result is encoded and displayed in 1080p?

[filmmusic]

A downscale to 1080p from a 4K scan is still better than that coming from a regular scan.

[dallywhitty]

Oversampling. A Blu-ray sourced from a 4K scan as opposed to a 2K scan will have a slightly better, more filmic appearance. I think.

Loldunno.

Somebody more knowledgeable will come along and explain it better but I reckon that's the gist of it. There is a benefit to using a 4K scan, just not a major one. There's future-proofing to consider as well, I guess. When a company announces they're performing a 4K restoration, you know it'll still be suitable when the next format comes along.

[chip75]

There's absolutely nothing wrong with 2K scans, we've had amazing results with them, but a 4K scan is generally preferable (it's always better to downscale than upscale), it makes restoration easier and it future proofs masters.

[xxxJohnDrakexxx]

Originally Posted by filmmusic

A downscale to 1080p from a 4K scan is still better than that coming from a regular scan.

I've heard this said, but has it actually ever been proven? Has there been a test with a 2k scan vs a 4k scan from the same source to 1080p that definitive proves it's better?

[42041]

The main benefit is that a 4K scan is almost certainly going to be done on a modern pin-registered scanner from the camera negative, as opposed to some janky old telecine and a lower-quality film source. But once you clear that hurdle, it doesn't really make a meaningful difference if the 1080p image is derived from a 2K or 4K DI.

[xxxJohnDrakexxx]

Originally Posted by chip75

but a 4K scan is generally preferable (it's always better to downscale than upscale)

But a 2K scan to 1080p is a downscale, not an upscale. 2,211,840 to 2,073,600 pixels.

[Bates_Motel]

Originally Posted by xxxJohnDrakexxx

I've heard this said, but has it actually ever been proven? Has there been a test with a 2k scan vs a 4k scan from the same source to 1080p that definitive proves it's better?

Yes, it has. Look at the films sourced from 4K masters and compare them to the 2K ones. Or any photo you take at a smaller then larger resolution.

It's also future-proofing.

[42041]

Originally Posted by Bates_Motel

Yes, it has. Look at the films sourced from 4K masters and compare them to the 2K ones.

I don't think there's anything you can conclusively determine from just that. Inglourious Basterds was a 2K DI, Django Unchained was a 4K DI, both blu-rays look stellar.

[chip75]

Originally Posted by xxxJohnDrakexxx

I've heard this said, but has it actually ever been proven? Has there been a test with a 2k scan vs a 4k scan from the same source to 1080p that definitive proves it's better?

You can do it yourself at home, pop something into your scanner and scan it at 150dpi then at 600dpi and scale the 600dpi image down to 150dpi. The results should be in the downscale's favour. Restoration is easier too, as they have more pixels to work with.

Most BD's 1080p video is actually blown-up slightly from the extracted image from a 2K scan. So whilst 2K has a higher resolution than 1080p, the 1080p image is roughly blown-up 10% from the 2048 x 1566 image (depending on the equipment used to shoot the movie or show).

[chip75]

Originally Posted by xxxJohnDrakexxx

But a 2K scan to 1080p is a downscale, not an upscale. 2,211,840 to 2,073,600 pixels.

The image on a BD is usually blown-up from the extracted area, so most BDs are upscaled about 10%. So it's slightly upscaled.

[Bates_Motel]

Originally Posted by 42041

I don't think there's anything you can conclusively determine from just that. Inglourious Basterds was a 2K DI, Django Unchained was a 4K DI, both blu-rays look stellar.

Obviously I mean the ones that have both version out, like Spider-Man and Glory. You can see differences between the 2K and 4K discs.

[Opips3]

Originally Posted by 42041

I don't think there's anything you can conclusively determine from just that. Inglourious Basterds was a 2K DI, Django Unchained was a 4K DI, both blu-rays look stellar.

Thank you much...Awesome!
I'll put Django Unchained was a 4K DI on list for 4K UltraHD.

[42041]

Originally Posted by Bates_Motel

I mean the ones that have both version out, like Spider-Man and Glory.

But that's what I'm saying - there's a huge difference between scanning camera negative on a scanner meant for post-production quality scanning, vs scanning interpositive on a machine meant to rapidly make home video masters. That's 99% of the quality difference you're seeing. If a 2K master is made to the same quality standard (like most new movies) it will not look meaningfully different from a 4K one on BD.

[joie]

Originally Posted by xxxJohnDrakexxx

But a 2K scan to 1080p is a downscale, not an upscale. 2,211,840 to 2,073,600 pixels.

Not necessarily, if they lop some pixels off the sides. 2048-1920=128, so chop 64 pixels off each side. UHD is also not 4096: 4096-3840=256, so chop 128 off each side.

[Bates_Motel]

Originally Posted by 42041

But that's what I'm saying - there's a huge difference between scanning camera negative on a scanner meant for post-production quality scanning, vs scanning interpositive on a machine meant to rapidly make home video masters. That's 99% of the quality difference you're seeing.

Same difference when it comes to scanning, as long as the source is good. And in my years as a photographer, cinematographer and editor, it always looks better to shoot large and RAW then downsize.

4K VS HD: Side By Side Comparisons (Part 3) (Using Same Camera) - YouTube

[c1nn1c]

Just like music, the better the source, the better the downconversion. Film preservation also plays a big part in it, especially if restoration work is needed.

[42041]

Originally Posted by Bates_Motel

Same difference when it comes to scanning, as long as the source is good.

4K VS HD: Side By Side Comparisons (Part 3) (Using Same Camera) - YouTube

The particulars of how that camera works has nothing to do with the question at hand.
The bottom line here is that I don't think anyone can reliably tell which modern DI-based movies (which is to say assuming a top quality 2K source) come from 2K masters (like the vast majority of big-budget blockbusters) and which come from 4K ones. I'm sure there is a difference, but there are much bigger factors.

[xxxJohnDrakexxx]

Originally Posted by Bates_Motel

4K VS HD: Side By Side Comparisons (Part 3) (Using Same Camera) - YouTube

The camera shoots 4k at 100Mbps vs 1080p at 24 Mbps using different codecs. Of course the output will look different.

[spectre08]

the main advantage to downscaling a 4K source into 2K vs capturing in 2K is sharpness.

You will simply get a sharper image with better defined edges without the artifacts that come from trying to sharpen an image after capture.

Another factor when scanning film is that film is not an orderly matrixed medium like a digital sensor is. It's made up of many photochemical receptors that are roughly round, and randomly distributed throughout the substrate. Different colors are also different sized.

When you scan film at 2K a larger portion of those receptors will overlap multple photo receptors in the sensor, and if multiple appear in the same receptor the sensor has to estimate what color to detect.

If you increase the density of the digital sensor you minimize the amount of overlap.

This is the biggest source of why 4K scans look more "film-like" than 2K. Because you're actually capturing the disorderly variations in the film more accurately.