Note that to view the composite image properly your browser should be set to 100%, and if you wish to view the full res images at the bottom of the page you would probably need to download them as your browser or blogger may only show them up to a certain size, and without looking at them with every pixel visible you can't really make a true comparison. A quick look by me on blogger showed the 8K and 4K images at the same size and consequently, because the former was substantially scaled down in this respect, there is no apparent difference in detail! The composite image successfully makes the point as far as I'm concerned, however.
As I understand it, Ultra HD (UHD) exhibits resolutions of 3840 x 2160 (current full HD is 1920 x 1080), hence UHD is four times the resolution of full HD (we'll leave 720p out of the equation as it's not really of concern). It is also being referred to as 4K - it's not technically 4K as that terminology refers to an industry standard that has, appropriately enough, just over four thousand pixels in width (specifically 4096, with 2160 in height), but I guess UHD is fairly close thus the term 4K is being adopted to mean the same thing. From here on in, any reference I make to 4K or 8K is in the context of a home cinema environment.
There is debate regarding how much resolution is required to extract all of the detail out of a 35mm negative - until actual demonstrations have taken place this would be difficult to determine. Personally I suspect that many older films in particular will not significantly benefit from UHD or above on the size of screens that are used in most homes. I believe the average screen size in the UK is around 42". Where I think UHD will come into its own is when it's displayed on larger screens (perhaps the average size will continue to go up over coming years) and the source material is of exceptional quality, for example if it's taken from a high resolution digital source or IMAX film.
Personally I watch material on either a 100" (approx) projector screen or a 46" LED TV. I feel that HD material (mostly delivered via Blu-ray Disc) can look absolutely stunning on either, subjectively speaking of course, although I generally prefer the scale offered by the larger screen from a projector. If I'm watching DVDs I feel that they look okay on the TV, sometimes surprisingly good (although that's largely down to some incredible technology built into my Sony that improves standard definition over the way it looked on older generation sets), but on any larger scale it just doesn't cut it against HD. Like many serious home cinema fans and movie collectors nowadays, I prefer to see a film in the best available quality, both in terms of video and audio, and that must come from a Blu-ray rather than a DVD. I am quite excited to see what UHD or 4K can offer us in the home (it would roughly equate to what most cinemas currently offer from their projectors) but the following experiment was undertaken with as much objectivity as I could muster, at the very least to quell my own curiosity in a realistic manner.
What I've done below is to show a quarter section of an 8K (in home cinema terms - four times the resolution of UHD) 'source' (from a photograph I took myself) - the reason I used a quarter section is because the camera will not take the equivalent of 8K images, hence I've had to take a 10 megapixel image and consider a cropped area of it as 25% of 8K for the purposes of this experiment. This is followed by a quarter section (to maintain comparative consistency) of a UHD duplicate of that source. This I feel simulates the resolution of a UHD image when taken from a higher quality original and can be compared accordingly. I've then also taken a HD duplicate from the source to simulate how you might see the image on a Blu-ray Disc. Because there is now some debate regarding whether it's better to scan a negative or print in 4K in order to create a film for HD, or just create a HD master from the outset, I've also created a HD image from the '4K master'. I appreciate that this does not necessarily reflect how a moving film might be scanned in reality but at the moment it's the closest thing that I can use to make an estimated judgement in the comparison of resolutions. How this would look in the home would also depend greatly on equipment and screen size, as mentioned in the opening paragraph.
To summarise, and each of the following is an equivalent resolution only, the first shot simulates 25% of an 8K source, the second 25% of a 4K capture of that source, the third 25% of a 2K capture of that source, and the fourth is 25% of a 2K capture of the 4K version. I've then rescaled everything but the 8K back to the same overall dimensions in order to facilitate comparative analysis of the detail that remains. The full grabs are at the bottom of this article but for the sake of ease on the part of the reader I have encompassed a small section of each grab in this 600 x 600 panel to illustrate my points.
If anyone has any thoughts (or amendments) you're welcome to forward them to me, but either way I hope you've found this little analysis useful or at least mildly interesting.
Paul W J Martin
25% of '8K' source (compressed to JPEG for the purposes of uploading to the net):
25% of 'HD or 2K' scan of source:
25% of 'HD or 2K' scan or '4K master':