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4K vs 2K - 8mm film transfer
Hearing from customers "do you transfer in 4K?" is what inspired me to write this highly academic blog. It is a blog that's worthy of a closer read if you are adamant about getting an 8 mm 4K film transfer. It might also be enjoyable if you like reading very geeky film stuff.
Let's first establish how much detail 8 mm film grain can hold and also cover some of the 2K vs 4K technical aspects (camera limitations and transfer workflow considerations.) Further, let's explore if offering upscaling from 2K to 4K is something FilmFix should consider.
Due to its very small size, 8 mm film is physically not able to hold more detail than 2K holds. So by going with 4K and hoping to get more details, the only thing you get is more detailed grain -- not a better image. Let's keep in mind though, it's a different story for the larger format films of 16 mm and 35 mm film.
In the image below the red rectangle represents a section captured during a transfer. A 2K transfer has a frame ratio of 16 to 9 and has 1920 by 1080 pixels.
Now, let us calculate the DPI (Dots Per Inch) of that section. This way we can check if with 2K we are above the granular detail the film can hold.
The first generation of 8 mm film (aka Normal 8 or Double 8) has a very small image.
We'll base our DPI calculation on the height of that red frame. The reason for that is because it is where we hit the limit of the frame. Zooming in (or out) will either crop parts of the image, or show parts of the top and bottom frame; both of which we want to avoid.
A Transfer Setup Note: We need to fine-tune the framing to obtain a proper framing prior to transferring a reel. So at the start of every new reel, the height is adjusted to match the height of the frame. The position can vary, because the exact positioning of the camera's pull-down claw can vary, also film shrinkage affects positioning.
Back to the math part: For a 2K transfer the formula is 1080 pixel / 0.130 inches, which results in approximately 8,300 DPI. The results show a 2K transfer holds over 2 times more information than what 8 mm film holds.
Now with Super-8 film we have a bit bigger frame to work from than with 8mm. This will result in bit better image, but let us check if 2K can hold it.
The second generation of 8 mm film is Super-8 film, and has a bit larger frame.
There the math is as follows: 1080 pixel / 0.158 inches results in an approximate 6,800 DPI. We are still well above 4,000 DPI.
The upshot is that 2K is absolutely adequate and 4K will not bring more detail.
In the old days of HD film transfer, we used to say 8 mm can only hold about a 720p resolution. 720p is the smaller of the two HD formats. This is why the very first professional film flash scanners where equipped with a 720p camera. It was only later that manufacturers started offering 2K transfer systems.
So let's check to see if 720p can hold the image.
The math for a 720p transfer is 720 pixels / 0.130 inches results in an approximate 5,500 DPI for 8 mm film, and an approximately 4,500 DPI for Super-8 film.
Super-8 film at 720 is starting to reach its limit but is still within what is considered acceptable. And the reason some transfer houses transfer all their film at 720p is because it allows for more productivity; they transfer it all at high speed. After that they upscale it to 2K and you never know about their trick. We don't do it that way. We capture in 2K from the outset.
(Important side note: a "Wolverine", or "Reflecta", is not a Professional Film Transfer System but a lower-end consumer transfer unit. The file it records is a highly compressed 8-bit MP4 file. Size: 1920 by 1080, but that is just the frame size. It's what is put into the file (an empty vessel) that counts. The quality of that stored image is what counts, not the pixel count of the frame. That's a different topic for another post.)
4K Monitors and UHD TVs
Over the years, monitors keep growing in size. These days Netflix requires all shows to be shot in 4K. In order for you to see that higher 4K resolution, you need a 4K monitor and need to pay Netflix extra for that better image quality.
Once these monitors found their way into our living rooms, naturally our customers started inquiring about 4K transfers.
A long time back I did some 4K camera research, and just for curiosity sake, I started looking to see what is out there. Things change quickly ... while people's film, in storage, continues to deteriorate.
4K Cameras with a CCD sensor
Researching the topic, I found I would lose the extended color depth of 10-bit if I used a 4K prosumer camera. They usually only offer 8-bit color depth if the sensor is a CCD sensor. This is not good! I know that this would not work for me, because I heavily rely on the 10-bits of color-depth during the color grading process, which I do by hand. 10 bits is critical to improve the color and exposure issues of strongly discolored film.
The above 4K camera offers 10-bit, but only when using a highly compressed 50Mbps file format, which does not yield a favorable image. Besides that, its sensor is a CMOS sensor, not a CCD sensor. What is required for a flash scanner like we use, is at least a CCD sensor or better yet a 3-CCD sensor, like ours.
I continued researching and found myself looking into $28,000 - $35,000 cameras that have some interesting 4K capabilities, but they would not permit me to perform the workflow I need with my transfers.
In short they capture 4K at 10-bit, but with the added steps in workflow, I would need to charge over 4 times what I am currently charging for a transfer and that would be just to capture the initial footage. All the tasks after the capture would also be much more time intensive on the computers, because jumping from 2K to 4K is not a doubling of the data but quadrupling. And with that, all the remaining processing and copying of data would take 4 times longer.
Video Newscasters Upscale 2K to 4K
Later, I found myself reading about what some professional newscasters do.
It was in one of their forums where I learned that still today a lot of them are shooting in 2K and end up upscaling the footage they shot in 2K to 4K, for the broadcast stations that require all footage to be delivered to them in 4K. And this is what brought me to a FULL STOP.
Upscaling! I have a lot of experience with upscaling.
I've offered upscaling of video tape transfers to bring SD (Standard Definition) to Full-HD for years now. And, going from 2K to 4K is just as possible and an easier process, because there is no de-interlacing requirement when processing two progressive images.
Upscaling 2K to 4K doubles the image pixel count in both height and width.
I found myself reevaluating each and every step of my transfer process as I described here on our website From RAW to FINAL. And sure enough ... I found a instance where I could conceivably justify a 4K up-scaling.
When is it best to upscale to 4K?
You'll probably notice that this topic is a bit academic but nonetheless worthy of a closer look.
It is during the image stabilization process where the image's grain gets seriously remapped and when an upscaling might be beneficial to retain some of that very fine grain structure.
The reason for that "remapping" is that during the image stabilization process, the image gets enlarged by 4% while zooming in, from 100% to 104%. Later that enlarged image's border gets cropped off back to 100%. To finalize the image stabilization process a very light sharpening is required to retain the grain's sharpness.
From that, one can conclude, the best time to upscale is at the same time the image stabilization step happens.
In order to test this idea, I produced two clips and set them side by side.
How the 4K vs 2K images stabilization sample was made
The difference between the two sides is that for the 4K side the image stabilization was performed within a 4K project — whereas for the 2K side the image stabilization was performed outside the 4K project — so within a separate 2K project. These are the steps in detail:
I created 4K project and imported 2K clip that gets automatically upscaled to fill out the larger 4K frame. Then, I applied the image stabilization to it and did some light sharpening.
In a separate 2K project, I performed the image stabilization and light sharpening. Later, I opened the above 4K project and imported that already pre-processed 2K image stabilized clip. I then upscaled the 2K project and placed the 4K and 2K side by side, as seen below.
A side by side 4K / 2K composite is a large 611 MB file -- the file is a 4K resolution size (3840 width by 2160 height). Note that the quality of very fine grain can really only be judged in a video clip that is being played back in real-time. A still image does not work very well for this.
Click and zoom in to see the image in full 1:1 pixel display. Note that these large frames show the grain 2× larger, so the grain gets 2× bigger which makes the grain look splotchy. You may notice that the 4K image looks a tad less cloudy.
When viewing the side-by-side clip below you'll see how much of the fine grain structure gets lost during the image stabilization process, when that step is not performed within a 4K project. It turns out it's minimal loss, nonetheless still noticeable when in motion.
How can I assess the difference without a 4K monitor?
It's only possible to discern the difference of this sample by viewing it on a 4K monitor. Since most people don't have access to a 4K monitor at their desktop computer, I decided to provide you with a link to the file (below) so that you can download it onto a USB stick. If you have access to a 4K monitor in your living room, this will be the ideal place to compare the two transfers.
If the only access you have is your computer's monitor, here is a 1920 x 1080 frame outtake of the 4K file. It's the red rectangle seen in the image below. You can play this clip on your desktop to compare the difference in grain. The grain is the same as what you'd see on your 4K monitor.
The sample below is only a zoomed in close-up portion of what you will see on your screen. The final transfer will not look like this. However, this will give you an idea of a 4K transfer as compared to a 2K. The 4K does bring more crisp edges but it adds substantial blotches of grain patches in motion. I looks busier and is distracting.
Red section is cropped to 1920 x 1080 size for viewing on a desktop monitor.
Download MP4 Sample
To download donut-hole, zoomed in 2K section, of the 4K sample, click here. It's 303 MB, so it will take time to download.
To download the full size 4K sample clip, click here. (611 MB file)
These sample clips have been encoded using the new "High Efficiency Video Codec" aka H.265 codec. Some older players may not be able to play back this type of mp4.
Considerations and Conclusion
If you have 8 mm film, we don't recommend that you get a 4K transfer.
1 - The benefit of getting a transfer in 4K is not very noticeable. Only a trained eye may see a difference, and it costs 2 times our regular price.
2 - If you will be considering our image enhancement option of grain reduction, or 'debris removal' as we now refer to it, you do not want a 4K transfer. Since with a 4K transfer you are after the grain, we would not apply any grain reduction to the file.
3 - If you're going to want to share this large file, first it needs to be highly compressed. It is in that compression you will lose all the benefit of the grain captured in a 4K transfer.
4 - If you want to be mindful of your carbon footprint, this is not a good choice. It takes a tremendous amount of electricity to process these very large files.
Conclusion: A 4K transfer will not benefit the image captured from 8mm film. The finest grain may look a bit sharper, but for reasons explained in detail above it's not beneficial.
Still, if you insist on having a 4K file we can do it - at a premium price.
We would capture in 2K (RAW Lossless instead of using the HQX SuperFine codec) and import that file into a 4K project. There is where all the color grading and image stabilization work would be performed. This 4K transfer varies from our usual processing explained in our step by step breakdown of our transfer process: From RAW to FINAL.
Author: Nathaniel Courtens Tuesday, August 4, 2020