5K compression vs 4K compression

[Mark Phelan]

So I had a thought today about file sizes and their relationship to one another. Say I want to output 1080p, 16:9. What is the better route, 5KHD with a higher compression rate or 4KHD with a lower rate? I'm thinking of two things here, one, which is going to provide the better quality and two, which would provide the smaller file size?

All things being somewhat equal, would a higher resolution image that was compressed greater be better than a lower resolution image with less compression? Reason why I'm asking is file management. If I'm out in the woods somewhere with a limited amount of storage space, which gives the best image for the file space available? Is this making any sense whatsoever?

[Keith Putnam]

You're really looking at two separate issues here: scaling and compression.

Scaling 5K to 1080 will produce a nicer result than doing so from 4K.

Once you have your 1080 video file, then you can choose a compression scheme that produces a result you like and a file format (and file size) you need.

[Blair S. Paulsen]

As a general rule there are more efficiencies available when compressing larger images, based on a file size to image size metric. If I had no time for testing and had to pick one, I'd go for the 5K at higher compression. That said, if the finish is 1080 you may get a better result from the 4KHD (3840 by 2160) format scaled to 1080.

It will be interesting to test such theory once we have the Epics in hand and can experiment. One thing I can swear to is that you do not want to shoot 2K for 1080 finish just to save storage space, the results are usually disappointing. YMMV.

Cheers - #19

[David Mullen ASC]

Personally, if all this is just going to be finished to 10-bit 1080P and broadcast in 1080i/720P, or end up in blu-ray.... you are going to get great results either way, shooting in 4K or 5K. I'd probably just stick to 4K HD (3840 x 2160) for a 1080P finish, 5K is probably overkill unless you have a lot of frame repositioning to do.

[Jeff Kilgroe]

There really isn't a "5KHD" format. The 4KHD format is the same as quad-HD or 3840x2160. Epic will shoot that that the same as the RED One, but will do it at lower compression ratios if you would like and Epic also records 16bit RAW too.

If you're finishing to 1080p, then anything at 4KHD and over is going to look amazing in terms of captured resolution. However, there's still the question of framing and field of view. Assuming you want to maintain the 16:9 aspect ratio of HD, the RED One also shoots 4096x2304. The largest 16:9 space you can record on Epic is 4800x2700, as the sensor is 1.89:1 and not 16:9 native, so it crops the sides of the sensor to get to the 16:9 aspect.

Not only do the larger formats capture more detail to oversample from, but they capture a larger image area and field of view.

As always test, test and test! Find the solution that fits the needs of you and your project. 4KHD is probably my most-used mode on the RED One. But I also can't wait to shoot 4800x2700 and 5120x2700 on Epic-X!!! I'm sure I will shoot plenty of 4KHD on Epic too. As that will match up with 4KHD footage on the RED One and on many productions there will be Epic and RED shooting simultaneously.

EDIT> Forgot to address the compression issues. For that we don't know just yet and that falls back to the testing. The way Epic works is the compression is expressed as a ratio, such as 5:1, 10:1, etc.. There are reasons to shoot with higher compression on the larger format, obviously -- to help conserve media space while shooting and after being the primary. 10:1 compression is the equivalent to REDCODE 28 on the RED One with REDCODE 42 being about 7.5:1.

[Mark Phelan]

You're really looking at two separate issues here: scaling and compression.

Scaling 5K to 1080 will produce a nicer result than doing so from 4K.

Once you have your 1080 video file, then you can choose a compression scheme that produces a result you like and a file format (and file size) you need.

I really do appreciate everyone's thoughts on this.

Keith, I was talking about compression in camera, not afterwards, it sounds like you were suggesting something for post. But I'm still wondering what we will find, is 5K at 4800x2700 better than 4KHD at 3840x2160 IF it is compressed greater, say a 10:1 ratio, due to it being a higher resolution to begin with. And if so, how will the file sizes compare with the 4KHD image that did not have quite as high a compression rate, say 7:1 ratio.

EDIT> Thanks, Jeff.

[Keith Putnam]

I really do appreciate everyone's thoughts on this.

Keith, I was talking about compression in camera, not afterwards, it sounds like you were suggesting something for post. But I'm still wondering what we will find, is 5K at 4800x2700 better than 4KHD at 3840x2160 IF it is compressed greater, say a 10:1 ratio, due to it being a higher resolution to begin with. And if so, how will the file sizes compare with the 4KHD image that did not have quite as high a compression rate, say 7:1 ratio.

Ahhh, apologies for misunderstanding.
Well, I can say from my limited experience that the Epic compression ratios up to at least 8:1 look incredibly, prisitinely clean in terms of compression artifacts, and I'm told the higher ratios will achieve similar cleanliness after another firmware update or two.
I believe that RC 42 on the MX is approximately equivalent to 10:1 on the current Epic chip though I'd need to look at the numbers more carefully to be more confident.
While the esteemed Mr. Mullen is right to say that the difference between scaling 5K and 4K to 1080 is essentially negligible in terms of the image quality of the 1080 image I'd submit that, having seen Epic 5K, you're going to want the 5K capture. It is like butter.
Regarding file sizes, you have to get pretty high up in the Epic compression ratios (like 12:1 or higher, I think) before the files sizes of the Epic Redcode start to get as small as the MX Redcode.

[Robin Moran]

Keith, Jim posted this on his Thoughts and Tips section. My estimate is that RC 42 is RC 7:1 (based on the chart).

I'm wondering if the RED One will not have RC iterations in upcoming builds to streamline the compression uses between the R1 MX, Epics and Scarlets.