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To shoot in 4K 60mbps or 1080 60mbps?

There is a forum out there for everything from breeding cats to aviation and there are a dozen video forums, but I can’t find an answer to this.

The Q is simple. Which of the two will give a better quality if rendering to 1080 at the end?

I suspect a 4K video compressed to 60mbps will be poor quality if there is any significant movement from one frame to the next e.g. a flying video. For equivalent quality to the 1080 video, the bit rate would obviously need to be something like 4x i.e. 240mbps.

So shooting at 1080 might actually produce fewer artefacts etc. A 1080 60mbps video is very good – about 10x higher bitrate than anything you see on youtube or vimeo. But obviously it much depends on the subject matter and how fast it moves.

The reason I am looking at 4K is because when doing lens correction you are applying pincushion distortion (to compensate for the camera’s barrel distortion) and that needs a crop afterwards, which would mean pixel replication if shooting at 1080.

Administrator
Shoreham EGKA, United Kingdom

Peter, forget about the pixels, you want more bitdepth. The limit of human vision is about 3 K, when seated in the best seat in a theatre, with perfect vision and in such a way that you can see the entire screen without moving the head. Going from 8 bits per channel to 10 or 12 is more beneficial. In your case a less compressed 1080p image is more than enough for internet, Blu-ray disc etc.

EBKT

The reason I am looking at 4K is because when doing lens correction you are applying pincushion distortion (to compensate for the camera’s barrel distortion) and that needs a crop afterwards, which would mean pixel replication if shooting at 1080.

I just finished playing around correcting for lens distortion in some RAW files. Unless I am missing something….

Barrel distortion pulls non-central pixels too close to the centre, and correcting for it means pushing them them back out again. So the barrel-distorted image contains all the pixels you need (albeit squashed up a bit), and some more pixels you won’t need, so no need for cropping I think.

White Waltham EGLM, United Kingdom

The limit of human vision is about 3 K

Sure; that is why I am outputting to 1080.

Barrel distortion pulls non-central pixels too close to the centre, and correcting for it means pushing them them back out again. So the barrel-distorted image contains all the pixels you need (albeit squashed up a bit), and some more pixels you won’t need, so no need for cropping I think.

The problem is that after the camera has barrel-distorted the image, it then crops it into a rectangle and that is what you get in the mp4 file. So when you pincushion-correct it, you get the four sides caving in. So you have to crop that into a (slightly smaller) rectangle. Then, if you started at 1080 an are outputting at 1080 again, you are replicating pixels.

That’s if I understand you right…

Administrator
Shoreham EGKA, United Kingdom

David, it’s the other way around.

Peter, I’ve been in the moving images business for 20 years, worked with all formats, and it’s still a hotly contested topic – is it better to have higher resolution at low bit rate vs. a lower resolution at high bit rate? I think there’s no clear answer. I saw Arri Alexa 2K tests vs Red 4K back in the days and could not see much difference. But compressions have become better and today I would always err on the side of resolution, simply because of one main reason: most cameras deal with lower resolution by cropping the sensor and using only parts of it. This is never a good idea as pixel size (nits) relatively goes up, you use only the central portion of the lens and therefore subject it to greater magnification (which will reduce it’s optical qualities). Not only that, because magnification goes up with a sensor crop, you’ll have much more apparent depth of field. This makes for less pleasing images to the eye.

Last Edited by AdamFrisch at 12 Jun 22:07

Peter, what camera do you have that shoots 4k in 60fps?

I occasionally use 4K on my Sony RX100V but I prefer to shoot in 1080 60fps minimum or 120fps, but resolution wise I don’t see any difference on small screens.

I found 4K comes useful only when cropping

Evo400

what camera do you have that shoots 4k in 60fps?

The Sony X3000 does 4K in 30fps or 1080P in 60fps (and more). See the IT section for the X3000 thread.

As you guess, there aren’t many action cams which do 4K in 60fps

I found 4K comes useful only when cropping

Exactly – otherwise one would be better spending time to find an editing workflow where the frame size is not changed; that ought to produce the best quality.

If the camera did not need lens correction (and the X3000 doesn’t need much) then I would never shoot in 4K. I would shoot in 1080P 60fps 100mbps.

As Adam says, this choice is not obvious.

Administrator
Shoreham EGKA, United Kingdom

The problem is that after the camera has barrel-distorted the image, it then crops it into a rectangle and that is what you get in the mp4 file. So when you pincushion-correct it, you get the four sides caving in.

OK, that intermediate in-camera crop would explain it.

The RAW file I was looking at was like the first picture below, which contains unfocused lens parts in the corners.

Correcting for lens distortion means “copying” pixels from slightly more central parts of the original, the second picture shows the result

The corrected image and the original have the same pixel-count, but some of the original pixels are discarded, which means the true resolution at the margins is now lower (33% in this case), but nothing had to be cropped. The yellow arrow in the distorted picture roughly shows the movement at a corner.

But I do take your point that you would need to start with higher resolution throughout the whole picture if you wanted to maintain quality at the edges of the corrected image.


White Waltham EGLM, United Kingdom

Are you sure it is the camera giving this distortion? Is the lens interchangeable? Looks like a lousy lens to me.

EBKT

Are you sure it is the camera giving this distortion? Is the lens interchangeable?

I am prettty sure it is the camera lens: I extracted the top image using “dcraw -w”.
I can also read the raw file (RW2) in my own software and then use the lens distortion parameters from the TIFF tags to correct the distortion.

Is the lens interchangeable? Looks like a lousy lens to me.

It is the built-in lens in a Panasonic Lumix DMC TZ70. I use it as a “point and shoot” camera.

White Waltham EGLM, United Kingdom
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