Shooting 4k and downscaling. No resolution benefits?

[richg101]

During some number crunching regarding resolution I have found an interesting theory regarding how beneficial shooting at high resolution to downscale is when factoring in resolution gains if there are any.  Mainly as to whether or not the Atomos Shogun is worthwhile to me over the in camera full hd of the A7S in order to gain resolution

This primarily focuses on use of typical 36x24mm full frame glass when used wide open or stopped down slightly - generally the way large sensor cameras are used.

 

Lets take the Helios 44-3.  a 58mm f2 lens which is considered a great non nonsense normal focal length for full frame with a pretty typical level of resolution.  it has a 40LP/MM resolution in the centre and a 20LP/MM resolution at the edges of a 36mm wide (full frame) frame.

 

So at f-2 the lens will resolve 40+20 / 2 x 2 (average Lines per mm across the full width of the sensor)   x 36 = 2160 pixels across the width of the frame, or around 2k.

 

Use the same lens on aps-c and we use the equation 40+25 /2 x2 x 24 = 1560pixels across the width of an aps-c sensor (not even full HD!!)

 

now, lets go to a GH4 in 4k mode.  a 15mm sensor width:-   40+35 / 2 x 2 x 15 = 1125 pixels across the width of the sensor.  - less than 720p!

 

 

So with this in mind, what are people's thoughts on this subject?  How many people actually have lenses capable of delivering 4k onto a full frame sensor, let alone on a gh4 in 4k crop mode.  Is the benefit of shooting 4k simply a way of achieving less in camera downscaling artefacts and more colour information?  Are most of those shooting 4k actually gaining any resolution advantage when using typical lenses?      

 

 

 

 

 

   

[Nikkor]

That only works out on paper. When I use vintage pre-ai nikkor glass wideopen on both the D3 (12mp) and the d800 (36mp) the resolution advantage is obvious.

[MattH]

The main point is that hd modes never give you true hd resolution. Regardless of what your lens can resolve.  Even with the c300 and 5d3 raw you are getting less than a downscaled still frame.  So a clean 4k downscaled should give as close to true hd resolution as possible. With, as you say, less (or smaller) digital artifacts. But yes to get pure 4k you would probably need a 6 to 8k sensor and a very sharp lens stopped down to an optimum aperture, and focused well. But once you get over pure 2k resolution it starts to get into the realm of who can tell the fucking difference anyway.  As for whether lenses will even give you 1080 lines: a kit zoom, probably not. A decent prime stopped down, close enough. And I would rather have a clean 900 lines than an artifacty 800.

[William Reynish]

Thing is, most 1080p cameras can't actually resolve 1080p. This is due to de-bayering, scaling and compression. Zoomed in 1:1, most 1080p footage is blurry, lacking super fine detail. 4K (itself not completely sharp when looking at it 1:1) downscaled to 1080p gives you 'proper' 1080p with superb detail, way sharper than 'native' 1080p cameras can resolve.

Oh, and as for lenses, most prime lenses can definitely resolve 4K. 4K is still 'only' 12 megapixels. Almost all stills cameras are higher res than that. If lenses couldn't out-resolve 12 MP, why would you ever need more than 12 MP for stills?

[fuzzynormal]

Who you gonna believe?  Maths or your lying eyes?  Just look.

[dahlfors]

I have no clues about that math.

But, I have shot a lot of stills on Nikon D200, which has a resolution near 4k at 3872 × 2592. I've used quite a few of the same lenses on the D800 (I've even tried using aps-c lenses!). So far, each lens has resolved more detail on the D800, although I've seen that a few hits their limit with D800 resolution, but not at D200 resolution - which is far above 1080p.

[richg101]

I must re affirm that I know that pretty much any lens will deliver when closed to f8-f11, but what i mean is with regard to use of lenses when near their wide open aperture - which tends to be where I'm at most of the time.  f2.8 or wider on full frame.  Now the otus lenses will deliver the required resolution for a d800e or a7r 36mpx even at f2.8.  but very few others do on paper.  Is it resolution gains we're seeing or is it simply a placebo?  If I shoot a landscape shot (36mpx still) on the a7r i'll be at f11 with a tripod and at f11 most lenses don;t quite deliver the required resolution.  at f2.8 it's like mush.    

[fuzzynormal]

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[Cinegain]

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​Good point. Although I wish it was made up out of more pixels.

[Nikkor]

If the question is if there is more usable information in a higher resolution image with vintage glass then I think the answer is pretty obvious.

Here an example, 50 years old nikkor-o 35 2 @ f2, shot with the d800. I turned off all sharpening and noise reduction. Then I downsampled the whole image to 1920 pixels with bicubig sharper, then I blew it up again to compare to the original file. The lens is not resolving 36mp but if stopped down to 2.8 it gets a lot better, nevertheless you can see smooth transitions and contrast differences down to what a bayer sensor permits.

If the question is whether it's better to downscale from 4k to 1080 or to record directly to 1080, then it totally depends on the camera and not on the lens, but usually it will be better to downsample on the computer.

 

[fuzzynormal]

​Good point. Although I wish it was made up out of more pixels.

​Just look really really hard at it. Also, do the skin tones look a little off to you?

[Julian]

I must re affirm that I know that pretty much any lens will deliver when closed to f8-f11, but what i mean is with regard to use of lenses when near their wide open aperture - which tends to be where I'm at most of the time.  f2.8 or wider on full frame.  Now the otus lenses will deliver the required resolution for a d800e or a7r 36mpx even at f2.8.  but very few others do on paper.  Is it resolution gains we're seeing or is it simply a placebo?  If I shoot a landscape shot (36mpx still) on the a7r i'll be at f11 with a tripod and at f11 most lenses don;t quite deliver the required resolution.  at f2.8 it's like mush.    

​At f/11 you are already losing sharpness due to diffraction on high megapixel cameras like the A7R. You don't have to stop down modern lenses that far to reach the best sharpness levels. A lot of high end zooms (such as the Canon 24-70mm f/2.8 II, 70-200mm f/2.8 II, 70-200mm f/4L IS, Tamron SP 70-200mm VC, Sigma 18-35mm 1.8 Art) perform very well at maximum aperture or closed down just one stop.

Look at the Sigma 18-35mm 1.8 for example: http://slrgear.com/reviews/showproduct.php?product=1609
Popular with micro four thirds users. Sharpness is excellent at maximum aperture in the center. No need to stop down.

Primes even more so. Look at the blur index for a Canon 300mm f/2.8L II for example: http://slrgear.com/reviews/zproducts/canon300f28lis2usm/ff/tloader.htm) pretty much excellent wide open. You don't have to buy an Otus or a super expensive Canon tele. The Sigma 50mm 1.4 Art comes very close. The cheap AF-S Nikkor 85mm f/1.8 is one of the sharpest lenses for Nikon, etc.

I don't consider the Helios a typical lens. Wide open it is pretty bad in terms of sharpness. Modern lenses are a lot better in that regard.

Anyway, Rich, you should rent/borrow an Atomos and see for yourself. Once you've seen the beauty of 4K, it's hard to go back imo.

[Julian]

Quick unscientific test (no tripod, not the same focal lenght, because of extra 4K cropfactor with GH4). Shot with GH4 and 14-42mm f/3.5-5.6 II kit lens that resolves 7 megapixels according to DxO Mark. Lens set at f/4 - pretty much wide open.

All 100% crops. 100MBPS UHD and 100MBPS 1080p. Same settings. Cine-D sharpness -5.

4K at 100% vs 1080p upscaled to 4K
 

4K downscaled to 1080p vs 1080p at 100%

4K downscaled to 1080p vs 1080p @ 100%

[jgharding]

C100/300/500 do a downscale from 4K in the body. If you record that from the HDMI ot's pretty damn sharp.

C100 MKii is the first to take all three 4K channels, then combine then downscale. So it appears it's even sharper 1080, and will upscale to 4K pretty well!

C series are very sharp, sometimes it feels like too much. I'm not yet delivering anything 4K so it doesn't bother me for now! I'd say if it's a huge effort for little reward don't do it, and if you can see the difference and feel it's worth it, do.

[Guest Ebrahim Saadawi]

Doing tests and removing all the variables. I think the best way is following

Shoot an 18mp still image... down sample that to 4K, now you have a perfect full 4K image, downsample to 1080p, now you have a perfect full 1080p image, now we can compare and test 1080p vs. 4K without external variables like the cameras' inability to resolve the marketed resolution.

1- Does shooting 4K then downscaling to 1080p, give a resolution advantage than shooting perfect full 1080p? No. You can't get more than 1080p resolution in a 1080p file, so if the camera is already achieveing the maximum 1080p resolution, you will not benefit resolution from downsampling 4K. 

4K downsamoled to 1080p



Perfect  full 1080p



Same resolution.

2- What about if you want to crop in the image, that's where 4K holds the advantage over full 1080p. 

Crop off 4K file



Crop off 1080p file



Bottom line is: if comparing perfect 4K to perfect full 1080p, 4K holds the following advantage

If viewing in 4k:

-It's 4 times the resolution/sharpness

If downscaling to 1080p:

-Ability to crop and reframe significantly
-Doesn't offer resolution advantage when not cropping

But another significant point is most 1080p camera shoot less than 1080p resolution, they have around 700p for example, so shooting 4K and downsampling to 1080p is the way to get full 1080p. At this point we're simply comparing 700p vs 1080p. When viewed at 1080p, the downsampled file is sharper, and has the ability to crop/reframe. This is the case in real world and why 4K is important, with cameras like the C100/C300 it's less important and is limited to the ability to reframe/crop. 

[Stephen de Vere]

On 12/29/2014 at 3:29 PM, William Reynish said:

Thing is, most 1080p cameras can't actually resolve 1080p. This is due to de-bayering, scaling and compression. Zoomed in 1:1, most 1080p footage is blurry, lacking super fine detail. 4K (itself not completely sharp when looking at it 1:1) downscaled to 1080p gives you 'proper' 1080p with superb detail, way sharper than 'native' 1080p cameras can resolve.

I guess you are referring here to hybrid stills/video cameras.

Even an ancient mid-range 1080 video camera like the Sony PMW-EX3 that doesn't use de-bayering can resolve the maximum HD resolution (1080 lines vertically). Plenty of others do it too.

The arrival of UHD/4k modes in hybrid stills/video cameras has at last provided the opportunity to get full res HD from stills cameras, albeit in postproduction (as long as the downscaling is done carefully) from the mostly sub full 4k resolution '4k' recordings.

[BrorSvensson]

resolution and sharpness of a lens is two very things different to me. Shooting 4k with a soft-ish lens will looks really smooth and not blochy. There will be lots of detail in the image but it may not be super sharp. 

[kidzrevil]

I'm using zeiss milvus glass and the gain in resolution is evident from the time I put it on

 

[andyson]

There's a new low light test shootout between the MBCC and FS100:

 

 

 

 

 

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[webrunner5]

On 12/28/2014 at 10:29 AM, William Reynish said:

Thing is, most 1080p cameras can't actually resolve 1080p. This is due to de-bayering, scaling and compression. Zoomed in 1:1, most 1080p footage is blurry, lacking super fine detail. 4K (itself not completely sharp when looking at it 1:1) downscaled to 1080p gives you 'proper' 1080p with superb detail, way sharper than 'native' 1080p cameras can resolve.

Oh, and as for lenses, most prime lenses can definitely resolve 4K. 4K is still 'only' 12 megapixels. Almost all stills cameras are higher res than that. If lenses couldn't out-resolve 12 MP, why would you ever need more than 12 MP for stills?

Actually 4k is Only 8.3mp. So Any old lens is able to resolve that many MP. 1080p is only 2mp. We are not talking serious amounts of data needed here.