2k RAW aliasing

IMO a properly matched OLPF is essential to high quality digital imaging. The lower the pixel resolution of the camera, the more critical it is.
As the article above pointed out, an OLPF filters optical details the sensor can't reproduce accurately anyway. Light behaves like a wave phenomenon and aliasing artifacts are like intermod distortion in audio. Aliasing creates spurious harmonics that show up as jaggies and chroma moire at detail frequencies both above and below what the sensor can cleanly resolve. Though the superficial impression is that the OLPF reduces resolution, in situations where aliasing is a problem, the effective clean resolution is actually higher with the filter.
 
Personally i simply don't understand why anyone would prefer 2K RAW over downsampled 4K in post.

The full capability of the 700 allows for 120fps in 4K (to an R5), so how many people actually need to shoot >120fps?

The O7 will record 4K compressed,possibly up to 60fps but it might also be able to record the 120fps burst. So exactly how much 120fps does everyone need?

So i think the FS700 (and the 5/55) offer more than enough slowmo for 99% of people. This leaves standard shooting rates in 2K. I simply don't see why anyone would want 2K when they have a 4K sensor and the datarates between 4K compressed and 2K RAW probably favour the 4K compressed. If that 4K compressed is 10 bit log then you're not loosing colour range either.

It seems such a speciality area that i don't get sticking a softening filter to get 2K RAW at all. Just buy a different camera!

2K RAW compared to 4K downsampled? No competition in quality terms...

cheers
Paul
 
paulcurtis said:
Personally i simply don't understand why anyone would prefer 2K RAW over downsampled 4K in post.l
Click to expand...

Firstly you get higher frame rates.

Secondly the data rate is 250mbs in stead of 1GBs (I approximate) which, I approximate, is 1/4 or 1TB for three hours rolled.

Hd has never been a problem for me, baked colours and compression artefacts are - 2k raw is perfect

S
 
+1
+1
+1

morgan_moore said:
Firstly you get higher frame rates.

Secondly the data rate is 250mbs in stead of 1GBs (I approximate) which, I approximate, is 1/4 or 1TB for three hours rolled.

Hd has never been a problem for me, baked colours and compression artefacts are - 2k raw is perfect

S
Click to expand...
 
morgan_moore said:
Firstly you get higher frame rates.

Secondly the data rate is 250mbs in stead of 1GBs (I approximate) which, I approximate, is 1/4 or 1TB for three hours rolled.

Hd has never been a problem for me, baked colours and compression artefacts are - 2k raw is perfect

S
Click to expand...


4K ProRes HQ 10 bit is 110MB/s (Normal ProRes is 73MB/s) vs 2K Sony RAW 62MB/s (these values are from an AJA data rate calculator so i'm assuming they're correct)

None of those data rates are really huge issues these days. You have the MkIII 5D spitting out 80MB/s onto CF cards.

I'm totally with you on colours and compression. But 10bit log from a 12bit linear source will realistically loose you nothing in terms of colour but the downsampling from 4K will dramatically increase edge resolution and reduce aliasing. There's enough footage out there to compare for yourself.

Personally unless there's quality scaling going on in camera (which there isn't - even the HD downsample is not that good IMHO), i don't see the point of not using 4K if you have it...

And how many times have you needed to sustain > 120 fps? Perhaps for you that's the kicker...

cheers
Paul
 
paulcurtis said:
Personally i simply don't understand why anyone would prefer 2K RAW over downsampled 4K in post.l
Click to expand...

I am not sure whether I got all what your wrote, sorry I am not native English. I use the FS700 as a all-round flexible camera. I don't see a need for 4 K at the moment from my client's side and as long as they ask for it I will be happy that I don't have to out overload my media archive and workflow. But 2K RAW in addition to all existing benefits would be a great option as I often have to deal with high contrast. I am quite keen on 2K RAW in my existing system and having not to mess around with another manufacturer.
 
Paul

Im not saying you are wrong.. or right.

I thought XAVCHD was about 110MBS, leading to a logic that 4k of same is 440mbs for a compressed codec.

As for the flexibility of the file, again Im not convinced of compressed formats, but Im not unconvinced either

Also as you change from standard to highFPS you may, or may not end up with a post muddle

simple old raw seems simple to me

S
 
Clermond said:
I am not sure whether I got all what your wrote, sorry I am not native English. I use the FS700 as a all-round flexible camera. I don't see a need for 4 K at the moment from my client's side and as long as they ask for it I will be happy that I don't have to out overload my media archive and workflow. But 2K RAW in addition to all existing benefits would be a great option as I often have to deal with high contrast. I am quite keen on 2K RAW in my existing system and having not to mess around with another manufacturer.
Click to expand...

All i'm really saying, and if i had samples i'd demonstrate, is:


The 2K RAW mode skips every other line on the sensor, this can produce jagged edges and aliasing as many people have observed. You are throwing away half of the sensor by doing this.

Conversely the O7 offers a compressed 4K (ProRes HQ)

The datarate for the RAW solution looks to be around 62MB/sec and i can see actually from a 4K ProRes file from the O7 that the rate is 92MB/sec.

If you shoot the same scene, in 2K and 4K compressed. Then took that 4K and scaled it down in post, the quality of that scaled 4K file would be considerably higher than the 2K file, in terms of noise, resolution and colour because you're supersampling that 4K original.

At the end of the day you end up with 2K files via both methods but one has gone through a scaling route.

Generally dealing with RAW files means 'developing' them and debayering so from a workflow view point there isn't that much in it.

The only reason for 2K RAW is

a) Higher speed (120 to 240fps)
b) You can choose the debayer method but in the case of 2K RAW you're stuffed anyway because your source is line skipped.

I hope this makes sense and i suspect i'm boring everyone with this everytime, but having worked with 700 footage in great detail i can see how bad the 1080p scaling is sometimes. For me, unlocking that 4K sensor gives me a new camera...

cheers
Paul
 
Not boring at all.

I can afford a fully pimped 700, a 5 and save for a recorder, or marginally, very marginally could get a 55 no recorder - confused.

Im pretty convinced that 4k raw is too data heavy and therefore confused/interested in the other options

I guess I want to deliver sparking HD but bare in mind an upgrade path to 4k

I like minimal lighting and max shovelling in post BTW, and want room to mis expose because nobody is perfect.

As for the 2k jaggies - they should be solved by the new filter, which is not available on the 700

S
 
Last edited:
morgan_moore said:
Paul

Im not saying you are wrong.. or right.

I thought XAVCHD was about 110MBS, leading to a logic that 4k of same is 440mbs for a compressed codec.

As for the flexibility of the file, again Im not convinced of compressed formats, but Im not unconvinced either

Also as you change from standard to highFPS you may, or may not end up with a post muddle

simple old raw seems simple to me

S
Click to expand...

I'm not saying you're wrong or right either! But i know what i've been looking at in post with 700 files and feel strongly about the use of down sampled 4K files. I have no interest in delivering 4K but i want the *best* 2K files i can get. And 2K RAW is not it.

RAW still needs to be processed. Dealing with thousands of individual files that make up a sequence can cause issues with many types of filesystem (windows for example). I bet most people take the RAW then produce a single movie file to work with. In which case use the 4K source and produce a 2K instead.

cheers
paul
 
morgan_moore said:
Not boring at all.

I can afford a fully pimped 700, a 5 and save for a recorder, or marginally, very marginally could get a 55 no recorder - confused.

Im pretty convinced that 4k raw is too data heavy and therefore confused/interested in the other options

I guess I want to deliver sparking HD but bare in mind an upgrade path to 4k

I like minimal lighting and max shovelling in post BTW, and want room to mis expose because nobody is perfect.

As for the 2k jaggies - they should be solved by the new filter, which is not available on the 700

S
Click to expand...

I've always felt that the 700 is a wolf in sheeps clothing and i love the Emount system as it bridges the gap between my stills and video.

Have you downloaded the 4K ProRes sample from CD, it's basically a brick wall and fountain but the quality of the edges on those bricks is pretty stunning at 4K, let alone down sampled. The 2K RAW files by comparison i'm pretty meh about. And i find the idea of sticking a OLPF for 2k in front of a 4K sensor madness.

I've been in the same position as you with the F5 and personally decided to go down the 700 and O7 route.

The only thing i've not found is really a like for like F5 and 700 in terms of noise and range. That would be interesting. But i know the 700 is capable of very good images.

There're some mxf's in another thread. Take these into Sony RAW viewer and play. Switch to the ACES workflow. It just looks right...

cheers
Paul
 
These files? - You have a recorder or what?

OT - if the FS100 of F3 put out raw the big pixels would probably create the best image.. which is kind of interesting ref the F3

S
 
I DL from the Ody site - but the colour was so wonk I was not keen

The 700 is also a bit crud with the onboard codec unlike the F5 (might be) which gives 50-100mbs for daily jobs and should get the bbc ticket naked

Im testing the 5 soon for myself.

I guess with the F5 you do the onboards or on a spacial project just go mental with the data and shoot 4kR unless you are offspeed

Again im seeing monitoring issues with the 700, LUTs and the like missing also the 700 talks badly to my DP6 with loads of blue time

I thought that the 5naked should at least equal the 700 and Ody in every way, but it is not so clear..

Emount is a bit janky but does allow for a booster which is a major plus

S
 
I agree with paul. Downsampling in post is the way to go. Cameras suck at it. That would be the only benefit of having 4K. It's like HD downsampled to SD creating a 4:4:4 image. So much info squashed into a smaller file makes it look a lot richer IMO.
 
indeed but you are assuming the camera can compress well - seems like six of one and half of the other.

Also it is not downsampling it is reading less pixels, just that creates jaggies unless the moire filter is upped.

S
 
Ian-T said:
I agree with paul. Downsampling in post is the way to go. Cameras suck at it. That would be the only benefit of having 4K. It's like HD downsampled to SD creating a 4:4:4 image. So much info squashed into a smaller file makes it look a lot richer IMO.
Click to expand...

If it was properly downsampled, it would not be a problem. Downsampled XAVC (and AVCH on FS700) is just fine on these cameras. It's raw that cannot be properly downsampled from 4K to 2K. To get proper 2K raw requires stronger AA filter, and the AA filter on these cameras is optimized for 4K raw, not 2K raw.
 
call me crazy, but I feel like I've seen more aliasing since I got my camera 'upgraded' to 3.0. Even in like high contrast shots (I did a medical shoot, very well artifically lit, and the doctor had a metal stethoscope on) I was getting a strange jagged fringe around the object. Same thing on green screen, although this was the first time I have done green screen with this camera, so I'm not sure what the before was like. All at 1080, standard speed ;-)

You think they took out the anti aliasing filter since we should be using the full sensor for 4k?
 
Last edited:
evilthought said:
If it was properly downsampled, it would not be a problem. Downsampled XAVC (and AVCH on FS700) is just fine on these cameras. It's raw that cannot be properly downsampled from 4K to 2K. To get proper 2K raw requires stronger AA filter, and the AA filter on these cameras is optimized for 4K raw, not 2K raw.
Click to expand...

2K RAW needs a sensor designed for 2K RAW, not a blurred 4K sensor. It's like looking out a window through venetian blinds, you're missing every other line and what's more because it's a bayer sensor the gaps are even bigger. Blurring it isn't going to make that much sense. Just buy a different camera.

Or that 4K sensor needs to be scaled in realtime down to 2K within the camera, which the 700 cannot do. I think it scales the lines horizontally because aliasing is much reduced there.


dapoopta said:
call me crazy, but I feel like I've seen more aliasing since I got my camera 'upgraded' to 3.0. Even in like high contrast shots (I did a medical shoot, very well artifically lit, and the doctor had a metal stethoscope on) I was getting a strange jagged fringe around the object. Same thing on green screen, although this was the first time I have done green screen with this camera, so I'm not sure what the before was like. All at 1080, standard speed ;-)

You think they took out the anti aliasing filter since we should be using the full sensor for 4k?
Click to expand...

I've always found the 700 aliasing quite a bit but first make sure you have no in camera sharpening going on, the V3 upgrade would have deleted any of your profile tweaks. Fringes sound more like sharpening so that could be the issue.

But the HD image has never been as smooth as i would have expected from a downsampled sensor, that's true.

Greenscreen work is generally okay, best to record externally. To be honest a lot of greenscreen issues are not sensor based but the way it's set up. One big issue i've encountered is diffraction of the light when you're shooting fairly wide and CA, it manifests differently in each colour channel and is a massive PITA to pull a key from (so the blue channel might be a different outline to the others because the light was bent around the subject differently. Anyway, i digress...

Check the sharpening first! But then i'd quite happily believe there have been changes to the scaling... I don't believe they changed the AA filter or anything, don't forget you've been able to take 4K photo images since day one and they look great. The OLPF is designed for 4K.

cheers
Paul
 
If I had the money to spend I think, at a pinch, I might buy an F5. With the 240fps now being enabled on the F5, the only difference between that and the (nearly doulbe the price) F55 is the global shutter and the wider colour gamut - something that I think you'll only miss on real high end stuff - in which case I might be tempted to buy an F65 instea! (which is probably only another 20% on top for a kit!).

In comparison to the FS700 the F5 delivers broadcast 10bit SLog2 XAVC internal - with the added possibility of simultaneously recording 16bit Raw with an attached R5. All in all, the F5 is more versatile camera.

What might give me pause for thought is the extra cost - which I could spend on some nicer lenses. That and the fact I'm not sure my (current) clients would be willing to pay the extra for the F5, since I only shoot docs for broadcast once, maybe twice a year. I think they could be convinced to spend the extra on an Odyssey as they will be able to see the imediate benefit of 10bit Log HD and 240fps continuous Raw, but not the jump to 16bit Raw. But if you already have the lenses, the F5 might be a worthwhile investment....
 
You must log in or register to reply here.
Back
Top