If you've ever wondered why the cheaper version
of two camera siblings is better for video
than its higher-resolution counterpart,
like the Nikon Z6 is compared to the Z7.
Or the Sony a7 III versus the Sony a7R III?
Well today's video's gonna explain that.
Let's get Undone.
[offbeat music]
♪ Gerald Undone ♪
♪ He's crazy ♪
What is happenin', everybody! I'm Gerald Undone.
And today we're talkin' about sensor readout in video.
More specifically, how your camera
takes the image that it sees, and turns it into 4K or 1080p.
These methods are where you might
have heard the terms "pixel binning"
or "line skipping", and that's exactly
what we're gonna compare. From a practical standpoint,
this information is useful when deciding
upon a camera for video, because it can often save you
quite a bit of money. Take the new Nikons, for example.
The recently released Nikon Z6, which only costs 60%
of its higher resolution counterpart, the Z7,
is a superior camera for video.
And this primarily has to do with the way
that the camera pushes down its image into 4K.
While I'm pointing at this camera,
I should mention that this Nikon Z6
was provided to me by Camera Canada.
Camera Canada has a fantastic selection
of Nikon bodies and lenses.
And it's the best choice for Canadians
looking to get their hands on the new Nikons.
So, make sure you check them out
using the links in the description below.
Okay, so for this video there are four techniques
I want to discuss, which are the ones
that you're most likely to encounter.
And they are: oversampling, pixel binning,
line skipping and cropping.
So, before we compare the processes,
let's explain why we even need one
in the first place. So, when you shoot video
with a hybrid photo camera,
the sensor isn't exactly configured
to match the resolution or aspect ratio of the final video.
Let's take the Nikon Z6 here, again.
Which has a resolution of 6000 by 4000 pixels.
Which is a 3:2 aspect ratio.
But an Ultra HD video has a 16:9 aspect ratio
and it's usually 3840 by 2160 pixels.
So, the camera has to use a method
of taking that photo-sized image
and making it video-sized and the method
that it's designed to use, is usually based
on the capabilities of the processor in the camera.
With that, generally the easier this method
is for the camera to perform,
the worse the end result quality will be.
So, let's start off with the easiest operation,
and thus the ugliest result, cropping.
With cropping, the camera basically just grabs
the 4K image that it needs out of the middle
of the frame, and ignores the rest
of the frame completely. This has two major drawbacks.
First, it changes your field of view.
Which is annoying when you switch
between photo and video modes.
But it also restricts you to the minimum amount
of data possible, when creating that 4K image.
This is the area where the latest Canon camera
has taken a huge amount of flak.
The end result when compared to other cameras,
is an image that's softer, less detailed,
and provides a sub-optimal field of view.
If we compare this to what the Nikon Z6 does,
which is oversampling,
and the best of the four methods that we're gonna discuss today,
we can really see the benefit of having
that extra processing power.
First of all, a little note on oversampling.
There's much debate over the correct usage
of terms oversampling and downsampling.
And I think much of this confusion comes from
the fact that these terms originate in frequencies,
in which samples serve a much more logical position amongst
the current theorems. But when it comes to video,
we're using them less to describe the sampling frequency,
and more to describe
the resolution capabilities of the sensor.
This is especially true when it comes
to post-production and you're trying to describe
the process of taking 4K video and pushing it down
into a 1080p timeline.
I suppose a more apt term would be
"overrezzing" or "downrezzing".
But regardless, the most simplistic way
of looking at it would be oversampling is starting
with a higher quality than needed.
Typically twice as high as the rate required.
And then downsampling is the decimation process,
where that signal is conformed back
to the required rate. Like I said,
the use of these terms, when it comes to video,
is debatable. But essentially what it means, is,
using a camera that is capable of 8K,
but then taking that 8K image to create
a brilliant 4K image. With less noise, aliasing,
moiré and colour anomalies.
So, let's talk a little bit about how it achieves
those things, so that we can better recognize
the shortcomings of the other methods.
First, let's talk about noise.
Noise is generally improved in two ways,
when it comes to downsampling techniques.
And those ways are averaging and shrinking.
So, let's look at noise shrinking first,
and then we'll get into averaging
when we talk about pixel binning.
Because noise is generated relative to pixel size,
an oversampled image will source from
smaller pixels, and thus, smaller noise.
So, if you needed 3840 pixels to fit
across the horizontal on this frame,
but you sourced it from a camera,
like the Nikon Z6, that uses 6000 pixels
in an oversampled image,
you would effectively be utilizing smaller pixels
than required to fill this frame.
These smaller pixels mean that the noise
is smaller, as well. Since the noise gets its size
and shape from the pixels it's created in.
This gives the appearance that an image is less noisy,
even if the quality of the noise hasn't changed.
The reverse is also true,
which is why your photographs seem noisier
when you heavily crop them.
And thus is one of the main reasons
why cropped 4K video is worse than oversampled video.
The same exact thing is true for aliasing.
In simple terms, aliasing is the jaggy edges you see
when an object doesn't have enough information to produce
a smooth look. Pixel size directly affects aliasing
in a logical way. If you have more, smaller pixels,
you can make finer shapes seem smoother.
But if you have fewer, larger pixels,
those same shapes will seem rough and jagged.
To put it in a fun way, try and form
a circle with four large squares.
And then try and form a circle with 400 small squares.
The second is much, much easier.
So, just like with noise, when you're sampling
from an image with a higher resolution,
and you press it down into 4K, you get less aliasing,
because you're using more, smaller pixels.
This is also what leads to moiré in your images.
Moiré is that fringing artifact
that makes patterns seem like they're moving.
Generally, you'll find that as aliasing increases,
so does the instance rate of moiré.
Now the common solution to solve these problems is an AA filter,
or Anti-Aliasing filter.
Sometimes called an Optical Low Pass Filter,
in certain cameras. But you can think
of these things more as a Blur Filter.
These filters are becoming less common,
as the pixel counts increase in cameras.
Because that makes the pixels smaller
and as we just discussed, more smaller pixels
means that you can create complex shapes
more smoothly and with less jaggies.
But, if you've ever tried to fix aliasing or moiré
in your images, you know that adding
a little bit of a blur effect can help remove it,
and that's essentially what these filters do.
And the inclusion of this filter is one
of the differences between the Nikon Z6 and the Nikon Z7.
And the same is also true for Sony.
In fact, a lot of what we say about
the Nikons can be mirrored under the Sonys.
The a7 III being the Nikon Z6. And a7R III being the Nikon Z7.
In this case though, it's the lower resolution,
less expensive camera that has the AA filter
and the higher megapixel camera,
the Z7 or the a7R III does not have one.
Now what's interesting, is that when it comes to video,
this is probably the opposite of what would
produce the best results. But we'll get into
that when we talk about the Super 35 modes.
But essentially, what I'm trying to say
is that these AA filters are based
with photography in mind, and are tuned for that purpose.
And what I mean by "tuned" is that you can
calibrate the filter to provide less blur
or more blur, and sometimes this can have
a heavy impact on the image.
And other times it can be quite subtle.
But in all cases, having an AA filter
will produce an image that's slightly
less sharp than if you didn't have one.
If you put all this information so far together,
you can really see why cropping is inferior.
We don't get to use the smaller pixels,
which means we're not going to see
any improvements when it comes to noise or aliasing.
Which means a higher incidence of fringing and moiré.
And to eliminate that, we need a stronger AA filter,
which means more blur, which means a softer image,
and it'll be a less detailed image,
because we don't get the greater detail
of the oversampled resolution.
And it changes your field of view.
So, what about line skipping?
Well, line skipping is what the Nikon Z7
and the Sony a7R III do when they're in full frame mode.
And it's pretty much what it sounds like.
Rather than crop the 4K out of the centre,
the camera skips lines of pixels to reduce
the readout to the needed resolution.
In this case, 4K. Now there's different algorithms
and methods to do this,
but if we go back to our example of
having 6000 pixels across the horizontal,
and you need 3840 for Ultra HD,
you just skip the 2160 that you don't need.
It's a bit more complicated than that.
And like I said, there's algorithms
that blend and recompile the image
during the skipping process.
But that's the most basic explanation
of how it works. Now, if we apply our criticisms
of cropping to this process, we can see some benefits,
but most of cons still remain. The benefits are that it's fast.
Maybe not as fast as cropping,
but still way faster and easier than oversampling.
This way the camera doesn't melt
in your hand when you're trying to process
the full sensor readout
of the 46 megapixel sensor, of the Nikon Z7.
That's higher than 8K, by the way.
But where it beats cropping,
is that it doesn't change your field of view.
Because not centralized cropping is taking place.
But it still suffers from the other problems.
Because if we skip the pixels, then we're not gonna have them
to improve aliasing. And we won't have them
for the averaging of noise.
Or the reduction of fringing and artifacts.
So, the image is still harsher, and less detailed,
than an oversampled one.
But this is where some strange trade-offs
start to occur because like we said earlier,
the larger cameras don't have the AA filter,
they don't have anything to help blur away
the fringing and the jaggies.
So, it may be sharper, but it's not necessarily
a good kind of sharper.
Now the Z7 and a7R III do have another way
of dealing with this,
which is sort of a combination technique,
which occurs when you enable the DX
or Super 35 modes on those cameras.
The first step is a crop,
which grabs only the centre 1.5x factor portion of the frame.
So, the 8256 horizontal pixels of the Nikon Z7 become 5504,
when you enable the 1.5x crop mode.
This will change your field of view,
because it's a proper crop.
Then the camera downsamples the rest of that image into 4K.
The lower pixel count, due to the 1.5x crop,
is easier for the processor to handle,
and thus it doesn't require binning
or line skipping when in this mode.
This gives you more effective pixels on the Z7
than if you used the full-frame
line skipping method, and still gives you
some of the benefits of the oversampling,
like found on the Z6.
Now it's not quite as strong as a benefit
as the Z6, because a Z6 has 6000 pixels
when doing the full sensor readout.
Or the Z7 only has 5504 when you're in DX mode.
But it does produce a nicer image
than the line skipped method.
And has 90% of the quality of the Z6,
with only one major con,
that again your field of view is going to change,
by that 1.5x crop. And this is where I said
that it's kind of the opposite for video
when it comes to which camera gets the AA filter.
For photos it makes sense, sure.
The Z7 has vastly more pixels than the Z6 does.
But when we're comparing these oversampled video modes,
because of the 1.5x crop,
the Z7 actually has fewer pixels,
than the Z6 and would be more in need
of the AA filter than the Z6 would be.
Now let's talk about the most complicated one
of the bunch, pixel binning.
Pixel binning has many more approaches to it
than the previous methods.
And the one that benefits the most from innovation.
The algorithms and measurements used
in pixel binning leave space for improvement through design,
that have created better results year over year.
With Sony currently discussing a complex
"weighted" pixel binning approach,
in their latest 8K sensor announcement.
But here's my simplified explanation of pixel binning.
Remember the colour science video
where we talked about the Bayer filter
your sensor uses to collect colour information
in a particular array?
Well, if we had more pixels than we needed,
and we wanted to push that down into 4K,
one way to do it would be to combine like pixels.
So, maybe in a block of 16 pixels,
we combine all four reds into one larger red,
all four blues into one larger blue,
and the eight greens into two larger greens.
That way you keep the same pattern
in your array, but you shrink your resolution by 4x.
And this is also where that noise averaging thing
we talked about earlier comes in.
By combining the pixels, the noise that comes along
with them will also be combined
and hopefully averaged to produce
a better signal-to-noise ratio.
The goal is to evaluate each of the those pixels
while choosing the best bits
that they have to offer when it comes to detail.
But also the areas that have the least amount of noise.
The techniques for doing this can get
much more complicated. And often these days,
involves assigning specific weight values
to a large array of pixels,
and then combining them in intelligent ways
to maximize their potency.
In short, your resolution goes down,
but your signal-to-noise ratio goes up.
Giving you a smaller, cleaner image.
The key takeaway here though,
is that pixel binning is not line skipping,
even though you may commonly see them
bundled together in camera reviews.
While ideally you wanna use oversampling,
when that's not available,
pixel binning is definitely preferable to line skipping.
It does, however, suffer the same issue
that any larger pixel configuration will:
increase aliasing, fringing, and moiré.
For the same reasons we mentioned before,
when you have bigger blocks to work with,
your shapes are jaggier and more susceptible to anomalies.
But in the case of pixel binning,
the blocks are cleaner,
and that's definitely an improvement.
Pixel binning doesn't change your field of view,
either, which is a plus.
But it does require more processing power
than line skipping or cropping.
But not quite as much as oversampling.
And that's where the limitations come from.
The higher quality readout methods
take longer to do, than the lower quality ones.
Which means you need a faster processor,
to be able to do them fast enough,
to generate an acceptable frame rate.
And the higher the frame rate,
the faster still the processor needs to be.
Faster processors require more power,
and generate more heat.
So, it's really all a balancing act between output,
power consumption, and heat control.
And in the case of the latest Nikons,
and the Sonys that came before them,
the Z6 while cheaper, balances those aspects better
than its bigger brother.
So, your cameras aren't going to melt in your hand
while processing the four to six mega pickle-
Pick--
Mega pickle.
But that's gonna be it for me. I hope you found this video
helpful or at least entertaining, and if you did,
make sure you leave it the old thumbs up
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feel free to hit the dislike button twice.
Alright... I'm done.