Cinematography

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Are LUT’s Killing Creativity And ERODING Skills?

I see this all the time “which LUT should I use to get this look” or “I like that, which LUT did you use”. Don’t get me wrong, I use LUT’s and they are a very useful tool, but the now almost default reversion to adding a LUT to log and raw material is killing creativity.

In my distant past I worked in and helped run  a very well known post production facilities company. There were two high end editing and grading suites and many of the clients came to us because we could work to the highest standards of the day and from the clients description create the look they wanted with  the controls on the equipment we had. This was a digibeta tape to tape facility that also had a Matrox Digisuite and some other tools, but nothing like what can be done with the free version of DaVinci Resolve today.

But the thing is we didn’t have LUT’s. We had knobs, dials and switches. We had to understand how to use the tools that we had to get to where the client wanted to be. As a result every project would have a unique look.

Today the software available to us is incredibly powerful and a tiny fraction of the cost of the gear we had back then. What you can do in post today is almost limitless. Cameras are better than ever, so there is no excuse for not being able to create all kinds of different looks across your projects or even within a single project to create different moods for different scenes. But sadly that’s not what is happening.

You have to ask why? Why does every YouTube short look like every other one? A big part is automated workflows, for example FCPX that automatically applies a default LUT to log footage. Another is the belief that LUT’s are how you grade, and then everyone using the same few LUT’s on everything they shoot.

This creates two issues.

1: Everything looks the same – BORING!!!!

2: People are not learning how to grade and don’t understand how to work with colour and contrast – because it’s easier to “slap on a LUT”.

How many of the “slap on a LUT’ clan realise that LUT’s are camera and exposure specific, how many realise that LUT’s can introduce banding and other image artefacts into footage that might otherwise be pristine?

If LUT’s didn’t exist people would have to learn how to grade. And when I say “grade” I don’t mean a few tweaks to the contrast, brightness and colour wheels. I mean taking individual hues and tones and changing them in isolation. For example separating skin tones from the rest of the scene so they can be made to look one way while the rest of the scene is treated differently. People would need to learn how to create colour contrast as well as brightness contrast. How to make highlights roll off in a pleasing way, all those things that go into creating great looking images from log or raw footage.

Then, perhaps, because people are doing their own grading they would start to better understand colour, gamma, contrast etc, etc. Most importantly because the look created will be their look, from scratch, it would be unique. Different projects from different people would actually look different again instead of each being a clone of someone else’s work.

LUT’s are a useful tool, especially on set for an approximation of how something could look. But in post production they restrict creativity and many people have no idea of how to grade and how they can manipulate their material.


Are LUT’s Killing Creativity And ERODING Skills? was first posted on February 17, 2020 at 9:39 am.
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Temporal Aliasing – Beware!

As camera resolutions increase and the amount of detail and texture that we can record increases we need to be mindful more and more of temporal aliasing. 

Temporal aliasing occurs when the differences between the frames in a video sequence create undesirable sequences of patterns that move from one frame to the next, often appearing to travel in the opposite direction to any camera movement. The classic example of this is the wagon wheels going backwards effect often seen in old cowboy movies. The cameras shutter captures the spokes of the wheels in a different position in each frame but the timing of the shutter relative to the position of the spokes means that the wheels appear to go backwards rather than forwards. This was almost impossible to prevent with film cameras that were stuck with a 180 degree shutter as there was no way to blur the motion of the spokes so that they were contiguous from one frame to the next. A 360 degree shutter would have prevented this problem in most cases. But it’s also reasonable to note that at 24fps a 360 degree shutter would have introduced an excessive amount of motion blur elsewhere.

Another form of temporal aliasing that often occurs is when you have rapidly moving grass, crops, reeds or fine branches. Let me try to explain:

You are shooting a field of wheat, the stalks are very small in the frame, almost too small to discern individually. As the stalks of wheat move left, perhaps blown by the wind, each stalk will be captured in each frame a little more to the left, perhaps by just a few pixels. But in the video they appear to be going the other way. This is  because every stalk looks the same as all the others and in the following captured frame,  the original stalk may have moved  say 6 pixels to the left. But now there is also a different stalk just 2 pixels to the right of where the original was. Because both stalks look the same it appears that the stalk has moved right instead of left. As the wind speed and the movement of the stalks changes they may appear to move randomly left or right or a combination of both. The image looks very odd, often a jumbled mess, as perhaps the tops of the stalks appear to move one way while lower parts appear to go the other.

There is a great example of temporal aliasing here in this clip on Pond5 https://www.pond5.com/stock-footage/item/58471251-wagon-wheel-effect-train-tracks-optical-illusion-perception

Notice in the pond 5 clip how it’s not only the railway sleepers that appear to move in the wrong direction or at the wrong speed but notice how the stones between the sleepers appear to look like some kind of boiling noise.

Like the old movie wagon wheels one thing that makes this worse is the use of too fast a shutter speed. The more you freeze the motion of the offending objects or textures in each frame the higher the risk of temporal aliasing with moving textures or patterns. Often a slower shutter speed will introduce enough motion blur that the motion looks normal again. You may need to experiment with different shutter speeds to find the sweet spot where the temporal aliasing goes away or is minimised.  If shooting at 50fps or faster try a 360 degree 1/50th shutter as by the time you get to a 1/50th shutter motion is already starting to be as crisp as it needs to be for most types of shots unless you are intending to do some for of frame by frame motion analysis.


Temporal Aliasing – Beware! was first posted on February 13, 2020 at 5:22 pm.
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How We Judge Exposure Looking At an Image And The Importance Of ViewFinder Contrast.

This came out of a discussion about viewfinder brightness where the compliant was that the viewfinder on the FX9 was too bright when compared side by side with another monitor. It got me into really thinking about how we judge exposure when purely looking at a monitor or viewfinder image.

To start with I think it’s important to thing understand a couple of things:

1: Our perception of how bright a light source is depends on the ambient light levels. A candle in a dark room looks really bright, but outside on a sunny day it is not perceived as being so bright. But of course we all know that the light being emitted by that candle is exactly the same in both situations.

2: Between the middle grey of a grey card and the white of a white card there are about 2.5 stops. Faces and skin tones fall roughly half way between middle grey and white. Taking that a step further between what most people will perceive as black, something like a black card, black shirt and a white card there are around 5 to 6 stops and faces will always be roughly 3/4 of the way up that brightness range at somewhere around about 4 stops above black . It doesn’t matter whether that’s outside on a dazzlingly bright day in the desert in the middle East or on a dull overcast winters day in the UK, those relative levels never change.

Now think about this:

If you look at a picture on a screen and the face is significantly brighter than middle grey and much closer to white than middle grey what will you think? To most it will almost certainly appear over exposed because we know that in the real world a face sits roughly 3/4 of the way up the relative brightness range and roughly half way between middle gray and white.

What about if the face is much darker than white and close to middle grey? Then it will generally look under exposed as relative to black, white and middle grey the face is too dark.

The key point here is that we make these exposure judgments based on where faces and other similar things are relative to black and white. We don’t know the actual intensity of the white, but we do know how bright a face should be relative to white and black.

This is why it’s possible to make an accurate exposure assessment using a 100 Nit monitor or a 1000 Nit daylight viewable monitor. Provided the contrast range of the monitor is correct and black looks black, middle grey is in the middle and white looks white then skin tones will be 3/4 of the way up from black and 1/4 down from white when the image is correctly exposed.

But here’s the rub: If you put the 100 Nit monitor next to the 1000 Nit monitor and look at both at the same time, the two will look very, very different. Indoors in a dim room the 1000 Nit monitor will be dazzlingly bright, meanwhile outside on a sunny day the 100 Nit monitor will be barely viewable. So which is right?

The answer is they both are. Indoors, with controlled light levels or when covered with a hood or loupe then the 100 Nit monitor might be preferable. In a grading suite with controlled lighting you would normally use a monitor with white at 100 nits. But outside on a sunny day with no shade or hood the 1000 Nit monitor might be preferable because the 100 nit monitor will be too dim to be of any use.

Think of this another way: Take both monitors into a dark room and take a photo of each monitor with your phone.  The phone’s camera will adjust it’s exposure so both will look the same and the end result will be two photos where the screens will look the same. Our eyes have iris’s just like a cameras and do exactly the same thing, adjust so that the brightness is with the range our eyes can deal with. So the actual brightness is only of concern relative to the ambient light levels.

This presents a challenge to designers of viewfinders that can be used both with or without a loupe or shade such as the LCD viewfinder on the FX9 that which be used both with the loupe/magnifier and without it. How bright should you make it? Not so bright it’s dazzling when using the loupe but bright enough to be useful on a sunny day without the loupe.

The actual brightness isn’t critical (beyond whether it’s bright enough to be seen or not) provided the perceived contrast is right.

When setting up a monitor or viewfinder it’s the adjustment of the black level and black pedestal which alters the contrast of the image (the control of which is confusingly called the brightness control). This “brightness” control is the critical one because if the brightness adjustment raises the blacks by too much then you make the shadows and mids brighter relative to white and less contrasty, so you will tend to expose lower in an attempt to have good contrast and a normal looking mid range. Exposing brighter makes the mids look excessively bright relative to where white is and the black screen surround is.

If the brightness is set too low it pulls the blacks and mids down then you will tend to over expose in an attempt to see details and textures in the shadows and to make the mids normal.

It’s all about the monitor or viewfinders contrast and where everything stits between the darkest and brightest parts pf the image. The peak brightness (equally confusingly set by the contrast control) is largely irrelevant because our perception of how bright this is depends entirely on the ambient light level, just don’t over drive the display.

We don’t look at a VF and think – “Ah that face is 100 nits”.  We think – “that face is 3/4 of the way up between black and white” because that’s exactly how we see faces in all kinds of light conditions – relative levels – not specific brightness.

So far I have been discussing SDR (standard dynamic range) viewfinders. Thankfully I have yet to see an HDR viewfinder because an HDR viewfinder could actually make judging exposure more difficult as “white” such as a white card isn’t very bright in the world of HDR and an HDR viewfinder would have a far greater contrast range than just the 5 or 6 stops of an SDR finder. The viewfinders peak brightness could well be 10 times or more brighter than the white of a white card. So that complicates things as first you need to judge and asses where white is within a very big brightness range. But I guess I’ll cross that bridge when it comes along.


How We Judge Exposure Looking At an Image And The Importance Of ViewFinder Contrast. was first posted on February 10, 2020 at 10:02 pm.
©2018 “XDCAM-USER.COM“. Use of this feed is for personal non-commercial use only. If you are not reading this article in your feed reader, then the site is guilty of copyright infringement. Please contact me at contact@xdcam-user.com