Not sure how much camera resolution you need for the project you're working on? This article talks about a few examples of what can alter the perceived resolution.
Visual effects is neck deep in resolution concerns, and I’m here to unpack some of that today. In order to argue back against the “bigger is better”, you will need to understand how resolution matters to us as viewers.
The grain of the film or sensor, the sharpness of the lens, the shutter angle, and the frame rate all alter the perceived resolution in various ways. I will discuss a few of these factors below.
A friend of mine was making work for a video billboard, and when he shared the specs with me, my jaw dropped. He told me that the video should be 400 pixels wide, smaller than standard def. That sounded crazy to me, that something 40 feet wide would only have 10 pixels per foot, a staggeringly low resolution. My friend explained that while billboards are huge, you never get that close to them, so you aren’t able to see the pixels.
There’s a real-life analog to this phenomenon: the sun and moon.Your distance from an object affects how big that object appears to you, and for viewable media, the only thing that matters is how big a screen is in your field of view.
Think of your field of view being a 360-degree arc parallel to the horizon, with objects taking up a portion of that arc. If it’s taking up half of that arc, it occupies 180 degrees of your field of view. The sun and moon each occupy one half of one degree of arc. To calculate how many pixels you need for your screen, you need only to measure the degrees of arc and convert that to pixels.
20/20 vision is 60 pixels per degree, but I like to round up to 100 pixels per-degree. Better safe than sorry after all. If you have a screen occupying 30 degrees of your field of view, a 3K image will be conservatively safe. There are a lot of other factors that go into increasing and decreasing resolution, but I want to set up a rule of thumb here.
For real world measurements, the easy way to check if a job needs to be more than HD is the hang loose gesture. If you extend your pinky and thumb as far away from each other as you can, and stick your arm straight out, the distance from thumb to pinky is approximately 20 degrees, so if the screen sticks out on either side, you’re gonna need more resolution.
The strangest in my book is frame rate. Doubling the frame rate on playback (e.g. shooting 48fps and playing back 48fps like they did for The Hobbit) makes an exceptionally sharp image, to the point where a 2K 48fps image may seem sharper than a 6K 24fps image. It’s very neat, but has consequences. For one, all props, hair, makeup, and sets look more real. Not movie-real, but movie set-real. If you have an opportunity to watch a film in high frame rate (HFR) do it. You may not like it, but it’s something worth understanding.
Grain also adds perceptual sharpness, and for my money you should work at 2K, upscale to 4K and then add grain.
If you are looking for a very informative video on which camera you should choose and what I consider the last word in the resolution discussion, I recommend Steve Yedlin’s (Director of Photography for Star War: The Last Jedi) resolution videos.
He breaks down the differences in film and digital cinema cameras, resizing algorithms and other contributing factors to perceptual sharpness.
His thesis isn’t that one camera is better than another, but that you should make an informed decision about your needs and choose a camera accordingly. (e.g. IMAX 11K film scans have more grain for a similar amount of sharpness to the Alexa 65’s 6K image, and a 6K scan of 35mm film is considerably noisier than any of the other formats he tests and only about as sharp as the Alexa XT’s 2.8k sensor.)Keep a look out for the soul crushing “this is what happens when your 4K master is compressed for broadcast” section late in video two. After spending an hour and a half talking about the nuances in grain and contrast, it’s brutal to see what compression does to the image. But conversely, when you’re watching it on your TV and it’s only occupying 15 degrees of arc, that’s probably fine. Resolution is funny like that.
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