Film grain, persistence of vision, sensor tubes, and experienced resolution.

At various times in my career I’ve had to think about image resolution, film grain, how to pull a clean image from a noisy video, and orbiting gamma-ray observatory sensor tubes. The question is: how much digital resolution is needed to represent the analog resolution of motion picture film? Or maybe it’s more of a statement: How to problematize the question of – “how much digital resolution is needed to represent the analog resolution of motion picture film?”, or at least have fun thinking about it.

When I worked at the visualization lab at UCR, in the dark ages, I remember a physicist talking about a project he was working on for an orbiting gamma-ray observatory that was going to map background radiation from outer space. They wanted to do this at a very high resolution. The problem was that the gamma particle sensor tubes they used could only resolve to a couple degrees at a time – basically 1/180th of the sky in a circle. A 180 sample map is not very high resolution. But he had a trick. The orbiting platform would be incredibly stable and predictable, so they could take a bunch of overlapping coarse passes with such accuracy that his software would be able to synthesize a much higher resolution of the sky – to fractions of a degree. This is how things like synthetic aperture radar work.

A little while later a mathematician came into the lab and wanted a still from the X Files credit sequence “The Truth is Out There”, for a presentation slide, but we couldn’t get a clean screen grab from the VHS tape. It was weird – the text and the background were stable, and at playback speed the image seemed clean enough – it’s only when we’d freeze a frame that the text melted into a fuzzy blob of static. So then I thought about it – basically every frame is like a gamma particle collection tube, the TV screen isn’t moving and neither are the text or the background. What if I were to “blend” a number of these frames together? Would a get a much clearer result? The answer was yes. And not just because of an NTSC fields vs frames thing – the more frames I combined the clearer the text became. What that blending method was I’ll leave up to the reader – and if you figure out let me know because I’ve forgotten. The point was that accumulating noisy images over time emphasized their similarities – the text, and deemphasized the differences – the smearing static. I’ve also used a similar technique to accumulate/synthesize a high resolution still from multiple low resolution renders each with slight camera shifts.

Okay so back to film grain and the resolution needed to represent a movie film frame with a digital frame. Here’s the fun part to mull over. A digital image is a regular grid of pixels in rows and columns. A film image is an irregular matrix of physical grains of stuff holding onto dyes of different colors – they aren’t uniform in size and certainly not uniform in location – and this all changes, randomly for every frame. Your brain does a great job of blending all of this together over time, just like blending together the video frames. How much digital resolution is needed to represent movie film? I remember when a 2K image was going to be more than enough. Now we’re pretty sure we need 4K. I wonder what kinds of phantom resolutions happen in our minds from the accumulation of unpredictable tiny grains of color? What kinds of resolution apertures we can synthesise out of all that noise? How do we experience different presentations of visual resolution?

here’s a link with some neat diagrams illustrating synthetic aperture radar:



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Over 20 years of experience in creative/technical supervision and design in Visual Effects, Feature Animation and Scientific Visualization.

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