Serene Life

by garik

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I was just looking at a highrise building whose windows had a horizontal grill in front of them. There were several clothes drying in these windows and the sun was casting shadows on the cloth. The pattern caused by the shadows and the grill together looked very much like moiré to me, especially when the cloth moved in the breeze.

Does the human eye see moiré in a similar way to digital cameras?

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I'm getting old. I didn't know moire was commonly refered to the effect seen in digital cameras, just that it was two overlapping patterns. :) ("what is the picture on the save button, dad?") –  Macke May 5 '13 at 19:37

6 Answers 6

up vote 10 down vote accepted

Human eyes see moiré in the overlapping of two regular patters. In photos you see the photographed pattern overlapped with the pixels, which form the second pattern.

Of course you can see moiré with your naked eyes, but you need two overlapped patterns in the scene. Your eyes don't add one of them.

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Yes, that would be a very good description of what I saw. There was a pattern formed by the horizontal bars of the grill, and an overlapping pattern created by the shadows... –  Chinmay Kanchi May 5 '13 at 14:43

"The pattern caused by the shadows and the grill together looked very much like moiré to me"

It was moiré. Two overlaying pattern causing combination patterns is what a moiré pattern really is.

When moiré pattern appears in a digital camera, one of the patterns is the pixel grid of the camera sensor. As humans doesn't have a pixel grid in their eyes, a moiré pattern can't occur from looking at a single pattern.

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Moire is a kind of "aliasing" - an effect where something is seen (or heard) incorrectly because the frequency of the source is too high for the sensor (in a picture high frequency is caused by repeating patterns where the individual pattern is too small to be recorded).

Aliasing does happen in the human eye (at least in theory - because you can't really see it) - but because the "pixels" in the eye are distributed randomly and not in a grid the results of the aliasing should be random noise and not moire patterns - this noise is cleaned up by the brain as part of the normal (and very extensive) processing of the vision system and you never actually notice it.

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Yes they do. I actually just noticed this on my drive into work last week. We have a couple of high rises off in the distance that we can see from the highway and with the lighting the way it was the other day and the angle of things, there was a distinct moire to the lines of the windows.

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Probably we do, but our "pixels" (rods and cones) are not evenly distributed, so it is not the same, and the resolution of our vision is different for the different colours (almost no blue cones, and twice green as red/yellow ones), so it is unlikely to produce the moire cased by two identical overlapping grids. So is this "similar" enough to be a yes to your question? Judge for yourself:

Look at this Paper

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I find it's helpful in cases like this to remember that the human eye isn't solely responsible for what we see. It's at least as important to consider how the human brain contributes to our vision. Virtually all optical illusions take advantage of our brain's tendency to "see" things that deceive us, including still images that appear to move when we look at them.

In practice, our brains are constantly re-evaluating and processing the raw information that's pouring into them via our eyes. I saw a fascinating experiment on a show called "Brain Games" on the NatGeo channel last week where two people saw different things in the same movie clip based solely on additional audio input given via headphones -- and they changed their minds when the two people switched headphones. When it comes to human vision, it's just not enough to measure the performance of the eyes themselves.

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