This seems to happen in real life when I look through a grid-like surface like, for example, a screen window. Is this the same process going on in real life or is it different?

Yes. Moire patterns are the product of two overlapping patterns. In pictures, this is between the camera's grid of sensors and the actual image. In this slide, it is between the shirt+tie and the implicit grid formed by dropping every other row/col.

Now I understand why it is recommended to wear solid color clothing when taking portrait photos, many cameras are not high resolution enough to avoid this aliasing artifact!

How come photos may look like the right hand picture on let's say a 2002 Canon camera, but once uploaded to a newer computer it may have visual changes (e.i lighting, contrast, etc), more definition, etc. ? What is happening to the pixels during transfer? Is it a pixel issue, is it a file issue (e.i. JPG vs RAW)? and do certain file types handle pixels sensing/editing/conversion differently or is it the camera itself that handles pixels?

Here's an interesting resource on Moire patterns: https://www.youtube.com/watch?v=d99_h30swtM

In this case, the shirt pattern is one dense pattern and every-other-pixel sampling is the other dense patter. When they are overlaid, it results in these weird additional effects.

@muuncakez Interesting question! I am unsure of the exact answer, since I don't know the specifics of the camera or how the JPEG encoding has changed since 2002. But here are a couple of considerations.

One possibility could be that there was no Optical Low Pass Filter (OLPF) in the camera. I don't if most cameras have this, Ren may know, but it was a common hack for photographers to get sharper images to remove this filter from the camera. The downside is that you may notice more Moire patterns as a result of removing this filter.

When photographs are taken in the camera, they go through the image processing pipeline, which can either output a RAW image, and do a bunch of transformations that turn it into a JPEG. More information on this pipeline can be found in this tutorial - https://www.eecs.yorku.ca/~mbrown/Brown_Tutorial.pdf on slide number 98. If you transfer the JPEG file to a modern day device, it may just be that the way your computer handles displaying JPEG has changed over time.

If you're comparing looking on the camera vs your modern day device, the display RGB and resolution could be different.

I'm only guessing here since I haven't seen your example, but if you'd like to talk about it more you can either go to ren's office hours or come to mine on friday night! Happy to chat more!

This is super interesting! An additional resource I found online is this youtube video: (https://www.youtube.com/watch?v=cvWF_Q5-Kt8&ab_channel=TheRoyalInstitution). It has a super cool lecture demonstration of Moire Patterns!

So this is why photos taken of computer screens look blurry. The pattern is caused by devices having different refresh rates.?

A clever application of moiré patterns in real life is Inogon lights or Inogon leading marks. These are shoreline beacons designed to help ships safely navigate through narrow channels and indicate underwater hazards. The lights are arranged in a specific configuration so that the moiré effect produces arrows that point to the target direction when viewed from either side and vertical parallel lines when directly aligned.

The US patent: https://patents.google.com/patent/US4629325

When I was looking for some of the interesting applications about Moire Patterns for imaging, I came across this concept called Moiré interferometry, which can be used to measure the deformation (strain) of materials under stress. I read a little about how it works here: https://wp.optics.arizona.edu/jcwyant/wp-content/uploads/sites/13/2016/08/MoireTechniquesLab12.pdf, but essentially the way it can be observed is that when the material deforms under stress, the grating on its surface also deforms. When this deformed grating is superimposed with another undeformed reference grating, we can observe moiré patterns.

If I wanted to take a picture of a computer screen with a weaker secondary camera, is my resulting photo (covered in blurry rainbow lines) because of differing refresh rates, the camera angle, Moiré patterns, or something else? Either way, glad to have some more information on dressing appropriately for photos.

This slide recalls me of when I took picture of a grid-like ("dot" shapes) screen (computer screen, projector screen) or cloth (especially the cloth of suits and ties), even with some of the newest-updated mobile phones or cameras. The outcome photo will have some weird "strips" on the screen or cloths, even though they cannot be seen by human eyes

I can remember often seeing pictures in a Moiré pattern way when I view screens from the side. Even on this slide, if I am on my laptop, I can make the first image look similar to the second image by viewing my laptop from certain angles. I'm guessing this is because I am skipping columns/rows by cutting them off in my new perspective? It's interesting to have a name for this type of change in an image!

I remember in the past the computer screens showed Moiré pattern. For now, when I look at computer screens by my eyes, I can't see Moiré pattern. But when I take photos of computer screens, it still shows Moiré pattern. Are the two kinds of Moiré patterns produced in the same way? I think the first is because of resolution, the second is because of sampling.

I always see a Moire pattern when I try to use my phone to take a photo of my computer screen. I'm guessing that's because my camera sensor grid is not completely aligned with the computer pixel grid?

The amount of applications for Moire patterns is astounding! While looking up ways Moire patterns can be used, I came across this article https://www.quantamagazine.org/when-magic-is-seen-in-twisted-graphene-thats-a-moire-20190620/ that describes how sheets of graphene, when layered and rotated by ~1.1 degrees, gains the property of superconductivity. The amount the sheet had been rotated was found to affect the energy required by electrons to tunnel through the sheets of the graphene superlattices, which allows the graphene to exhibit superconductivity at that very specific angle.

@YiweiIvy If you move your camera does the Moire pattern disappear at some point when they become aligned? But I guess if the grids have different mesh sizes we can never make the Moire pattern to disappear by simply moving the camera.

Maybe this is also a tip for designers and fabric manufacturers to consider pattern sizes that minimize the risk of moiré when captured in digital photographs. Would love to hear more about how different anti-aliasing techniques might be applied in practical scenarios!

Do browsers / image viewers implement checks to determine what the optimal sampling rate is to reduce artifacts such as moire patterns?