Weird Aliasing with striped shirts, What causes it?

Does anyone know what causes the weird look of finely striped shirts

in digital images? I recently had my photo taken and I was wearing

a shirt with thin stripes, and the stripes came out all wavy and

weird looking? What causes that, and is it avoidable/predictable?

What if you were taking portraits of a client and they wore

something like that? Does the affect happen in the camera or just

when viewed/printed at certain resolutions?

Is it aliasing (jaggy edges) or moire (interference patterns)? The former is caused by excessive sharpening, the latter by the absence of an optical low-pass filter in the camera.

How to avoid? Shoot with film.

Jeepers Creepers. With TV this was discovered in the 1940's. Striped shirts give weird artifacts on TV sets, and are well documented in "how to use TV cameras" manuals of the 1950's. Interference patterns with picket fences and striped patterns go back many centuries. With TV this weird banding effect is more common on an uncontrolled news shot, where a chaps shirt's pattern messes with the scans lines of the TV. Also the shirt might be too loud, and bloom abit. With westerns with movies, wagon wheels often get backward appearing rotation even in a 1920's movie; using a rotor shutter camera, that strobes to the wagons spokes.

have a look here for an explanation with some examples.

 

http://www.wfu.edu/~matthews/misc/DigPhotog/alias/index.html

Walters link describes it very well, and Yes it's a well recognised thing that happens with video and TV - that's why you'll never see a TV presenter wearing strips. IIRC, there isn't anything that you can do about it after the fact. The best that you can do is avoid fine pinstripes altogether - change the shirt if possible.

It's usually an issue of what camera was used. Most cameras have an AA (anti-aliasing) filter that eliminates the moire that you saw.

 

Some cameras with well documented problems in this ares include the Nikon D70 (a low cost camera, which might appear in low budget portrait operations), the Kodak SLR/n and SLR/c (higher resolution for higher budgets) and the Camerz (for institutional and corporate portraits).

 

It can also be a problem when viewed, because the resolution has to be reduced for viewing, and any time you reduce resolution, you can get moire, unless you apply an AA filter. Most viewing software doesn't have any moire filtering capability, so you'll almost always get it when you view, but not in the final print.

 

Printing software needs to increase resolution, and increasing resolution does not introduce moire (although if the camera gave you moire to begin with, you'll sure see that in the print).