Talk:Moiré pattern

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[edit] Old stuff not previously in a section

I deleted the following text because the explanation seemed questionable:

 "[moiré patterns sometimes occur when scanning halftones], 
 when the image interferes with itself on either side 
 of the scanner's glass surface."

I wonder whether this explanation is a fact, or only a theory. Another possible explanation is aliasing from undersampling the halftone pattern. Jorge Stolfi 20:52, 24 Mar 2004 (UTC)


The two above concepts are both correct. Scanners scan in lines. The spacing of those lines combined with halftone patterns creates moire patterns.


Should this article include some description (and example?) of the use of moiré patterns in 1960's pop art? [[User:GK|gK ¿?]] 06:33, 18 Nov 2004 (UTC)


common in lamps of the 60s and 70s had concentric spirals of differing pitch. One spiral is rotated and moire patterns emerge. Beer companies also made really interesting lamps that used moire patterns to simulate water flowing.



Moire was merged into this article. JRM 15:07, 2004 Dec 3 (UTC)

[edit] Moire in art reproduction

Moire patterns can ocur when items at a regular frequency are not at proper angles to generatee a pleasing pattern. Yes, scanning screened images is a prime example of how moires occur in the reproduction industry. Image: moiredots.png --Dkroll2 17:29, Dec 27, 2004 (UTC)

In everyday life.... I first observed moire patterns in fences. When you drive parallel to a chain link fence that has another parrellel chain link fence behind it, you can see large diamond shapes moving across the fence. They are moire patterns. They are diamond shapes because the chain links are diamond shaped. Circular grating creates circular moire patterns.

Helicopter blades moving at high speads create a virtual moire pattern. It is an illusion that makes the blades appear to spin in the reverse direction. The illusion is a moire pattern created by the speed of the blades in relation to the sampling speed of the human eye.

  • I have to comment on this. You see the effect only in a video or film rendition of the helicopter, not in "real life". The effect is due to video and film "dividing" time into discrete fragments, or frames. The human eye doesn't do this. However, due to our persistence of vision, we see the effect when viewing the record. Just my two cents... --Janke | Talk 16:01, 7 August 2005 (UTC)
Not true. Look at a spinning tyre. It does appear to spin backwards. This is, however, not Moire interference but the stroboscopic effect

[edit] Bad Link

I commented out one of the links at the bottom of the page because it is broken. The site still exists, however, so I imagine that the info is still out there, but someone needs to track it down and fix the link.

[edit] Moirés in digital images of TV screens

Couple of points/questions:

  • The arrow marks a scan line, but I belive the moire pattern from this is just another example of the next point.
  • The remaining patterns, I believe, are not necessarily due to "interference" but that the resolution of the CCD is insufficiently small to satisfy the sampling theorem. It's not interference, but aliasing.

Cburnett 06:02, August 6, 2005 (UTC)

The camera used was 5 megapixels, so there are more than enough pixels for interference to occur. The uploaded image is reduced in size. The arrow actually marks where the first scan started - we see an image containing one partial, one full scan, interlaced. --Janke | Talk 06:11, 6 August 2005 (UTC)
Moire patterns are not a result of interference. Interference has no meaning in this context since it generally means noise, but noise doesn't cause moire patterns. 5 MP can still be insufficient to satisfy the sampling theorem.
In this case, the resolution of each pixel needs to be less than half the width of the black border around a pixel since it's the "highest frequency". Like I said, I believe it to be aliasing causing the moire patterns, not "interference" (please define this if you intend on using it further as well as in the article itself). Cburnett 04:53, August 10, 2005 (UTC)
Better now? I removed "interference", which I originally used as a general term, not a technical one. Please feel free to clarify the text further. --Janke | Talk 15:38, 11 August 2005 (UTC)

[edit] another example of bad resampling

image:GaFlag2001.jpg versus

Observe how the stripes on the first and last flags appear slanted as a result. Btyner 16:14, 17 May 2006 (UTC)

[edit] Another example of a Moiré pattern

Image:Hjalmar Hammarskjöld.jpg --Oden 23:34, 25 July 2006 (UTC)

[edit] Interferometric approach

I think the Interferometric Approach section is exactly wrong, but I'd welcome comment on this.

The problem is that adding the two sine waves models what would happen if you projected two sine waves onto a screen. It does not model the effect of superimposing a transparent sine-wave pattern onto another (transparent or opaque) sine-wave pattern, which is what we're talking about in the rest of this article. To model superimposition we need to multiply the sine waves and not add them.

Multiplying two sine waves close in frequency gives you the sum of two sine waves: one at the mean frequency and one at the difference frequency. It is the difference frequency that (It's exactly the same effect as heterodyne or synchronous detection in radio receivers, only in space rather than in time).

Also, you can't use the sine function directly to denote degrees of transparency, because it can take negative values. Transparency should vary from 0 to 1, which can be done by using ½(1+sin) in place of sin.

My editing skills aren't up to altering the mathematical formulae on this page but in any case I thought people should have a chance to comment first.

JoeBruno 12:05, 22 August 2006 (UTC)

Yes, you are right, and the analysis shown doesn't explain why the low-frequency envelope appears as such a prominent signal. It's easy to fix by specifying that the physical model of overlying transparent objects is multiplication of their transmittances, and that the sinues are logs of transmittances, or (negative) densities. Then, the final result, the sum is still a density, and the envelop component leads to a real intensity signal at that frequency when the log is exponentiated to get an optical intensity back. Then you avoid issues of negatives, multiplying sines, etc., and can still use an interferometric approach. Maybe I'll work on it later... Dicklyon 16:25, 22 August 2006 (UTC)

[edit] Animated image removal poll

Moiré patterns formed as a result of interference of parallel lines rotated by an angle of 0° to 6°
Moiré patterns formed as a result of interference of parallel lines rotated by an angle of 0° to 6°

I propose we remove from the article this visually obnoxious and distracting animation. Please response here with "*Support" or "*Oppose" followed optionally by a comment. Dicklyon 16:29, 22 August 2006 (UTC)

Hearing no objection, I'll take it out for now. If you object, say so or put it back. Dicklyon 20:30, 30 August 2006 (UTC)

[edit] pronunciation

someone should add the pronunciation of the word ... 'cause i dont know it

Sounds like as good a reason as any; in the meantime, try a dictionary. Dicklyon 23:17, 13 October 2006 (UTC)

but the dictionary wiki suggested i try here! you can see the predicament im in. and my speach is tomorrow!!

quick web search suggests "more-ay", "more-RAY", "moa-ray", "mwa-RAY", etc. Pick one. Dicklyon 20:58, 20 October 2006 (UTC)