Talk:Moiré pattern

message: The Etymology section (added on March 12, 2014) seems to be a prank. It links to an article about a supposed Swiss photographer named Ernst Moire who could not himself be photographed. I'm pretty sure that moire patterns are named after moire fabric, of which there is an etymology at http://en.wikipedia.org/wiki/Moire_(fabric), but I don't have a source for that. I'm just going to go ahead and delete the bogus Etymology section and if someone has a better source for how moire patterns came to be called that in contexts other than fabric, they can add one back in.  — Preceding unsigned comment added by 64.223.163.225 (talk) 02:17, 19 March 2014 (UTC)
thread_title: Bogus "Etymology" Section

message: 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)
thread_title: Old stuff not previously in a section

message: 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.
--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)
replies: text: Just for the record, there is no such thing as "sampling speed of the human eye". The eye does not sample. Unless there were some new discoveries in that field, in which case I welcome links.
--Xerces8 (talk) 10:02, 28 August 2014 (UTC)
thread_title:  Moire in art reproduction 

message: versus 
Observe how the stripes on the first and last flags appear slanted as a result. Btyner 16:14, 17 May 2006 (UTC)
thread_title:  another example of bad resampling 

message: --Oden 23:34, 25 July 2006 (UTC)
thread_title:  Another example of a Moiré pattern 

message: 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)
replies: text: 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)
thread_title:  Interferometric approach 

message: 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)
replies: text: 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)

text: That can't work as described, because a click on an image always takes you to the image page, with the very same image (possibly larger), with copyright and other info. Notinasnaid 09:35, 11 April 2007 (UTC)
thread_title: Animated image removal poll

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

message: I restored the removal of nonlinear.  Moire patterns do not result when optical patterns are added linearly, as by the projection of two patterns onto one screen.  They require a nonlinearity, which is how the difference frequency components can be generated when they are not present in the originals.  The typical nonlinearity is an "and" or an "or" function, depending on how the patterns are combined.  For example, a stack of two transparent patterns is transparent when the first is transparent AND the second is transparent.  For ink on paper, a spot gets ink if either one OR the other pattern would have ink at that spot.  Linear combination, pretty much the definition, does not generate new frequencies. Dicklyon 05:59, 10 January 2007 (UTC)
replies: text: For completeness, I'm adding a comment here (I thought I already had) that I was the person who deleted the nonlinearity reference. I'm not yet convinced, but I will consult the reference. Thanks. Victor Engel 17:42, 10 January 2007 (UTC)

text: I would like to see more detail about the nonlinearity. For example, if both component images are themselves nonlinear, then of course, the combination image is likely to be nonlinear. It sounds like what's being suggested here is that if both component images are linear images and the combination is nonlinear, than moire will result. Is that about the size of it? Victor Engel 20:53, 10 January 2007 (UTC)
replies: text: I'm not sure what you mean by the images themselves being nonlinear.  Consider any real scene, like the original brick wall image in the article.  Is it linear?  Nonlinear?  Does it matter?  I don't think so.  But if you multiply it by a grid of delta functions or sampling apertures to create samples of it, you get aliasing or moire pattern due to that nonlinear multiply operator.  Viewing it through a wire mesh has the same effect, since the mesh interacts nonlinearly with the original scene, like sampling it does.   But projecting the original image onto a screen, and then projecting an image of a wire mesh on the same screen will not create a moire pattern, since those images just add their intensities linearly; a nonlinear warp of that image could, however induce a moire, and it's possible that in some cases there might be enough nonlinearity in your eye to induce some weak moire; but it's still due to a nonlinear interaction of the patterns.  Dicklyon 22:48, 10 January 2007 (UTC)
replies: text: Interesting that you don't know what I mean by the images themselves being nonlinear since my original reason for removing "nonlinear" from the article was that it was not clear what was meant by that. It certainly didn't seem to follow from the link to the nonlinearity article. I'm still unclear whay you mean by nonlinearity as it relates to Moire. Victor Engel 04:41, 11 January 2007 (UTC)
replies: text: Well, we have to go back to what it means to be linear.  A function or system f(x) is linear if the response to a sum of inputs is equal to the sum of the responses to the the inputs separately.  The photoreceptors in your eye are not linear, but to first order they're close enough over a range of stimuli to model them as linear in optical intensity.  So if you have an optical pattern x and your eye's cones respond as f(x), and another pattern y to which you respond f(y), then if you project the sum of those patterns into your eye, you get x+y and respond as f(x+y) = f(x)+f(y).  That sum of x and y that you projected into your eye is a linear combination, and your eye responds linearly, and sinusoids are the eigenfunctions of continuous-domain linear systems (see LTI system theory), so no new frequencies are generated in the process; to the extent that your eye is not really quite linear it may generate weakly some difference frequencies that you perceive as weak moire patterns.  Now, take those same x and y and combine them with something other than a sum; say min(x,y) or max(x,y) or x*y.  The resulting optical pattern has strong "distortion" terms, with sum and difference frequencies and such, and when you project that into your eye or a linear sensor system it will respond strongly to those frequencies that were not present in either x or y but are present in their nonlinear combination; that's how moire patterns are formed.  The nonlinear articles alludes to these min, max, and times operators when it says "nonlinear systems is not subject to the principle of superposition, as linear systems are". Dicklyon 05:45, 11 January 2007 (UTC)

text: You call the interaction between the patterns non-linear.  The description of the effect is non-linear (with its quadrates and sines), but not the interaction.  You mention step funtions and sampling rates: these may be discontinuous but that does not make them non-linear in the sense that the term is commonly used nowadays in dynamics.  So I say remove this adjective from the intro, and just speak of "interaction of the optical patterns". Tom Peters 23:12, 10 January 2007 (UTC)
replies: text: I did not mention either step functions or sampling rates.  And the point of the impulse functions or sampling apertures was not their discontinuity, but rather their effective multiplication.  Consider for example a mesh of fuzzy holes, with 0 transmission in the mesh lines, 1.0 in the centers of the holes, and varying smoothly and continuously from 0 to 1 around the edge of the holes.  Lay that over another pattern, or illuminate a pattern through it, and you have effectively a product, a nonlinear combination of the two patterns, which will likely give rise to a moire pattern.  Try it.  Then, try projecting two patterns from two overhead transparency projectors onto one screen, so the optical intensities combine linearly, and you'll see that you can't make a moire pattern that way.  You can do such experiments in photoshop if you're careful and knowledgeable enough, but since by default it does operations in the nonlinearly gamma compressed space, it's not so easy to simulate linear interactions of optical patterns there. Dicklyon 05:45, 11 January 2007 (UTC)

text: Take a look at the animation above, or this still version that's easier to analyze.  What do you see?  Step way back until you can't see the lines at all any more.  Do you see just a gray area with some bright stripes running across it?  I do.  What makes those stripes bright?  If you look carefully, you can see that there are fewer black pixels in those bright rows, because where the lines land on top of each other you only get 1 black pixel instead of the 2 that you get in other rows.  In the animation, the light stripes follow the places where the lines overlap each other and give less blackness than when they don't.  This low-frequency pattern of light stripes in gray is not in the original fine stripe patterns--it is induced by the nonlinearity, which you can take to be min(x,y) if x and y are optical intensity, or max(x,y) if x and y are an amount of ink, or x*y if x and y are 0 for black and 1 for white.  But there's no way that a combination like x+y would generate such a pattern, because when you'd stand back far enough to blur it out there'd be nothing left but the sum of the average gray values of x and y.  Get it? Dicklyon 05:55, 11 January 2007 (UTC)
thread_title:  Nonlinear interaction 

message: I think that this small experimental site I've put together with a friend should be added to the external links
http://www.pompandclout.com/moire/
it is meant as an exploratory realm for us (and potentially others) to explore the visual qualities moiré patterns as they relate to art and design.
I also think that "conflict of interest" guidelines don't have to be taken so literally, given the direct and obvious correlation between the content of this wikipedia page and the site I'd like to add. I'm not trying to be an arrogant a$$... just not used to this.
thanks, would love to see the site up and think others would appreciate it.
-ryan 72.195.135.6 08:31, 11 April 2007 (UTC)
replies: text: I disagree.  The guidelines of WP:COI should be taken very seriously.  Your job is to convince someone else to add it, since if you add it yourself it will be removed. Dicklyon 22:12, 16 April 2007 (UTC)

text: Why can't I convince you? do you think the stuff we've done is uninteresting/nontechnical/sophomoric/groundbreaking/all of the above?72.195.135.6 15:20, 18 April 2007 (UTC)
thread_title:  Moiré Corps. 

message: I'm amazed that not only does this article not mention descreening (a software option for optical scanners), but apparently it isn't mentioned anywhere on Wikipedia at all.  Is there some technical reason for it to not be mentioned, or has the term simply never come up and it might as well be included?  —Preceding unsigned comment added by 4.254.115.210 (talk) 21:24, 16 October 2007 (UTC)
thread_title:  Descreening? 

message: Does anyone else think that the use of the word "interference" is somewhat confusing? Perhaps
as mentioned above "superposition" is a better description of the phenomenon, personally I think
interference suggests that amplitudes of light waves are interfering, as in diffraction. Clearly
Moiree patterns are a geometric optic phenomenon. What does anyone else think?
Yes, this has nothing to do with optical interferences.  These are spatial interferences, just a contrast effect. It is not a geometric optic phenomenon neither.
Right on!! Interference connotes wave amplitude and phase differences. These are well treated in all optics texts--which, incidentally, do not discuss the moire phenomenon, even in passing! Moire has nothing to do with wave optics. Moire is completely explained by a careful examination of the light paths from the source through the pattern (eg. screens) to the detectors. There is nothing mysterious about the perceived patterns. They are completely explained by the position of printers ink on the page. Ones subjective impressions from these patterns have nothing to do with physics. Moire may better belong in a discussion of optical illusions.  — Preceding unsigned comment added by Orblau (talk • contribs) 04:36, 31 May 2012 (UTC)
thread_title:  Interference 

message: Is it worth mentioning that there is a Moiré effect when using an image extractor looking for the correct pattern/position of the images while aligning everything, specifically noticed in an app known as "Tile Molester"(Google it)?  —Preceding unsigned comment added by Cm0n3y34 (talk • contribs) 01:57, 11 June 2009 (UTC)
thread_title:  Image files (Specifically within "ROM"s) 

message: I thought this photo of the World Trade Center buildings would be a good moiré pattern photo to include in the article, especially as a photo of a real thing and not a diagram.  This thumbnail's pattern differs from the diamond-shaped moiré in the original, too, showing some effects of downsampling.  Anyway, the article is so full of photos already that I'll defer to those who have worked on the images before.  Comet Tuttle (talk) 21:43, 5 January 2010 (UTC)
thread_title:  Another picture candidate 

message: this is very interesting: http://www.demoscene.tv/page.php?id=172&lang=uk&vsmaction=view_prod&id_prod=13916
some reference to related research perhaps?  —Preceding unsigned comment added by 213.221.224.21 (talk) 22:56, 27 February 2010 (UTC)
thread_title:  interesting use of moire patterns 

message: I think the article has too many images at right. A gallery should really be used instead when there are this many images. SharkD  Talk  02:03, 11 June 2011 (UTC)
thread_title:  Gallery 

message: It would be nice to have algorithms for the actual patterns. I.e. formulas to create them independently of the underlying shapes. SharkD  Talk  04:47, 26 June 2011 (UTC)
thread_title:  Algortihms 

message: Sorry, but I just read the etymology section and it makes no sense as written, as far as I can see. I don't know the etymology of the word (that's why I was reading it) so I cannot offer to correct it, but I am a linguist and I am pretty sure that what it says doesn't make sense. --A R King (talk) 13:33, 10 April 2014 (UTC)
thread_title:  Etymology again 

message: § Marine navigation begins
: The moiré effect is used in shoreside beacons called "Inogon leading marks" or "Inogon lights"... 
The  photo of an Inogon light at the start of this section does indeed show a pattern pointing to the right, but there are no arrows in the ordinary sense of the word. Instead, there are several lines converging to the right but not meeting. Where traditional arrow symbols (→, ⇒, ⇨) have just two lines that converge to meet at an angle, joined there by a third line that bisects the angle (the shaft of the arrow), the Inogon light displays multiple lines that do not meet, and there is no shaft.
I suggest replacing the sentence I have underlined with
: The moiré effect creates a set of lines that converge to the left or the right, suggesting arrowheads (<, >) pointing towards an imaginary line marking the hazard or line of safe passage. As navigators pass over the line, the "arrowheads" on the beacon appear to become vertical bands before changing back to arrowheads, now pointing in the reverse direction.
--Thnidu (talk) 00:30, 4 November 2019 (UTC)
replies: text: Perhaps they could be described as "chevrons pointing towards..." Jruderman (talk) 00:16, 3 May 2020 (UTC)
thread_title:  Marine navigation: "arrows" 

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