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Moiré effect on fabric

Paul Rotheroe , Feb 04, 2009; 05:32 a.m.

The photograph accompanying this question is a section of a photo taken with a Canon 5D with a 24-105 mm zoom lens. As you can see there is a strong moiré effect on the material of the jacket. Other photographs taken indoors and outdoors of the same jacket some have a moiré some do not. Is there anything to do to avoid or eliminate the moiré? Would a film camera have given better results? Any suggestions or explanations would be appreciated.


Moiré on jacket

Responses


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Ronald Moravec , Feb 04, 2009; 06:44 a.m.

I have seen this come and go depending on the screen magnification which tells me it is something other than moire. I had it on a dark green small fine knit shirt when I was photographed by the company photographer with a a Canon. When I told him about it, he said it was not moire. He is now a Canon education rep so I presume he knows what he is talking about.

Mike Earussi , Feb 04, 2009; 08:00 a.m.

It's obviously a digital artifact so a film camera would not have produced this.

Allard K , Feb 04, 2009; 09:02 a.m.

Moire in photography is mostly a digital problem, you need two grids for it. The sensor grid and the clothing grid make two. Be aware that it might be a problem of the grid of pixels on your screen display. If the problem still looks the same when you have zoomed in to the original image to 400% or so it is a real problem in the image.
It is normal that you do not see it in all the pictures, because the occurrence of this effect depends strongly on how big the jacket is in you photograph.
Most digital cameras have so-called anti-aliasing filters in front of their sensors to prevent this problem but sometimes those are not good enough (they limit resolution, which is a good reason to not make them too strong). Did you shoot in JPEG? If you shot RAW, using a different RAW converter (or different demosaicing algorithm, if your converter lets you choose) may help. Also applying less sharpening and/or a bit of blur or luminance noise reduction during raw conversion can help.

Matt Laur , Feb 04, 2009; 09:47 a.m.

You absolutely CAN have a film image do this. The clothing has a grid pattern, and the fact that you're looking at it on a computer screen means that - with no escape - you've got another grid. That's all it takes to induce the interference pattern.

If the image file has been properly handled when it's being down-sampled for lower-resolution display, this won't happen. But a very common problem (and it never ceases to amaze me that people do this) is the placement of a JPG image like this into web content, and then the use of HTML instructions in the image tag that tell the browser to show the image at a different size. So, if you've produced an image that's 800 pixels wide, and it preserves enough of the textile detail to still show it... and then in the HTML image tag that tells someone's web browser to show the image, that 800 pixel dimension is set to, say, 600 pixels... trouble! The web browsing software, with no attempt to prevent Moire patterns, is going to simply throw away two of out every eight pixels. Unintelligent image resizing by browsers and Flash run-time software can cause havoc that way. Always make sure your images are displayed at the same resolution you rendered the file.

Paul Rotheroe , Feb 04, 2009; 11:02 a.m.

Thank you for your replies. The moiré is not a screen problem. The image was shot in RAW formaat and processed in Lightroom 2. I think I'll need to follow Allard K suggestions and see if I can eliminate it.

Dan Ferrel , Feb 04, 2009; 07:29 p.m.

You absolutely CAN have a film image do this. The clothing has a grid pattern, and the fact that you're looking at it on a computer screen means that - with no escape - you've got another grid. That's all it takes to induce the interference pattern.

Only to add to that, when you scan the film onto the computer there's another grid from the scanner.

To Paul, are you seeing this in the camera? If not then it may be something in your post processing. Is your dpi in the RAW converter set to 72dpi? If so I would change that. Even if it's not I would start with the dpi setting and go from there. Are you shooting RAW or sRAW?

Robert Lee , Feb 04, 2009; 11:33 p.m.

Is there anything to do to avoid or eliminate the moiré?

It can be avoided if you're mindful when shooting.

  1. Pull back on the framing. This shifts the fabric texture frequency up (relative to the sensor) so that the camera's anti-aliasing filter prevents the moire.
  2. Push forward on the framing. The fabric texture is shifted down in frequency where it can be sampled by the sensor without aliasing in the first place.
  3. If capturing the detailed fabric weave is unimportant, shoot the image so that the fabric is blurred - open up the aperture to narrow the depth of field. This can work if the plane of interest, say the eyes in portraiture, is different from the rest of the framing.

If you're getting this problem on scanning film, set the scanner to the highest optical resolution supported. After digitization, resize the file down to the desired size using anything but the nearest neighbor algorithm.

Dennis Carbo , Feb 06, 2009; 07:43 a.m.

Not that this was an option but....Digital Backs in Multi Shot mode are usually a better choice when shooting fabric ...as long as its not moving LOL...The multi shot feature prevents moire

Paul Rotheroe , Feb 06, 2009; 08:35 a.m.

A postscript to the moiré problem. I tried lots of different methods using Photoshop to remove the moiré, none worked to my satisfaction. I then downloaded a 30-day demo of Capture One 4 Pro. The program has a moiré filter and that filter produced perfect results.


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