Moiré effect on fabric

Discussion in 'Portraits and Fashion' started by paulroth, Feb 4, 2009.

  1. 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.
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  2. 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.
     
  3. It's obviously a digital artifact so a film camera would not have produced this.
     
  4. 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.
     
  5. 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.
     
  6. 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.
     
  7. 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?
     
  8. 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.
     
  9. 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
     
  10. 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.
     
  11. Will this show up in print? I'm assuming not since the computer screen is a factor, right? But then this happens with film too, or is that just when you scan and view it on a computer?
     
  12. It takes two things to give you that pattern, so if #1 is your camera sensor and #2 is the fabric, it will show up in print. You'll know if its your screen acting as the second influence if the pattern dissappears as you zoom in and out. If it is your screen, it won't show up in print.
    Zooming slightly either direction will change the pattern relative to the sensor, so not all frames will have moire.
    To eliminate the moire in PS, you have a few options. When dealing with a black tux (which is my common experience), I simply add a new layer, set the blend mode to color, and paint away sampling from the tux jacket that is not effected. You can also make a selection, copy it, blur it slightly, then set the blend mode to "color" to eliminate the color part of the moire. As far as a pattern due to varying tone, I find cloning on two blank layers set to lighten and darken usually yeild acceptable results. I haven't tried any plug-ins, but will be looking into the one mentioned above.
     
  13. Hi, has this issue been discussed in terms of using Photoshop's LAB? Dan Margulis writes how to get rid of moire. I tried doing it and will try to upload it. Please let me know if it is acceptable as getting rid of moire. It took me about 3 minutes to do this, so I hope to use workflow more often when given moire problems in images.
    Thanks.
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  14. Dear Tae Moon. The Lab method has made the moiré less obvious. I'm sure in some situations it would be the complete solution so it would be interesting to see how to apply it.
     
  15. Hi Paul,
    As this technique is not mine, I credit Dan Margulis. Photoshop LAB Color, the Canyon Conundrum and Other Adventures in the Most Powerful Colorspace, ISBN: 0-321-35678-0 from PeachPit Press. I highly recommend the book (although there is unconfirmed talk about another edition), as it serves photographers who must do their own post production. As such, please contact me off-list for a detailed explanation.
    The reason why I found this image difficult is because most moire reducing examples are shown from a dark colored suit. You can do a moire search and you'll see another posting that is similar but the suit is dark. In dark suits, this moire reduction technique is more successful. So this technique needs some improvements in terms of getting rid of moire in light colored suits but it does well in the dark colored suits.
     

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