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moire controls - how to get rid of moire on a black shirt??

1090 Views 11 Replies Latest reply: Apr 27, 2012 9:51 AM by léonie RSS
Kirsti Abernethy1 Calculating status...
Currently Being Moderated
Apr 26, 2012 12:44 PM

help! i've taken an image & the client wants it printed but there is a nasty moire on the guy's black tshirt. how do i best deal with this? can i use the moire control in RAW fine tuning?

when i tried this adjustment, the moire went away but only for the duration it took to process - then it appeared again after it stopped processing.... ? why?!

am probably not understanding something very basic here, but would really appreciate some help! anyone?

MacBook Pro (13-inch Mid 2010), Mac OS X (10.6.8)
  • Keith Barkley Level 5 Level 5 (5,140 points)

    Does it show up in the print?

     

    You might need to do a gaussian blurr on the t-shirt - just what the anti-alias filter in the camera is supposed to do.

  • dbmoore Calculating status...

    Hi Kristi

    Moire is a nasty effect when real.  Make sure you are looking at the image at 100 % view, if its there at 100% then you have it for sure.  If it prints then Keith is right about using gaussian blur but I might add that you can blur the one or two channels (in Photoshop) that showsn the worse.  There are techniques about using lab to blur the A & B channes also. 

     

    Sometimes when making a print if you change the dpi that will help,  make it 240 per inch or 360 per inch.  Are you using a high end digital back like Sinar or Phase one?  Good luck

    Cheers

  • léonie Level 8 Level 8 (46,405 points)

    The moire adjustment is exactly the control to use to get rid of nasty moire and aliasing -

    when i tried this adjustment, the moire went away but only for the duration it took to process - then it appeared again after it stopped processing.... ? why?!

    This looks, like you were looking at the old preview or the unprocessed master - have you toggled the "m" key to switch between master and preview? Also you may wish to update/delete the previews.

     

    I second Keith Barkley's suggestion to use an additional gaussian blur, if necessary. Also, since moiree is most noticable by the color and the shirt is black, you might try to brush in "Black and White" to get rid of the colors.

     

    Regards

    Léonie

  • Kirby Krieger Level 6 Level 6 (11,555 points)

    OP:  All good advice here -- and don't move forward without confirming the moiré problem at 100%, as dbmoore recommends.

     

    I would add to Léonie's clever advice that you will get even better results brushing in the "Color Monochrome" adjustment than you'll get with the (misnamed) "Black & White" adjustment.

     

    Somewhat frustratingly, the Color Monochrome brick does not let you sample a color from your image.  ("Hello?  Apple?  Pass Auf!") ... so here it gets a wee bit twicky:

     

    Use the Color Brick eyedropper to assign the color of the t-shirt to one of the available six slots.  _Make no adjustments with the Color Brick_.  In fact, you can "uncheck" the Color Brick adjustment.

     

    Then activate the "Color Monochrome" Brick.  Note that clicking the color swatch brings up the OS X color picker, whereas clicking the drop-down arrow brings up an Aperture-specific color picker.  Click the color swatch.  In the OS X color picker, click the magnifying glass (for consistency, this should be an eyedropper, but some of the runnels in the orchard are ahead of others).  Using your mouse cursor, which should now be a magnifying glass, click the square color sample you created in the Color Brick.  Brush this over the moiré.  Lower the intensity of Color Monochrome Brick as much as you can without introducing any moiré.

     

    Sell your print.

     

    NB: if anyone knows a better, quicker, more direct way to do this, my ears are as the ocean to its many rivers.

     

    (Added:  Can you post the RAW file somewhere?)

  • dbmoore Level 1 Level 1 (95 points)

    Wow  I will have to work with that for awhile to fully comprehend all the moves.  Thank you, Kirby.  Color moire is one thing but if she has moire in the Luminace values gaussian blur. noise,  and re shooting may be the only option.  I hate Morie.  This is not "My Dinner with Morie".

    David

  • léonie Level 8 Level 8 (46,405 points)

    you will get even better results brushing in the "Color Monochrome" adjustment than you'll get with the (misnamed) "Black & White" adjustment.

    clever, Kirby!

     

    am probably not understanding something very basic here,

     

    @Kirsty:

     

    Some basics on moiré, just in case - please don't feel offended, if you know all that already:

     

    moiré can be caused by scaling down or subsampling an image with repeated patterns, whenever you reduce the number of pixels below twice the number  of the repetition factor.

    For example: if your image shows 100 parallel black lines on a white background and you view this or print this with image dimensions smaller than 200x200 pixels you will probably see random moiré patterns, depending on the resolution of your image. The only cure is to remove any repeating pattern before you scale down the image for printing or viewing. And this removal is done by smoothing with gaussian blur. The radius of the smoothing filter needs to be larger than the distance between the repeating elements. Usually Aperture will automatically add such a filter when you are scaling down the image for printing or exporting, but the big problem is moiré when you are taking pictures with a digital camera and the smoothing filter in the camera is not sufficient.

     

    Say, you take a picture of a picket fence - 3000 picket elements in parallel lines mapped to a 3000x2000 pixels image. Your image most certainly will have a bad case of moiré.

    Such pictures need to be taken in a way, that no moiré is possible:

    • Take the image at a very high resolution - with more than 6000 pixels width for this example - the best option,
    • or zoom in until the number of pickets is less then half the number of pixels per in either dimension
    • or take a blurred image so that the picket elements are not recognizable as seperate elements, e.g. by using a larger aperture.

     

    Here the raw fine tuning can be used to apply a blur after the image has been taken, but there really is no promise that moiré can be removed reliably, if the image has been taken in a way that Shannon's sampling theorem has been violated.

     

    HTH

     

    Léonie

  • léonie Level 8 Level 8 (46,405 points)


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  • léonie Level 8 Level 8 (46,405 points)

    My previous post got interrupted by ASC maintainance work, before I could correct the typos and could explain what I really meant to say -sorry:

    The recommendations by Keith, David, and Kirby are great and probably may work in your case, but there simply cannot exist a general procedure to remove moiré from an image that has been sampled incorrectly with too few pixels. You have to find a specific solution in each case, and need to know something about the images and build your correction procedure on that knowledge. That is why I suggested to use the fact that the shirt is supposed to look black and go from that. A gaussian blur afterwards on the lumiosity channel may be necessary, as David pointed out.

     

    The big problem with a blur-filter to remove moiré is: The moiré artefacts usually are much larger than the size of the original repeated texture elements causing the moiré. If you filter the image before sampling - right in the camera - a small filter size will suffice, and your image will have optimal sharpness. But if you need to filter the moiré-corrupted image afterwards to remove the moiré you will need a much larger filter radius and loose much more details, and your image will look blurry.

     

    Regards

    Léonie

  • léonie Level 8 Level 8 (46,405 points)

    i've just looked at the RAW MASTER image in 100% and the moire isn't there - so does that mean it won't be there when i print it 20 x 20?

    Then the  moiré shouldn't be there when you print using Aperture, but make a testprint with the correct dpi on cheap, regular paper - don't waste expensive photo paper on it.

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