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by Aditya

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What is the most reliable way to trigger moire artifacts in an image straight out of a digital camera?

I know that resizing an image can cause it but I want to see it all full-resolution and be able to do it reliably so that I can compare two nearly identical cameras that I have here, the Pentax K-5 IIs and K-5 II which differ only in the lack of anti-alias filter of the former. In particular, I would like to see a pattern which causes moire with the K-5 IIs but not the K-5 II. Hopefully it is repeatable enough because I would be running tests to see how lens performance interacts with moire.

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4 Answers 4

up vote 7 down vote accepted

The patterns from Moire Demonstration Kit work best and print themselves without moire more easily than the test patterns from the Moire Fringe AF Adjustment Method answer — either circles or fine mesh.

The concentric-circle patten in particular should be very effective, as it has decreasing distance between each circle making it almost guaranteed to interfere with your camera's sensor-pixel grid.

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Note that you'll have to print these out with laser printer. I made the mistake of trying to produce one with my inkjet, and of course got moire patterns in the printout. –  mattdm Nov 27 '12 at 1:13
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"in the printout" made me laugh. :D –  John Cavan Nov 27 '12 at 1:46
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Glad I was not the only one who noticed. I just managed to get clean output for these and will try them out tomorrow. –  Itai Nov 27 '12 at 3:53
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Good idea. The patterns though were not so reliable, so I found some better ones. You'll be able to see the demo shortly! –  Itai Nov 27 '12 at 17:08
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Check out the moire demo if you like. I find it very interesting to see moire interact with the lens sharpness and diffraction. Play with the aperture settings in the demo towards the bottom of the page and you will see. –  Itai Dec 5 '12 at 4:41

Take a picture of anything with a small repeating pattern. Preferably set up the perspective so that the size of the pattern as it ends up on the sensor varies accross the picture. This varies the frequency of the pattern on the sensor, which is useful since different effects may appear at different frequencies. It will also help in comparing the cameras since the effects will start at different frequencies depending on the level of optical anti-aliasing in the camera.

One example of such a pattern that should be easy to find is a large brick wall. That has many repeating cycles of the same pattern with reasonable contrast. You can change your distance and/or zoom to get the brick pattern to be different frequencies on your sensor. Take the picture at a angle, and the frequency will change accross the picture.

The best pattern would be a infinite checkerboard. A real checkerboard doesn't have enough patterns to be all that useful. You might find some wallpaper or a large open tiled floor or something. You could possibly print a checkerboard pattern on paper by using 3x3 or 4x4 blocks of printer pixels for each square. That sould provide anough patterns to be a useful aliasing test when framed properly.

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That sounded good to me too but unfortunately does not work. The perspective causes the repeated pattern to get hidden outside of the DOF. Stopping down only helps with a small range of apertures between the lens sharpening enough to get moire and diffraction setting in! –  Itai Nov 27 '12 at 16:50
    
@Itai: I see what you mean. Taking the picture sideways near to a small object won't work if you want a range of frequencies. However, with a large object like a brick wall it should still work because everything is far enough to be in focus at the same time. –  Olin Lathrop Nov 27 '12 at 23:00

If you happen to be in Paris then you can you can stop by the Centre Pompidou (the inside out modern art museum), head up to the fourth floor and walk to the end of the atrium where you'll find this piece:

It's a series of wire shapes in front of a striped background which represents the most severe moire torture test I've ever put a camera through.

If you don't happen to be in Paris then any fabric with a tight weave will represent a reliable and realistic moire test subject.

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"What's this trip to Paris in your expense report? That seems quiet extravagant. Explain yourself!" / "Well, sir, I needed to do a test for this new camera without an anti-aliasing filter...." –  mattdm Nov 26 '12 at 23:39

Jeans with rough texture (like brand new jeans) can somewhat reliably produce moire. The lighting needs to be edged enough to rake the jeans surface.

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