The moiré effect can produce interesting and beautiful geometric patterns. In the machine vision world, however, the phenomenon can degrade the quality and resolution of captured images. It can occur when the image from a camera is reproduced on a computer display and then rendered in a screened or dot-matrix format. The fine matrix of dots in the original image almost always conflicts with the matrix of dots in the reproduction. This generates a characteristic criss-cross pattern on the reproduced image. Moiré patterns can also be created by plotting a series of curves on a computer screen. In this case, the interference is caused by the rasterization of the finite-sized pixels. For example, the illustrations below show a number of concentric circles plotted with a range of uniform spacings. Note the phantom lines and curves that appear.
- If your captured images show a heavy moiré effect, try rotating the camera or the object. Experiment with the angle of rotation to achieve the minimal moiré pattern.
- Change the position of the camera. A simple change in the camera angle can result in significant moiré reduction.
- Change the focus. The moiré effect is most noticeable in images with high sharpness. Overlapped fine details boost the effect.
- Try a lens with a different focal length. This can reduce the moiré effect.
In some cases, you may not be able to completely eliminate the moiré effect by using these techniques. But they should at least give you a noticeable improvement in your results.