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What is the Moiré Effect?

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  • Written By: Sherry Holetzky
  • Edited By: Bronwyn Harris
  • Last Modified Date: 09 October 2014
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You have likely seen various types of optical illusions, including those in which an image can appear in different ways or can appear to be very different things. When an image is altered and becomes an optical illusion due to the way sets of lines or dots are arranged, this is known as the moiré effect. You may have noticed a similar effect when viewing something through the mesh of a window screen or when driving past fence rows.

To get a better perspective, you can create your own image to observe the moiré effect. Simply draw a set of parallel lines and then draw another set of parallel lines over them at a slight angle. Continue as many times as you like to strengthen the moiré effect and develop new and interesting patterns. Similar methods can be used in creating artwork.

The moiré effect also occurs when an already scanned image is then rescanned. You may have seen examples of this if you have ever tried to photograph a TV screen or images on a computer monitor, because the resolution is eroded. The dot-matrix in the original image clashes with that in the finished product when an image is duplicated through photography. If you then try to print or otherwise copy the photo reproduction, you will end up with a poor quality image.

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The moiré effect may also alter the appearance of images that have been resized. If you’re working with photo software or other graphics programs, and you attempt to increase or decrease the size of a scanned image, you may encounter the moiré effect. This is especially true if the image has been saved in a low-resolution format.

The JPEG format is not advised for saving graphics that you intend to reproduce, even if a moiré effect removal tool is available in your graphics software. JPEG stands for Joint Photographic Experts Group, named after the group who created the format. It is used to compress files to a smaller, more manageable size, but the trade off is the loss of detail. The PNG, or Portable Network Graphics, format appears to be a better choice. It supports full color and retains more detail. Although you will lose the convenience of compression and be required to use larger files, you shouldn’t have to worry as much about the moiré effect.

While it is possible to remove the moiré effect to some degree as you touch up your images, this will usually result in blurring. In fact, in some cases, using various types of blur features may be recommended to help decrease the moiré effect and improve the quality of an image. However, this will obviously lead to images that are not as sharp and clear as the original, so use with care. You may want to save the image in different formats and experiment with the various options, keeping one untouched image from which to make copies.

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