The moiré effect occurs when groups of lines or dots are arranged in a certain way, distorting an image. It can be observed by drawing parallel lines at a slight angle. Moiré can also occur when an image is rescanned or resized, and can be reduced through image retouching or using a different file format, such as PNG. However, using blur functions to reduce moiré may result in a loss of image quality.
You’ve probably seen various types of optical illusions, including ones where an image can appear in different ways or can look like very different things. When an image is distorted and becomes an optical illusion due to the way groups of lines or dots are arranged, this is known as a moiré effect. You may have noticed a similar effect when you look at something through the mesh of a window screen or when you walk past rows of fences.
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 often as you like to reinforce the moiré effect and develop new and interesting patterns. Similar methods can be used in creating works of art.
Moiré also occurs when an already scanned image is rescanned. You may have seen examples of this if you’ve 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 collides with that of the finished product when an image is duplicated through photography. If you then try to print or otherwise copy the photographic reproduction, you end up with a poor quality image.
Moiré can also alter the appearance of images that have been resized. If you’re working in photo software or other graphics programs and try to scale a scanned image up or down, you may experience moiré. This is especially true if the image was saved in a low resolution format.
The JPEG format is not recommended for saving graphics that you intend to reproduce, even if a moiré removal tool is available in your graphics software. JPEG stands for Joint Photographic Experts Group, named after the group that created the format. It is used to compress files to a smaller, more manageable size, but the trade-off is the loss of detail. PNG format, or Portable Network Graphics, seems to be a better choice. It supports all colors and retains more details. While you’ll lose the convenience of compression and be required to use larger files, you shouldn’t worry as much about moiré.
While it is possible to remove moiré to some extent while retouching images, it usually results in some blurring. In fact, in some cases, using various types of blur functions may be recommended to reduce the moiré effect and improve the quality of an image. However, this will obviously lead to images that are not as crisp 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, while keeping an intact image from which to make copies.
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