About noise and noise reduction
Image noise looks like random black, white, or colored pixels in an area of a photo where there should be solid color, such as a dark night sky. In digital photography, noise is typically more visible in the dark areas of a photo.
There are many causes of image noise. You will increase image noise if you use a high ISO setting (such as ISO 800) to capture a photo, or if you extend the exposure time. (You would typically use a high ISO setting and extend exposure time to take a photo in low light.) However, image noise can be caused by dead or stuck pixels in a digital camera’s image sensor. Similarly, dust on a camera lens or scanner bed can cause noise by blocking or reflecting light.
Images generally have two types of noise: luminance and color. Luminance noise is random variations of brightness, and particularly in gray areas, may appear spotted when there should be a solid color in the area of the image.
Color noise is random variations of color in the image.
Noise is visually distracting, so in most cases you will want to reduce noise in your photos. However, if you reduce noise too much you may unintentionally reduce image sharpness.You can use the Noise Removal tool to remove both luminance and color noise in your images.
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