Noise is the digital equivalent of grain in film. It’s random electrical signals captured by the photosites on the camera sensor, and usually this background noise level is so low compared to the brightness of the captured picture itself that you just don’t notice it.
Random ‘speckling’ in an image caused by variations in the light levels captured by the photosites on the sensor. Noise is worse with the smaller photosites on small sensors and at higher ISO settings generally. You can get ‘chroma’ (coloured) noise and ‘luminance’ noise (general ‘grittiness’) the same colour as the background.
If you never thought you’d need to pay attention to the Lightroom noise reduction settings, you might need to think again. Like a lot of photographers I shoot RAW files on the assumption I’m going to get better image quality by processing the images myself rather than leaving it to the in-camera JPEG processing. That’s fine […]