High- and low- frequency details

Each individual pixel in a photo has a  specific brightness value, and these values change as parts of the image become brighter or darker. Frequency measures the rate of change between one pixel and the next. In the man’s shirt here, the rate of change is very low, so this is a low-frequency area. But in the wonderful wrinkled face, the rate of change is much higher, so  this is a high-frequency area. The Texture slider works on a specific range of frequency, nearer to the high end. It targets fine details, but doesn’t amplify image noise.