Complex sentence: Unsharp masking (USM) is an image manipulation technique familiar to many users of digital image processing software, but seems to have first been used in Germany in the 1930s as a way of increasing the acutance, or apparent sharpness, of photographic images.
Split into simpler sentences: Unsharp masking (USM) is an image manipulation technique, often available in digital image processing software. It was first used in Germany in the 1930s as a way of increasing the acutance, or apparent sharpness, of photographic images.