Grainy artifacts in digital images — result from aggressive compression or botched demosaicing. Most visible in shadows and pushed ISO.
You know the feeling: you're sitting at the editing bay, zooming into a dark scene — and suddenly you see this grainy, irregular structure that looks like coffee grounds. Not the organic grain of film emulsion, but something digital and annoying. This happens when sensor data goes wrong during conversion into image information, or when compression has been too aggressive.
Coffee grounds typically arise in three scenarios: Firstly, with high ISO settings — the sensor is noisy, and the camera's error correction algorithms try to smooth things out, but produce these characteristic flecks instead of clean grain. Secondly, with faulty or low-quality debayering processes, when color information is reconstructed from the sensor's Bayer mosaic. Thirdly, with aggressive chroma subsampling or codec-related compression — especially in dark areas where the algorithm makes radical savings. The material then doesn't look natural, but digitally degraded.
Practically, you'll immediately recognize coffee grounds in the preview when you zoom into the shadow areas. It's not homogeneous like film grain, but looks blotchy, inorganic — as if the algorithm is literally rolling dice. In editing, it becomes problematic when you need color correction: if you try to smooth it out, you destroy details. If you try to accept it, the whole scene looks cheap.
The remedies are known: choose RAW material instead of compressed codecs, use ISO more intelligently (prefer exposure correction), use high-quality debayering software when working with raw data, and apply selective denoise filters in editing (temporal denoise, luminance-only noise reduction) — but targeted, not blanket. Some DoPs accept slight coffee grounds as a sacrifice for exposure safety. More professionally: don't let it happen in the first place — through conscious sensor choice, correct debayering, and appropriate codec selection in the workflow.