If the reducer has a single input, it will be applied separately to each band of the collection; otherwise it must have the same number of inputs as the collection has bands.
The reducer output names determine the names of the output bands: reducers with multiple inputs will use the output names directly, while reducers with a single input will prefix the output name with the input band name (e.g., '10_mean', '20_mean').
| Usage | Returns | 
|---|---|
| ImageCollection.reduce(reducer, parallelScale) | Image | 
| Argument | Type | Details | 
|---|---|---|
| this: collection | ImageCollection | The image collection to reduce. | 
| reducer | Reducer | The reducer to apply to the given collection. | 
| parallelScale | Float, default: 1 | A scaling factor used to limit memory use; using a larger parallelScale (e.g., 2 or 4) may enable computations that run out of memory with the default. |