[null,null,["อัปเดตล่าสุด 2025-07-25 UTC"],[[["\u003cp\u003eUse \u003ccode\u003eimageCollection.reduce()\u003c/code\u003e to reduce an \u003ccode\u003eImageCollection\u003c/code\u003e to a single image by applying a reducer function pixel-wise.\u003c/p\u003e\n"],["\u003cp\u003eEarth Engine provides built-in reducers for common statistics like median, mean, min, max, and more.\u003c/p\u003e\n"],["\u003cp\u003eThe output of \u003ccode\u003ereduce()\u003c/code\u003e is a multi-band image where each pixel represents the reduced value across the input images.\u003c/p\u003e\n"],["\u003cp\u003eBand names in the output image are appended with the reducer name (e.g., \u003ccode\u003eB1_median\u003c/code\u003e).\u003c/p\u003e\n"],["\u003cp\u003eReduced images have no projection, requiring explicit scale setting for further computations.\u003c/p\u003e\n"]]],[],null,["# ImageCollection Reductions\n\nConsider the example of needing to take the median over a time series of images\nrepresented by an `ImageCollection`. To reduce an `ImageCollection`,\nuse `imageCollection.reduce()`. This reduces the collection of images to an\nindividual image as illustrated in Figure 1. Specifically, the output is computed\npixel-wise, such that each pixel in the output is composed of the median value of all the\nimages in the collection at that location. To get other statistics, such as mean, sum,\nvariance, an arbitrary percentile, etc., the appropriate reducer should be selected and\napplied. (See the **Docs** tab in the\n[Code Editor](https://code.earthengine.google.com) for a list of all the reducers\ncurrently available). For basic statistics like min, max, mean, etc.,\n`ImageCollection` has shortcut methods like `min()`,\n`max()`, `mean()`, etc. They function in exactly the same way\nas calling `reduce()`, except the resultant band names will not have the\nname of the reducer appended.\nFigure 1. Illustration of an ee.Reducer applied to an ImageCollection.\n\nFor an example of reducing an `ImageCollection`, consider a collection of\nLandsat 5 images, filtered by path and row. The following code uses `reduce()`\nto reduce the collection to one `Image` (here a median reducer is used simply\nfor illustrative purposes):\n\n### Code Editor (JavaScript)\n\n```javascript\n// Load an image collection, filtered so it's not too much data.\nvar collection = ee.ImageCollection('LANDSAT/LT05/C02/T1')\n .filterDate('2008-01-01', '2008-12-31')\n .filter(ee.Filter.eq('WRS_PATH', 44))\n .filter(ee.Filter.eq('WRS_ROW', 34));\n\n// Compute the median in each band, each pixel.\n// Band names are B1_median, B2_median, etc.\nvar median = collection.reduce(ee.Reducer.median());\n\n// The output is an Image. Add it to the map.\nvar vis_param = {bands: ['B4_median', 'B3_median', 'B2_median'], gamma: 1.6};\nMap.setCenter(-122.3355, 37.7924, 9);\nMap.addLayer(median, vis_param);\n```\nPython setup\n\nSee the [Python Environment](/earth-engine/guides/python_install) page for information on the Python API and using\n`geemap` for interactive development. \n\n```python\nimport ee\nimport geemap.core as geemap\n```\n\n### Colab (Python)\n\n```python\n# Load an image collection, filtered so it's not too much data.\ncollection = (\n ee.ImageCollection('LANDSAT/LT05/C02/T1')\n .filterDate('2008-01-01', '2008-12-31')\n .filter(ee.Filter.eq('WRS_PATH', 44))\n .filter(ee.Filter.eq('WRS_ROW', 34))\n)\n\n# Compute the median in each band, each pixel.\n# Band names are B1_median, B2_median, etc.\nmedian = collection.reduce(ee.Reducer.median())\n\n# The output is an Image. Add it to the map.\nvis_param = {'bands': ['B4_median', 'B3_median', 'B2_median'], 'gamma': 1.6}\nm = geemap.Map()\nm.set_center(-122.3355, 37.7924, 9)\nm.add_layer(median, vis_param)\nm\n```\n\nThis returns a multi-band `Image`, each pixel of which is the median of all\nunmasked pixels in the `ImageCollection` at that pixel location. Specifically,\nthe reducer has been repeated for each band of the input imagery, meaning that the median\nis computed independently in each band. Note that the band names have the name of the\nreducer appended: `'B1_median'`, `'B2_median'`, etc.\nThe output should look something like Figure 2.\n\nFor more information about reducing image collections, see the\n[reducing section of the `ImageCollection` docs](/earth-engine/guides/ic_reducing). In\nparticular, note that images produced by reducing an `ImageCollection`\n[have no projection](/earth-engine/guides/ic_reducing#composites-have-no-projection). This means\nthat you should explicitly set the scale on any computations involving computed images\noutput by an `ImageCollection` reduction.\nFigure 2. A false color composite of the median of Landsat 5 scenes in 2008."]]
