Pan-sharpen multispectral imagery in the Google Earth Engine Code Editor with one line of code:
varsharp=geeSharp.sharpen(img.select(["B4","B3","B2"]),img.select("B8");
To pan-sharpen an image, separate the lower resolution multispectral bands and the higher resolution panchromatic band into two images and pass them to the geeSharp.sharpen function. For example:
// Import the geeSharp modulevargeeSharp=require("users/aazuspan/geeSharp:geeSharp");// Load an example Landsat 8 TOA image to sharpenvarimg=ee.Image("LANDSAT/LC08/C01/T1_TOA/LC08_047027_20160819");// Select the 30 m spectral bands to sharpenvarms=img.select(["B4","B3","B2"]);// Select the 15 m panchromatic bandvarpan=img.select(["B8"]);// Pan-sharpen!varsharpened=geeSharp.sharpen(ms,pan);By default, pansharpening in geeSharp uses the Smoothing Filter-based Intensity Modulation (SFIM) algorithm because it is fast and produces consistent, high-quality results. However, you may want to experiment with other methods. You can do that by passing an algorithm name to the sharpen function.
varmethod="brovey";varsharpened=geeSharp.sharpen(ms,pan,method);Most sharpening functions just require the unsharpened multispectral bands and the high-resolution panchromatic band as inputs, but some algorithms (like Gram-Schmidt) may accept other parameters. You can add those parameters after the method name when calling sharpen.
// The Gram-Schmidt algorithm may require additional parameters depending on the size of your image.varmethod="GS";vargeom=ee.Geometry.Point([-122.41676185101713,47.26851080476613]).buffer(1000);varscale=30;varmaxPixels=1e13;varsharpened=geeSharp.sharpen(ms,pan,method,geom,scale,maxPixels);Print geeSharp.methods for a full list of supported algorithms, and see the documentation for descriptions.
Image quality metrics measure the distortion between a reference image and an image that has been modified, such as a pan-sharpened image.
// Choose a metricvarmetric="RMSE";// Reproject the unsharpened image to the sharpened resolutionvarreproj=unsharpened.resample("bicubic").reproject(sharpened.projection());// Calculate the metricvarquality=geeSharp.quality(reproj,sharpened,metric);Warning
Metrics are affected by spatial resolution, so when comparing unsharpened and pan-sharpened images, always resample and reproject the unsharpened image to high resolution first to ensure an accurate comparison!
Most quality metrics just require an unmodified and a modified image and return a dictionary mapping band names to metric values, but some metrics require other parameters (e.g. ERGAS requires the high and low spectral resolution) and some return a single image-wise value (e.g. RASE and ERGAS). Print geeSharp.metrics for a full list of supported metrics and see the documentation for descriptions.