gis-tools-ts/dist/readers/image/lanczos.js

A collection of geospatial tools primarily designed for WGS84, Web Mercator, and S2.

import { copyImage, createImage, resizeImage } from '..';
/**
 * # Lanczos Resampling
 *
 * ## Description
 * Perform a 2D Lanczos filter on an image. the Lanczos resampler creates some regions that are
 * darker than any in the original and others that are lighter than any in the original. This
 * Fourier transform method is useful in spatial/GIS applications, especially downscaling raster
 * data.
 *
 * ## Usage
 * ```ts
 * import sharp from 'sharp';
 * import { lanczos, createImage } from 'gis-tools-ts';
 * // pull in the image you want to downscale
 * const pattern = await sharp('./pattern.png')
 * .raw()
 * .toBuffer({ resolveWithObject: true });
 * // setup the destianation image
 * const patternHalf = createImage(4, 4);
 * // resize down into patternHalf
 * lanczos(pattern, patternHalf);
 * ```
 *
 * ## Links
 * - https://en.wikipedia.org/wiki/Lanczos_algorithm
 * - https://en.wikipedia.org/wiki/Lanczos_resampling
 * - https://gis.stackexchange.com/questions/10931/what-is-lanczos-resampling-useful-for-in-a-spatial-context
 * - https://icess.eri.ucsb.edu/gem/Duchon_1979_JAM_Lanczos.pdf
 * @param source - the source image
 * @param dest - the destination image
 * @param sx - source starting x point [Default: 0]
 * @param sy - source starting y point [Default: 0]
 * @param sw - source width to use [Default: source width - sx]
 * @param sh - source height to use [Default: source height - sy]
 * @param dx - destination starting x point [Default: 0]
 * @param dy - destination starting y point [Default: 0]
 * @param dw - destination width to use [Default: destination width - dx]
 * @param dh - destination height to use [Default: destination height - dy]
 * @param use2 - use 2nd lanczos filter instead of 3rd [Default: false]
 */
export function lanczos(source, dest, sx = 0, sy = 0, sw = source.width - sx, sh = source.height - sy, dx = 0, dy = 0, dw = dest.width - dx, dh = dest.height - dy, use2 = false) {
    sx |= 0;
    sy |= 0;
    sw |= 0;
    sh |= 0;
    dx |= 0;
    dy |= 0;
    dw |= 0;
    dh |= 0;
    if (sw <= 0 || sh <= 0 || dw <= 0 || dh <= 0)
        return;
    if (sx === 0 &&
        sy === 0 &&
        sw === source.width &&
        sh === source.height &&
        dx === 0 &&
        dy === 0 &&
        dw === dest.width &&
        dh === dest.height) {
        resizeImage(source, dest, use2);
        return;
    }
    const croppedSource = createImage(sw, sh);
    const croppedDest = createImage(dw, dh);
    copyImage(source, croppedSource, sx, sy);
    resizeImage(croppedSource, croppedDest, use2);
    copyImage(croppedDest, dest, 0, 0, croppedDest.width, croppedDest.height, dx, dy);
}
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