geotiff
Version:
GeoTIFF image decoding in JavaScript
67 lines • 2.8 kB
JavaScript
;
var __importDefault = (this && this.__importDefault) || function (mod) {
return (mod && mod.__esModule) ? mod : { "default": mod };
};
Object.defineProperty(exports, "__esModule", { value: true });
const basedecoder_js_1 = __importDefault(require("./basedecoder.js"));
/**
* class WebImageDecoder
*
* This decoder uses the browsers image decoding facilities to read image
* formats like WebP when supported.
*/
class WebImageDecoder extends basedecoder_js_1.default {
/**
* @param {import('./basedecoder.js').BaseDecoderParameters} parameters
*/
constructor(parameters) {
super(parameters);
if (typeof createImageBitmap === 'undefined') {
throw new Error('Cannot decode WebImage as `createImageBitmap` is not available');
}
else if (typeof document === 'undefined' && typeof OffscreenCanvas === 'undefined') {
throw new Error('Cannot decode WebImage as neither `document` nor `OffscreenCanvas` is not available');
}
}
/** @param {ArrayBuffer} buffer */
async decodeBlock(buffer) {
const blob = new Blob([buffer]);
const imageBitmap = await createImageBitmap(blob);
let canvas;
if (typeof document !== 'undefined') {
canvas = document.createElement('canvas');
canvas.width = imageBitmap.width;
canvas.height = imageBitmap.height;
}
else {
canvas = new OffscreenCanvas(imageBitmap.width, imageBitmap.height);
}
// Draw the image onto the canvas to extract the pixel data.
// Note: createImageBitmap always returns RGBA data.
const ctx = /** @type {CanvasRenderingContext2D} */ (canvas.getContext('2d'));
ctx.drawImage(imageBitmap, 0, 0);
const imageData = ctx.getImageData(0, 0, imageBitmap.width, imageBitmap.height).data;
// Return the correct channels to the caller
const samplesPerPixel = this.parameters.samplesPerPixel || 4;
if (samplesPerPixel === 4) {
// RGBA, return as is
return imageData.buffer;
}
else if (samplesPerPixel === 3) {
// RGB, remove alpha channel before returning
const rgb = new Uint8ClampedArray(imageBitmap.width * imageBitmap.height * 3);
for (let i = 0, j = 0; i < rgb.length; i += 3, j += 4) {
rgb[i] = imageData[j];
rgb[i + 1] = imageData[j + 1];
rgb[i + 2] = imageData[j + 2];
}
return rgb.buffer;
}
else {
throw new Error(`Unsupported SamplesPerPixel value: ${samplesPerPixel}`);
}
}
}
exports.default = WebImageDecoder;
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