Correcting image-colours to work with browsers that don't support 2d context in OffscreenCanvas

index.js

// Around line 127
createImageBitmap(file).then((ibm) => {
	let ctx;

	if (typeof OffscreenCanvasRenderingContext === "function"){
		const canvas = new OffscreenCanvas(ibm.width, ibm.height);
		ctx = canvas.getContext("2d");
	}
	else {
		const canvas = document.createElement("canvas");
		ctx = canvas.getContext("2d");
		ctx.canvas.height = ibm.height;
		ctx.canvas.width = ibm.width;
	}

	ctx.drawImage(ibm, 0, 0);
// rest of file