ImageBitmapRenderingContext: clarify behaviour with `premultiplyAlpha: "none"` createImageBitmap option and canvas about html HOT 2 OPEN

      // fetch an image with alpha channel and put it on a canvas with transferFromImageBitmap
      const url = "https://cdn.glitch.global/073b6ba0-42e6-4706-9e9d-9dfacb8f3a8b/TransparentCat-repro.png?v=1708264432674";
      const imageBitmap = await fetch(url)
        .then(response => response.blob())
        // this makes the difference on Chrome, but does not affect the result on WebKit/Firefox
        .then(blob => createImageBitmap(blob, { premultiplyAlpha: "none" }))
        .then(imageBitmap => imageBitmap);

      // create a canvas
      const canvas = document.createElement("canvas");
      // setting width/height is probably not needed as the transferred image takes over
      canvas.width = imageBitmap.width; 
      canvas.height = imageBitmap.height;
      // alpha parameter here does not influence the readback result, but does influence how the canvas is displayed on the page (seems to always be premultiplied, but with or without black background)
      const ctx = canvas.getContext("bitmaprenderer", { alpha: false });
      ctx.transferFromImageBitmap(imageBitmap);
      
      // turn canvas to PNG and download it
      const a2 = document.createElement("a");
      a2.innerText = "Download readback";
      // this should contain unpremultiplied data – approx. same RGBA data as in the original
      a2.href = canvas.toDataURL("image/png");