Resizing a custom value renderer image in a tooltip

I created a custom value renderer in a C# extension to display images obtained from API calls. One of the uses of this custom value render is to display these images in a tooltip, similar to "Image For URL".

In my code, in the "RenderCore()" function, I recieve the image from a stream and set it using "result.SetImage(image)". Here's an example: 

protected override void RenderCore(
	ValueRendererSettings rendererSettings, ValueRendererArgs renderingArgs, ValueRendererResult result)
	string value = renderingArgs.DataValue.ValidValue.ToString();
	Stream stream = DownloadApiImage(value); //Custom function
	Image image = Image.FromStream(stream);

	result.SetImage(image); //Cannot figure out how to resize this

The image displays correctly, but I am unable to resize it using the "Size" slider in the "Edit Tooltip Value" window. It just displays the image in its full size. Sometimes, these images can be quite large and cover majority of the screen, which can be qutie annoying if they aren't sized down. How can I make the "Size" slider affect the custom value renderer image in a tooltip?