A good workaround to get the noise removed from the image is to use a combination of filters in GIMP. In this case, it will be faster to edit the rendered image outside of LuxRender. The trick is quite simple and requires only a small addition in GIMP. Open the rendered image, and in the Layers panel, create a copy of the layer where the image is placed.
The trick consists of adding some Gaussian blur to the top layer and then reducing the opacity of this layer. It will make the blurred image blend with the layer below.
As a result, we will have an image with a slight glow effect, but without most of the noise from the image.