Pixpipejs

This does the following :

opening a distant image file with AJAX request, using pixpipe.UrlImageReader
creating a pixpipe.Image2D with the same size as the first, but monoband.
run a pixpipe.ForEachPixelImageFilter on the monoband image to create a radial gradient (values in [0, 1])
blend the loaded image and the gradient using a pixpipe.ImageBlendExpressionFilter
displaying the final output in a canvas using pixpipe.CanvasImageWriter

Note that using a parametric math expression with pixpipe.ImageBlendExpressionFilter is generally slower.

The original image:

The transformed image, with a radial gradient: