Pinch is a free compression distortion filter for Photoshop, and anything else - like Paint.NET - that supports 8bf files (it won't run stand-alone),

The default settings are sensible. Open Pinch, drag a slider, and the image is pulled into/ pushed out from the centre. If this pulls the borders of the image inwards, the out-of-range values are coloured black.

Release the Lock button and you're able to adjust horizontal and vertical settings independently.

If you don't like the black "out of range" colour, this can be set to whatever shade you like, or disabled entirely (the original border remains).

You can also set your preferred interpolation method to nearest neighbor, bisquare, bicosine and bilinear, although the default bicubic seemed good enough to us.