An external app launcher was added to v1.0.77.0. The Home Basic edition can configure one external editor to be launched on the current image (it can be any program that accepts an image file on the command-line, e.g. Photoshop, The GIMP, Paint.NET, PhotoME, ...). The Professional edition supports several editors and let you pick the image version to edit, e.g. JPG or RAW if both are present:
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