-mix (add two inputs), scale (bilinear and Lanczos), sharpen
-(both by unsharp mask and by Wiener filters), saturation (or desaturation),
-vignette, and white balance.
+mix (add two inputs), overlay (the Porter-Duff “over” operation),
+scale (bilinear and Lanczos), sharpen (both by unsharp mask and by
+Wiener filters), saturation (or desaturation), vignette, and white balance.