-mix (add two inputs), overlay (the Porter-Duff “atop” operation),
-scale (bilinear and Lanczos), sharpen (both by unsharp mask and by
-Wiener filters), saturation (or desaturation), vignette, and white balance.
+mix (add two inputs), luma mix (use a map to wipe between 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.