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Blur, diffusion, glow, lift/gamma/gain (color correction), mirror,
-mix (add two inputs), overlay (the Porter-Duff “atop” operation),
+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.