vignetter

/vɪnˈjɛtər/
noun
  1. A device or tool used to create a vignette effect on photographs or images.
    • The old vignetter was a simple cardboard cutout placed in front of the lens.
    • Modern photo editing apps have a digital vignetter that mimics the classic effect.
    • He attached a vignetter to his camera lens to soften the edges of his portraits.