the vignetting tool allows you to adjust the brightness of the corners of your image, either elliptical or circular; it has three methods to select; works with presets

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midwinter beach, with vignette

Capture One Vignetting

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With Capture One Vignetting you add a mood to an image
fisherman repairing his boat

Capture One High Dynamic Range

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The HDR tool can adjust the darkest and brightest areas of your image