What is Quickproof in Capture One's processing tab and how to use it in the best way?
The Quickproof format in the Process Recipe tool is designed to allow extremely fast processing of images to JPEGs of basic quality. It simply converts the Capture One preview file to a JPEG so that only minor processing takes place. The size of the Quickproof JPEG is determined by the preview size set in the Capture One preferences, so it cannot be changed within the Process Recipe section.
NOTE: If you change the size of the preview in preferences, existing image previews have to be updated so that the changes take effect. In order to update the existing images, select those in the Browser, right-click on any thumbnail, and select Regenerate previews from the context preview.