Dot for dot proofing: how to zoom into the dots without losing the big picture

In proofing, the accurate reproduction of prints is pursued. One of the major properties which determine the appearance of prints, is the halftoning. We refer to digital proofing methods as dot for dot proofing when they try to reproduce this property. We identify three basic requirements for a good dot for dot proof: colorimetric match, halftone match and print colorant match. They can be met simultaneously because they relate to different scales of resolution. The best starting point for a dot for dot method is the final rasterised separation data. Then, the proofing workflow maximally shares its processing components with the printing workflow, which helps minimising differences. Since print and proof generally differ in resolution and colorants, colour and resolution conversion are basic components of dot for dot methods. We propose a general flow in which an intermediate colour space is used. The fundamental issue is to accurately handle the colour information together with the halftone information. Normally, an image either represents the colour accurately by giving contone values, or the halftoning by giving high resolution binary data. Therefore, the choice of image representation in a processing flow becomes critical. Solutions can be found in hybrid representations containing information about both, or in dual representations.