The conversion of one video standard into another with di!erent "eld and scan rates is a key feature for modern TV receivers and multimedia video equipment. Therefore, a new vector-based nonlinear conversion algorithm has been developed which applies nonlinear center weighted median (CWM) "lters and yields a very good interpolation quality. One of the main properties of this algorithm is vector error tolerance. This property will be derived in this paper and its advantages will be shown. Assuming a 2-channel model of the human visual system with di!erent spatio-temporal characteristics, there are contrary demands for the CWM "lters. One can meet these demands by a vertical band separation and an application of the so-called temporally and spatially dominated CWMs. Hereby interpolation errors of the separated channels can be compensated by an adequate splitting of the spectrum. By this means, a very robust vector error tolerant upconversion method can be achieved which signi"cantly improves the interpolation quality. By an appropriate choice of the CWM "lter root structures main picture elements are interpolated correctly also if faulty vector "elds occur. To demonstrate the correctness of the deduced interpolation scheme picture content is classi"ed. These classes are distinguished by correct or incorrect vector assignment and correlated or noncorrelated picture content. The mode of operation of the new algorithm is portrayed for each class. Whereas for correlated picture content the mode of operation can be shown by object models the operation mode is shown for noncorrelated picture content by the output probability distribution function of the applied CWM "lters. The new algorithm has been veri"ed for a 100 Hz upconversion by objective evaluation methods and by comprehensive subjective test series. Within these tests for critical test sequences a gain of about 2 dB PSNR in the objective tests and about 0.4 evaluation grades in the subjective test series could be achieved. ( 1999 Elsevier Science B.V. All rights reserved.