Scan conversion between 1050 2:1 60 Hz and 525 1:1 30 Hz U and V color components

In an MPEG (Motion Pictures Experts Group) video coding system, a color component downsampling from 1050 2:1 60 Hz to 525 1:1 30 Hz line scan formats must be carried out on the U and V color component source signals. One scheme presently used to accomplish the required U and V downsampling, called frame-based color subsampling, is thoroughly analyzed. In addition, field-based color downsampling is analyzed and compared with the frame-based color downsampling. The maximum vertical and temporal resolution of the original U, V signals is 1050 tvl and 30 Hz. An analysis in the vertical-temporal Fourier-transform domain shows that the best possible vertical and temporal resolution of the frame-based approach is 525 tvl and 15 Hz. For the field-based approach the maximum possible vertical and temporal resolution is 265.5 tvl and 30 Hz. The fact that the temporal resolution is reduced by one half in the frame-based approach leads to blurring of horizontal edges on moving objects, although in quasi-stationary picture sequences this approach performs well in the sense that vertical aliasing artifacts can be reduced by the use of a proper vertical filter.<
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