18-11-2021, 08:20 PM
There are two things that have made standards conversion harder, especially where interlace is involved. When th original framestore converters were designed in the 1960s and 70s (BBC analogue, DICE and ACE) the main sources of images were cameras and telecine. Both had limited vertical resolution, you didn't get really sharp vertical detail of the sort you get from digitally originated graphics. Cameras (though not TK) also had limited temporal response. In other words they smeared motion somewhat. In film camera terms that's equivalent to a shutter angle approaching 360 degrees.
As cameras improved, notably with solid state sensors replacing tubes, you could work at the equivalent of narrow shutter angles. This sharpens up movement nicely but makes life harder for a standards converter. It's harder to get away with assumptions that both vertical and temporal frequency response will be smoothly rolled off. Motion is nearly always aliased anyway, wagon wheels going backwards is a common artefact. Make that sharp rather than a bit blurred (narrow shutter angle) and the conversion compromises don't really work properly.
This is all going well beyond what we need for simple line rate conversion.
As cameras improved, notably with solid state sensors replacing tubes, you could work at the equivalent of narrow shutter angles. This sharpens up movement nicely but makes life harder for a standards converter. It's harder to get away with assumptions that both vertical and temporal frequency response will be smoothly rolled off. Motion is nearly always aliased anyway, wagon wheels going backwards is a common artefact. Make that sharp rather than a bit blurred (narrow shutter angle) and the conversion compromises don't really work properly.
This is all going well beyond what we need for simple line rate conversion.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
