10/19/2020

4:1:1 more appropriate for 4:3, 4:2:0 more appropriate for 16:9

 In the last posting in February I came down on the side of 4:1:1 for regular normal (plain) VHS resolution capture.

I still think that is true, in particular for high velocity action sequences and where post capture Editing of the captured material may be a possibility.

 But also, the geometry of traditional SD capture renders the pixel Aspect ratio as 4:3 which is much closer to a "square" shape, than a 16:9 wide-screen pixel Aspect ratio.

 So for two reasons, 1. the limited TVL horizontal resolution of the VHS format, and 2. the shape of the pixel due to Aspect ratio.. choosing a 4:1:1 capture format may have advantages over a 4:2:0.

I am vaguely aware of a difference between pixel "display" Aspect ratio versus pixel "capture" or sampling Aspect ratio.. and that there is a terminology assigned to those differences. It can become quite confusing.

 It comes up when trying to display a wide screen formatted video in a viewer or display device without a proper attribute in the file header to indicate the intended shape of the pixels to be displayed.. aka the "wide screen attribute".

This leaves me with thinking (in simple terms) that reserving DV capture for VHS and MPEG2 capture for S-VHS is an appropriate choice.. but especially when capturing Wide-Screen movies or video that is in the wide screen display format.. it is literally focusing more of the horizontal color sampling on the horizontal wide screen major axis in that case.

Broadcast video is a whole other situation, but video capture from a VHS tape is vastly different from video capture from a Broadcast signal.. since there actually are more TVL resolution in the horzontal axis to be captured. In that case it becomes a question if 4:2:2 or 4:2:0 is the better choice since 4:1:1 would clearly not be preferred.

In the days when Broadcast signals were over NTSC this would be an interesting debate, but in the current era where transmissions are "digital" and mostly MPEG-TS or MPEG-PS it makes more sense to just capture the digital signal for storage, rather than converting back to Analog and then capturing to Digital.