How does a LCD screen TV stretch pixels?

EricLNZ wrote on 1/15/2020, 4:12 AM

I'm hoping one of you brainy folk can answer this as I cannot find the answer on the net.

When I play from a usb thumbdrive a SD PAL video which has a PAR involving stretched pixels for both 4:3 and 16:9 how does my TV handle this. It correctly "stretches" the pixels to give the correct image shape. TVs have, I assume, pixels that are square and fixed in shape and cannot be stretched. So how does it achieve the effect of "stretching? Does it duplicate the occasional pixel to give the illusion of stretching?

Comments

Former user wrote on 1/15/2020, 8:15 AM

I would think the player does the stretching, not the actual TV. If you are plugging the drive into a TV, there still has to be player software or hardware to interpret the video.

Musicvid wrote on 1/15/2020, 9:10 AM

"Stretching" is a common visual metaphor for [Mapping + Interpolation / Decimation]

Pixels, the smallest discrete visual unit, don't actually come in different shapes. PAR is a factor, not a dimension.

DAR Example (NTSC DV):

  • 720x480 * 1.2121 PAR -> 853.333 x 480 -> [MOD2] -> 854x480 DAR
  • 720x480 * 0.9091 PAR -> 654.552 x 480 -> [MOD2] -> 654x480 DAR

DAR Example (PAL DV)

  • 720x576 * 1.0926 PAR -> 786.672 x 576 -> [MOD2] -> 788x576 DAR
  • 720x576 * 1.4568 PAR -> 1048.896 x 576 -> [MOD2] -> 1048x576 DAR

DVD PAR, unfortunately, is slightly different, thus the thin black bars we're used to seeing in DV -> DVD conversions.