Originally Posted by timmyotule
I'm not really following you here Mark.
The projector is getting a signal of a fixed resolution. If it is HD it is 16x9. When you enable the 'vertical stretch' it keeps the source the same width and stretches the middle 75% of the source to fill the panel.
But the projector's 16:9 mode also electrically stretches the image. That is why it appears geometry correct. When I choose letterbox mode like 4 x 3 zoom, the image is not geometry correct becuase the projector is not electrically stretching the image. The problem is, some projectors lock to 16:9 for HD. This works however on almost all projectors for SD...
The 'vertical stretch' mode may be intended for using other viewing modes that 16x9 but whatever its intent is in order from it to take an image that doesn't fill the panel and make it fill it by cropping the top and bottom and just using the middle 75% of the image it has to stretch it.
The Letterbox mode or 4 x 3 zoom modes were never intended for 16:9 native or enhances program - that was what the 16:9 mode was for. The reason some projectors don't appear to offer VS is becuase they were designed to prevent consumer confusion by taking out mode choices by the consumer - very plug and play and would always work for HD to give geometry correct images.
So what your seeing when the image appears VS'd is the native format before the display stretched it.
Image comes in with black bars top and bottom. It's as wide as the panel. Width doesn't change. Middle part of image now fills panel. It had to stretch it.
But that is the thing, it is not wide as the panel, and why the 4 x 3 mode works for full screen height 16:9 programing when using a lens. You have to think of it as a 4 x 3 frame, even though it is native 16:9, and what you see then is that the display on letter box mode zooms that frame in to fill the width, then at that new width, a 4 x 3 frame is taller, so it cuts the top and bottom off. That is how and why the scaling works for both SD media and HD media, but the source MUST BE set 16:9 or it will not work...
Some projectors just may not do it if you change the source because it's been programmed to not allow the function when in 4:3 mode because the makers didn't want to include the funtions in that mode to prevent users from doing something they thought they shouldn't.
Correct, and letter box is traditionally a 4 x 3 mode...