I remember the VT100 interlace setting. Yes, it changed the signal generated. I don't know if it also changed the characteristics of the monitor but I would think not.
It gave slightly higher resolution (the expectation would be double but the tube didn't have focus that good) at the cost of a horrible juddering display. I don't remember it being there on the later VT220. On Mon, May 20, 2024 at 7:43 PM Will Cooke via cctalk <cctalk@classiccmp.org> wrote: > > > > On 05/20/2024 12:06 PM CDT CAREY SCHUG via cctalk <cctalk@classiccmp.org> > wrote: > > > > > > > so, just curious. how do digital TVs (and monitors) work? I presume the > dots are a rectangle, not sloping down to the right, no half a line at the > top and bottom. Do they just assume the brain can't tell that (for the > converted old analog tv signal) the image therefor slopes UP very slightly > to the right from what it "should" be? and the top line is blank on the > left side because that is the interlace frame? > > > > <pre>--Carey</pre> > > > > Well, the slope is VERY slight. Approximately 1/500 of the picture > height.Probably impossible to detect with the eye. In the old days when us > older folks were young, the TV camera image was generated the same way, > with a scanned beam. So then the generated image matched the displayed > image. But Around the end of the 70s when solid state image sensors > started coming into use, the generated image didn't match that displayed on > the CRT. But nobody noticed. Now, almost all pictures are generated by > some type of solid state generator and the lines aren't angled, and neither > are the displayed lines. So, again, it matches. > > The NTSC signal defines 525 lines per "frame," each frame made of two > "fields" of 262 1/2 lines (I may have frame and field mixed up.) In one > field, the half line is at the top. It is at the bottom on the other. But > out of those 525 total lines, only around 480 (I forget exactly) are > displayable. The non-displayed lines are split between the top and > bottom. So the two half-lines aren't diplayable. Those non-displayed > lines are used for all sorts of things, including closed captioning. > > Old analog TVs and monitors make any changes for different types of > signals; they just (attempted to ) displayed whatever was thrown at them. > > Will >
