On May 20, 2024, at 09:35, Paul Koning via cctalk <cctalk(a)classiccmp.org> wrote: I think you have that backwards. TVs use interlace. Older PC displays may do so, or not; typically the 480 line format was not interlaced but there might be high resolution modes that were. The reason was to deal with bandwidth limitations. Flat panel displays normally support a pile of input formats, though only the "native" format (the actual line count matching the display hardware) is directly handled, all the others involve reformatting to the native format. That reformatting generally results in some loss of display quality, how much depends on how well the relevant hardware is designed. And interlaced formats are often supported not just for the VGA input (if there is one) but also for DVI/HDMI inputs. To get the accurate answer you have to check the specification sheet. paul

On May 20, 2024, at 10:06, CAREY SCHUG &lt;sqrfolkdnc(a)comcast.net&gt; wrote: Wayne, you must be one of those thirty-something techies from another thread. for those of us in our 60s and 70s,.... setup mode? huh? old TVs and monitors were purely analog. No on-screen displays and non-volatile memory bytes for setup. adjustments for size and position were rheostats. interlace (on TVs) was because the incoming sigonal started SLIGHTLY later for the interlaced frame and the horizontal sync was slightly different (advanced?) on the incoming signal relative to the vertical sync. With digital, the conversion of the analog input to digital for the display has to start recording only half the first line. and whatever conversion there is because on the analog display, the scan line is at a slight angle, lower on the right, so the interlaced frame starts at the same vertical height, in the middle, as the other frame started on the left side. 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> > On 05/20/2024 11:46 AM CDT Wayne S via cctalk &lt;cctalk(a)classiccmp.org&gt; wrote: > > > IIRC, didn’t most older pc monitors have a setup mode where one of the options was interlace or non-interlace. > > > Sent from my iPhone > >>> On May 20, 2024, at 09:35, Paul Koning via cctalk &lt;cctalk(a)classiccmp.org&gt; wrote: >> >> I think you have that backwards. >> >> TVs use interlace. Older PC displays may do so, or not; typically the 480 line format was not interlaced but there might be high resolution modes that were. The reason was to deal with bandwidth limitations. >> >> Flat panel displays normally support a pile of input formats, though only the "native" format (the actual line count matching the display hardware) is directly handled, all the others involve reformatting to the native format. That reformatting generally results in some loss of display quality, how much depends on how well the relevant hardware is designed. And interlaced formats are often supported not just for the VGA input (if there is one) but also for DVI/HDMI inputs. To get the accurate answer you have to check the specification sheet. >> >> paul >> >>> On May 20, 2024, at 12:13 PM, CAREY SCHUG via cctalk &lt;cctalk(a)classiccmp.org&gt; wrote: >>> >>> This may have been covered before, VERY early in this tread. >>> >>> I think I tried a game on a flatscreen, and had issues. I don't know if it applies to the radio shack Color Computer, the interest of the original poster. >>> >>> many games and entry pcs with old style tv analog format, don't interlace, and tube TVs nearly all (except maybe a few late model high end ones?) are fine with that, but I seem to recall that most or all digital/flat screen can't deal with non-interlace. >>> >>> <pre>--Carey</pre> >>

On May 20, 2024, at 10:51, Paul Koning via cctalk &lt;cctalk(a)classiccmp.org&gt; wrote:  VT100? I don't think so. And yes, it has a setup menu, but that's setup of the terminal functionality, not the monitor part. The earliest monitors could only handle one format. A major innovation was "multisync" where the monitor would determine the horizontal and vertical sweep rate and line count, and display things the right way. The first PC I owned had one of those, and as far as I can remember it had nothing that one would call a "setup menu". The reason interlace matters is not the very slight slope of the scan line in analog monitors, but rather the fact that alternate frames are offset by half the line spacing of the basic frame, so each frame sweeps out the gaps in between the lines scanned by the preceding frame. It matters to get that right, otherwise you're not correctly displaying consecutive rows of pixels. In particular, when doing scan conversion (from analog format to a digital X/Y pixel raster) you have to offset Y by one every other frame if interlace is used, but not if it isn't. paul

The setup on the earlier monitors was sometimes call “ODB” , don‘t know why. Was equivalent to setup. Sent from my iPhone cctalk(a)classiccmp.org&gt; wrote: cctalk(a)classiccmp.org&gt; wrote: series let you choose interlace if you needed. setup of the terminal functionality, not the monitor part. was "multisync" where the monitor would determine the horizontal and vertical sweep rate and line count, and display things the right way. The first PC I owned had one of those, and as far as I can remember it had nothing that one would call a "setup menu". line in analog monitors, but rather the fact that alternate frames are offset by half the line spacing of the basic frame, so each frame sweeps out the gaps in between the lines scanned by the preceding frame. It matters to get that right, otherwise you're not correctly displaying consecutive rows of pixels. In particular, when doing scan conversion (from analog format to a digital X/Y pixel raster) you have to offset Y by one every other frame if interlace is used, but not if it isn't.

On 05/20/2024 1:02 PM CDT Wayne S via cctalk &lt;cctalk(a)classiccmp.org&gt; wrote: In the vt100, setup menu “B” had an interlace on or off setting. I just looked it up.

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?

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