20 May
2024
20 May
'24
11:36 a.m.
On 05/20/2024 12:06 PM CDT CAREY SCHUG via cctalk
<cctalk(a)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