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All of this contributes to the final measure of resolution, what you see in terms of
Venetian blinds, picket fences, or polka dot clothing.
Resolution Factoids,.
While all (NTSC) TV sets and program material (broadcasts, tapes, disks, etc.) use the
same 525 scan lines, the advertised resolution (240, 425, 500, etc.) refers to the horizontal
resolution which is the number of side by side dots that can be reproduced within any one
line.
The number of scan lines is the limit for vertical resolution, the number of dots in a
column that can be reproduced. It is pretty much the same for all decent NTSC TV sets of
moderate or large size.
If the video signal is converted and processed digitally at any time, there will be a
horizontal pixel count. This pixel count becomes the upper limit for horizontal
resolution. (Such as if signal is put through the Ken-A-Vision USBAD2 or what happens
in a 7600 or MVP camera).
Both horizontal and vertical resolution also depend on how tiny a spot can be produced
on the screen. The finite number of scan lines and, for digital video, the number of pixels
horizontally also limit the smoothness of diagonal lines and the resolving of position of
fine details.
Traditionally, "lines of resolution" is correctly measured across the largest circle (must be
a circle not an ellipse) that fits in the space you are talking about. However some
advertisers exaggerate using the entire screen width or using some electronic formula that
only covers part of the circuitry. Modern standards stating resolution or screen
dimensions in "pixels" (dots) reflect the entire screen width or height, not just the circle.
For NTSC, the picture occupies approximately 480 of the 525 scan lines. For video
broadcasts the portion of a scan line that is visible can hold up to about 440 dots so a grid
480 high by 440 wide represents the maximum amount of picture detail possible.
Advertised resolution applies to blacks, grays and whites only. Color resolution is much
less. The human eye and brain are less sensitive to lack of color within fine detail.
“Lines of Resolution” for video include both the black lines and the white spaces
between them in a test pattern but not the gaps if any between scan lines or between
phosphor dots/stripes.
The more brightness and color changes, representing picture detail, the greater the
circuitry bandwidth and broadcast channel apace needed. Horizontal resolution is the first
to be affected by bandwidth limitations.
(11 pages)
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