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cannot make spots small enough, what should be individual closely spaced dots will be a
continuous blur..
Published Resolution is for Black and White
(Applies to transmission and storage and also to displaying of video)
All horizontal resolution figures published for video, if not otherwise qualified, apply to
blacks, grays, and whites only. All of this has to do with maximum signal frequency and
limits on what will fit into the broadcast channel or on VHS tape, etc. The luminance
signal, also called luma, or Y, contains all the information needed to produce the video
picture but in black and white. It is transmitted or recorded with enough bandwidth to
carry the desired or maximum possible horizontal resolution of the subject material.
Color is broadcast using a second signal (called the chrominance, chroma, or C signal). It
has much less bandwidth, in some cases as low as 0.5 MHz allowing only 40 lines (broad
stripes) of horizontal resolution. Small horizontal details (dots along a scan line) therefore
cannot be of alternating contrasting colors. The human eye and brain do not notice loss of
color in the finer details of a motion picture as much as they sense blurring of the light
and dark content.
Improved color resolution is a significant factor in the quality of digital TV programs
such as on DVD.
Both the Black Lines and White Spaces Count
Resolution is measured using charts with closely spaced dots, parallel lines or
approximately parallel lines, the more that can be distinguished in a given area, the better
the resolution. In order to see a series of dark lines we must have light spaces in between
them. For film, "lines of resolution" count only the dark lines, not the spaces in between.
Because video has much lower resolution than film, video people count both the dark
lines and the light spaces as "lines" in order to have larger numbers to talk about. The
term "television line" or "TVL" thus refers to scan lines vertically or the smallest possible
dots on a line horizontally. In response to this, film folks have resorted to using the
phrase "line pair" to stand for a dark line together with the light space to one side.
Sometimes the scan lines are thin enough that dark gaps are seen between them. These
gaps, and also the dark boundaries between red, green, and blue bars or dots on the
picture tube face, do not count as lines of resolution.
An Example (NTSC broadcasting)
To show a movie (motion picture) in the theater, still pictures are flashed on the screen
one after another, 24 frames of the film strip per second. For TV programs it is 30 frames
per second. Once we start discussing things that repeat many times per second we must
bring the words cycles, megahertz, and frequency into our discussion. (Hertz is short for
"cycles per second".)
The first number that comes to mind when talking about NTSC video is 525, the number
of horizontal stripes or scan lines drawn across the screen to construct the picture. The
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