Television – Image signal processing circuitry specific to television – Color television signal processing
Reexamination Certificate
2000-01-06
2002-11-12
Hsia, Sherrie (Department: 2614)
Television
Image signal processing circuitry specific to television
Color television signal processing
C348S712000, C348S713000, C348S680000, C348S679000
Reexamination Certificate
active
06480241
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to an apparatus for transmitting an S-video signal from a video source over a transmission line having a length typically detrimental to the S-video signal and the processing of the S-video signal for enhancing the signal within selected frequency bands for overcoming transmission line loss. More particularly, the invention relates to the processing of chrominance and luminance signal components for enhancing brightness and resolution typically reduced through the transmission line loss.
BACKGROUND
As is well known in the television and video industry, a composite video signal includes luminance and chrominance components that are combined or encoded, such as in an American standard signal established by the National Television System Committee (NTSC) of the Federal Communications Committee (FCC). By combining these signals, the quality of the final signal available is reduced because precise decoding for viewing a final image has yet to be achieved. The original frequency response parameters for the video signal specified in the NTSC standard required a total frequency response of 4.5 MHZ as illustrated by way of example with reference to FIG.
1
. This includes all picture information for horizontal and vertical scanning, flyback for retrace, and sound. This does not take into account the 1.5 MHZ separation distance required between TV channels. The total system requires 6 MHZ. Further, the frequency response of a system is directly proportional to the amount of resolution available on an associated monitor screen. The higher the frequency, the smaller will be each picture element, and the better the resolution.
With the introduction of color, an additional bandwidth of approximately 1 MHZ was required. The standard required this color or chrominance information to have a frequency range between approximately 3 MHZ and 4.5 MHZ. This provided the color bandwidth needed but at the same time limited the upper end frequency response for luminance. Such requirements limit picture information changes in a “super detail” area. By way of further example, a frequency response as in
FIG. 1
extending to approximately 15 MHZ is applicable for HDTV. More and more, video equipment manufactures are developing new ways of using this standard information within video systems with a goal of achieving improved picture quality. The present invention, as will be herein described, addresses improving the picture information, especially in this super detail area, when transmitted over a long transmission line.
By way of example, instead of using the composite signal to provide picture information directly, the composite signal is processed for providing luminance and chrominance signals on separate signal channels. By separating the luminance and chrominance signals, interference and difficulty in controlling the picture detail is dramatically reduced.
As is well known in the art, chrominance (chroma) defines the color information in a composite video signal and describes the hue and saturation of a picture, but not the brightness. The brightness and contrast are described by the luminance component of the signal. The luminance is a monochrome component of a color video signal. Compatible color systems present luminance values of an image in a signal which is essentially that of an equivalent monochrome transmission. The hue and saturation values of the image are transmitted on a color sub-carrier wave located within a frequency band of the luminance signal, and is recoverable from it. By arranging scanning frequencies to be rigidly tied to the color sub-carrier frequency, the spectrum components of the chrominance signal (hue and saturation) are interleaved in frequency with those of the luminance signal. Therefore, since the chrominance signal contains essentially no luminance information, it has no noticeable effect on monochrome reception. The chrominance signals are recovered in color receivers and are combined therein with the luminance signal to recreate the primary color video signals such as in the FCC/NTSC composite color signal.
Separating the luminance and chrominance signals improves picture quality but it is well known that such luminance and chrominance information is limited to transmission over cable lengths within a few meters before significant degradation of the signal information makes the picture unacceptable to the user or viewer. There is a need in the industry to provide for the transmission of such luminance and chrominance signal information over varying lengths of transmission cable or lines with the further feature of permitting the user to adjust the picture quality, determined by luminance and chrominance, to the taste of the user. There is a further need to be able to adjust for varying lengths of cable or transmission lines selected for the convenient of the user.
The frequency response for the video signal after being transmitted over significant transmission line lengths plays an important role. By way of example, consider the sensitivity of the video signal for systems using a frequency band width of 4.5 MHZ with different carrier video components needed to make up a complete video signal used by television. Picture, synchronization, sound, and color makes up this composite format. The scan rate frequency used is 15,750 Hz. During operation, this scanning frequency sweeps a dot along the face of a monitor picture tube varying the intensity of the dot proportional to the amplitude of the signal. The resolution defined by the quantity of dots that are displayed is directly proportional to the frequency response of this composite video envelope. In other words, a frequency response having higher frequencies will result in a sharper video image on the monitor.
By way of example, should the band width of the composite video signal be 3 MHZ, the actual resolution would be determined as follows: First, determine the time it takes for one line of picture information to travel from the left side of a monitor screen to the right side before retrace occurs. Since the scan frequency is 15,750 Hz, the time to complete one scan can be calculated by finding the reciprocal of the frequency, which is 63.3 micro seconds. Next, determine the time it takes for 3 MHZ to produce one picture element or 2 dots. One element is made up of movement through 2 dots. The same rule follows, take the reciprocal of 3 MHZ, which is 0.333 micro seconds. That is the time it takes to produce one element or 2 dots. This means that approximately 6 dots appear in one microsecond. Finally, multiply the 6 dots times the scan rate of 53.5 micro seconds (63.5 less 10 used for retrace) which provides the number of dots to go across the whole screen. The result is about 314 dots that can be scanned with one sweep trace at 3 MHZ.
Consider a video signal having a response with a frequency band width of 4 MHZ and redetermine the resolution. The reciprocal is 0.25 micro seconds. Again, it takes 2 dots to make up one element. That is 8 dots times 53.5 micro seconds and you get 426 dots of resolution. It is thus quite obvious how much frequency response can change the picture detail. More picture elements provide better the picture detail, but more picture elements demand more frequency bandwidth.
When color television was introduced in the 1950's, a certain amount of the video bandwidth was sacrificed in order to accommodate the need for color information. By colorplexing (colorcoding) or providing a matrix during the transmit procedure of video, the colors retrieved from the three color camera, (red, green, blue) are encoded to produce 2 sets of color sidebands, one labeled I and the other Q. These 2 color mixtures are transmitted together, one being 90 degrees out of phase with the other. Since the human eye sees fine picture elements in black and white, color need only satisfy viewing the large objects. The amount of bandwidth needed for I and Q was then limited to only 1.5 MHZ, as illustrated by the frequency range for the chrominance signal
Gordon J. Gow Technologies, Inc.
Hsia Sherrie
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