United States Patent [19] M 3.551111

United States Patent [19] [11] Patent Number: 4,660,074 Schine [45] Date of Patent: Apr. 21, 1987 [54] NTSC COLOR TELEVISION Primary Examiner-John W. Shepperd TRANSMISSION WITHOUT CHROMA Attorney, Agent, or Firm—Freilich, Hombaker, Rosen & CRAWL Fernandez [76] Inventor: Jonathan M. Schine, 626 S. Hudson [57] ABSTRACT Ave" Los Angeles’ Calif‘ 90005 An improved color television transmission compatible [21] Appl' NW 787,156 with NTSC standards produces a controlled horizontal _ scan rate at about 15,768 Hz with 227 cycles of color [22] Flled: Oct- 15’ 1985 subcarrier per line, and a controlled horizontal scan rate [51] Int. cu ...................... .. H04N 9/44; H04N 11/14 at about 60-070 HZ to Produce frames of two interlaced [52] ‘‘‘‘ " 358/16; 353/17 ?elds each at a rate of about 30.035 Hz with 227.5 cycles [58] Field of Search ...................... .. 358/11, 12, 16, 17 Qfthe color subcarrier Per ?eld Phase Shifted 180° 0f the color subcarrier at the beginning of each ?eld, thereby [56] References Cited eliminating “chroma crawl,” and reducing the size of Us, PATENT DOCUMENTS the teeth in the “zipper" effect produced by NTSC encoded color at the edge of vertical color borders. The """"""""""""""""""" vertical scan rate is controlled by dividing a clock fre 4’295’157 10/1981 Machid 358/17 quency of four times the color subciar‘rier by four to 4$001908 2/1985 Mandeberg 358/11 produce the color subcarner, and dividing the clock 4,517,587 5/1985 Aizawa et aL _ 358/17 frequency by some set of multiples to produce the hori 4,s5s,349 12/1985 Sasuki ................................. .. 358/17 zontal Scan rates with 227 cycles of color Subvarrier Per line plus one-half cycle. FOREIGN PATENT DOCUMENTS 1214333 12/1970 United Kingdom ................ .. 358/17 4 Claims, 2 Drawing Figures 21 m 3.551111: 24! H 2s 20 / + :25 v ‘ RESET CS0. 6 27 ~26 2 ___ _5 RESET U. S. Patent Apr. 21, 1987 4,660,074 10 Y , \ l J COMPOSITE R > I COLOR COLOR G ' ' SIGNAL r MATRIX ENCODER ‘ . CAMERA s 7 Q r ' ‘ I x \_ j A I V H 12 I3 3.58 MHz ‘ H COLOR SUBCARRIER " SYNC > MODULATOR GEN COMPOSITE SYNC STAGE (FIG. 2) r 14/ COMPOSITE 'VIDEO OSC- ,PO '5,» POWER F l G. I AMP 21 . 4/ 3.58MH2 24, — 2 --—>-H 2O 23 r_> +65 25 1 k1 P-rS_| 123 _j_ 525 > v ,2 .v CLK V - RESET osc. ' - RING COUNTER H. $2 5 N? / L47 "*4 + . CP Q ‘ ‘ G ~ 1 ,U ‘U D _ 26 G2 K 27 i i Q ~ ___ _ _| o ; 5 ,, RESET _J_ _\;.I?'/_:T/’ ‘T FlGZ 4,660,074 1 2 3.6 MHz above the picture carrier. To avoid interfer NTSC COLOR TELEVISION TRANSMISSION ence with the monochromatic video signal even that WITHOUT CHROMA CRAWL high in the single sideband of the video signal, the color subcarrier frequency was chosen to “interleave” in the BACKGROUND OF THE INVENTION 5 gaps of the integral multiples of the line-scanning rate This invention relates to color television, and more where there is no great amount of video information. particularly to a method and apparatus for an improved These gaps occur at odd multiples of one-half the line color television transmission that is free of chroma scanning rate. crawl and compatible with the standards of the National This need to interleave the color subcarrier sidebands Television Systems Committee (NTSC). with the‘ picture carrier single sideband thus required The term “chroma crawl” refers to the effect of a the color sub-carrier to be at some odd multiple of one jagged vertical edge of an image due to the color encod half the line-scanning rate, which is a multiple of 455 for ing and decoding process. The effect is most apparent at the color subcarrier to be placed high in the video single a border between contrasting colors. When viewed in a sideband, but below the audio carrier. This odd multiple pattern of a calibrating color bar pattern, the jagged 5 of half the line frequency also results in a minimum beat edge resembles a zipper. It will always be present in frequency with the audio carrier. ' every video scene as a color distortion, and be quite The precise color subcarrier chosen was 3,579,545 Hz noticeable, particularly in still pictures if viewed at a to have 227.5 cycles of the color subcarrier per line close distance. What is more disturbing is that the scan, thus inverting the color subcarrier phase 180° for “teeth” of the “zipper” progress (crawl) upwardly on each successive line. That would tend to cancel any the screen. This can make the zipper effect very notice effect of interpreting luminance transitions of color in able, even when viewed from a distance, because the the demodulation process, but instead produced the color distortions produced on the image appear as effect described above called “chroma crawl.” This is waves, such as waves in the fabric of an article of ap because each ?eld has only 262.5 lines. The half line at parel having a pattern of thin stripes, or some other the end causes the phase of the color subcarrier to be pattern having parallel lines with a signi?cant vertical shifted only 90° for the beginning of the next ?eld. So, component over substantial distances. in a sequence of four successive ?elds of two frames, the The NTSC color system transmits encoded color phase of the subcarrier is 0°, 270°, 180° and 90°. This is information on a subcarrier derived in the following so because 227.5 Hz/line times 262.5 lines equals way. First I and Q signals are derived from red (R), 59,718.75 cycles per ?eld, and ll9,437.5 cycles per green (G), and blue (B) camera signals in a color matrix frame. Consequently, on a ?eld to ?eld basis, the lumi according to the following equations: nance transitions interpreted as color will appear, albeit to a lesser extent, and it will appear to crawl up the 35 television screen. SUMMARY OF THE INVENTION Alternative color matrixing is given by the following In accordance with the present invention, the upward equations: moving pattern at the edges of luminance is eliminated by control of the vertical scan rate to end each scan line I=0.27(B— Y)+0.74(R - Y) with one full cycle of the color subcarrier, instead of one half of a cycle, by causing the horizontal sync gen Q=0.41(B- Y)+0.48(R— Y) erator to drop one half cycle at the end of each line. where Y is the luminance signal given by the equation: This is accomplished by feedback control on a clock 45 pulse counter for the vertical and horizontal sync gener ator to reset at the end of every line, i.e., at the occur rence of every horizontal sync pulse (H), thereby short Then the I and Q signals are modulated by the subcar ening the line by one half cycle of the color subcarrier rier in phase for the I signal and in quadrature for the Q during each raster line. Consequently, there will be 227 signal. At the receiver, the phase encoded I and Q color cycles of the color subcarrier per line, instead of 227.5 signals are decoded by synchronously demodulating the cycles, except at the end of a ?eld, for a phase inversion inphase and quadrature components to recover the I of the color subcarrier from ?eld to ?eld, thus eliminat and Q color signals. A receiver matrix then recovers the ing chroma crawl. This is all done at the transmitter; the R, G and B signals from the recovered I and Q signals, receiver will respond to the horizontal and vertical sync using Y signals, if necessary. 55 pulses (H and V) thus generated and transmitted to The monochromatic television standard already in assure that each ?eld displayed includes 525 lines of 227 place required a frame of 525 lines at a rate of 30 Hz cycles of the color carrier. using interlaced ?elds of 262.5 lines per ?eld at a ?eld The novel features of the invention are set forth with rate of 60 Hz. This requires a horizontal scan rate of particularity in the appended claims. The invention will 15,750 Hz which produces a monochrome signal having 60 best be understood from the following description when components at integral multiples of the horizontal scan read in conjunction with the drawings. rate. In order to transmit the color subcarrier in the 6 BRIEF DESCRIPTION OF THE DRAWINGS MHz band alloted to a television channel by the FCC, it was necessary to select a color subcarrier frequency FIG. 1 is a general block diagram of a television high in the picture carrier single sideband, but suf? 65 camera connected to a transmission station, which may ciently below the sound carrier to avoid interfering be a broadcast or cable station. with the audio signal, which is 4.5 MHz above the pic FIG. 2 is a functional block diagram of a preferred ture carrier. That placed the color subcarrier at about embodiment of the invention. 4,660,074 3 4 upon the setting of a D-type ?ip-?op 26 by a horizontal DESCRIPTION OF PREFERRED sync pulse (H). That enables an AND gate 6;, the EMBODIMENTS output of which not only resets the ring counter 22 via Referring ?rst to FIG. 1, there is shown a color tele the OR gate G1 but also resets the D-type ?ip-?op.

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