United States Patent [19] [11] Patent Number: 4,660,074 Schine [45] Date of Patent: Apr. 21, 1987

[54] NTSC 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

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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 , 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 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. In vision camera 10 with an external sync generator 11 and that manner, two cycles of the input to the ring counter a matrix 12 for combining red, green and blue color (which is 4 times the color subcarrier) is dropped once signals, or red, blue and luminance, to produce I and Q per line during the horizontal retrace. As a conse chroma signals to be encoded by a color subcarrier quence, the horizontal scan frequency is advanced one produced by the sync generator at precisely 3,579,545 half cycle of the color subcarrier at the start of every Hz (usually by dividing down a crystal oscillator oper raster in order to provide 227 cycles of the color subcar ating at four times the color subcarrier frequency). rier during each raster, instead of 227.5 cycles as in the ' For simplicity, it is assumed that direct luminance conventional implementation of the NTSC standard. from the camera is used in an encoder 13 together with The half cycle assures that during each scan line the the color transmission primaries I and Q from the color color subcarrier will be precisely in phase. While this matrix 12 to produce an NTSC composite color signal. would eliminate the chroma crawl effect, it would cre A modulating stage 14 combines the composite color ate a more objectionable “picket fence” effect, which signal with a composite sync signal that includes not the NTSC system sought to avoid. Modern color televi only the vertical and horizontal sync pulses (H and V) sion receivers and monitors employ comb filters, or but also the color carrier bursts to form a composite notch ?lters, that will eliminate any vestige of the video signal. The signal is then carrier “picket fence” effect, but monochrome receivers are modulated and applied to a power ampli?er 15 and to a not so equipped. Therefore, to retain compatibility of transmitting (not shown) for radiation to re the color television signal with monochrome receivers, ceivers, or to a cable system for transmission to receiv it is necessary to alternate the phase of the color subcar ers. rier for every ?eld. To accomplish that, the vertical All of the foregoing is conventional in nature. What is 25 sync pulse inhibits the ?ip-?op 26 for one horizontal new is the manner in which the vertical and horizontal sync period. An RC circuit 27 is adjusted to stretch the sync pulses are generated to control the number of leading edge of a negative vertical sync pulse for that color carrier cycles per line and ?eld, as will now be period. As a consequence, instead of resetting the described with reference to FIG. 2. A crystal oscillator counter 22 early by one half cycle of the color subcar 20 generates a stable frequency that is four times the rier at every horizontal sync pulse, the counter is so color subcarrier of about 3.58 MHz. A divide-by-four reset at every horizontal sync pulse except the ?rst one counter 21 then produces the stable color subcarrier in each ?eld (during vertical retrace) to shift the phase required by the encoder 13 (FIG. 1). of the color subcarrier for the next ?eld by half a color The output of the oscillator 20 is also divided down subcarrier cycle. by a counter 22 to generate a lower frequency signal 35 The result of freezing the in phase condition of the used to generate the horizontal and vertical sync pulses. color subcarrier for all rasters of a ?eld, and shifting the This is done by arranging for a normal reset feedback phase 180° during the vertical retrace period for the via an OR gate G1 to cause dividing the input by seven. rasters of the next ?eld, is that the “zipper effect” is not This may be done with a 74HC4017 integrated circuit only made stationary, but the teeth of the zipper are which normally divides the input by ten, but may be 40 made smaller, namely the size of one line width in done by a 7-stage ring counter that produces successive height and a half cycle of the color subcarrier in depth. output pulses at stages 1 through 7, and then automati In conventional NTSC color television, the teeth are cally recycles itself without the need of a feedback gate. two line widths high and the zipper effect progresses What is illustrated is a lO-stage ring counter (the equiva (crawls) upwardly, due to the fact that the number of lent of the 74HC4017) with means for resetting the 45 lines in a frame are not even, thus producing what is counter to zero after the seventh pulse is counted via called “chroma crawl.” - the OR gate G1 from the output count of 7. A divide-by This freezing of the zipper effect by eliminating seven output thus produced is taken from an earlier chroma crawl and reducing the size of the zipper teeth count of 2 in each cycle of the counter. The frequency results in other advantages, such as obviating the need of that output (2,044,990 Hz) is then divided by 65 in a for “color framing” while running or editing video tape. circuit 23 to obtain a frequency of 31,536 Hz, and then This is so because line scans of each frame will be identi by 2 in a circuit 24 to obtain the horizontal sync pulse cal, i.e., all the line scan of a frame will be in phase with (H) at the rate of 15,768. The output of the circuit 23 is corresponding line scans of a successive frame. It also also divided by 525 in a circuit 25 to obtain a vertical simpli?es “freeze framing” for the reason that only two sync pulse (V) at the NTSC rate of 60.07 Hz. In a pre ?elds are required to complete a frame, and not four ferred embodiment, a phase-stabilizer circuit 23a is in successive ?elds, and there is no need to decode and cluded between pin 2 of the ring counter 22 and the re-encode the color video when using two-?eld storage frequency divider 23. Such a phase-stabilizer circuit for freeze frames. Still other advantages are an im may be implemented with a voltage controlled oscilla proved picture with less ?icker when converting to tor (VCO) having a crystal for control of its frequency 60 other international television standards, such as PAL at 2.044 MHz with feedback to a phase detector imple and SECAM. mented with a balanced demodulator the output of The luminance/ artifacts of this im which passes to the voltage control input of the VCO proved color coding scheme are 180“ out of phase from through an RC ?lter having a long time constant to line to line of interlaced ?elds. This tends to cancel the eliminate jumps in phase at the H and V sync pulse 65 visual perception of color artifacts due to visual integra outputs. tion. A conventional NTSC receiver will respond to The OR gate G1 also resets the ring counter 22 early vertical sync pulses of the modi?ed composite video from the count of 5 once during each raster (scan line) signal to achieve at the receiver precisely what is done 4,660,074 5 6 at the camera, which is a ?eld scan having 59,7185 half cycle of the color subcarrier, thereby to invert the cycle of the color subcarrier per ?eld. Otherwise, the phase of the color subcarrier during successive scan desired 227.5 cycles of color subcarrier per line lines of interlaced ?elds. achieved under the conventional NTSC standard 2. A method as de?ned in claim 1 wherein said verti would be out of phase by 90° from ?eld to ?eld over cal scan rate is produced by dividing said clock fre four frames. quency by some set of multiples to produce said hori» In the broadest aspects of the invention, this is accom zontal and vertical scan rates with 227.5 cycles of color plished by controlling the horizontal sync and the verti subcarrier per line, and once every scan line at the end cal sync to end each line with a full cycle of subcarrier, thereof, skipping one half cycle period of said color rather than controlling only the color subcarrier and subcarrier in the generation of the horizontal sync horizontal sync to end each line with a half cycle of pulses except during a vertical sync pulse for the next color subcarrier as in the NTSC system. The feature of ?eld, thereby causing each ?eld to have the color sub the NTSC standard of inverting the color subcarrier carrier with the same phase, and with the phase in phase every scan line of a frame is retained; what is verted every ?eld of every interlaced frame so that the changed by also controlling the horizontal and vertical phase of the color subcarrier in each ?eld is 180° out of sync is that the horizontal sync pulse interval is short phase with the color subcarrier of the next ?eld. ened by one half cycle of the color subcarrier every 3. In a color television transmission system compati ?eld to avoid the progressive phase shift of the color ble with NTSC standards, an improvement comprised subcarrier from field to ?eld by 90°, thus eliminating the of means for generating a color subcarrier at bout “chroma crawl” effect present in conventional NTSC 20 3,579,545 Hz by dividing down a clock frequency of standard television. As an additional advantage, the four times the desired color subcarrier, means for divid color subcarrier and the aural carrier intermodulator ing said clock frequency to produce a controlled hori beat is kept at a precise 180° phase reversal every scan zontal scan rate at about 15,768 Hz with 227 cycles of line to cancel any intermodulation beat per line that color subcarrier per line, and means for dividing said may otherwise be present. 25 Although particular embodiments of the invention clock frequency to produce a controlled vertical sync have been described and illustrated herein, it is recog pulse at a rate of about 60.07 Hz to produce frames of nized that modi?cations and variations may readily two interlaced ?elds, each at a rate of about 30.035 Hz occur to those skilled in the art. Consequently, it is with 59,7185 cycles of said color subcarrier per ?eld, intended that the claims be interpreted to cover such and means for extending the horizontal sync period for modi?cations and variations. the ?rst line of every ?eld by one half cycle of color What is claimed is: subcarrier. 1. A method for an improved color television trans 4. An improvement as de?ned in claim 3 wherein said mission compatible with NTSC standards of interlaced means for producing said horizontal and vertical scan ?elds comprised of the steps of generating a color sub rates with 227 cycles of color subcarrier per line, is carrier at about 3,579,545 Hz by dividing down a clock comprised of means for skipping two cycles of said frequency of four times the desired color subcarrier, clock frequency once every scan line at the end thereof dividing said clock frequency to produce a controlled in the generation of the horizontal sync pulses, except horizontal scan rate at about 15,768 Hz with 227 cycles the ?rst line of every ?eld, whereby the color subcarrier of color subcarrier per line, and dividing said clock 40 during each scan line of every ?eld is in phase and the 1 frequency to produce a controlled vertical scan rate for horizontal sync pulses of each successive ?eld are de interlaced ?elds, each at a rate of about 30.035 Hz with layed one half cycle of the color subcarrier at the begin~ 59,7185 cycles of said color subcarrier per ?eld, and ning of each ?eld. extending the horizontal shift pulse by the period of one * * * * Ill 45

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