Color framing videotape recording apparatus and method
[ Apr. 15, 1975 COLOR FRAMING VIDEOTAPE RECORDING APPARATUS AND METHOD Primary ExaminerRobert L. Griffin Assistant ExaminerMitchell Saffian Attorney, Agent, or Firm-Limbach, Limbach &amp;  
 [75] Inventor: Nikola &#39;Vidovic, Santa Clara, Calif. Sutton [73] Assignee: International Video Corporation,  
  Sunnyvale, Calif. [57] ABSTRACT [22] Fil d; M i, 15, 1974 Automatic color framing for editing in a video tape recorder is provided by associating one of the two pos- [211 App! 451525 sible color frame phases with one of the two possible phase relationships between the off-tape color burst [52] U.S. Cl. 358/4 and the incoming video color If this association [51] Int. Cl. H04n 5/78 results in the locking of the Video p recorder to the 58 Field of Search 358/4; l78/6.6 A, 6.6 R, incorrect color frame, the association of the input 178/69 5 TV 695 C13 color burst phase relationship to the color frame phases is reversed to provide correct color framing in sub- 5 References Cited sequent edits in response to the off-tape to input video UNITED STATES PATENTS color burst phase so long as the input video horizontal 3 735 0&#39;5 5,1973 Mesak 358/4 sync to color burst phase remains substantially con- 317611604 9/1973 Ozawa et al. 358/4 9 Claims, 17 Drawing Figures 2 PHA6ES 0F COLOR FRAME PULSES 15 Hz) 1 420 M0l Cfi0ME ELECTKONIC m LOGIC 270 Piiii&#39; g &#39;gg&#39; SWITCH m FIGURE 9 (FROM FLIP-FLOP 73, FIG. M) L 422 [424 TAPE PHASE LOCKED COLOE BURST Loops COLOR FRAME PHASING CIRCUITRY INPUT PHASE LOCKED PHASE COLOR o BURST LOOP SHIFTER EDIT LOCK BUS TENIEUAPR 1 5197s SHEET C 1 BF 1 7 CLOCK SIGNAL GENERATOR 2/ Q W&#39; I I r REF. PULSE STRIPPED l 23 PHASE LOCKED LOOP I 36 m PULSE I a 1! AND 1 COMPARE V60 (K v GATE5 Q AUTOMATIC I I 7 STATION SWITCH/N6 I &#39;L 4 COMPOSITE L I NC I 37 h r v VSTAL I LOCK &#34;f&#34; CONTROLLED DETECTOR 05c. I L CLOCK SIGNAL L 1L fh 0%? ?7 I FIEIID r 1%? A9 I RESET FRAME DETECTOR (7 87 105 GENERATUR FIELD PULSE +2 SERVO I 69 NORMAL OUTPUTS ,KEsEr I REFER- Q RECORD f NOT ADVANCED ENCE c? DIV/DE I 7lx H 58 1 ADVANCE COUNTER {H 42 PLAYBACK l, K 2) K HZ EDIT 2H ADVANCE m) LOGIC I RECORD 33 59 I J /77 I M I I I- 1 L NE UP 92 CLOCK ED T l REFERENCE J DMDER K1 TIME BASE CORRECTOR 7 MONOCHROME LINE REFERENCE PULSE OUTPUT 95/ E89 FRAME RATE RESET I01 95 FIELD REFERENCE OUTPUTS 99 DIVIDER (T0 SERVO) (K2) 98 F I Er 1A PATENTEUAPRI 5 @925 SHEEF 07 0F 17 m E H g 22:2: sa 53s SE28 NEE ma ma e. 225% 3528 cccccccccccccc E3 5 E 52$ a 7 EEQ 3E2 $5 556 658 $33 Em PATENIEBAPR 1 51.975 3.878557 saw 08 or 17 I I I i Z I I I w L5 2 [1i 12X E REFERENCE CONTROL VAR! BLE &#34;A&#34; ?I&#39;PITENTEUAPR I 51975 3, 878,557 SHEET 12 Jr &#39;1? HOK/Z. T0 PHASE TACH REF. PULSES ERROR DETECTOR l2 (6 KHZ) VOLTAGE CLOCK I I II 309 DELAY w 331 INHIBIT NORMAL &#34;SET RESET FLIP A FLOP TRIGGER 315 V A VOLTAGE INHIBIT NORMAL CDNTROLLED CONTROL ENABLE 518 3B CLEAR DIGITAL COMPARATOR COUNTER LATCHES COLOR FRAMING VIDEOTAPE RECORDING APPARATUS AND METHOD 1 BACKGROUND OF THE INVENTION The present invention relates tov video tape recorders (VTRs) and, more particularly, to electronic editing of NTSC color television signals on aVTR. The present invention is useful in all types of high quality VTRs, including both quadruplex and helical scan type VTR&#39;s.  
  In the process of editing tapes on a VTR, either a series of&#39;new segments are recorded in sequence (assemble&#34; editing) or a new segment is recorded in a previously recorded segment (insert&#34; editing). In either case, the precise timing&#34; of the ultimately recorded sequence must not vary and particularly the timing at the beginning and end of segments must match that of adjacent segments. By timing is meant the phase of the horizontal synchronization pulses of the recorded video signal. Such requirements are well known in the art.  
  Typically, in playback modes of VTR operation, the off-tape horizontal pulses are locked to a reference signal (horizontal lock) by means of a phase locked servo arrangement which controls the rotational phase of the mechanical scanner member which carries the VTR record/playback heads.  
  A problem in editing is that the horizontal lock is obviously inoperative during record. A prior art technique is to place the VTR in the tachometer mode (i.e. the playback timing is not finely controlled by locking the horizontal pulses to a reference, but instead is coarsely controlled, the scanner tachometer is phase locked to reference tachometer pulses, such tachometer pulses occurring at a slower rate than the horizontal pulses and such pulses not related to a signal reproduced by the VTR) and manually adjusting the tachometer reference (or equivalent) to secure zero hori- 4 zontal error which is usually adequate to assure proper timing in subsequent edit record sequences. This approach requires additional set up time and operator skill.  
  An automatic means for securing zero horizontal error during edit record sequences is the subject of US. patent application Ser. No. 356,839 of Bert H. Dann, filed May 3, 1973, now abandoned, entitled Videotape Recorder Editing Apparatus. According to the teachings of that application, the horizontal error during edit playback is stored to provide the same error correction during edit record sequences thereby maintaining the same timing throughout the recorded material.  
  Nevertheless, a further problem occurs in the editing of color television signals. In order to fully appreciate this problem one must consider not only the nature of the color television signal itself but also the action of time base correctors which are almost universally employed in high quality VTRs, particularly VTRs used in broadcasting. These problems are discussed in an article The Problems of Splicing and Editing Color Video Magnetic Tape by C. A. Anderson in the IEEE Transactions on Broadcasting, Vol. BC-IS, No. 3, September, I969.  
  First, with regard to the color television signal itself, there are two points to consider. With respect to a par ticular video source, a color frame is two monochrome frames. That is, because the NTSC color burstshifts phase each frame, it is two frames before 1 the same phase is repeated. Also, the phase of the color burst with respect to the horizontal sync pulse is not defined. While this phase relation will typically be stable as to a particular video source, it will not be the same in different video sources. It will therefore be apparent that the color frame is not uniquely defined in any manner.  
  Second, with regard to time base correctors, a typical correction scheme in a color VTR includes two variable delay lines in series to remove residual time base errors still present despite a horizontal locking of the VTR servo systems. The first delay line is controlled by an error signal derived by comparison of off-tape to the input video horizontal sync pulses. The input video signal is the signal which is to be edited into material previously recorded on the tape. In most circumstances the input video signal will have a highly stable horizontal sync and color burst and the phase relation between sync and burst, whatever it may be, remains stable. The second delay line provides a fine correction under the control of an error signal comparing off-tape burst to a subcarrier derived from the input video signal. As will be explained, it is this last correction that causes color editing problems.  
  As part of the VTR lock-up sequence, the VTR synchronizes the off-tape monochrome frame to the input video monochrome frame. Because there is no way to identify the color frame the machine has a fiftyfifty chance of locking to the correct color frame. In either case, the VTR proceeds to achieve horizontal lock to the input video signal. Thus, the horizontal sync pulses are closely in phase at the output of the machine and even more closely in phase at the output of the first delay line in the time base corrector. However, prior to the second delay line, the phase difference between the reference subcarrier and the off-tape color burst is either 9 or 9 180 depending on which phase of the color frame the VTR happened to lock to. The phase angle 6 indicates the difference in phase between the input video color burst and the off-tape color burst due to the undefined phase relationship between the horizontal sync and color burst of any NTSC color television signal. In either case, the second delay line will resolve the phase difference 9 or O 180.  
  However, at an edit point, if the second delay line suddenly must change from resolving a 9 to a 9 180 error or vice-versa there is an abrupt 180 shift. Such a shift is equivalent to I40 nanoseconds of delay and results in a disturbing and noticeable sideways jump in the reproduced picture from the VTR. This effect is particularly disturbing in animation.  
 SUMMARY OF THE INVENTION sync and burst derived from a single stable generator) the phase of the horizontal sync to burst in the input video signal and in the off-tape video signal will each remain constant. However, the relative phase of the off-tape burst and input video burst will either be 9 or O 180 depending on which phase of the color frame that the VTR happens to lock to. By comparing the input color burst to the off-tape color burst the relative phase relation of those two bursts can be stored. Then, for example, a test edit can be made to provide a visual determination if the VTR locked to the wrong color .FIGS. 6A-N are a series of waveforms useful in understandingFIG. 4.  
  FIG. 7 is a timing diagram useful in understanding FIG. 4.  
 frame Phase y looking for a de ays jump in the re- FIG. 8 is a block diagram of a scanner servo system produced picture at the edit point. Circuitry is then of a video tape recorder particularly adapted for use programmed to select the correct phase of the color with the present invention. frame by comparing the relative off-tape to input video FIG 9 i a block diagram of a capstan servo system color burst phases. For the particular input video signal f a vid o t e recorder particularly adapted for use source and off-tape video signal the relative burst phase 10 with the present invention. requires a selection of a particular color frame phase. FIG. 10 is a block diagram of one embodiment of the Having found that relationship the VTR will automatio t llabl delay of FIG. 8. cally lock o h rr c l r fr m p n p r g FIG. 11 is a block diagram of the digital delay portion the two color burst phases. The VTR may even be f FIG 10, turned off and days or weeks may pass once this rela- P10. 12 is a block diagram of an alternative emboditionship is initially determined and automatic lock to ment of the controllable delay of FIG. 8. the correct frame will still occur so long as the horizon- FIG 13 i a blo k diagram of the A/D and D/A portal sync to color burst phase of the input video signal io f FIG 12, (1068 not Change n i y. FIG. 14 is a block diagram of a time base corrector These and other advantages and features of the inte the operation of which is useful to an undervention will be recognized more fully as the detailed standing of the present invention. description of the preferred embodiments, claims and FIG 15 is a block diagram of one embodiment of the accompanying drawings are read and understood. i v ti n,  
  FIG. 16 is a more detailed block diagram of an em- BRIEF DESCRIPTION OF THE DRAWINGS bodimem of the invention FIG. 1 is a system block/diagram of an input synchro- HA4.) a 5.61165 of waveforms useful m understanding the invention. mzlng signal processor particularly adapted for use with the present invention. DESCRIPTION OF THE PREFERRED FIG. 2 is a block diagram showing use of the input EMBODIMENTS Synchronizing signal Processor 1 in edit m In order to completely understand the present inven- 3 15 a block diagram showmg an alternanve tion, various details of an exemplary VTR are disclosed of n for the purposes of a complete disclosure. It will be un- Q- 4 IS a general block diagram 9 the mlscount derstood that the invention is not limited to the context Phasing System useful understanding the Servo 3 of the particular VTR of which portions are herein detems particularly adapted for use with the present lnscribed. The overall exemplary VTR is described in vention. greater detail in the following copending applications FIG. 5 is a block diagram of the logic block of FIG. and patents, assigned to the present assignee, all of 40 which are incorporated herewith by reference:  
 Patent No. Title Issued Inventor(s) 3,783,398 FM PULSE AVERAGING 1- 1-74 Bert H. Dann DEMODULATOR 3,809,809 TECHNIQUE FOR DETECT- 5- 7-74 Nikola Vidovic ING LONG DURATION PULSES FROM A TRAIN OF SHORT DURATION PULSES 3,862,355 HELICAL SCAN WIDEBAND 1-21-75 Barett E.  
  TAPE RECORDER APPARA- Guisinger TUS AND METHOD 3,852,617 PASSIVE PEAK 12- 3-74 Nikola Vidovic DETECTOR AND LEVEL SHIFTER 3,843,957 VIDEO PROCESSING 10-22-74 Nikola Vidovic CURCUIT 3,806,794 PHASE SHIFTER 4-23-74 Nikola Vidovic APPARATUS Application Ser. No. Title Filed Inventor(s) 285,919 SYNCHRONIZING PULSE 9- l-72 Bert H. Dann and PROCESSOR FOR A Nikola Vidovic VIDEO TAPE RECORDER 285,917 VIDEO TAPE RECORDER 9- 1-72 Kenneth Louth METHOD AND APPARATUS 354,227 MAGNETIC TAPE 4-25-73 Frank S. C. MO and TRANSPORT SYSTEM Vernon Natwick 355,220 VIDEOTAPE RECORDER 4-27-73 Barrett E.  
  AND REPRODUCER Guisinger and VELOCITY COMPENSATOR Bert H. Dann APPARATUS 356,380 VIDEO TAPE RECORDER 5- 2-73 Kenneth Louth METHOD AND APPARATUS