EP0177570A1

EP0177570A1 - Jitter-free still-framing

Info

Publication number: EP0177570A1
Application number: EP85901806A
Authority: EP
Inventors: David L. Funston; Carl N. Schauffele; Thomas C. Nutting
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1984-04-05
Filing date: 1985-03-25
Publication date: 1986-04-16
Also published as: WO1985004777A1

Abstract

Le but de la présente invention est que les deux champs de chaque image soient capturés simultanément et qu'alors seulement ces champs soient mis en séquence séparément pour, par exemple, un affichage intercalé sur la face d'un poste de télévision standard. Puisque les deux champs de chaque image sont capturés ensemble, on évite une instabilité entre les champs pendant le cadrage immobile (ainsi que le flou d'image qui en résulte).The object of the present invention is that the two fields of each image are captured simultaneously and only then these fields are sequenced separately for, for example, an interleaved display on the face of a standard television set. Since both fields of each frame are captured together, jitter between fields during still framing (and resulting image blurring) is avoided.

Description

JITTER-FREE STILL-FRAMING

BACKGROUND OF THE INVENTION 1• Field of the Invention

This invention relates in general to elec- tronic imaging systems, and more particularly to such systems which employ television for image dis¬ play purposes. (As discussed herein, "television" shall be taken to be of the American standard...i.e. 525 raster lines,_.30 frames per second, two inter- laced fields per frame etc...although, as will be apparent, the invention is applicable as well to other television standards, e.g. those employed in PAL and SECAM.) 2. Description Relative to the Prior Art An exciting new "burst" technique has been indicated for use in the display of motion picture scenes on television sets: Imagine, for example, a video camera adapted to feed video signals--via some suitable transmission link—to a television set. A "burst" corresponding to a first movie scene is fed by the camera-transmission link to the television set; then a second scene-representative "burst" is fed by the camera-transmission link to the tele¬ vision set; then a third; and so on. At the end of each such "burst", the last frame thereof is left as a continuous still frame appearing on the face of the television set until the start of the next occurring "burst"...this being in contrast to the prior art practice of having the face of the tele- vision set go dark or (worse still) bright between movie scenes.

The camera operator, in the above example, determines the time duration of each video "burst". Conventional video cameras supply video information at the frame rate of 30 frames per second, albeit that each frame is comprised of two fields apiece, each occurring at the field rate of 60 fields per second. As is the current practice, conventional video cameras capture the two fields (f, and f„) of each frame in different succes¬ sive sixtieths of a second. This unfortunately gives rise to a problem associated with the above referred to inter-burst still frame display, viz. in the event scene motion had occurred between the suc- cessive fields of the displayed still frame (as is likely), then the display of that frame will be (and will so appear) less sharp than the "movie" frames from which it was derived. This is because a tele¬ vision viewer really sees, successively, 60 differ- ent hal -resolution fields per second, whereas while looking at the above indicated, still-framed inter- burst image, the eyes of the viewer integrate two similar, but different, fields which destructively combine to fuzzy the still frame image. SUMMARY OF THE INVENTION

To reconcile the aforedescribed problem, the concept of the invention provides that both fields of each frame be captured simultaneously, and that only then are such fields to be separately sequenced for, say, interlaced display on the face of a standard television set. Since both fields of each frame are captured together, inter-field jitter (and image fuzziness produced thereby) is avoided. Attendantly, utilization of the "burst" concept is productive of as much picture sharpness during still framing as occurs during motion picture scenes.

Structure-wise, the inventive concept employs a frame (not field) imager and a 30 Hz shutter for intercepting image radiation, and for cyclically imaging onto the imager at the indicated frame rate. The imager is then read out in such a way as to produce successive interlaced field sig¬ nals for (recording and/or for) application to a television set. Because the signals applied to the television set are (from the standpoint of the tele- vision set) conventional, the television set oper¬ ates conventionally; but because the field signals of each frame originate concomitantly, there is no blur-producing inter-field jitter attendant when¬ ever, say at the end of a "burst", the television displays a still frame.

Since an interline transfer type imaging device, by its nature, is productive of signals corresponding to successive interlaced image fields, a frame-converter according to a presently preferred form of the invention employs such a device in con¬ junction with a 30 frame per second shutter, thereby to produce successive pairs of concomitantly gener¬ ated field signals. During operation in a movie burst mode, the imaging device output signals are processed to a television set (transmission link) without processing by any internal frame-converter storage means; and only during inter-burst opera¬ tion, while still framing, are field signals pro¬ cessed to-and-from storage means within the frame- converter. As to signal processing during the still frame mode of operation, minimal logic is required because the frame-converter output signals occur in precisely the correct line-by-line order necessary for proper operation of the television set. With the above as background, reference should now be had to the following figures for a detailed description of the invention:

Fig. 1 is a block diagram of apparatus embodying the invention, Fig. 2 is a perspective view, partially in block form, of one embodiment of the invention, Fig. 3 is a schematic block diagram of apparatus according to the invention,

Fig. 4 is a set of waveform diagrams useful in describing the apparatus of Fig. 3, Fig. 5 is a block diagram of another apparatus embodying the invention,

Fig. 6 is a perspective view, partially in block form, of the embodiment of Fig. 5,

Fig. 7 is a schematic block diagram of apparatus acccording to the invention,

Fig. 8 is a set of waveform diagrams useful in describing the apparatus of Fig. 7, and

Fig. 9 is a schematic block diagram of a switching circuit useful with the invention. DETAILED DESCRIPTION

Referring to Fig. 1, a system for use in apparatus such as that employing the aforementioned "burst" technique is shown having (a) a frame imager and store 10, and (b) a cooperating shutter 12. The frame imager and store 10, in turn, includes an electronic imaging device 14 (solid state, e.g. CCD, CID, photodiode, etc., or Vidicon, or the like) and a signal store 16, the imaging device 14 being dis¬ posed to receive image signal-generating radiation via the shutter 12. (As used herein, the term "generating" shall refer to the signal creation process as caused by incident radiation. Con- trarily, signal "producing" shall pertain to the process by which signals are, or may be, applied to cooperating devices.) Pursuant to the invention, the shutter 12 is operated F times per second (e.g. at a frame rate of 30 frames per second) for expo¬ sure durations (E_™) less than 1/F seconds (e.g. less than l/30th of a second). Despite the fact that the signal store 16 stores, by virtue of the operation of the shutter 12, a new full frame of concomitantly generated video signal information each l/30th of a second, the signal store 16 is operated so as to produce (readout device IP) two differently composed (i.e. f, ≠ f„) interlaced video field signals—during successive (i.e. differ¬ ent) sixtieths of a second--from such concomitantly generated signal information. In other words, although the video field signals produced by the signal store 16 occur in successive sixtieths of a second, such field signals both derive from concomi¬ tantly generated signals in the imaging device 14.

Turning now to Fig. 2, a solid state imag¬ ing device 10' of the frame transfer type (See, for example, Charge Transfer Devices, Sequin and Tompsett, page 153, Library of Congress 63-12814, as representative of the state of the art) is shown cooperating with a rotary shutter 12' and signal receiving electronics 18'. (Primed notations have been employed to indicate corresponding parts in the various figures.) Frame transfer imaging devices, as is known, have light sensitive (14^f) and signal storage (16') areas. _As employed herein, full frames of signals generated in the light sensitive area 14^f are rapidly shifted into the (masked) storage area 16', during vertical retrace times, for subsequent line-by-line readout via a register 20. The shutter 12', which intercepts image radiation, is driven by a motor 22 and serves to cause the imaging device 10' to be exposed once every thir- tieth of a second. A positionable blade 24, forming part of the shutter 12', serves to provide adjust¬ ment to the duration (E_τ) of exposure of the imaging device 10'. As noted above, prior art util¬ ization of the imaging device 10' has called for such device to be exposed twice (for each of the two fields per frame) every thirtieth of a second... whereas according to the invention both fields of each frame are generated concomitantly, but produced sequentially (for interlace purposes). Electronics 18' serve to provide the sequenced readout of the stored (16') fields as will now be more fully described with reference to Figures 3 and 4:

As depicted in Fig. 3, the frame transfer imaging device 10¹' has 484 lines of 380 photo¬ sensitive picture elements (pixels) apiece in its imaging area 14''. (The difference between 484 and 525 video lines corresponds to vertical retrace time.) Similarly, the masked storage area 16'' has a like number of storage sites. After the imaging area 14' ' of the imaging device 10'' is (first) ex- posed (at a 30Hz rate) via the shutter 12'' (wave¬ form a, Fig. 4), a frame transfer pulse (waveform b) is applied to an AND gate 30 to cause a high fre¬ quency frame shift clock (waveform c) to be applied to the imaging device 10'' during the vertical re- trace time associated with the frame in question. In rapid fashion, therefore, a frame of image sig¬ nals generated by the exposure are shifted to the storage area 16'' of the imaging device 10''. (Note should be made that the exposure duration is...as indicated in Fig. 4, waveform a...variable, as may be provided by adjustment of the positionable blade 24. Fig. 2.) A frame of pixel signals having been rapidly shifted to the storage area 16'', the imag¬ ing area 14'' again generates, in response to (a second) actuation of the 30 Hz shutter 12'', a second frame of pixel signals. During the time (waveform d) that the (second) exposure occurs, pixel signals residing in the storage area 16'' are clocked (under control of an AND gate 34) line-by- line into the output register 20'' of the device 10''; and thence to an analog-to-digital convertor 32 under control of a pixel clock. Again and again, frames of video signals generated in response to the operation of the 30 Hz shutter 12'' are processed as has just been described. Pursuant to the invention, every other line of concomitantly generated pixel signals of each given frame is routed to one or the other of a pair of field stores 36, 38 for sequenced processing of such stored fields to a television set or recorder. That is, having captured, via the shutter 12'', a full frame of concomitantly generated video signals, signals corresponding to the odd lines thereof (field f, , waveform e) are processed into the appropriately numbered registers 39 of the field store 36, and signals corresponding to the even lines of such frame (field f₂, waveform g) are processed into the appropriately numbered registers

41 of the field store 38. Thereafter, for each successive frame, the field f, (waveform h), and (then) the field f₂ (waveform i), are processed sequentially out of the Fig. 3 circuit.

The analog-to-digital convertor 32 applies its output pixel signals to a pair of AND gates 40,

42 (within a switching circuit 43) which are alter- nately enabled by a flip flop 44 that is operated at the line rate. Thus, every other line goes to a different one of the field stores 36, 38 as de¬ scribed above. To assign appropriate register addresses to the lines of video signals exiting the analog-to-digital convertor 32, the line signal out¬ put of the AND gate 34 is switched between a pair of l-to-242 counters 46, 48 by means of a switching circuit 50 comprised of a pair of AND gates 52, 54. In all respects, the circuits 43 and 50 work the same way. As each count is indicated by the count¬ ers 46, 48, decoding circuits 54, 56 arm respective AND gates 58, 60 for respective line-ass gnment to the registers 39, 41.

To produce the sequenced f, and f„ fields of each frame of concomitantly generated pixel signals, l-to-242 counters 62, 64 are employed for use in addressing, respectively, the registers of the field stores 36, 38. Under control of an AND gate 66 (waveform h), the counter 62 cyclically counts to 242...and only then does the counter 64 do likewise (waveform i) . As the respective counts of the counters 62, 64 get decoded (68, 70), the field store registers (first those 39 in the field store 36, and then those 41 in the field store 38) get addressed to disgorge their respective lines of pixel signals into a digital-to-analog convertor

80. Attendantly, the 30 times per second capture of full frames of video information is converted to a 60 field per second (interlaced) format that is playable by a television set, albeit that the two fields of each given frame are structurally differ¬ ent (f, f«, meaning "no repeat fields"), and are concomitantly generated.

As discussed above, since the two fields of each television-displayed frame are concomitantly generated, there can be--in case of a still frame display of a given frame--no inter-field jitter (fuzziness) resulting from between-field motion of . the imaged subject.

To switch back and forth between a movie and still format, a flip flop 82 is actuated by an appropriate pulse input. Assuming that the flip flop 82 has been actuated to the movie mode, AND gates 84 close to permit updated field signals corresponding to the successive movie frames to be applied to the field stores 36, 38. In the event, however, that the flip flop 82 is again pulsed, signifying a switch to a still frame mode, AND gates 86 close, thereby causing the field signals stored by the field stores 36, 38 to re-circulate...over and over through the field stores...until the next- occurring pulse input to the flop flip 82. Thus, the system of Fig. 3 can be switched from a full resolution movie image to a full resolution still image pursuant to the aforedescribed "burst" concept. As indicated above, a presently preferred form of the invention employs an interline transfer type imaging device instead of a frame-transfer device and its attendant need for noise inducing field stores (36, 38). Such a preferred embodiment is indicated in Fig. 5 which shows an imaging device 110—for example, a device of the same form as ICX016AK, available ^"from SONY Corp.--disposed to receive image signal-generating radiation via the shutter 12. Pursuant to the invention, the shutter 112 is operated F times per second (e.g. at a frame rate of 30 frames per second) for exposure durations (E„) less than 1/2F seconds (e.g. less than l/60th of a second) . Despite the fact that the imaging device 110 captures, by virtue of the operation of the shutter 112, a new full frame of concomitantly generated video signal information each l/30th of a second, such device 110 is operated so as to produce two differently composed (i.e. f, f f«) inter¬ laced video field signals—during successive (i.e. different) sixtieths of a second--from such concomi- tantly generated signal information. In other words, although the video field signals which exit the imaging device 110 are produced thereby in successive sixtieths of a second, such field signals (i.e. the odd-line and even-line fields) both derive from concomitantly generated signals in the imaging device 110. (This, incidentally, is the basis for limiting exposure durations E„ to less than l/60th of a second: To expose an interline transfer type imaging device before signals corresponding to a second field have started to be clocked from the imaging device would cause the second-field signals to be contaminated by photocharge generated by the subsequent exposure.)

Turning now to Fig. 6, an interline trans¬ fer type imaging device 110' is shown cooperating with a rotary shutter 112' and signal receiving electronics 118'. Interline transfer type imaging devices, as is known, have rows and columns of light sensitive areas; and, typically, column-wise masked areas for receiving alternate lines of photo- signals. As employed herein, fields of signals are shifted into the column-wise areas, during vertical retrace times, for subsequent line-by-line readout via a register 120'. The shutter 112', which inter¬ cepts image radiation, is driven by a motor 122' and serves to cause the imaging device 110' to be ex¬ posed once every thirtieth of a second. A position¬ able blade 124', forming part of the shutter 112', serves to provide adjustment to the duration (F„) of exposure of the imaging device 11 ^r; and a timing wheel 123', having an index aperture 125', cooper¬ ates with a lamp-and-photocell assembly 127' to pro¬ vide frame clock timing for the imaging device 110'. As noted above, prior art utilization of the imaging device 110' has called for such device to be exposed twice (for each of two fields per frame) every thirtieth of a second...whereas according to the invention both fields of each frame are gener¬ ated concomitantly, but produced sequentially (for interlace purposes). Electronics 118' serve to apply sequenced concomitantly generated signal fields, via a transmission link, to a television set...and, as heretofore indicated, the transmission link may comprise recording apparatus.

Referring to Fig. 7, an interline transfer type imaging device 110" has 484 lines of 380 photo-sensitive picture elements 150 (pixels) apiece. (The difference between 484 and 525 video lines corresponds to vertical retrace time.) As is known, under control of a photogate clock (Fig. 7) alternate rows of pixel charges are dumped, on a field-by-field of basis, into masked columnwise charge coupled registers 152, the "field 1" gate clocks cooperating with the odd numbered rows of the imaging device 110' ', and the "field 2" gate clocks cooperating with the even numbered rows of the imag- ing device 110''. In response to a line clock, the charge coupled registers 152 empty their columns of "field" signals., row-by-row into an output charge coupled register 120' '...the register 120'', in response to a pixel clock, applying in succession 484 lines (for each frame) of concomitantly gener¬ ated photocharge signals to electronics 118''. Given that the apparatus of Fig. 7 is operated in its movie burst mode, output signals from the imaging device 110'' are applied by a switch 154a to encoding electronics 156 (comprising amplifiers, modulators, etc.); and thence, via a transmission link, to a television set 158. (As indicated, the switch 154 —as well as a switch 154b ganged therewith--is depicted as comprising part of a switching circuit 157. To facilitate understand¬ ing of the workings of the apparatus of Fig. 7, the circuit 157 is deliberately shown simple..and functional. A preferred form of switching circuit, however, is depicted in Fig. 9.) Since the succes- sion of interlace field signals are of the correct form (i.e. each frame thereof is comprised of lines 1, 3, 5...483 followed by lines 2, 4, 6...484) and occur at the field rate of the television set 158 (despite the fact that each frame of interlace fields is comprised of concomitantly generated signals), such signals may be applied to television set 158 without further processing via storage devices.

All the while the television set 158 re¬ ceives its line-by-line input signals, such signals are applied, in digital form (analog-to-digital con¬ verter 159), line-by-line, to respective registers 160, albeit that no use is made of such signals while the apparatus of Fig. 7 operates in its movie burst mode. By so applying (digitized) video line signals to the registers 160, the registers are operated in synchronism with the video applied to the television set 158, as will be described below.

To change the operation of the apparatus of Fig. 7 to its still frame mode, the switches 154a, b are actuated. Immediately the output of the inter¬ line transfer type imaging device 110'' is removed from the encoding electronics 156; and, instead, analog versions (digital-to-analog converter 162) of the line signals processed by the registers 160 are successively applied to the electronics 156. How such successive processing is effective is as follows: A line counter 164—reset periodically by a frame clock, and operated in response to a line clock—has its count continuously decoded (166) to arm successively AND gates 168 in an array thereof. Accordingly, the AND gates 168—one-by-one--process therethrough the outputs of respective OR gates 170. Each OR gate receives either a respective line signal (movie burst mode) appearing at the output of the analog-to-digital converter 159, or a recircu¬ lating line signal (still frame mode)...an array of recirculating AND gates 172 (in response to opera¬ tion of the switch 154b) serving to assure such dis¬ junctive signal processing. To load (and unload) each set of digital line signals into (and from) its respective registers 160, pixel clocks (respective of the registers 160) are applied line-by-line to registers 160 from a circuit 174 comprised of AND gates 176. Like the AND gates 168, the AND gates 176 are armed one-by-one by the decoded output of the line counter 164.

It will be appreciated that--because the interline transfer type imaging device 110'' is pro¬ ductive of line signals in the precise order neces¬ sary for correct operation of the television set 158--each register 160 can be signal-loaded in sequence. Attendantly, there is no need--with apparatus according to this embodiment of the inven- tion--to employ logic-intensive reshuffling of con¬ comitantly generated line signals so that corre- sponding fields produced thereby will be composed of the right order of frame lines.

As noted above, operation of the registers 160 is kept in line-sync with signals applied to the television set 158. This is an important consider- ation because, irrespective of when the switches 154a, b are actuated while switching between movie burst and still frame modes, line-sync means the display of the television set will be coherent, and will appear correct, i.e. video lines 1 to 484 will appear from the top to the bottom on the face of the television set. Using the switching circuit 157 of Fig. 7, however, can result in displayed still frames being formed of video lines from two differ¬ ent frames. Assuming, for example, that the switches 154a, b are actuated in the middle of a frame time, a first group (lower numbered lines) of registers 160 will be loaded with video information of one video frame, and a second group (higher numbered lines) of registers 160 will be loaded with video information from a next earlier occurring video frame. Notwithstanding the fact that the video information contained in successive frames is quite similar on a line-by-line basis, constructing a video display from two different video frames may be objectionable in some instances. Accordingly references should now be had to the switching cir¬ cuit of Fig. 9, which circuit functions to assure that switching between movie burst and still frame modes can only occur at discrete frame times, there¬ by to assure that all displayed lines of any given st ll frame will be from the same frame:

The circuit 157 of Fig. 7 may be replaced by the circuit of Fig. 9 at the- connection points a through e. Upon actuation of a pushbutton 180, a flip flop 186 is set. With the flip flop 186 set, an AND gate 184 applies the frame clock to an OR gate 194, which passes the frame clock onto a second flip flop 188. This first occurence of the frame clock following actuation of the pushbutton 180 causes the flip flop 188 to be set, making its Q output a logic ONE and its Q output a logic ZERO. The Q output is fed back to the set input of the flip flop 188 via the OR gate 194, forcing the flip flop 188 to remain set. The Q output is also applied both to the recirculating AND gates 172 (Fig. 7) and to the analog switch 190 causing infor¬ mation stored in the Fig. 7 registers 160 to be applied to the encoding electronics 156. Thus, the circuit of Fig. 9 works to assure that still frames displayed by the television set 158 are composed of video lines from the same video frame. The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. For example, although a mechanical shutter has been identified for use with the invention, obviously other forms of shutters may be employed as well. In this regard, then, it would be within the scope of the invention to combine the shuttering function (12) with the photo-integration (14) of the imager, e.g. by zero¬ ing the photosites of the imager, and then control¬ ling,the start and stop of photo-integration.

Another variation of the invention would eliminate the recycling of video information (86) during still framing: Instead, bursts of video movie information would be recorded on, say, a recording disc; at the instant the record button (82) is released, a coded message is recorded with the last-occurring frame of each such movie burst. During subsequent playback of the recording, a burst-by-burst presentation is effected as follows: a movie presentation is made until a first code is read; the code then calls for repetitive playback (still picture) of the last-occurring frame of the burst. When the playback is again advanced to a next-occurring movie burst, still-framing is terminated until the coded last frame of the next- occurring burst is detected. Thereafter, the cycle repeats for each of the recorded bursts.

Claims

What Is Claimed Is:

1. Apparatus for producing video signals for application to a television set for producing high resolution images thereon regardless of whether said images are movie or still frame images, said apparatus comprising a) imaging means for receiving image radiation and for converting said radiation into corresponding video signals, b) means for shuttering said radiation at the frame rate of said television set, thereby to produce successive frames of successive odd-line and even-line fields of concomitantly generated video signals, and c) means for transferring the succes¬ sive odd-line and the even-line fields of video signals to said television set at the field rate of said television set.

2. The apparatus of Claim 1 further com- prising means for selectively adjusting the exposure duration effective by said means for shuttering.

3. The apparatus of Claim 2 wherein the adjustment to said exposure duration is limited, in time, to a period that is less than the reciprocal of said television set field rate.

4. The apparatus of Claim 1 further com¬ prising means for selectively and repeatedly apply¬ ing to said television set a given frame of succes¬ sive odd-line and even-line field signals, thereby to produce a high resolution still image on the face of said television set.

5. The apparatus of Claim 1 wherein said imaging means is an interline transfer type imaging device disposed to produce at the output thereof successive odd-line and even-line fields of concomi¬ tantly generated video signals.

6. The apparatus of Claim 1 further com¬ prising selection means for receiving the output of said imaging means, said selection means being com¬ prised of a) means for storing the particular frame of field signals which occurs at the end of a burst of video signals, and b) means for first applying said burst of video signals to said television set and there- after repeatedly applying thereto the frame of video signals stored by said means for storing.

7. The apparatus of Claim 5 further com¬ prising selection means for receiving the output of said imaging means, said selection means being com- prised of a) means for storing the particular frame of field signals which occurs at the end of a burst of video signals, and b) means for first applying said burst of video signals to said television set and there¬ after repeatedly applying thereto the frame of video signals stored by said means for storing.