US3671666A

US3671666A - Apparatus for producing corrected photographic color rastered reproductions

Info

Publication number: US3671666A
Application number: US800072A
Authority: US
Inventors: Eberhard Hennig
Original assignee: RUDOLF HELL KG
Current assignee: RUDOLF HELL KG
Priority date: 1968-02-22
Filing date: 1969-02-18
Publication date: 1972-06-20
Anticipated expiration: 1989-06-20
Also published as: FR2002400A7; DE1622336A1; GB1256145A; DE1622336B2

Abstract

A method and apparatus for producing a color corrected and rastered reproduction wherein a continuous tone picture is photoelectrically scanned and combined with the output of a second scanning head which scans a raster pattern to be superimposed over the picture and the outputs of the two heads are combined and applied to a recording head through a threshold circuit. A cathode ray tube is provided for allowing the method to be monitored so as to assure that the proper reproduction is occurring.

Description

United States Patent Hennig [is] 3,671,666 1 June20, 1972 [54] APPARATUS FOR PRODUCING CORRECTED PHOTOGRAPHIC COLOR RASTERED REPRODUCTIONS Eberhard Hennig, Ascheberg, Germany Assignee: Rudoli Hell Kommandltgesellschaft Filed: Feb. 18, 1969 App]. No.: 800,072

Inventor:

Foreign Application Priority Data Feb. 22, 1968 Germany ..P 16 22 336.2

US. Cl ..l78/6.7 R, 178/52 A Int. Cl. .H04n 1/06, H04n 1/20, H04n 1/4] Field of Search 1 78/67 R, 5.2 A, 6.6 R

References Cited UNITED STATES PATENTS 1,854,315 4/1932 Schmook ..l78/6.7X

3,436,472 4/1969 Kyte ..ns/m 3,461,229 8/1969 Oppenheimer ..ns/mx Primary Examiner-Hemard Konick Assistant Examiner-Steven B. Pokotilow Attorney-Hill, Sherman, Meroni, Gross & Simpson ABSTRACT A method and apparatus for producing a color corrected and rastered reproduction wherein a continuous tone picture is photoelectrically scanned and combined with the output of a second scanning head which scans a raster pattern to be superimposed over the picture and the outputs of the two heads are combined and applied to a recording head through a threshold circuit.

A cathode ray tube is provided for allowing the method to be monitored so as to assure that the proper reproduction is occurring.

4 Claims, 2 Drawing Figures APPARATUS FOR PRODUCING CORRECTED PI-IOTOGRAPHIC COLOR RAS'I'ERED REPRODUCTIONS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates in general to a method and apparatus for recording rastered pictures. of originals by photoelectrically scanning continuous tone pictures and preferably for producing rastered corrected photographic color separations by means of electronic color scanners.

2. Description of the Prior Art In the prior art half-tone pictures are always rastered in relief and offset printing. Consequently, the corrected color separations produced for the purpose of reproducing colored half-tone pictures must be rastered. The color separation printing plates are chemographically etched and formed from the colored half-tone pictures.

One prior. known method provides raster-ing of photographic color separations after recording while it is being photographically copied together with a contact raster foil. The raster fields of a contact raster arevignetted in known manner, in other words, the density of the blackness decreases continuously from a maximum value in the middle of the field to the edge. A film of very high contrast and with a pronounced threshold of sensitivity is used as the copying material.

Because of the vignetting of the contact raster and the threshold sensitivity of the film, a condition is reached where the size of each raster dot is determined by the local brightness value of the continuous tone picture.

In place of a vignetted contact raster, a sharply defined glass raster may sometimes be used which is placed at a certain distance in front of the continuous tone picture so that its raster elements are formed with the same degree of fuzziness as the vignetting.

The known method for later rastering has, however, a drawback due to the unfavorable and unavoidable property of the film material. As is known, the steepness of the film gradation and the position of the threshold of the sensitivity which define the sizes of the raster dots are influenced by the developing time, the temperatureand the condition of the developing liquid in the developing tank as well as by the agitation of the film in the developing tank.

The uncertainty of the size of the rastered dots thus caused has an especially disturbing effect, when it is to be used to produce color separations which will then be combined to form multi-colored prints.

SUMMARY OF THE INVENTION The invention provides a method and apparatus in which picture signals are obtained by photoelectrically scanning the unrastered continuous tone picture and then recording it in raster fashion according to the invention with a superimposed raster having a vignetted raster field or a raster effectively equivalent which is superimposed over the original picture. The electrical scanning pulses obtained from said such superimposition are fed to a recording head which is controlled thereby through a threshold value circuit.

When the imprecise threshold of the sensitivity of the film material is reached, the method according to the invention allows a threshold to be retained by electrical circuit means which can be maintained sufficiently constant without much However, if it is desired to produce color separations from a colored picture original, then each color separation should have a different raster angle to avoid the formation of a moire structure. In this case the rastering is preferably done by photoelectrically scanning the raster foil by means of a separate scanning head. and the scanningpulses which are thereby obtained or superimposedon the picture pulses.

If a sharply defined raster is to be used in place of a vignetted raster, the raster elements are focused on the scanning head with the same degree of fuzziness as the vignetting.

There is already known a method for direct rastered recording in which the raster dots are produced by lightfiashes whose intensity is controlled by the brightness via the scanned picture original. This method is very expensive and results in expensive equipment and also leads to difl'iculties because of the requirement for altering the raster angles. With the present invention, on theother hand, an alterationof the raster angle can be accomplished by simply moving the raster foil.

As is known, the'gradationcurve of a very hard film material has a certain edge obliquity, whereby therecorded raster dots become unclear. In some cases, this may be desired, particularly if partialcorrections of the printed type can be made by subsequent etching of the raster elements. If, on the other hand, sharply defined .raster dots are desired, this may be achieved by the present invention, by utilizing an overdriven amplifier which is fed with electric scanning pulses. The overdriven amplifier changes Lheshape of the scanning pulses, which due to the vignetting of the raster fields, consists in a wavy voltage whichhas oblique flanks, into a voltage of square waveform. whose steep edgescause sharp definition of the drawing.

To test the raster dots before the final recording or to be able to correlate the gradation range of the picture original initially to thecorresponding range of the variation of the size of the raster dots, an auxiliary device may be used. This consists in acathode ray tube having a target whose horizontal beam deflection is controlled in response to the picture scanning movement and whose vertical beamdeflection is controlled by the picture scanning advanceandwhose dot brightness is controlled in dependence upon the amplitude of the electric pulses appearing at the output of the-threshold value circuit. The screen of the cathode ray tube produces a picture which may be continuously-monitored.

Other and further objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed disclosure thereof and the drawings attached hereto and made a part hereof.

' BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates an original picture 2 that might be, for example, a multi-colored picture which is attached to the surface of a drum I mounted on a suitable drive shaft 27. The picture difficulty. The, threshold value is determined by .the level of a l isscanned by-a'photographic scanning head 3 which is mounted ona mechanical movement 30 that moves it longitudinally of the drum as the drum is rotated.

A drum' 4 isalsomounted on the shaft 27and a recording medium 5 ismounted on the surface of the drum and a recording head 6 which includes a light source 7 is moved by the mechanical movement 30 relative to the drum 4 to record on the medium '5' the color separation of theoriginal. A motor 28 drives the shaft 27.

' A screen 10, which carries'the'raster pattern to be superposed over the picture content, isattached to the surface of a third drum 9 also mounted on the shaft 27 and which is scanned photographically by means of a scanning head 11 which is also driven by the mechanical movement 30. The mixing or superimposing stage 12 receives inputs from the scanning head 11 and the scanning head 3. A color computer 8 is mounted between the scanning head 3 and the mixing stage 12 to provide for desired color emphasis.

The raster pulses from the scanning head 11 and the output of the scanning head 3 are combined in the mixing stage 12 and the output pulses of the mixing stage are fed to a threshold stage 13 and to an amplifier 14 which supplies an input to the recording head 6.

A cathode ray tube is used as a monitoring device to check the raster structure produced. The tube 15 has a target screen 26 as best shown in FIG. 2 which retains the recording produced by the cathode ray beam as an electrostatic charge image. Such a charge picture is retained for a longer time than if it were recorded on a persistence screen.

The cathode ray tube 15 has vertical deflecting plates 16 which are driven by a voltage supplied by a variable potentiometer 17. The wiper contact of the potentiometer I7 is connected to the mechanical movement which drives the scanning heads 3, 11 and 6 so that the vertical deflection beam is controlled as a function of the advance of the picture scanning.

Horizontal deflection plates 18 are connected to the output of a time base generator 19 which is triggered by an output of the scanning head 11. A single trigger pulse results in a single horizontal deflection of the cathode ray beam and subsequent beam fly-back. The trigger pulse occurs once per revolution of the drum 9 at the commencement of the scanning of the raster and as a scanning pulse during scanning either the edge of the raster foil or a special locating mark on the edge of the foil which is drawn more heavily than the raster elements. At the same time as this beam deflection, the scanning pulses occurring at the output of the threshold limiting stage 13 control the brightness of the light spot produced by the cathode beam through the Wehnelt cylinder 20. Motor 29 drives mechanical movement 30.

An enlarged image of the raster is formed on the screen 26 so that cathode ray tube as shown in FIG. 2, may be used as a monitor.

The lines which form the raster pattern extend at a certain small angle to the horizontal due to the continuously varying vertical deflection voltage corresponding to the advance of the scanners. However, since the speed of advance is very small in comparison to the scanning speed, the tilt of the lines is very negligible.

The method, according to this invention, may be used to advantage in picture telegraphy so as to reproduce a picture sent unrastered as a rastered picture at the receiver and it also can be used when metal cylinders are to be engraved by means of laser beams.

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.

We claim as our invention:

1. Means for reproducing a rastered picture from a continuous tone picture comprising:

a first driving means;

three drums driven by said first driving means;

a first scanning head in scanning relation to the first drum and the continuous tone picture mounted thereon and producing an electrical output;

a second scanning head mounted in scanning relationship to the second drum and a raster pattern mounted on said second drum and said second scanning head producing an electrical output;

means for mixing the electrical outputs of said first and second scanning heads for efiectively masking the image;

a recording head reproducing an image mounted in scanning relationship to the third drum and receiving the output of said mixing means and converting said output to an image;

a recordin medium mounted on the third drum; and,

a second riving means connected to the first and second scanning heads and the recording head to move them relative to the drums.

2. Means for reproducing a rastered picture according to claim 1 comprising a threshold circuit between said mixing means and the recording head.

3. Means for reproducing a rastered picture according to claim 2 comprising a cathode ray tube monitor connected to said threshold circuit and producing said rastered picture.

4. Means for reproducing a rastered picture according to claim 3 comprising means for horizontally and vertically scanning the beam of said cathode ray tube and synchronizing it with the drums and scanning heads.

Claims

1. Means for reproducing a rastered picture from a continuous tone picture comprising: a first driving means; three drums driven by said first driving means; a first scannIng head in scanning relation to the first drum and the continuous tone picture mounted thereon and producing an electrical output; a second scanning head mounted in scanning relationship to the second drum and a raster pattern mounted on said second drum and said second scanning head producing an electrical output; means for mixing the electrical outputs of said first and second scanning heads for effectively masking the image; a recording head reproducing an image mounted in scanning relationship to the third drum and receiving the output of said mixing means and converting said output to an image; a recording medium mounted on the third drum; and, a second driving means connected to the first and second scanning heads and the recording head to move them relative to the drums.