DE1772687A1 - Method and apparatus for reproducing halftone images - Google Patents

Description

PaienfanwäUm _Λ «

Dipl. In- ». H.;: - iiclc *

Dipl..Pilyv \\ , fjjTiJfi «Munich! 5, i ^ c:» jtr.23

Toi. 538ÜS86

Grosfield Bleotronlcs Limited

766 Holloway Road, Munich, (feo June 1968

London, N. 19, England (Attorney File M-396)

Method and apparatus for reproducing halftone images

In an image reproduction process, the tonal values are the Present in the reproduced image in equally spaced points of different sizes is known as halftoning. It can run through it that a fine checkerboard pattern of dark and light fields having a contact grid with one of the The image to be reproduced is brought into contact with the photosensitive layer to be coated. The SohwÄrsunga Change about the "dark and light Raeterfelder is something ausfSmlg" and if the changes in the image are displaced and the combination is subjected to a suitable non-linear process, a point arrangement is created in which the image changes have been transformed into changes in the point-to-point plan.

The nioht-

Use a film with a very linear effect steller order achieved, i.e. a gradation at which above a certain exposure threshold after the development a blackened area arises, and below this

109044/0439

As soon as the pil »remains colorless. A disadvantage of such a system is that the halftone screen is placed in front of the film absorbs a large proportion of the light directed onto the film.

The inventive method for reproducing halftone images is characterized in that it is light-sensitive Layer »on which the halftone image is to be reproduced, exposed by a light source without the need for a raster P and the light source share changes produced by scanning the image to be reproduced element by element of an electrical signal and of changes in an electrical signal that occur when a photocell is exposed a change generated by the light beam scanning the halftone screen is controlled.

The light source can be modulated on-off, so that the on-off cycle is repeated with the frequency of the raster signal changes and the "bin" period changes with the image signal level in each cycle. It is also possible to modulate the light source in a proportional manner depending on the combined effects of image-representing and random-representing changes, and to choose a film with very little gradation. It is also possible to use the system in a way that lies between these two possibilities.

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BATH ORIGINAL

The raster signal can be generated by scanning a halftone screen with a light source and a photoelectric device in Synchronization with the scanning of the image generated by another light source and another photoelectric device or by scanning a halftone screen with a light source modulated by an electrical signal generated by elementwelses scanning of the image to be reproduced. if Erwünsohtj can only be part of a grid or even a one Individual point representing raster element are scanned. In a further possibility, a « The signal representing changes in halftone raster is stored, e.g. in a magnetic core memory or on a magnetic tape or an electronic shift register, and this Signal is taken from memory when it is needed to combine with the imaging signal

To facilitate understanding of the invention with reference to \ the accompanying Selchnungen some examples of the devices and screens used in the practice of the invention are described nüher.

Figs. I, 2 and 5 show different versions of the device

to carry out the invention,

Fig. 3 'shows a partial raster pattern that is used to generate

of the full raster signal is used, and

109844 # Η39

Flg. K shows a scanning pattern that will be used

can «when a single point element is scanned.

In the apparatus shown in Fig. 1, the analyzing drum 2 and the exposure drum 4 are on the same of one

_Ä Motor 8 driven shaft 6 attached. The slide to be reproduced is attached to the analysis drum 2, in which a prism 10 is located for reflecting the light from a lamp 12 through the slide. The prism 10 is attached to an analyzer head 16 containing a photomultiplier by means of an army, the photomultiplier being directed at the slide lying on the drum through a lens system 18 opposite the reflecting surface of the prism the prism 10 reflected light through the slide, since the photo

w multiplier generates electrical signals with an amplitude corresponding to the intensity of the light received.

The analyzing head 16 is attached to a spindle 20, eo dad When this spindle is rotated by a motor 22 via a gearbox 21, the analyzer head 16 and the reflecting prism 10 move move along the spindle parallel to the shaft 6. This longitudinal movement of the analyzer head and the rotation of the shaft 6 cause » dae the photo multiplier is the one lying on the analyzer drum

• ♦ ■ - BATHROOM

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Dia scans adjacent lines in a Rtiha iron, and swKX * in the event of a threat from the wave, one each up to the all «Pia is scanned.

The light-sensitive layer to be exposed is wrapped around the cylindrical exposure layer 4. A lighting head 23 contains a lamp which is irradiated with the light values to be imaged on subsequent elements of the rotating emulsion and is attached to the spindle 20 driven by the motor 22. Therefore, the lamp moves relative to the light-sensitive layer parallel to the shaft 6 at a speed which corresponds to the magnitude of the analysis head over the slide to be imaged.

The driven by motor 8 shaft 6 also deceptive to the the Analyslerabtaster 2 opposite end a Rasteranalyslerabtaster 20 · This 1st in the embodiment de »Analysieret" - i taster similar and comprises a light source 31, a fixed also on the Velle 20 Analyslerkopf and 32. The signals from the analyzer tubes 16 and 32 ″ are grounded to a comparator 34. The comparator 34 combines the two signals and compares them to a reference level. The combined signal exceeds the reference level for a period each cycle, the length of which depends on the density of the image signal from the analyzer head 16 depends. The Bellohtungskopf 23 is during this Porloden

t excited. As a result, it insists on the llchfaopfindllohen

.5.

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Layer depicted image from Eleoentar points, their surfaces correspond to the density of the corresponding elements of the Dlae. If so desired, it can be arranged that the points of are of different blackening, so that β is the combination of the Plhe height of each point and its shortening la relation to The corresponding element is blackened on the slide.

FIG. 2 shows another embodiment in which a light point scanner using a cathode ray tube replaces the third drum on the solid 6. The line deflection electrodes of the cathode ray tube 44 are supplied with deflection signals from a deflection control system 46, the system 46 receiving line synchronization signals from a photocell 28 attached to one side of the shell 30 rotated by the motor 8 and a lamp yz being attached to the other side of the window . The disk 30 has a slot so that with each rotation of the shaft 6, once in impulse from the photo cell 28 to the deflection control system. wear wiM. The deflection control system also receives an image control signal from a potentiometer 47, the contact arm of which is driven by the motor 22 rotating the spindle 20.

On this catfish is a light point grid on the front of shaft 44 built up. A grid 48 is placed between the front of the stirrer and a light collector 50 and a photomultiplier 52. The exit of the photomultiplier

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"BAD ORIGINAU

is an electrical signal with changes caused by the through the scanning of the interposed grid 48 generated light modulation arise. This signal is sent to an amplifier 54 and from there applied to a comparator 56. Since the signal from amplifier 54 is derived #lrd by a light beam scanning raster 48, it exhibits cyclical changes the image changes in the comparator 56 are superimposed. As above the resulting signal level is compared with a reference level which is chosen so that in each cycle of the cyclic Change the combined signal to the reference signal for one of the diameter of the picture exceeds a certain perlode. While At this perlode of the cycle, the comparator 56 sends an excitation signal to the exposure head 23.

When a cathode ray tube is used to scan the grid, as shown in FIG. 2 is shown »may be a small section of the contact grid (which can be enlarged) can be scanned instead of the entire grid. The pole frequency of the deflection system «

1st on · to be modified accordingly and it / of course necessary » See below to ensure that the resulting point pattern is reproduced without any distortion in spite of the higher repetition frequency of the scanning cycle of the cathode ray tube. If * the point of light reaches the edge of the grid part »it has to go to a new one Position that is an exactly integer multiple of Marginal spacing is removed along one or both grid axes »

to report discontinuities. This is done through the Complicated need to arrange the grid at an angle to the image ohms and to have different angles for color work for different color components in order to create Avoid moire patterns.

In the example shown in FIG. 3, a scanning cell of a certain length is selected, since it begins and ends at corresponding points in the dot pattern. The usual Raeterwinkel is 15 °; In the example shown, the following of the halftone grid with respect to the grid is four units in one direction and fifteen in the other, resulting in an angle of tan "T5 ~~~" ° α ^βϊ * J · ** 5 & minutes. Values from one unit and four units in the two directions can also be used a screen angle van woraue approximately 14 ° is formed. The control of the light point scanner »in de? Line orientation is connected to the scanning trcBEcel during the trammeluadrotation. If required, digital control of the row tipper can "be carried out".

Instead of an angled grid of the type shown in Fig. 2, the time bases for the light track scanner can generate deflection properties so that the vertical return has a horizontal component to ensure that at the end of the return it is one of the end points of the last ¹ each corresponding starts «

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BATH ORIGINAL

The horizontal and vertical components change with the required screen angles. In such an arrangement, the screen sample can be a single point. An example of the type of scan pattern needed over the 1st field in Pig containing the point. 4 shown. The scanning of a cell on the image begins at an arbitrary point in Fig. K and increases in value until the boundary is touched. It then runs back over the opposite boundary "as added, and continues like this until * is the line. The next image cell starts at the grid sarapel at a position that has been shifted a little to the left of the original starting point and follows a similar (but not identical) path, etc.

In the modified device shown in Fig. 5, the Comparator of Flgn. 1 and 2 supplemented by another circuit.

In FIG. 5, the changes in the image properties are applied to the comparator 62 via a conductor 16a and the master signal changes are applied to the comparator 62 via a conductor 60, as in FIG forwards the changes in the video signal or a reference level signal. In this case the Korn · * parator switches the switch "on" for periods corresponding to the video signal level, and the * Sehalter gives "while it is" on ", since ·

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to

Image signal directly to the exposure lamp. Therefore, this method gives a variable density record and is of particular use for etching a rotogravure cylinder, where small, shallow holes are required in light areas and large, deep holes are required in dark areas of the image.

In a further Ausfühpungsform the device is for Scanning the grid light source used is modulated by the image signal. The resulting mixed signal is in the comparator compared with a fixed reference signal.

BATH

Claims (1)

Crcefiald Elfctranioa Limited Holloway Road, Munich, June 20, 1968 London, H. 19 «England (Lawyer File M-398) Claims ■ 1. Method zur.Reproduktion von halftone images, characterized in that I that the light-sensitive layer on which the halftone image is to be reproduced is exposed by a light source without intermediate points of a grid and the light source is jointly scanned by element-wise s of the au i ^ pjPo ^ u ^ ej «ndleÄ_SllÄfts_ produced changes in an electrical signal and changes in an electrical signal which correspond to the changes produced by exposing a photocell to light which has scanned a jar of light. > ~~ 2. The method according to claim I, characterized in that the da8 together with the changes in the picture and the hasters signal ·> changes controlled light source at constant intensity in each cycle of the raster signal changes for one of the Perlode "on" depending on the amplitude of the image signal will. - 1 -109844/0439 BAD OR1G ¹ N ^AL 3. The method according to claim 1, characterized in that the changes in common by the image signal and the RasterslgnsltSnderungen controlled Lichtuelle in each cycle of Rasterslgnalünderungen for a depending from the QrSOe of the image signal period "ain ^rt is switched, namely at a in Tens it Mt , which also depends on the quality of the image signal. 4. The method according to claim 1, 2 or "*> _t characterized in that the raster signal ayn- by scanning a halftone raster W ohron is generated with the scanning of the reproducing image, 5 * A method according to claim 4, characterized in that is used a by scanning the image to be reproduced signal arising modulation of the raster scanning light source. 6 »Method according to claim 4, characterized in that the scanned grid by a light source of constant intensity / and the electrical signal from a photoelectric device that receives light from grid ^{7 is} combined with the image signal. 7. The method according to claim 6, characterized in that, in order to obtain the raster signals, part of a contact raster for the image to be reproduced is repeatedly scanned during the single scanning of the image . - 2 -109844/0439 BATH ORIGINAL The method according to claim 1, characterized in that this raster part consists of a single point and that the scanning light point between subsequent crossings of the point achieves a return deflection in two mutually perpendicular directions at an angle to the scanning direction, 9 * Method according to claim 1, characterized in that a Raster signal is stored in non-optical form and is stored synchronously with the scanning of the image. 10. Device for performing the method according to claim 1, characterized by one or more mutually exclusive Troasseln and drive means aura rotating the drum or trophy s my two AnalysierabtastkÖpfs and one Belichtungsabtasticopfj are attached as "Dab them different parts of the drum flMche or Fl & address the various drums scan, and" if the au reproduced image and a Hastar at various points of the drum or drums in front of the AnalysierkSp fm are arranged, the signals from the two heads represent the densities of successively scanned image or raster elements ^ and through a comparator, which is connected to "Bnpfong the signals and to apply a control signal to the exposure head when the combined signals exceed a reference level," wherein the control signal modulates a light source in order to expose a sheet located on the remaining Troanel or Trooneltell. 109β ** λΐ439 1772S8 ⁷ 11. Device for performing the method according to claim 1, characterized by a first electro-optic scanner for scanning and generating the image to be reproduced the one / densities of sequentially scanned image elements representing electrical signal, a xwide elekfcrooptlechen scanner with a cathode ray tube for generating UH) gene of a light spots / a befindli- auöerhalb the tube _ just scan raster, and a device fotoölektrisehen z \ m Create "eine3 the densities successively sampled Elenente of Hasters performing elektriaohen signal and duroh Elnon comparator s.un receiving the signals and to apply a control signal to the exposure controller when the combined signals exceed a reference level to modulate a light source that exposes a photosensitive sheet. 12- ■> device according to · '. Claim 10 or 11, characterized in that the output of the comparator controls switching means which apply a signal representing b U to the exposure head or scanner fite »the period during which the combined image display and signal end signals • Exceed dtn level. OR! GIN _AL