GB1570773A

GB1570773A - Mixing of picture signals in the production of printing surfaces

Info

Publication number: GB1570773A
Application number: GB690878A
Authority: GB
Original assignee: HELL R GmbH
Current assignee: HELL R GmbH
Priority date: 1977-02-26
Filing date: 1978-02-21
Publication date: 1980-07-09
Also published as: FR2382033A1; DE2708421C2; CH631270A5; JPS541101A; FR2382033B1; DE2708421A1; JPH0232617B2

Abstract

In the method, a picture copy is scanned optoelectronically and recorded again as printing forme, picture signals being mixed prior to the recording. The mixing operation is controlled by a per se two-level control signal (S) with a gradual transition between the levels inside a mixing region. The control signal (S) may be derived, for example, from a picture signal, a colour signal, a mask signal or certain characteristics of the picture copy. A first picture signal (A) to be mixed is modulated with the control signal (S). A second picture signal (B) to be mixed is modulated with the inverted control signal (1 - S) added to a reference signal. The modulated picture signals are then added in order to obtain the mixed signal (C). The main fields of application are the inset copying of picture copies in order to obtain graded junctions at picture contours, and colour and/or tonal corrections in order to alter the influence of correction signals in certain areas gradually. <IMAGE>

Description

(54) IMPROVEMENTS IN OR RELATING TO THE MIXING OF PICTURE SIGNALS IN THE PRODUCTION OF PRINTING SURFACES (71) We, DR.-ING. RUDOLPH HELL GMBH, a German Body Corporate, of 1-5 Grenzstrasse, 2300 Kiel 14, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to mehods of mixing picture signals in the production of printing surfaces, in which a pictorial original is scanned opto-electronically and is reproduced as a printing surface.

The inveniton can be applied to colour and black and white scanners, engraving machines and also in colour display apparatus. Picture signals should also be understood to include signals for measured colour values, colour separation signals and any form of correcting signal. Therefore, the invention also relates to circuits and apparatus for carrying out the method.

The objects to be achieved by the invention will be explained using the example of a colour scanner.

A colour scanner is used to produce corrected colour separations for use in multicolour printing. To produce colour signals, the coloured pictorial original to be reproduced, is held mounted on a rotating scanning drum and is scanned point by point and line by line by an opto-electronic scanning member. The colour signals, which represent the proportions of given colours at the points which are scanned, pass to a colour-correcting circuit from whose output the colour separation signals, which are arrived at in accordance with the laws of subtractive colour mixing, and possibly signals for a black separation and an under colour removal signal become available to allow the usual "magenta", "cyan" "yellow" and "black" separations to be reproduced. The colour separation signals are amplified and fed to respective exposing lamps which act as reproducing members and whose brightness is modulated by the appropriate colour separation signal.

Mounted on a reproduction drum, which also rotates, are films which are exposed point by point and line by line by the exposing lamps.

The exposed films, once developed, form the required colour separations for the production of printing surfaces for multi colour printings.

Flat-bed apparatus may of course be used instead of drums, if desired.

A problem in reproduction techniques which is encountered in black and white and colour reproduction is the combining of two or more originals, also known as montage. One original may, for example, contain a background design and the other a foreground design or text. What combining generally involves is causing certain parts of the original or restricted areas of different originals to appear simultaneously and adjacent to one another in the reproduction.

Germant patent specification no. 1172540 discloses a method in which the originals to be combined are mounted on a scanning drum next to one another and are scanned simultaneously by respective scanning members to produce picture signals. The picture signals are fed in turn to an exposing lamp via an electronic switch which is operated by a control signal and the lamp reproduces the desired combination of pictorial matter with supposedly sharp outlines in the boundary regions.

However, since the change in the brightness of the exposing lamp cannot follow the jump in the picture signal caused by the switching over without delay, light or dark borders often appear in the reproduction and these look extremely unsightly.

In the known method, a mask is used to control the switch and this mask contains areas correspondings to the parts of the originals which are to be used and which follow one from each other without interruption or areas which correspond to the parts to be masked out. To produce the control signal for the switch, this mask is scanned by a scanner in synchronisation with the originals and in register with them.

So that here too unsightly borders may be avoided in the reproduction, the shape of the mask must be very accurately matched to the outlines of the parts of the originals, which means that the manufacture of the mask is expensive and timeconsuming.

Undesirable borders also occur if the scanning and reproduction do not correspond line for line.

Such defects can be avoided in accordance with the invention if there is a steady change-over between picture signals in a narrow zone at the boundary regions.

Progressive transitions are often desirable for editorial reasons also.

Other requirements in reproduction techniques are to alter colour and/or tonal value corrections in physically restricted areas of the pictorial original.

For example, a slective correction may be required only in a specific area or it may be desired to exclude an area from the selective correction. Also, a correction to tonal value is often required at a translation in the original from coloured to non-coloured. Such areas may be defined by suitably shaped control masks or determined by a colour selecting circuit.

In British patent specification No.

1,400,806 the boundary regions are stored at data on positions in an X. Y co-ordinate sysem. During reproduction, data on the actual position of the scanning member is compared with the stored positional data.

In all known methods the correcting signals are changed over abruptly at the boundaries by a switch. However, what is often required is a smooth change in the correcting effect at the boundaries.

Similarly, in black and white and colour reproduction, it would be desirable to operate the various adjusters in the signal path for the picture or colour signals by means of control signals with the adjusters coming into action under the control of the control signals not suddenly but gradually within certain transitional zones.

One object of the invention therefore is to provide a method of mixing picture signals when producing printing surfaces by means of which progressive transitions can be achieved at outlines in the original picture and in the effect of correcting signals.

Accordingly, the invention consists in a method of mixing picture signals for the production of a printing surface of the kind in which a pictorial original is scanned opto-electronically and is reproduced on a reproduction surface, comprising modulating a first picture signal to be mixed by a control signal, and modulating a second picture signal to be mixed by a signal comprising the difference between a reference level signal and said control signal, the said control signals determining the onset and characteristics of the mixing, and combining the modulated first and second picture signals to produce a mixed signal.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which show certain embodiments thereof by way of example and in which: - Fig. 1 shows an embodiment of mixing circuit, Fig. 2 is a graphic representation of signal waveforms, and Figs. 3 to 6 show various examples of applications of the mixing circuit shown in Fig. 1.

Referring now to the drawings, Fig. 1 shows an embodiment of a circuit arrangement for mixing two picture signals, in which a first signal A is fed via an input 1 to an algebraic combination device in the form of a modulator 2 in a mixing circuit 3 and a second picture signal B via an input 4 to a similar algebraic combination device in the form of a second modulator 5. The modulator 2 also has applied to it a control signal S which is fed in via an input 6 and the modulator 5 has applied to it a control signal (1 -S) derived frorn signal S and whose level is inverted by means of an inverter 7. The control signal determines the point at which the mixing comes into action and the characteristics of the mixing.

The modulators 2 and 5 are preferably linear multiplying stages.

The inverter 7 consists of an operational amplifier with negative feedback whose inverting input has the control signal S applied to it. The inverted control signal S has added to it a constant voltage which is selected in such a way that the output signal from the inverter 7 is equal to zero when the control voltage S is at a maximum.

The outputs of modulators 2 and 5 are connected to a further combination device, which in this case is in the form of an adding stage 10, if necessary via correcting stages 8 and 9 which are only indicated in broken lines in Fig. 1.

At the output 11 of the mixing stage 3 appears a mixed signal C=SXB+(1-S) xA.

The correcting stages are generally arranged in the signal paths for signals A, B or C to provide a tonal and/or colour correction.

In a preferred version of the mixing stage 3, correcting stages 8 and 9 directly follow the modulators 2 and 5 and an adding stage 10 is provided in the form of a centre-tapped potentiometer. In this way a balance adjustment can be made to the output signals from the modulators 2 and 5 independently of the control signal S.

Advantageously, the control signal S which is used is a mask signal, a colour signal or a signal derived from the colour signals.

Fig. 2 shows the mixed signal C and waveforms for the signals A and E which are acted on in the mixing stage 3, in a transitional zone 12 which is bounded by the values S=0 and S=1 of the control signal S and whose width can be altered by means of the waveform of the control signal S.

If the control signal S shows a steady rise in the transitional zone 12, then the changes in the individual signals A and B are steady also and, as shown by the form of the mixed signal C, there is a smooth change-over from signal A to signal B in the transitional zone 12.

If the signals A and B are equal in size, the mixed signal C is independant of the control signal S and directly proportional to signal A or B.

In Fig. 2 the control signal S is shown as rising linearly in the transitional zone 12, but any desired waveform is of course conceivable.

Fig. 3 shows an example of the mixing circuit applied to the combining of pictorial originals using a black and white scanner.

Mounted on a rotating scanning drum 14 are two pictorial originals 15 and 16 of which parts 17 and 18 are to appear combined in the reproduction.

To produce the picture signals A and B, the pictorial originals 15 and 16 are scanned point by point and line by line by opto-electronic scanning members 19 and 20 which move along the scanning drum 14 parallel with it. The picture signals A and B pass to inputs 1 and 4 of the mixing circuit 3. The picture signal C which becomes available at the output 11 of the mixing circuit 3 is fed to a gradation stage 21 at which a gradation dependant on the kind of printing, the printing process and the print carrier has been preselected.

The picture signal C, having been modified in the gradation stage 21 and amplified in a final amplifier 22, modulates the brightness of a reproducing member 23 in the forming of an exposing lamp which moves along parallel to a similarly rotating reproduction drum 24 which carries a film 25 to act as a reproduction medium.

On the film 25, the reproducting member 23 exposes the parts 17 and 18 of the two pictorial originals 15 and 16 which are to be combined point by point and line by line.

A control mask 26, which contains the areas of the pictorial originals 15 and 16 which are to be combined with one another in the form of black and white data, is mounted on the scanning drum 14. The control mask 26, which could also be arranged on a separate mask drum, is scanned point by point and line by line by a further scanner 27, synchronously with the pictorial originals 15 and 16, to produce the control signal S.

In conformity with the black and white data given by the control mask 26, the scanner 27, which is connected to input 6 of the mixing circuit 3, supplies a binary control signal (S=0; S=1) which is used to switch either picture signal A or picture signal B through to the reproducing member 23 via the mixing stage 3.

In the embodiment being described while the scanning of the mask takes place the areas surrounding the picture points scanner are evaluated at the same time. The evaluation of the surrounding areas may on the one hand take place by computing surrounding area data from stored picturepoint data and on the other hand by unsharp scanning of the mask using an aperture which is of greater diameter than the picture-point aperture of the scanning members 19 and 20 (a surrounding area aperture). As an example, if the control mask 26 is scanning unsharp the basically binary control signal S is produced with a gradual change-over in a transitional zone at the outlines of the control mask, as a result of which smooth transitions are achieved at the edges of the extracted parts of the originals. The width of the transition zone is advantageously preset by the diameter of the aperture.

Fig. 4 shows a second example of the mixing circuit applied to a colour scanner.

As an example, in so-called part correction of originals, what is involved is subjecting areas of a pictorial original characterised by their position or nature to a modified correction. In this case the correction may relate to colour or tonal value (gradation). Often, it is desired not that the modified correction shall come into action suddenly in the boundary regions but rather that a progressive correcting effect shall be achieved, which is done by suitably mixing differently corrected colour signals.

Mounted on a rotating scanning drum 30 is a coloured pictorial original 31 which is scanned point by point and line by line by a scanning member 32 which is fed along parallel to the scanning drum 30.

In the scanning member 32 the light from scanning is divided into three part beams so that they may each be fed to one colour channel. Assigned to the colour channels are colour filters for colour division and opto-electronic transducers to produce three colour signals R, G and B which represent the proportions of respective colours at the points scanned on the original. The colour signals pass simultaneously to two correcting stages 33 and 34, one of which is preset for a correction to the whole of the original 31 and the other of which is preset for a correction to a part 31' of the original.

Two differently corrected trios of colour signals A and B become available at the outputs of the correcting stages 33 and 34 to enable the colour separations to be produced.

The correcting stages 33 and 34 are connected to the inputs 1 and 4 of a mixing circuit 3' which is suitably expanded in comparison with the mixing stage 3 shown in Fig. 1 to allow for the larger number of input signals.

The three colour separation signals C (Mg, Cy, Ye) are fed via the output 11 of the mixing stage 3' and via final amplifiers 35 to respective exposing lamps 36 which act as reproducing members.

Mounted on a similarly rotating reproduction drum 37 are films 38 which act as reproduction media. The exposing lamps 36, whose brightnesses are modulated by the respective colour signals assigned to them, move axially past the reproduction drum 37 in unison and expose the films 38 point by point and line by line.

Once developed, the exposed films 38 form the required magenta, yellow and cyan colour separations.

Located on a mask drum 39 which rotates synchronously with the scanning drum 30 is a mask 40 which contains the area 40' which is to be differently corrected to act as control data. A scanner 41 having a surrounding area aperture scans the mask 40 and produces the control signal S which is fed to input 6 of the mixing circuit 3'.

Fig. 5 shows a third example of an application of the mixing circuit.

When reproducing a colour original, the need occasionaly arises to alter the gradation as dictated by the coloured or noncoloured nature of the original.

The colour signals are then modified either in accordance with a colour gradation or in accordance with a grey gradation.

In this case the change between gradations should take place not suddenly but gradually as dictaged by the transition in the original from coloured to non-coloured or vice-versa.

The colour signals R, G and B, which are obtained by scanning the pictorial original 31 opto-electronically using the scanning member 32, are first fed to a colour correcting stage 43 to allow the magenta (Mg), cyan (Cy) and yellow (Ye) colour separaitons signals to be formed.

The colour separation signals pass simultaneously to a colour gradation stage 44 and a grey gradation stage 45. The gradation stages 44 and 45 are connected to the inputs 1 and 4 of the mixing stage 3'.

The output signals C from the mixing stage 3' are fed via final amplifiers 35 to exposing lamps 36 which expose the films 38. In accordance with the invention, the control signal S for the mixing circuit 3' is obtained from the colour separation signals by means of a recognition circuit 46.

The recognition circuit comprises a first transformation stage 47 in which a signal formation equation X=0.5 Ye+0.5 Cy-g.

X is formed from the colour separation signals Mg, Cy and Ye using the transformation equation X = 0.5 Ye + 0.5 Cy - Mg.

In a following quantifier 48 is produced a signal /X/. In a second transformation stage 49, a signal Y is produced from the colour signals Cy and Ye using the transformation equation Y = 0.87 Cy - 0.87 Ye. A second following quantifier 50 produces a signal /Y/. The signals /X/ and /Y/ are summed in an adding stage 51 to give the control signal S, which is fed to the input 6 of the mixing circuit 3'.

When "colour" is scanned in the pictorial original 31, the value of the control signal S is at a maximum. When on the other hand "grey" is scanned, the control signal S is zero. When there is a gradual change over from colour to grey, the control signal S also changes gradually. What may also advantageously be used as the control signal S are the black separation signal, the undercolour removal signal (the UCR signal) or a difference signal formed from the maximum and minimum colour signals.

In an advantageous refinement, the gradation stages 44 and 45, as shown in Fig. 1, may also be arranged after the modulators 2 and 5 in the mixing circuit 3'.

Another refinement is to use the mixing circuit to perform the function of a balance adjuster, the balance of the input signals A and B being affected by the control signal S.

Fig. 6 shows the use of the mixing circuit as such a balance adjuster between a colour separation signal and the black separation signal. In this arrangement, the colour signals R, G and B which are obtained by scanning a pictorial original are fed to a first colour computer 52 for the magenta, cyan and yellow colour separations and to a second colour computer 53 for the black separation. One (A) of the colour signals passes to the input 1 of the mixing circuit 3 via a colour-selecting switch 54, and the black separation signal (B) is applied to the input 4 of the mixing circuit 3.

Once again the control signal S may be a colour separation signal or the undercolour removal signal, but it could also be derived from a control mask, a colour or a shade in the original.

The input signals A and B to the mixing circuit 3 may also be two colour signals. In this case the mixing circuit 3 is used to set the white or black-colour balance.

It is however also possible for the mixing circuit 3 to have the white-colour and black-colour correcting signals applied to it, in order to adjust the strength of the correcting signals. The output signal C from the mixing stage 3 is then added into a main channel as a correcting signal.

WHAT WE CLAIM IS: - 1. A method of mixing picture signals for the production of a printing surface of the kind in which a pictorial original is scanned opto-electronically and is reproduced on a reproduction surface, comprising modulating a first picture signal to be mixed by a control signal, and modulating a second picture signal to be mixed by a signal comprising the difference between a reference level signal and said control signal, the said control signals determining the onset and characteristics of the mixing and combining the modulated first and second picture signals to produce a mixed signal.

2. A method according to claim 1, wherein the respective picture signals are modulated multiplicatively.

3. A method according to claim 1 or 2, wherein the control signal is caused to alter steadily in a transitional zone to produce a steady-change over between the picture signals in this zone.

4. A method according to claim 3, wherein the control signal is generated by scanning a control mask and at the same time evaluating the areas surrounding the picture points scanned from the control mask.

5. A method according to claim 3, wherein the control signal is generated by unsharp scanning of a control mask using an aperture whose diameter is greater than the aperture used for sharp scanning of the pictorial original.

6. A method according to claim 5, wherein the transitional zone is determined by the diameter of the aperture.

7. A method according to claim 1 or 2, wherein the control signal derives from the coloured or non-coloured nature of the original.

8. A method according to claim 6, wherein the control signal is a colour signal or a signal derived from the colour signals.

9. A method according to claim 7, wherein two signals (X,Y) are produced by different transformations of the co ordinates of the colour signals (Mg, Cy, Ye) and the control signal is formed by adding the amounts of said two signals (X,Y).

10. A method according to claim 9, the transformations of co-ordinates take place in accordance with the equations.

X= 0.5 Ye + 0.5 Cy - Mg Y = 0.87 Cy - 0.87 Ye.

11. A method according to any one of the preceding claims wherein the picture signals to be mixed are produced by the opto-electronic scanning of two originals to be combined, and the control signal is produced by unsharp scanning of a control mask.

12. A method according to claim 11, wherein the colour signal is subjected to colour and/or tonal value correction.

13. A method according to any one of claims 1 to 6, wherein a single picture signal is divided and the two identical signals so generated each subjected to a different correction, the differently corrected signals providing the first and second picture signals to be mixed.

14. A method according to any one of claims 1. to 6, wherein the picture signal is divided and the two identical signals so generated each subjected to a different tonal-value correction, the differently cor rected signals providing the first and second picture signals to be mixed.

15. A method according to claim 1, 2 or 7, wherein a tonal-value correction is performed on the modulated picture signals.

16. Apparatus for use in the reproduction of pictures comprising opto-electronic scanning means operative to scan an image and to generate first and second picture signals in response to the scanned image, means for generating a control signal for controlling the mixing of said first and second picture signals, and a mixer having a control signal input to which said control signal generating means is connected, said mixer comprising first and second inputs to which said first and second picture signals are, in operation, respectively applied, means for algebraically combining said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. separation signal. In this arrangement, the colour signals R, G and B which are obtained by scanning a pictorial original are fed to a first colour computer 52 for the magenta, cyan and yellow colour separations and to a second colour computer 53 for the black separation. One (A) of the colour signals passes to the input 1 of the mixing circuit 3 via a colour-selecting switch 54, and the black separation signal (B) is applied to the input 4 of the mixing circuit 3. Once again the control signal S may be a colour separation signal or the undercolour removal signal, but it could also be derived from a control mask, a colour or a shade in the original. The input signals A and B to the mixing circuit 3 may also be two colour signals. In this case the mixing circuit 3 is used to set the white or black-colour balance. It is however also possible for the mixing circuit 3 to have the white-colour and black-colour correcting signals applied to it, in order to adjust the strength of the correcting signals. The output signal C from the mixing stage 3 is then added into a main channel as a correcting signal. WHAT WE CLAIM IS: -

1. A method of mixing picture signals for the production of a printing surface of the kind in which a pictorial original is scanned opto-electronically and is reproduced on a reproduction surface, comprising modulating a first picture signal to be mixed by a control signal, and modulating a second picture signal to be mixed by a signal comprising the difference between a reference level signal and said control signal, the said control signals determining the onset and characteristics of the mixing and combining the modulated first and second picture signals to produce a mixed signal.

X= 0.5 Ye + 0.5 Cy - Mg Y = 0.87 Cy - 0.87 Ye.

control signal with one of said picture signals, means for algebraically combining a signal representing the difference between said control signal and a reference level with the other of said picture signals, and means for combining the products of the algebraic combinations to provide a mixed picture signal.

17. Apparatus according to claim 16, wherein the alberaic combining means are each arranged to multiply the signals combined thereby.

18. Apparatus according to claim 17, wherein the means for combining the algebraic products is arranged to add said products.

19. Apparatus according to claim 18, wherein said mixer includes first and second linear multiplication stages to which said first and second picture signals are respectively connected, and said control signal input are connected to the input of said first linear multiplication stage and to the inverting input of an operational amplifier having negative feedback, the arrangement being such that the control signal is inverted and has a constant voltage added thereto such that the output signal from said amplifier is zero when the said control voltage is at a maximum, the output of said amplifier being connected to said second linear multiplication stage.

20. Apparatus according to claim 19 wherein the means for combining said algebraic products is a centre-tapped potentiometer.

21. Apparatus according to any one of claims 16 to 20 and including a pair of opto-electronic scanning devices for generating said first and second picture signals, and a further opto-electronic scanning device adapted to scan a mask to generate said control signal.

22. Apparatus as claimed in any one of claims 16 to 20, and including an optoelectronic scanning device for generating a primary picture signal, a pair of correction devices to which said primary signal is applied, said correction devices being operative simultaneously to apply different corrections to said primary picture signal so as to generate said first and second picture signals.

23. Apparatus according to any one of claims 16 to 18, wherein said optoelectronic scanning means includes filters operative to divide light from the scanned image to provide a set of colour signals, and further including a pair of connecting stages to which said set of colour signals are applied, said connecting stages being operative simultaneously to apply different connections to said set of colour signals to generate first and second sets of picture signals, and wherin said mixer is operative to mix the similar colour signals of each set so as to provide at its output a set of mixed colour signals.

24. A method of mixing picture signals substantially as hereinbefore described with reference to either Figures 1 and 2, or any one of Figures 3, 4, 5 or 6.

25. Apparatus for use in the reproduction of pictures substantially as hereinbefore described with refernce to either Figures 1 and 2, or any one of Figures 3, 4, 5 or 6.