GB2121164A - Determining shape of mask - Google Patents

Abstract

A method and device for the determination of the boundaries of a mask (3) in a photographic copying device. The device, which can operate with variable or exchangeable masks, comprises an electronic evaluation circuit for the detection, storage, and evaluation of density values of a section of a pattern to be copied, information concerning the boundary edges of the mask (3) used being derived from the dark/bright transitions and bright/dark transitions, respectively obtained by scanning a light spot across the mask 3 by means of a cathode ray tube 1 and sensing the transmitted light by a detector 5. <IMAGE>

Description

SPECIFICATION Method and device for the determination of the physical size of a mask format used in a photographic copying apparatus The invention relates to a method of and device for the determination of the physical size of a mask format used in a photographic copying device of the type wherein, by means of variable formats of masks or by exchangeable differently shaped masks, at least a part of a pattern is scanned and the density values indicative of the boundary edges of the mask are converted into electric signals.

The invention can particularly be used in copying devices of the controlled contrast compensation type.

In the course of copying patterns, for example aerial photographs, it is often desired to take special details or sections from such photographs which details or sections have to be framed by respective mask formats. Photographic copying devices including exchangeable or variable mask formats are known. The different mask formats permit negative formats of different sizes to be copied or even enlarged sections to be produced from patterns.

It is also known to control automatically the exposure, where the density values or colour values of the patterns are scanned and fed into an exposure control unit. In such an exposure control unit the size of the mask format is an important parameter. It is known to provide markings on the mask for automatic detection of the format and size of a mask scanned by special sensors. Such markings can be bore holes or indentations into which pins of resilient contact switches fit (DE-PS 1209871), or magnetic members which are scanned by magnetically controlled switching means (DE-AS 2659449).

Such copying devices have the disadvantage that a corresponding number of encoding positions have to be provided for a great number of mask formats.

A further disadvantage is that only the original masks from the producer can be used, which limits the application of the device, in particular, when copies of sections are desired, since it is neither feasible nor economical to have in store masks for every section of a pattern.

To eliminate these disadvantages it is known to provide photographic copying devices with mask formats the boundary edges of which are manually adjustable to outline the area to be copied. The actual positions of the format limitations or edges are detected by potentiometers connected thereto (DE-OS 2843975) or by optical and magnetic markings, respectively, (DE-OS 2936667). However, such solutions require a high expenditure on equipment. Furthermore, errors can be involved made by the operator.

In a further known device, disclosed in DE-OS 2833423 the light passing through an adjusted mask format and through a calibrated filter is measured by a photoelement and the free area outlined by the mask format is determined therefrom. However, the length of the boundary edges of the mask format cannot be detected thereby. To know this, that is, the exact dimensions of the framed free area of the mask, is of particular importance in copying devices equipped with means for a controlled compensation of contrast. Such copying devices have long been known (for example from the DE PS 10243454, or the DE-AS 1422460). In these devices the pattern is line-scanned, in most cases by use of a cathode ray tube, and, simultaneously, differences in contrast are compensated by exposing a photolayer by a respectively varied speed and/or brightness of the moving exposure light spot.

In these known devices, the adjustment of the format size is performed by manually operated potentiometers which control the maximum deflection of the light spot of the cathode ray tube (DE-OS 3010945). Misadjustments are particularly troublesome with this arrangement, however, since when the opaque mask is inadvertently scanned the degree of compensation is falsified and, hence, no optimal copy is produced.

Furthermore, the manual adjustment of the mask format dimensions is comparatively time consuming.

It is an object of the invention to obviate the above disadvantages and to increase the output of a photographic copying device.

It is a further object of the invention to provide a photographic copying device in which the actual physical size and position of the mask format is detected and evaluated.

In accordance with the present invention there is provided a photographic copying device including exchangeable or variable mask formats in which at least a part of a pattern is scanned and the resulting light density values are converted into electrical signals; an evaluation circuit operates on the electric signals for detecting the boundary edges of the mask using the bright/dark and dark/bright transitions. The invention can be used in copying devices including means for controlled compensation of contrast. The latter term is widely known in the art and in particular in photogrammetry. Advantageously, the evaluation circuit is electrically connected to a circuit for control of the pattern to be scanned.

The evaluation circuit preferably comprises a differential member for the signal voltages obtained from and corresponding to the density of the pattern, a logic circuit and a storage for the boundary limitations. In such a copying device the format limitations can be determined by several different techniques.

In a first method the pattern is line-scanned; subsequent to a first dark/bright transition, the coordinates (x1, y,) of this point (dark/bright transition) are stored, subsequent to the next bright/dark transition and dark/bright transition, respectively, the co-ordinates (x2, y1) of this second point (dark/bright transition) are stored.

In the course of the further line-scanning of the pattern, the number of bright/dark transitions per line is detected and the absence of these transitions for several lines is evaluated as a signal for having reached the bottom boundary edge. The line co-ordinate y2 is then stored and the scanning is stopped, or a further scanning is performed to detect possible further "windows" in the mask, the boundary edges of which are detected according to the same procedure.

In a second method, line-scanning is again performed initially, until the co-ordinates (x1, y') and (x2, y") corresponding to the first dark/bright transitions and bright/dark transitions, respectively, are stored. Subsequently, the pattern is scanned along a column in a strip limited by x and x2, and the co-ordinates of two subsequent bright/dark or dark/bright transitions (x, y1) (x, y2) are stored.

A third method according to the invention is particularly suitable for a photographic copying device having means for the controlled compensation for contrast. According to this method, after starting the copying operation the pattern is initially line-scanned with an increased speed and preferably low brightness of the scanning light spot. Subsequent to the first dark/bright transition, at least the co-ordinate (x1) of this point (transition) along the line is stored and the scanning operation is continued.

Simultaneously, the masked area is copied.

Subsequent to the following bright/dark transition and dark/bright transition, respectively, at least the co-ordinate (x2) of this point (transition) is stored and the further scanning and copying is only performed within the strip limited by x1, x2.

The following bright/dark transition marks that the bottom edge of the mask has been reached.

The scanning operation is then discontinued.

A particularly simple embodiment of the copying device according to the invention is obtained when said third method is varied as described hereinafter.

The co-ordinates of the bright/dark transitions and the dark/bright transitions, respectively, in each scanning line are exceeded by the scanning light spot by a definite amount and this is done for each new scanning line so that the transition coordinates for each line are detected and stored.

The arrival at the bottom boundary is signalled by the absence of transitions for several lines. The scanning operation is then stopped. This method has the advantage that simple and cheap analog stores can be used for storing the format limitations.

In order that the invention may be more readily understood, reference is made to the accompanying drawings illustrating diagrammatically and by way of example only, one embodiment thereof and wherein: Fig. 1 is a schematic view of a copying device including electronic detection and control means; Fig. 1 a is a schematic and exploded view of a detail of 1; Fig. 1 b is a schematic view of a detail of Fig.

1 a; and Fig. 2 is a pulse sequence diagram.

The copying device of Fig. 1 comprises a cathode ray tube 1 for emitting a scanning spot (not shown), a projection lens 28, a pattern 2 to be copied, for example, an aerial photograph, a format mask 3 constituted of a left-hand boundary edge (limitation) 3/ and a right-hand boundary edge (limitation) 3r, the top and bottom edges of said mask 3 not being visible, the photosensitive sheet 4, a light diffusing sheet 27 and a photodetector 5. These components are aligned on an optical axis x-x. The pattern 2, the mask 3 and the photosensitive sheet 4 are arranged adjacently to one another and in the image plane of the projection lens 28. For the sake of clarity, the circuits necessary for performing contrast compensation are omitted.

The photodetector 5 is connected via a line 6, a differentiating member 7 and a pulse shaper stage 8 to a logic unit 9. In order to produce the scanning movement for the light spot of the cathode ray tube 1 an x-deflection generator 10 and a y-deflection generator 11 are provided and connected to respective deflection plates 12, 1 3 of the cathode ray tube 1. The x-deflection is effected by a delta voltage which is produced by a saw tooth generator 14 and an integrator 1 5.

Two analog stores 16, 17 serve to store the format limitations and are series connected to respective comparators 1 8, 1 9 each of which is connected to the x-deflection unit. The two analog stores 1 6, 1 7 are also connected to the logic circuit 9 via control lines 20, 21. The outputs of the analog stores 1 6, 17 are each connected to the second inputs of the comparators 1 8, 1 9. Via two terminals 22, 23 an additional specific voltage value can be superimposed on the output voltages of the analog stores,16,17. The outputs of the comparators 18, 19 are each connected to clock-pulse inputs of the generator 14.

Two control lines 24, 25 connect the logic circuit 9 to the x-generator 10 and to the ygenerator 11, respectively.

The output signal from the clock-pulse generator 14 and a control signal 26 for starting the copying operation, respectively, are fed into two further inputs of the logic circuit 9.

In Fig. 1 a the assembly constituted by the pattern 2, the mask 3 and the photosensitive sheet 4 are shown in more detail in a front view, considered in the direction of light propagation. In this assembly, the pattern 2 is followed by the mask 3 and then the photosensitive material 4.

The mask 3 frames a section of the pattern 2 by its frame portions 3/ and 3/iforming the left-hand part of the frame, and 3riforming the righthand part of the frame and 3t, 3ti and 3b and 3bi constituting the top and bottom portions of the frame of the mask 3, where istands in all cases for "inner". The dashed line indicates the scanning trace of the light spot emitted from the x-ray tube 1 (Fig. 1), its course being along a y1 co-ordinate direction starting at an x1 co-ordinate at a point of time t1 (Fig. 2) up to an x2 co-ordinate at the boundary edge 3ri.

The point t2 corresponds to the reversal of the scanning direction of the light spot (RPr=right- hand reversal point). The return scanning trace of the light spot is along the co-ordinate y'1 from the point t3 up to the left-hand side reversal point which coincides with the point of time t4 (Fig. 2).

The distance between the left-hand point of reversal (RP1) and x1, and the distance between x2 and Rpr correspond to AU1 and AUr, respectively, in Fig. 2.

The operation of the device and method according to the invention are now described hereinafter in relation to an embodiment where the boundary edges (format limitations) of a mask are derived only from dark/bright transitions.

A desired section of the pattern 2 to be copied is framed by the mask 3 and thereafter the copying operation is started by a signal 26 fed into the logic unit 9 which activates, via the deflection generators 10 and 11 and the integrating member 15, the deflection plates 12 and 1 3, respectively, of the cathode ray tube 1 which is simultaneously energised via an operation voltage source UB.

The scanning or exposing light spot (not shown in the drawing) which is deflected in the xdirection as described hereinbefore is projected by the projection lens 28 upon the pattern 2, passes the latter and impinges upon the left-hand frame portion 3/ (Fig.1 a) and moves along the dashed line along the y, co-ordinate. When it arrives at t1, that is, at the inner edge of the left-hand frame portion 3/, the scanning spot (which also becomes the imaging beam from now on) impinges upon the photodetector 5 after passage through and exposure of the photosensitive material 4 and after being diffused at the diffusing sheet 27. The scanning spot produces a voltage pulse in the photo-detector 5, indicated at t1 in Fig. 2a of Fig.

2. The pulse is fed via the line 6 into the differentiator 7 where, after differentiation, a pulse is produced which is formed into a shape in the pulse shaper 8 readable by the logic circuit 9 (Fig. 2b). The logic circuit 9 detects from the polarity of the square pulse voltage applied to the integrator 1 5 whether a right or a left-hand format limitation is concerned, and, via the corresponding control line 20 or 21 feeds the pulse indicated by the first spike in Fig. 2c into the associated store for storing the actual value of the x-deflection voltage. The scanning spot moves on and exposes the photosensitive material 4 through the pattern 2. Any contrast compensation necessary can be effected through intensity modulation and/or speed modulation.When the light spot arrives at the inner right-hand boundary edge 3ri, the mask blacks out the imaging beam so that the photodetector 5 does not receive light any longer. This is indicated by the trailing edge of the first pulse of Fig. 2a and the downward spike in Fig. 2b.

The scanning spot moves on by a definite length, though the lateral limitation of the mask aperture has been reached. This is necessary, for example to obviate the possibility that a dark area in the pattern (high density area) in the vicinity of the edge portion might deceive the logic into inadvertently cutting a column along another x2 from the format mask. Another reason is to ensure detection even when the mask portions 3r and 3/ are not parallel to the corresponding edges of the pattern 2, that is, detection of the mask takes place even when it has been inserted slantingly into the unit. This is achieved by superimposing two additional voltages AU1 and ARr as described hereinafter.

When the scanning spot has arrived at the right-hand reversal point RPrt the square wave pulse generator 14 changes polarity as illustrated in the waveform of Fig. 2d at t2 and the scanning spot moves back along a trace determined by the y11 coordinate direction. At the point t3 in Fig. 1 a which corresponds to the point of time t3 in Figs.

2a, 2b and 2c, the second dark/bright transition takes place, that is, the scanning light spot moves from the inner boundary edge 3r, to the unmasked section, and, hence, the photodetector 5 receives light so that a voltage pulse is produced in an analogous manner to the first dark/bright transition at t,. The voltage pulse is processed in an analogous manner to the first dark/bright transition described hereinabove, the pulse for storing the actual x-defiection voltage being fed from the logic circuit 9 into the other store so that the x-deflection values corresponding to the format limitations are stored in the two stores 16, 17.

Two predetermined voltages AU1 and AUras referred to hereinabove are applied to the input terminals 22, 23 (refer to Fig. 2e) which are superimposed onto the output voltages of the stores 1 6, 1 7 to ensure that the mask format boundaries are transgressed by a predetermined amount. The scanning spot thus moves on for a definite length, even though the boundary limitation has been reached.

The actual deflection voltage applied across the deflection plates 12 at the point of time t1 is fed into the comparators via the line 29 where it is compared with the modified store 1 6, 1 7 voltages, that is, to the x-deflection voltage plus the voltages AU1 and AU" respectively. When the comparison of the actual x-deflection voltage is equal or less than the store 1 6, 1 7 contents (voltages) then a reversal pulse is fed into the squarewave pulse generator 14 via the lines 31 and 30, respectively, depending on the direction of reversal.

In Fig. 2e the curve of the triangle generator 10, constituted by the square wave generator 14 and the integrator 15, is shown. When the scanning spot moves from the right to the left (Fig. 1 a from t3 boundary edge 3rj to the boundary edge 31) a continuous comparison takes place in the comparators 1 8, 1 9 between the actual voltage applied via line 29 (Fig. 1) and the stored voltage obtained at t1 plus the superimposed voltage AU1.

The curve 2e decreases from the first voltage peak (for example, 2 volts) to the valley point which is not, as initially, at zero volts, but on the dashed line indicative of AU1 (for example, 0.3 volts). At this point t4, the generator 14 gets the reversal order and not at a later point of time where the curve would have reached zero-level as it has at the starting point. That means, that the scanning spot does not move up to the utmost feasible point on the left-hand mask frame portion 31.

The triangular curve again rises to the second peak, the voltage of which again is determined by operation of the comparators 1 8, 1 9 which compare the actual x-deflection voltage to the voltage stored at t3 (second dark/bright transition) plus the superimposed voltage A. Hence the reversal point takes place at t5 and not at a later point of time.

This operation is repeated for each new dark/bright transition and the actual x-defiection values are fed into the stores 1 6 and 17 for each new line so that a time consuming maximum sweeping of the format limitations is superfluous, apart from the fact that the stores have to store the respective voltage values only for a short time, which renders them simple and economic. So, for example, each store can be embodied by a capacitor and an electronic switch (transistors). At each point of reversal (t2, t4, t5 etc) the generator 14 delivers via a line 32 a shift pulse to the logic 9 which, via line 25, feeds a y-co-ordinate direction shift pulse into the y-generator 11 so that another scanning line y1, y1', etc. can be swept by the scanning spot.This line scanning is continued in the above described manner until the bottom boundary edge is reached which results in the absence of any further darklbright transitions and the scanning operation is stopped. The absence of any dark/bright transitions for a plurality of lines is detected by the logic circuit 9, and in consequence thereof the scanning and exposing procedure is stopped. The automatic detection of the format limitations available by the copying device according to the invention and the control of the scanning spot permits both an increase of the output of the device as well as a considerable reduction in the possibility of operator errors.

The components mentioned can be realised by simple electronic members. Thus the differentiator 7 can be an R-C-combination, the pulse shaper a monoflop, the logic 9 can be a microprocessor, and the integrator 1 5 an R-Ccombination. The method and device is not restricted to the above embodiment, and, for example, it is feasible to scan the four mask frames 3t, 3b, 3r, 3!, which, however, requires the incorporation of four stores for the four limitations. These stores must be capable of storing the contents for a longer time and this can be realised by the use of digital stores and respective A/D converters. Furthermore, it is feasible to use the bright/dark transition for evaluation and detection of the format.However, the evaluation of the dark/bright transition yields a higher evaluation safety, since only each first pulse of the differentiated signal in each line has to drive the logic so that even considerably strong density differences of a pattern do not falsify the determination of the format limits.

It still lies within the scope of the invention to line scan the pattern 2; after arrival at the first dark/bright transition, the respective co-ordinates x1, y1 thereof are stored, and after the next bright/dark transition and dark/bright transition, respectively, the co-ordinates x2, y'1 of this second transition are stored, the number of bright/dark transitions and dark/bright transitions per line are detected and upon the absence of any bright/dark transitions and dark/bright transitions, respectively, for at least two lines, the line coordinate y2 is stored and the scanning operation is stopped.

A further method for the format detection is described in connection with Fig. 1 b. The pattern 5 is scanned by the light spot along a line paralled to the x-direction. When the light spot arrives, after sweeping the top frame portion of the mask 3, at the first darklbright transition of the coordinate x1, y' thereof is stored and evaluated by the electronic components as mentioned hereinabove. At the next bright/dark and dark/bright transition, respectively, the coordinates x2, y" thereof are stored and evaluated, the light spot returns to the left-hand side.

Halfway between x2, x1, the line scanning is stopped and a vertical scanning is performed in a column parallel to and between the x1 and x2 coordinate directions. The co-ordinates of the two subsequent bright/dark and dark/bright transitions x, y, (top edge of mask 3) and x, y2 (bottom edge of mask 3) are detected, stored and evaluated.

Thus, in rapid and simple manner the format of the mask has been determined. In a next step, the exposure of the pattern within the limits drawn by the mask 3 is started, which is indicated by the upward direction of the arrow A in Fig. 1 b.

It is also feasible to line scan the pattern 2 in a first mode of operation at an increased speed and/or at a reduced scanning brightness of the scanning spot. After the first darklbright transition, at least the co-ordinate x1 thereof located on the respective line is stored, and in a second mode of operation, the scanning is continued at a reduced speed, at which the pattern is simultaneously copied. After the next bright/dark transition and dark/bright transition, respectively, at least the co-ordinate x2 thereof is stored, the further scanning and copying being only performed within a strip limited by the values x1, x2m. Subsequent to the next bright/dark transition, the scanning operation is stopped.

Claims (9)

Claims

1. A method for the determination of the physical limits of the format of a mask in a photographic copying apparatus having an electronic evaluation arrangement for scanning any mask format constituted by at least two boundary limitations in the course of exposing a section of a pattern to be copied through said mask, the method comprising (a) scanning said mask along lines which are substantially parallel to an x-co-ordinate direction, but mutually displaced by y within the pattern size, (b) storing the co-ordinates x1, y1 of a first dark/bright transition indicative of a transition from a lefthand side mask portion to an unmasked portion, and (c) storing the co-ordinates x2, y'1 of a second bright/dark and dark/bright transition, respectively, which are indicative of a transition from the unmasked portion to a right-hand side mask portion and from a right-hand side mask portion to said unmasked portion, respectively.

2. A method as claimed in claim 1, wherein steps (b) and (c) are repeated and respectively yco-ordinates for x1 and x2 are obtained and wherein the scanning operation is stopped at the absence for at least two scanning lines of any further dark/bright and bright/dark transitions y2 for the respective line co-ordinate then being stored.

3. A method as claimed in claim 2, wherein steps (a), (b) and (c) are performed at a high scanning speed and at a reduced brightness of the scanning light spot.

4. A method as claimed in claim 2, wherein the repetitions of steps (b) and (c) are performed substantially within limitations determined by the x1, x2 co-ordinates at a simultaneous copying operation.

5. A method as claimed in claim 1 , wherein a column is scanned within and defined by x1 and x2, and wherein the method comprises the further steps of detecting a first bright/dark transition and dark/bright transition, respectively, indicative of a top limitation of said mask, storing the coordinates x, y1 of said first bright/dark transition, further scanning along said column, detecting a second bright/dark transition and dark/bright transition, respectively, indicative of a bottom limitation of said mask, and storing the coordinates x, y2 of said second bright/dark transition, starting exposure within the detected limitations.

6. A device for the determination of the physical size of a mask in a photographic copying apparatus comprising, about a common axis one after another.

(a) a cathode ray tube for producing a light spot, said cathode ray tube including x-deflecting means and y-deflection means for said light spot; (b) a projection lens having an image plane; (c) an assembly including a pattern to be copied, a mask composed of at least two boundary limitations for framing a section of said pattern, said limitations representing dark/bright transitions and bright/dark transitions, respectively, a photosensitive sheet, and a diffusing sheet, said pattern, said mask, said photosensitive sheet, and said diffusing sheet being arranged adjacently and substantially parallel to one another on said axis and in said image plane; and (d) a photodetecting means for detecting said dark/bright transitions and said bright/dark transitions, and for producing an electric signal from said dark/bright transition and bright/dark transitions, respectively; the device further comprising: (e) a differentiating and pulse shaping means connected in series with said photodetector for converting said electric signals into pulses; (f) a logic device; (g) at least two stores, each of which has two inputs and one output, said stores being associated with respective ones of said two boundary limitations; (h) at least two comparators, each having two inputs and one output; (i) a y-deflection generator for producing a ydeflection voltage; and (j) an x-deflection generator constituted by a square pulse generator and an integrator, said xdeflection generator being for producing an xdeflection voltage, said x-deflection generator being connected to said x-deflection means of said cathode ray tube, and being adapted to apply said x-deflection voltage across said x-deflection means for bi-directional x-deflection of said light spot, and further being connected to respective first ones of said two inputs of each of said two comparators, and to second ones of said two inputs of each of said two stores, said one output of each of said two stores being connected to the other of said two inputs of each of said two comparators, said one output of each of said two comparators being connected to said x-deflection generator, said pulse from said pulse shaping means being fed into said logic device and said logic device in dependence on said pulse being arranged to store said x-deflection voltage in a respective one of said two stores, each of said comparators being arranged to compare the stored x-deflection voltage with said x-deflection voltage applied across said x-deflection means, said two comparators being arranged to feed the comparative signal into said x-deflection generator via the respective one of said two comparator outputs, said x-deflection generator being further arranged to feed an x-direction reversal signal into said logic device which is then arranged to feed a respective y-deflection signal into said y-deflection generator in dependence on said x-direction reversal signal.

7. A device as claimed in claim 6, wherein each of the two outputs of said two storages is provided with an additional input for superimposing an additional voltage AU to each of said stored x-deflection voltages.

8. A method for the determination of the physical limits of the format of a mask in a photographic copying apparatus substantially as hereinbefore described with reference to the accompanying drawings.

9. A device for the determination of the physical size of a mask in a photographic copying apparatus, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.