EP0000202B1 - Device for controlling the line width variation of characters produced by a photographic composing apparatus - Google Patents

Description

The invention relates to a device for checking the line thickness change of fonts, which can be produced with the aid of a photo typesetting system.

For some years now, the lead type has been replaced by the typeset in the graphic industry. It is possible to estimate the point in time from which only books of bibliophile character from lead will be printed in Central and Western Europe. Because the new technology mentioned brings significant time and space savings to graphic companies. On the other hand, however, it also brings with it new technical problems. In particular, the problem of quality assurance in photo typesetting is different from that in lead typesetting.

The main thing that is set in the photo set nowadays is with the help of a light source, a typewriter (photo typesetter), a size and thickness device and one or two cassettes for the photo material.

In the projection photo set, a light source (incandescent or flash light) illuminates a negative of the sign and projects it onto the photographic material at the desired scale using size optics.

In jet photo setting, the recording light source, which contains a steerable cathode or laser beam, builds up the mark in the desired size in lines or dots on the photo material. It takes over the "driving program" from another light source that scans a negative sign. However, digitally stored information can also direct the recording beam. In the case of jet photo typesetting, the exposed sign (letter) consists of veil lines or lines or dots that cannot be identified individually by the naked eye only because its resolving power is not sufficient for this.

If one examines the quality-determining characteristics of the font rendering, two groups of defects are found: a first group includes errors in the positioning of the characters, a second group the deformation of the characters. Positioning errors are crooked letters, poor line alignment, irregular letter spacing (Dickten) and irregular weft. The deformation of the font acts as a rounded corner, combined with a loss of the inside and outside shapes, as a breaking off of serifs, as a contour blur and as a change in line width.

Undesired changes in the weight of the line result in individual letters, words, lines or entire text sections and text pages appearing bolder or leaner than intended. Printed matter that has such defects appears neglected, and legibility is reduced because the reader is unsure whether a bold line means an intentional highlighting in the text or is due to an unintentional technical defect. Avoiding unwanted line thickness changes that are still outside the tolerance accepted by the eye is therefore of great importance in the quality assurance of the photo set.

Line thickness changes can occur at different stages of production: The optical system of the exposure unit of the photo typesetting system can have defects and consequently deliver irregular results, the light source itself can be subject to fluctuations or signs of aging, which usually has an immediate effect as a line thickness change in the set. Furthermore, the photoset film emulsion used can fluctuate or the film development can lead to different results, which in turn appears as a change in the line thickness. When copying the photoset film onto the offset printing plate, changes in line thickness can also occur, as can the subsequent printing process itself.

• 1) die messmikroskopische Methode und
• 2) die densitometrische Methode.

There are essentially two methods known for measuring changes in line thickness in a photo set:

• 1) the measuring microscopic method and
• 2) the densitometric method.

In the measurement microscopic method, a microscope is used which is magnified around 100 times or more and which has a measurement graduation of 0.01 mm or finer. This enables the stroke width of letters to be measured directly. The method is suitable to determine the tolerances of the line thickness change, which is still accepted by the eye of the reader. However, the method is laborious and time-consuming to monitor the tolerances once established in daily operating practice. Microscopes with 100x magnification are already laboratory instruments and unusual for photo typesetting experts. The field of view is so small that it does not usually capture an entire letter, which makes it difficult to find suitable measuring points in the script.

The densitometric method is based on the knowledge that the widening of the font and the widening of the halftone dot have the same causes and can therefore be measured using the same methods. A widening of the halftone dot causes a halftone field to become darker and consequently indicates a higher density value when measured with the densitometer.

If a suitable grid, for example a micro measuring field, is placed on the photo record carrier at the place that would otherwise take up a letter negative, and one is exposed Grid in the same way as a letter on the photoset film, so this field can be measured after development with a densitometer. With a stronger exposure, which results in an increase in the line thickness of the letters on the one hand and a darkening of the grid on the other hand, the densitometer shows a higher value. With a weaker exposure, which results in a decrease in the line thickness and a brightening of the grid, a lower density value appears on the densitometer.

The two measurement methods described are suitable, on the one hand, for defining standard values for the line width and, on the other hand, for determining the tolerances of the line width change which are still accepted by the eye. Tolerance values are defined, which is done with the help of test series.

Such a series of tests can be produced as follows: For a certain font and size, tests first determine the line width that results in an optimal typeface in terms of legibility and appearance. With the specified line width, several photo text blocks are exposed. Within these text blocks, however, individual lines are deliberately exposed with different exposure times, so that these lines either appear leaner or fatter than the rest of the text. Test persons then determine the critical change in the line thickness at which fatter or leaner lines or texts are disruptive to the eye.

The critical line thickness change, which will subsequently be called line thickness tolerance, changes slightly from font to font and also with the font size. Larger grades allow a slightly larger line width tolerance than smaller ones. The line thickness tolerance can be specified in micrometers or in density differences on a defined grid.

The target value and tolerance of the line width can be determined for each font and each degree using the methods described. Since this is a unique task, the effort and time required are negligible. However, the situation is different with the daily monitoring of the setpoints and tolerances once established in the operational practice of the photo set. The methods mentioned appear tedious and time-consuming because of the necessary daily repetition. In practice, therefore, there is a need for a device which allows the control of the target values and tolerances quickly and with simple means.

Devices for checking the quality of an image consisting of halftone dots, to be processed in a reproduction and printing process and located on a support are already known, which consist of at least one measuring element with at least one measuring symbol which is designed such that the disappearance of a part it is a direct measure of the relative enlargement of the grid points of the image (CH-PS 554 751). However, such devices cannot readily be used to check the setpoints and tolerances of the font size in the photo set, because photo set fonts do not consist of a large number of individual halftone dots like pictures and because other criteria have to be taken into account in the photo set than when reproducing or printing.

The invention has for its object to provide a device for quick and easy control of the font thickness change of a photo typesetting that can be produced with a photo typesetting system.

To achieve this object, the device according to the invention is characterized by a bright control field with more than one dark surface element, the smallest distance of at least two surface elements and the smallest width of the surface elements being selected such that the distance between the surface elements and is exceeded when a given tolerance for font size is exceeded if the tolerance falls below this, the surface elements disappear.

Further advantageous features of the invention are characterized in the subclaims.

The invention creates for the first time a control device, by means of which the reaching of the upper and lower tolerance for the font thickness can be made immediately visible in the typesetting. Such a device can therefore be used in an advantageous and simple manner to assign each font type its own tolerance, which depends on its special peculiarities, and in this way to ensure that each font type is reproduced within the tolerance assigned to it in the photo set.

• Fig. 1 in starker Vergrößerung einen Ausschnitt aus einem Fotosatzschriftträger, welcher den Buchstaben "i" sowie zwei Ausführungsformen der vorliegenden Kontrollvorrichtung trägt,
• Fig. 2 denselben Ausschnitt, der sich nun auf einem belichteten und entwickelten Fotosatzfilm befindet, wobei dieser Ausschnitt durch Projektion enstanden ist,
• Fig. 3 den Ausschnitt nach Fig. 2, bei welchem eine Strichstärkenzunahme eingetreten ist,
• Fig. 4 einen Ausschnitt nach Fig. 2, bei welchem eine Strichstärkenabnahme eingetreten ist,
• Fig. 5 in starker Vergrößerung eine weitere Ausführungsform der vorliegenden Kontrollvorrichtung, welche ähnlich wie die Vorrichtung nach Fig. 2 durch Projektion enstanden ist, und
• Fig. 6 die Vorrichtung nach Fig. 5, bei welcher eine Strichstärkenzunahme eingetreten ist.

Exemplary embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. It shows:

• 1 is a large enlargement of a section of a photo record carrier, which carries the letter "i" and two embodiments of the present control device,
• 2 the same section, which is now on an exposed and developed photo-set film, this section being created by projection,
• 3 shows the detail according to FIG. 2, in which an increase in line thickness has occurred,
• 4 shows a detail according to FIG. 2, in which a decrease in the line thickness has occurred,
• Fig. 5 in high magnification another embodiment of the present control device, which is similar to the device 2 is created by projection, and
• Fig. 6 shows the device of Fig. 5, in which an increase in line thickness has occurred.

In Fig. 1 a section of a photo record carrier 1 is shown in a large magnification. On this carrier 1, which is usually made of glass, a letter i, designated by 2, and two possible embodiments 3 and 4 of the present control device are shown. The black areas 5 and 6 are opaque to these control devices, while the white areas 7 and 8 are transparent.

The first embodiment 3 of the control device has the shape of a line grid. The second embodiment 4 of the control device has the shape of a so-called square grid. The width of the opaque and the transparent lines or squares of these control devices is the same size as the line width tolerance of the font that is present on the photoset carrier in question.

From Fig. 1 it can also be seen that the width of the opaque and transparent lines 5,7 and squares 6,8 of this control device is practically 1/3 of the width of the letter i. The length of lines 5 and 7 in the first embodiment of the present control device is smaller than the height of the respective letter 2, but this length can either be the same size or in some circumstances even greater than the height of the letter.

As far as the number of these lines 5 and 7 is concerned, of course at least two surface elements 5 and 7 are required. It goes without saying that the more lines 5 and 7 or squares 6 and 8 the respective control device contains, the easier it is to check the line thickness change.

As can be seen, the present control device contains at least one grid field 3 or 4, the grid points 6 or 8 or grid lines 5 or 7 of which correspond exactly to the line width tolerance in terms of their width and their smallest spacings. This grid 3 or 4 is also exposed and a white letter at the end of a line or a text column on the photo record carrier 1 and co-developed it. If, during the exposure and development of the photoset film, an increase in line thickness occurs that reaches the critical limit, i.e. the line width tolerance, the fine lines or halftone dots in the grid of the control device broaden at the same time in such a way that the gaps are just filled, and the field thereby becomes a solid black surface, which can easily be determined with the naked eye or with a magnifying glass.

Conversely, if there is a decrease in the line thickness in the exposure and development of the photoset film, which reaches the lower tolerance limit, the fine lines or halftone dots in the grid of the control device become so narrow that they disappear completely, which can also be easily determined.

The control device thus allows defects in the photosetting film to be recognized with regard to the line thickness tolerance immediately after the film has been developed. As a result, such a photo replacement film can be eliminated in good time before further processing, whereas otherwise the defect can usually only be recognized from the finished print result, in which case the damage is much greater. The present control device also allows an assessment as to how a photoset film identified as defective must be repeated so that the identified defect is no longer present in the repetition.

This now described application of the present control device and a still further embodiment of the same will now be described and discussed in more detail.

FIG. 2 shows a section of an exposed and developed photo-setting film, which was created by projecting the pattern according to FIG. 1. In this case there was no change in the line thickness and therefore the widths of both the letter i and the control devices 3 and 4 shown are unchanged, but positive in the photographic sense. The control devices 3 and 4 shown are still available as a grid.

Fig. 3 shows the corresponding sections of an exposed and developed photoset film, with an increase in line width has occurred, which is within the line width tolerance. From letter i, which is denoted by 2, a richer letter has been created by adding a contour 9. The sum of two opposing contour widths 9 is assumed to be the same size as the line width tolerance. The same increase 9 can also be seen in this FIG. 3 for lines 73 and squares 83 of control devices 3 and 4. The contours 9 just fill the space 63 and 53 between the grid points 73 and 83 of the control devices 3 and 4, since this distance is the same as the line width tolerance. The grid area of the control devices is shown on the photo set film as a full area, which is visually easy to recognize.

FIG. 4 shows the corresponding section 1 from an exposed and developed photographic set film, a line thickness decrease having just occurred which corresponds to the line width tolerance. From the letter i, designated 2, a narrower letter is formed by omitting a contour 10. The sum of the two contours 10 lying opposite one another is the same size as the line width tolerance. The the same decrease was also effective on lines 53 and squares 83 of the control devices. The contours 10 cause the width of the lines 73 and grid points 83 of the control devices to decrease to zero, so that they disappear. The grid area of the control devices is shown on the photo set film as an empty area, which is visually easily recognizable.

In the simple cases described above, it is assumed that the lines or the raster elements of the control devices collapse or disappear solely on the basis of an increase or decrease in the line width during the exposure and further processing of the photoset film. This simplest case assumes that the resolving power of the optical system of the photosetting system and the resolving power of the photographic layers used are infinitely high, or at least much higher than the line thickness tolerance.

As is known, the resolving power as a physical quantity is specified in line pairs per centimeter or per millimeter and thus defines the finest stroke width, which can still be reproduced. The resolution of photo typesetting systems and the usual photo typesetting films is usually limited. For this reason, the lines or halftone dots of the control device do not disappear only when the line thickness tolerance falls below or exceeds, but already when the limit set by the resolution requirements is reached. In order to take this into account, the width of the control elements - lines or grid points - is selected in the control device described so that it corresponds to the sum of the two widths, which can be derived on the one hand from the line width tolerance and on the other hand from the resolving power.

An example should explain this fact in more detail: The line width tolerance for a certain font size is ± 6 micrometers. The width of the lines and their spacing in the control device would therefore have to be 6 micrometers without taking into account the resolving power. The resolving power of the photosetting system used is 500 line pairs per centimeter.

A line pair that can just be mapped therefore has a total width of 20 micrometers, and the individual positive or negative line accordingly has a width of 10 micrometers. Finer lines can no longer be mapped, they disappear or collapse into a surface. The line width of the lines or the diameter of the screen dots in the control device must therefore be 6 plus 10 = 16 micrometers.

Another embodiment of the present control device is shown in FIGS. 5 and 6. FIG. 5 shows the first of the control devices 3 from FIG. 1 together with the letter i, designated 2. This control device 3 is shown in FIG. 5 as it arises from the control device 3 shown in FIG. 1 by projecting it. This control or Grid 3 whose grid points or lines 75 correspond to the line thickness tolerances, a further control or grid 11 is set aside. The grid points or lines 12 of this further control or grid field 11 are finer or coarser, but together they form an area with the same tonal value, i.e. with the same area coverage as is the case with the first-mentioned grid 3. The smallest diameter of the band-shaped surface elements of the first control device 3 and their smallest distance 55 is larger (twice as large in the present example) than the corresponding surface elements 12 in the additional control field 11. The surface elements 75 in their entirety form the first field 3, the surface elements 12 on the other hand, together form the second field 11. The area coverage of the two fields 3 and 11 1 with respect to their surface elements 25 and 12 is of the same size, and in the example shown it is practically 50%. This means that the surface elements each cover 50% of the total area of the respective field3 or 11 to which they belong. The two fields 3 and 11 can also have a different total area from each other.

Visually, the two grid fields 3 and 11 formed in this way appear in the same brightness level, but they differ in their grid fineness and consequently in their behavior when the line width changes. If a line thickness change occurs during a transfer process in the photo set, then the lines 75 or 12 or grid points of the first as well as of the second grid field 3 or 11 widen or narrow, however, since the grid field with its coarser lines or grid points for geometric reasons has a smaller sum of edge zones per unit area, the change in the line thickness in this coarser grid causes a smaller tonal shift than in the finer grid. As a result, a difference in brightness or tonal value occurs between the two raster fields, which is perceptible to the eye, but which can also be measured with a densitometer. If the first grid is darker than the second, coarser grid, the line width has increased, and if it is lighter, the line width has decreased. If both fields have the same tonal value, there is no change in line width.

Since in field 11 the so-called sum of Edge zone of the surface elements is larger (twice as large in the example shown) than in field 3, the same increase in line width in this field causes a greater increase in area than in neighboring field 3, and consequently also a stronger darkening. Fig 6 is intended to make this fact clearer. The letter i, which is designated by 2, has become a richer letter by the addition of a contour 9. The same contours 9 have also been added to the band-shaped surface elements 53 and 12 of the fields 3 and 11. However, since the field 11 has more surface elements 12 (twice as many) as the first field 3, it experiences a greater tonal value increase through these added contours than the field 3. The tonal value difference can be determined visually or densitometrically and serves as a measure of the change in the line thickness.

Claims (5)

1. Apparatus for controlling the stroke strength variations of a photoset document produced with a photo-setting installation, characterised by a light control field with more than one dark surface element, wherein the minimum gap between at least two surface elements and the minimum breadth of the surface elements are so selected that, on exceeding a predetermined stroke strength the gap between the surface elements disappears and, on falling below this tolerance, the surface elements disappear.

2. Apparatus according to claim 1, characterised in that the minimum gap and the minimum breadth of the surface elements are so selected that, on exceeding and falling below the predetermined stroke strength tolerance plus the stroke strength of the finest line which can be reproduced by a photo-setting installation in which the apparatus is to be used, the gap between the surface elements and the surface elements respectively disappear.

3. Apparatus according to claim 1 or 2, characterised in that the surface elements have the form of a strip, a circular surface, a rectangle or a square.

4. Apparatus according to one of claims 1 to 3, characterised in that, besides the control field, a second control field is provided which comprises more than one surface element, wherein the minimum gap between at least two surface elements and the minimum breadth of at least one surface element are smaller or greater than the corresponding breadth or gap of the surface elements in the first control field.

5. Apparatus according to one of claims 1 to 4, characterised in that the surface elements are arranged in the manner of a raster of lines and/or points, in which the breadth and the spacing of the raster lines or raster points correspond to the stroke strength tolerance.

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