EP0016234B1 - Method for visually testing the reproduction quality of printed matter obtained by cathode ray tube composition - Google Patents

Description

Technical field

The invention relates to a field of reproduction technology, namely to the visual control of the reproduction quality of printed products which are produced by means of cathode ray photo sets.

Underlying state of the art

• - bei der Herstellung von Filmsatz und
• - bei der Faksimile-Fernübertragung von Druckvorlagen, z.B. Zeitungsseiten über Telefonleitungen.

In naher Zukunft dürfte auch die Ganzseitenbelichtung von Zeitungssatz auf Fotopapier oder gar direkt auf Druckplatten ein weiteres Anwendungsgebiet der Kathodenstrahlröhre werden. Die Herstellung von Schriftsatz auf fotografischem Wege findet in der grafischen Branche eine immer grössere Verbreitung und Bedeutung. Es darf heute angenommen werden, dass der Bleisatz sukzessive durch den Filmsatz abgelöst werden wird. Neben den wirtschaftlichen und technologischen Vorteilen des Filmsatzes ist dieser jedoch mit dem Problem der Qualitätssicherung behaftet.The use of a cathode ray tube for the production of artwork is found today in two areas, namely

• - in the production of film typesetting and
• - for the facsimile remote transmission of print templates, eg newspaper pages via telephone lines.

In the near future, full-page exposure of newspaper sets on photo paper or even directly on printing plates is likely to become another area of application for the cathode ray tube. The production of typesetting by photographic means is becoming increasingly widespread and important in the graphics industry. Today it can be assumed that the lead type will be successively replaced by the film type. In addition to the economic and technological advantages of film typesetting, however, this is associated with the problem of quality assurance.

• - Schriftspeicher auf Magnetkern- oder Halbleiterbasis zum Abspeichern der Bildinformation.
• - Lichtquelle in Form einer Kathodenstrahlröhre mit extrem feiner Auflösungsdichte.
• - Optisches Element, welches das auf der Kathodenstrahlröhre projizierte Zeichen auf das Fotomaterial abbildet.
• - Einer oder zwei Kassetten zur Aufnahme von Film oder Fotopapier.

Unter den qualitätsbestimmenden Merkmalen der Schriftwiedergabe findet man zwei Gruppen von Mängeln: eine Gruppe beinhaltet Fehler in der mechanischen Justierung und Positionierung von einzelnen Buchstaben und ganzen Zeilen. Eine zweite Gruppe umfasst Fehler bei der optischen Übertragung, also bei der Belichtung und Entwicklung der Textspalten. Zu dieser Gruppe zählen hauptsächlich die Schwärzung oder Dichte, die Strichstärkenänderung und die Schriftschärfe.The following elements are used today in cathode ray photo set:

• - Magnetic-core or semiconductor-based font memory for storing the image information.
• - Light source in the form of a cathode ray tube with extremely fine resolution density.
• - Optical element which maps the character projected onto the cathode ray tube onto the photographic material.
• - One or two cassettes to hold film or photo paper.

There are two groups of deficiencies among the quality-determining features of font rendering: one group contains errors in the mechanical adjustment and positioning of individual letters and entire lines. A second group includes errors in the optical transmission, i.e. in the exposure and development of the text columns. This group mainly includes the blackening or density, the line thickness change and the font sharpness.

A change in the weight of the lines manifests itself in the fact that individual lines or entire text groups appear bolder or leaner than the surrounding text. This is perceived as unattractive by graphic specialists and also by non-specialists, since it makes the overall appearance of a printed matter appear restless and unkempt. In addition, the legibility of such a text is reduced, since the reader believes that when he finds a bold line, he will find an intended emphasis on the text.

The blackening or density on photo paper should be so high that there is such a high contrast between the drawing elements and the paper white that it enables a photographic recording on a graphic film.

Line thickness change and density are two characteristics that run largely parallel, which means that a change in the line thickness can also be expected to change the density.

It is known from silver salt photography that a visible silver image can only be created by combining the two processes of exposure and development, the intensity of both processes having to be matched to one another and to the photographic material, and each change in intensity of one of the two processes produces a different result. Above all, different exposure intensities cause changes in the density and line thickness of the photoset, which means that the letters appear bolder and darker with increased intensity and become gray and leaner with lower exposure intensity. There is therefore a processing area for the production of photo typesetting columns in which the optimum in font quality can be achieved. This range is called the normal range in the following. Furthermore, there is an area in which a line broadening takes place and an area in which a line narrowing takes place. These areas are referred to below as positive areas and negative areas.

• 1. Die messmikroskopische Methode für die Kontrolle der Strichstärkenänderung.
• 2. Die densitometrische Methode für die Kontrolle der Dichte und der Strichstärkenänderung.
• 3. Die mikrodensitometrische Methode für die Kontrolle der Dichte und der Strichstärkenänderung.
• 4. Die Verwendung spezieller Kontrollstreifen.

The following methods are known for checking the above characteristics:

• 1. The measuring microscopic method for checking the line thickness change.
• 2. The densitometric method for the control of the density and the change of line thickness.
• 3. The microdensitometric method for the control of the density and the line thickness change.
• 4. The use of special control strips.

In the measuring microscopic method, a microscope is used, which is equipped with an eyepiece screw micrometer. After finding a suitable measuring point, the line width can be read on the scale division in the eyepiece. However, since the beginning and end of the line to be measured on the paper column cannot be determined exactly due to the lack of edge sharpness, this method is subject to a certain degree of uncertainty when determining the effective line thickness.

In the densitometric method, the degree of coverage of a grid field exposed on the photo setting machine is measured in order to control the change in line thickness. If the individual points or lines of the grid widen, the area coverage increases, the field appears darker, and a higher measured value can be determined with the densitometer. With microdensitometric Method, the density is continuously scanned across the entire width of the line to be measured with a measuring gap opening of 0.5 to 5 µ and recorded as a function of the location coordinate on a writing instrument connected for this purpose. The line thickness and the density can then be measured or read from the recorded density profile.

Furthermore, DE-AS-2401 672 describes control strips for assessing the image quality, with the aid of which a change in density and line thickness can also be determined. For this purpose, measuring elements are provided which have recesses which grow overexposed and then look like a normal grid point. In the case of underexposure, the recesses become larger, the total area coverage decreases, which is why such elements are also called negative elements. In addition, measuring elements are provided which have small satellite-like points outside the normal raster point (normal element), which disappear in the case of underexposure and increase in the event of overexposure and thus increase more than the normal element in the total area coverage. These elements are also called positive elements.

These individual elements are suitable for visual control using a magnifying glass or a microscope; the entire control strip is evaluated densitometrically.

All of these methods have the advantage that there are exact measurement values that are not subject to the subjectivity of the human eye. However, expensive and complicated measuring devices are required for the control, and the graphic staff is not trained to operate them properly. Another disadvantage, especially with the first and the last-mentioned method, is the enormous amount of time required for the measuring process.

If you imagine the future technical and personnel organization in a newspaper typesetter, where the sentence columns are no longer produced exclusively by typographically trained specialists and where several columns of text can be exposed and developed in one minute, these methods are too complex and complex.

Disclosure of the invention

The present invention is therefore based on the object of specifying a simple method for visually checking the reproduction quality of printed products which are generated by means of cathode ray photo sets.

Brief description of the drawings

The invention is explained in more detail below with reference to FIGS. 1 to 4.

• Fig. 1 ein Beispiel für den Fall einer Unterbelichtung,
• Fig. 2 ein Beispiel für den Fall einer Normalbelichtung,
• Fig. 3 ein Beispiel für den Fall einer Überbelichtung und
• Fig. 4 ein Diagramm für das Verhalten der Messelemente innerhalb des Schwankungsbereichs der Belichtung.

Show it

• 1 shows an example for the case of underexposure,
• 2 shows an example in the case of a normal exposure,
• Fig. 3 shows an example of the case of overexposure and
• 4 shows a diagram for the behavior of the measuring elements within the fluctuation range of the exposure.

Best way to carry out the invention

Fig. 1 shows a field in the lower area of which the word "underexposed" can be seen. The entire field consists of three types of surface elements, which differ in their behavior with underexposure, normal or overexposure. Here, the special circumstances of the exposure area in question and the known normal, negative and positive elements were used. The different behavior of these three elements is explained by the fact that there are latent reinforcements in the positive element and latent weak points in the negative element. These places can be called latent because their effectiveness is almost non-existent in the normal range. The normal element changes only slightly within the entire processing area. The positive element changes in the negative area very similar to the normal element, but shows a clear tendency in the positive area to enlarge its area. The negative element also changes in the positive area very similarly to the normal element, but shows a clear tendency in the negative area to reduce its area.

In Fig. 1 the basic structure of the field consists of normal elements. In the lower area, below the white center line, in which the term "underexposed" appears, there are negative elements where the writing is. In addition, there are three minus signs on the right and left of the writing in the form of negative elements. In the upper area, above the white center line, positive elements are arranged in the form of the lettering “Overexposed”, which is not visible in FIG. 1, but this is clearly expressed in FIG. 3.

It can clearly be seen that the positive elements are reproduced like normal elements in the case of underexposure, the negative elements below the center line have clearly lost surface coverage compared to positive and normal elements and thus appear strongly.

Fig. 2 shows the case of normal exposure, in which all three types of elements are reproduced approximately the same and appear as a homogeneous surface, i.e. the exposure is optimally adjusted.

Fig. 3 shows the case of overexposure. The negative elements below the center line are depicted like normal elements, but the positive elements grow more strongly in terms of their area coverage, as a result of which they appear strongly contrary to FIGS. 1 and 2.

4 shows the tone value behavior of the three elements to one another within a large processing area in the form of a diagram.

In the normal range, all three elements have approximately the same area and therefore have almost the same tonal value, as a result of which they are visually indistinguishable from one another, which can be seen from FIG. 2. It can be seen from the diagram that the percentage area coverage of the positive element increases more when overexposed than that of normal and negative elements, which behave almost the same. In the event of underexposure, the area coverage of the negative element drops sharply, whereas normal and positive elements drop less and equally strongly.

The basic idea of the present invention, as was already apparent from FIGS. 1 and 3, is to mix these elements in a suitable form to form a control field.

If positive elements or negative elements are now mixed with normal elements, the mixing takes place in such a way that the more strongly changing elements take the form of a special character, a figure, a letter or an entire text within the weakly changing elements (normal element) can be checked very easily in which processing area the relevant text column was produced or whether a change in density and line width has occurred.

Claims (4)

1. Method for visual inspection of the reproduction quality of printed matter produced by means of electron beam photo-composition, characterised in that negative, normal and positive elements are combined into symbols or words within an inspection area, in such manner that an unacceptable processing section is detectable immediately by the observer.

2. Method according to claim 1, characterised in that negative and normal elements are combined within a partial area, so that an insufficient exposure or development is detectable.

3. Method according to claim 1, characterised in that positive and normal elements are combined within a partial area, so that an excessive exposure or development is detectable.

4. Method according to claims 2 and 3, characterised in that the elements are combined in such manner that the words "underexposed" and "overexposed" are recognisable.

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