JPS59120806A - Apparatus for measuring image area - Google Patents

Abstract

PURPOSE:To accurately measure even the area of an image covered with a transparent substance, by a method wherein a light detecting element permitting the permeation of only light having a polarization surface which crosses linearly polarized light incident to an image to be measured at right angles is provided between the image to be measured and a photoelectric conversion part and only the light parallel to the permeation axis of the light detecting element among reflected lights is received by the photoelectric conversion part. CONSTITUTION:The laser beam from linear polarization type laser 41 is converted to light having circular polarization while passed through a 1/4 wavelength plate 42 and the converted light is further converted to linearly polarized light again by a polarization element 43 to be reflected by a scanning mirror 25A and the reflected light is allowed to irradiate a printing plate 30 to scan the printing plate 30 in the X- and Y-directions thereof by a scanner 25B and the revolution of the scanning mirror 25A by a stepping motor 22. In this case, the polarization element 43 and the scanning mirror 25A are integrally revolved and the relative angle of the polarization surface of linearly polarized light after passing the polarization element 43 and the incident surface on the scanning mirror 25A is always constant at the arbitrary angular position of the revolution of the scanning mirror 25A to a Y-direction and the deflection surface and the incident surface of the irradiated light are always kept constant.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an image (
The present invention relates to an image area measuring device for determining the area occupied by each region and its ratio with respect to a binary image (hereinafter referred to as a binary image).

Conventionally, devices for calculating the area of a binary image have been used, for example, to measure the ratio of the area of the area to which ink adheres (image area) to the area of the area to which ink does not adhere (non-image area) from a printing plate of an offset printing machine. A so-called picture area ratio measurement device is known. As shown in FIGS. 1 and 2, this picture area ratio measuring device includes a pair of linear light sources 2 and 3, such as fluorescent lamps, arranged in parallel on both sides of a plurality of photoelectric conversion elements 1 arranged in a row. Then, these are moved in parallel along the upper surface of the printing plate 4, or the printing plate 4 is moved in parallel. On the other hand, the reflected light from the printing plate 4 received by the photoelectric conversion element 1 is converted into an electrical signal, and the ratio between the printed area and the non-printed area of the printing plate 4 is determined based on this electrical signal. It is.

In general, printing plates made by offset printing are usually 0.5 m
The size ranges from 0.5 m x 1.2 m x 1.4 m. In order to accurately measure the image area of such a large surface to be measured, uniform illumination and light receiving characteristics are required over the entire surface. However, in the case of the above-mentioned device,
Because fluorescent lamps are used as linear light sources, it is difficult to keep the amount of light emitted stable and uniform for long periods of time, and it is also difficult to maintain the sensitivity of multiple photoelectric conversion elements at the same level. , there is a problem that uniform light receiving characteristics cannot be expected.

Moreover, since the entire optical system must be moved in parallel along the printing plate during measurement, there is a drawback that high-speed measurement cannot be expected.

Therefore, a possible method for solving these problems is to scan a binary image two-dimensionally with a light beam to obtain the image area of the binary image.

In this method, as shown in FIG. The photoelectric converters 15 are arranged in close proximity to each other, and the laser beam from the laser 17 driven by the laser driving device 16 is directed to the X direction of the surface to be measured 11 by one optical deflector 13 and the other optical deflector While scanning the surface to be measured 11 in the Y direction, the photoelectric converter 15 receives reflected light from the surface to be measured 11 and converts it into an electrical signal. The image area of the surface 11 is calculated and the result is outputted to a magnetic card 20 or the like via an output section 19. However, this method has the following problems.

For example, let's look at how the amount of light received by the photoelectric converter 15 changes depending on the position of the laser light spot in the X direction when laser light is scanned in the X direction. Now, as shown in FIG. 4, the light receiving surface 15A of the photoelectric converter 15 is parallel to the surface to be measured 11, and the perpendicular line drawn from the center point of the light receiving surface 15A to the surface to be measured 11 is the surface to be measured 11. The intersection point is the origin 0 in the X direction, and from the origin 0 x
Consider the case where there is a light spot at a certain position. Here, the height from the surface to be measured 11 to the light receiving surface 15A is z, and the height from the light receiving surface 15A is
The distance from to the position of the light spot is r, the solid angle that the light receiving surface 15A makes with respect to the position of the light spot is α,
When the angle that A makes with respect to the direction of the light spot is θ,
It may be considered that the amount of received light I is proportional to the solid angle α.

Now, assuming that the light-receiving surface 15A has a unit width and a length of 2l, the solid angle α is approximately (assuming α<1) α≒2l/r・cosθ... It can be expressed as (1). In this equation (1), cosθ=z/r, r
Since 2=z2+x2, the amount of light received is as follows. If this is illustrated using x as a variable, it will look like Figure 5. For example, if x is about the same as z, the amount of light received at the center (x = 0) will be reduced to approximately half. .

Therefore, the present inventors have developed a device that can solve the problems of conventional devices including these problems. This one is the 6th
As shown in the figure, the surface to be measured 11 is curved with a constant curvature in the Y direction, a laser 21 is placed on one side of the central axis of the curvature, and a stepping motor 22 is placed on the other side. An optical deflector 25 and a photomultiplier tube 26 operated by an optical deflector control device 24 are mounted on a mounting frame 23 that is rotated about an axis.
, and then the light-receiving surface 26 of the photomultiplier tube 26.
A light shielding plate 27 is provided between A and the surface to be measured 11, and the electric signal received and converted by the photomultiplier tube 26 is transmitted to A.
The signal is configured to be supplied to the microcomputer 29 via the /D converter 28.

Here, if the scanning mirror 25A of the optical deflector 25 is located at the intersection of the central axis and the normal line set at the center of the surface to be measured 11, and the photomultiplier tube 26 is placed close to the scanning mirror 25A, the stepping When the laser beam from the laser 21 is scanned in the Y direction of the surface to be measured 11 by the operation of the motor 22, the distance from any position in the Y direction of the surface to be measured 11 to the light receiving surface 26A of the photomultiplier tube 26 is substantially constant, so the amount of received light can be made constant at any position in the Y direction. On the other hand, if the light shielding plate 27 is positioned on a perpendicular line drawn from the center point of the light-receiving surface 26A of the photomultiplier tube 26 to the surface to be measured 11, as shown in FIG. 7, the position of the light spot will be at the origin o. It can be seen that the amount of light shielding is at a maximum when the distance from the origin o is reached, and the amount of light shielding decreases as the distance from the origin o increases. Therefore, under the conditions that the height from the surface to be measured 11 to the light receiving surface 26A is 300 mm, the length 2l of the light receiving surface 26A is 22 mm, and the width w of the light shielding plate 26 is 3 mm, By changing the height z1 to
When 1=280 mm, it becomes like a solid line, so by changing z1, the distribution of the amount of received light can be made equivalently uniform in scanning in the X direction. Incidentally, even if an optical filter having a concentration distribution in which the transmittance increases from the origin o to the periphery is used instead of the light shielding plate 27,
Similar results are obtained. Further, similar results can be obtained even if a correction table regarding the amount of received light is provided and the calculation section performs calculations based on this correction table. On the other hand, although it is of course possible to perform similar uniform light reception correction in the Y direction, it is actually difficult to accurately equalize the two-dimensional distribution, so the method described above is preferable in the Y direction.

In this way, the device shown in FIG. 6 has solved the problems of the conventional example, but there may be another problem. Normally, in this type of binary image, the surface of the image is often coated with a transparent film in order to prevent staining of the image surface. For example, in the case of printing plates for offset printing presses, the surface of the printing plate is made transparent after the image areas are formed by development treatment in order to prevent the hydrophilicity of non-image areas from being impaired due to oxidation due to contact with air or hand marks. Covering with a rubber film (called gumming) is carried out.

The surface to be measured, whose surface was protected by a transparent film, was placed in the sixth
When measured with the device shown in the figure, when the laser beam is located at the center in the X direction, most of the reflected light that enters the photomultiplier tube 26 becomes specularly reflected light from the surface of the transparent protective film.
This results in the inconvenience that information corresponding to the image area of the object to be measured cannot be obtained.

In order to prevent this, for example, the distance between the scanning mirror 25A and the photomultiplier tube 26 must be adjusted from the scanning mirror 25A to the surface to be measured so that a reflection angle of about 45 degrees can be secured for all reflection points on the surface to be measured. The size should be about the same as the distance to. However, since the maximum size of printing plates for offset printing machines is 1200 mm x 1360 mm, in order to accurately measure the image area of such a large surface to be measured over the entire surface, the distance from the scanning mirror 25A to the surface to be measured must be It is necessary to set the length to about 1200 mm, which causes structural difficulties and is not a practical method.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image area measuring device that has a compact structure and can accurately measure the image area even in the case of an image whose surface is coated with a transparent substance.

It is generally known that when linearly polarized light is incident on a transparent object, the reflected light is linearly polarized light, and when linearly polarized light is incident on an absorbing object, the reflected light becomes elliptically polarized light. The measurement principle of the present invention focuses on this polarization property. Linearly polarized light is incident on an image of the surface to be measured whose surface is covered with a transparent film, and only light with a polarization plane perpendicular to the polarization plane of the linearly polarized light is used. By receiving the light, it is possible to perform measurements excluding specularly reflected light from the surface of the transparent film.

More specifically, linearly polarized light is emitted from the light source section, and the light is scanned onto the image to be measured by the optical scanning section. Then, if the surface of the image to be measured is covered with a transparent film,
The light reflected from the transparent film becomes linearly polarized light, and the light reflected from the image to be measured becomes elliptically polarized light.

On the other hand, on the light-receiving side, an analyzer is installed between the image to be measured and the photoelectric conversion unit, which transmits only light with a plane of polarization perpendicular to the linearly polarized light incident on the image to be measured. The above objective is achieved by removing reflected light and allowing the photoelectric conversion unit to receive only the light parallel to the transmission axis of the analyzer out of the reflected light from the image to be measured.

Examples of the present invention will be described below.

FIG. 9 shows the entire embodiment of the present invention.

Here, in describing the same embodiment, the same components as those shown in FIG. 6 are given the same reference numerals, and the explanation thereof will be omitted or simplified.

This embodiment includes a light source section 31 that emits linearly polarized light, and a printing plate 3 that is curved in an arc shape to emit the linearly polarized light from this light source section 31.
0, a photoelectric conversion unit 33 that receives reflected light from the printing plate 30 and converts it into an electrical signal according to the amount of received light, and is arranged on the light-receiving surface side of the photoelectric conversion unit 33. an arithmetic unit 35 that calculates the image area of the printing plate 30 based on the analyzed analyzer 34 and the signal from the photoelectric conversion unit 33;
It is composed of.

The light source section 31 includes a linearly polarized He-Ne laser 41.
and a quarter-wave plate 4 that converts the linearly polarized light from the linearly polarized He-Ne laser 41 into light having circularly polarized characteristics.
2, and a polarizer 43 that converts the circularly polarized light converted by the quarter-wave plate 42 into linearly polarized light again and makes it incident on the scanning mirror 25A.

The laser 41 and the quarter-wave plate 42 are arranged coaxially with the rotation axis of the stepping motor 22 so as to share an optical axis. Furthermore, the polarizer 43 is arranged on the mounting frame 23 so that when the transmitted light enters the printing plate 30, it becomes linearly polarized light with a plane of polarization parallel to the plane of incidence (the plane containing the incident light and the reflected light). scan mirror 25
It is attached so that it can rotate integrally with A.

Further, the optical scanning section 32 is composed of the same components as those shown in FIG. 6. That is, it is composed of a stepping motor 22, a mounting frame 23, and an optical deflector 25 consisting of a scanning mirror 25A and a scanner 25B.

These components, together with the laser 41 and the quarter-wave plate 42, are attached to a machine frame 51 shown in FIG. 10. An optical system installation part 53 is formed in the machine frame 51 above a printing plate mounting base 52 that fixes the printing plate 30 in a curved arc shape. The scanning mirror 2 is placed at the center point P of the arc of
5A, the photoelectric conversion section 33 is attached close to its center point P. In addition, other components are appropriately arranged.

Thereby, the light incident on the scanning mirror 25A from the light source section 31 is transmitted to the scanning mirror 25A by the operation of the scanner 25B.
As the scanning mirror 25A is rotated around the optical axis by the operation of the stepping motor 22, the printing plate 30 is rotated in the X direction as the scanning mirror 25A is rotated around the optical axis by the operation of the stepping motor 22. 30 in the Y direction.

The photoelectric conversion unit 33 also includes a photomultiplier tube 26 attached to the mounting frame 23 via a holder 61, and an amount of light received by the photomultiplier tube 26 during scanning of the printing plate 30 in the X direction. A light shielding plate 27 is used to make the light uniform. The holder 61 includes the images shown in FIG.
As shown in FIG. 2, a light receiving hole 62 is formed at a position corresponding to the light receiving surface of the photomultiplier tube 26, and a light shielding plate 27 located on the opening surface side of the light receiving hole 62 is connected to the holder 61.
It is attached with a fixing screw 63 so that the distance g between the two parts can be adjusted.

Further, as shown in FIGS. 11 and 12, the analyzer 34 is adjusted so that its transmission axis is perpendicular to the transmission axis of the polarizer 43, and is attached to the opening surface of the light receiving hole 62 of the holder 61. It is being

Therefore, the reflected light from the printing plate 30 is subjected to the uniformity correction effect by the light shielding plate 27, and then enters the analyzer 34. Then, only the reflected light having a polarization plane perpendicular to the polarization plane of the light incident on the printing plate 30 is transmitted by the analyzer 34, and is photoelectrically converted by the photomultiplier tube 26.

The calculation unit 35 also includes an A/D converter that converts the signal photoelectrically converted by the photomultiplier tube 26 into a digital signal.
a microcomputer 29 that operates the converter 28, the stepping motor 22 and the scanner 25B according to a predetermined program, and calculates the image area of the printing plate 30 based on information provided from the A/D converter 28; It is composed of. The microcomputer 29 controls the light source section 31 through the operation of the scanner 25B.
The light from the printing plate 30 is scanned in the X direction, and during the scanning in the X direction, data given from the photoelectric conversion unit 33 is sequentially captured at predetermined timing, and the data is sequentially stored in a predetermined storage area. Make me remember. Here, after the scanning on one X scanning line is completed, the stepping motor 22 is rotated by a predetermined angle to scan in the X direction again, and in the scanning in the X direction, the data given from the photoelectric conversion unit 33 is It sequentially captures data at predetermined timings and sequentially adds them to the designated storage area. By repeating this process, the entire surface of the printing plate 30 is scanned. As a result, in the storage area, Y
The cumulative value in the direction is stored.

Incidentally, the data for each predetermined unit in the X direction stored in these storage areas is used as data for setting the amount of ink for each ink zone in an offset printing press.

Next, the operation of this embodiment will be explained. Linearly polarized laser 4
The laser light emitted from the laser beam 1 is converted into light having circular polarization characteristics by passing through the quarter-wave plate 42 . 1/
The light that has passed through the four-wavelength plate 42 is again converted into linearly polarized light by the polarizer 43, and then reflected by the scanning mirror 25A and irradiated onto the printing plate 30. As the printing plate 30 rotates, it is scanned in the X and Y directions.

At this time, since the polarizer 43 and the scanning mirror 25A are rotated together, the polarization plane of the linearly polarized light after passing through the polarizer 43 and the incident plane on the scanning mirror 25A (incident light and reflected light) The relative angle with the Y plane of the scanning mirror 25A is
It is always constant at any angular position of rotation in the direction. Therefore, at any position in the Y direction of the printing plate 30,
The plane of polarization and the plane of incidence of the irradiated light are always kept constant.

Now, as shown in FIG. 13, when the reflected light from the scanning mirror 25A is incident on the printing plate 30 whose surface is covered with the transparent film 30A, the incident light is reflected and refracted on the surface of the transparent film 30A. Divides into light.

This reflected light is linearly polarized light with the same polarization plane as the incident light.
It becomes a noise component during measurement. On the other hand, the refracted light is reflected on the surface of the printing plate 30 and is emitted to the surface through the transparent film 30A. This light is elliptically polarized and has a signal component corresponding to the image area of the printing plate 30.

The reflected light having both components is first subjected to a uniform light reception correction effect by the light shielding plate 27, and then reaches the analyzer 34. The transmission axis of the analyzer 34 is the transmission axis of the polarizer 43, that is, the printing plate 30.
Since the plane of polarization is adjusted to be perpendicular to the polarization plane of the incident light, the specularly reflected light from the surface of the transparent film 11A is absorbed, and the transmission axis of the analyzer 34 and the light reflected from the surface of the printing plate 30 are adjusted to be perpendicular to the polarization plane of the incident light. Only light with parallel polarization planes is transmitted through the analyzer 34.

The light transmitted through the analyzer 34 is photoelectrically converted by the photomultiplier tube 26 and then taken into the calculation section 35, where the image area of the printing plate 30 is calculated according to the procedure described above.

Therefore, in this embodiment, while the linearly polarized light is scanned in the X and Y directions of the printing plate 30 by rotating the scanning mirror 25A, the printing plate 30 is placed between the photomultiplier tube 26 and the printing plate 30 on the light receiving side. Since the analyzer 34 is provided to transmit only light having a plane of polarization perpendicular to the light incident on the transparent film 30, when measuring the printing plate 30 whose surface is covered with the transparent film 30A, the light from the surface of the transparent film 30A can be measured. The specularly reflected light of printing plate 3 is removed.
Of the light reflected from the surface of the transparent film 30A, only the light parallel to the transmission axis of the analyzer 34 is received by the photomultiplier tube 26, so the image area is not affected by the light reflected from the surface of the transparent film 30A. can be measured accurately. Furthermore, in terms of structure, it is only necessary to use linearly polarized scanning light and to provide the analyzer 34 on the light receiving side, so it can be made compact. In particular, in this embodiment, the linearly polarized light emitted from the linearly polarized laser 41 is converted into light having circularly polarized characteristics by the quarter-wave plate 42, and this light is rotated integrally with the scanning mirror 25A. The transmitted light is transmitted to the printing plate 30 by the polarizer 43.
When it enters the scanning mirror 25A, the transmitted light is converted into linearly polarized light with a plane of polarization parallel to the plane of incidence.
When scanning the printing plate 30 in the X and Y directions by
The plane of polarization of the incident light can be kept parallel to the plane of incidence at any point during the scan, and therefore only the light reflected from the surface of the printing plate 30 can be reliably received on the light receiving side.

Incidentally, the intensity of reflected light and refracted light on a transparent film varies depending on the angle of incidence, but is also related to the angle between the polarization plane of the incident light and the plane of incidence. When incident light has a plane of polarization parallel to the plane of incidence, the intensity of refracted light is maximum and the intensity of reflected light is minimum. On the other hand, when the incident light has a plane of polarization perpendicular to the plane of incidence, the intensity of the refracted light is minimum and the intensity of reflected light is maximum.

Therefore, in order to improve measurement accuracy, the polarizer 4 should be used so that the plane of polarization of the light incident on the printing plate 30 is parallel to the plane of incidence.
It is desirable to adjust 3.

In the above-mentioned embodiment, the case where the linearly polarized laser 41 was used as the light source was explained, but as the light source,
For example, a similar effect can be obtained by a combination of a non-polarized laser and a polarizing filter, or a combination of an ordinary incandescent light bulb, a collimator lens, and a polarizing filter. Further, in each of the examples, a printing plate for an offset printing machine was used as the object to be measured, but the present invention is not limited to this.

As described above, according to the present invention, it is possible to provide an image area measuring device that has a compact structure and can accurately measure the image area even in the case of an image whose surface is covered with a transparent film.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams for explaining the measurement principle of the conventional picture area ratio measuring device, Figure 3 is a diagram showing the basic principle of the image area measuring device, and Figure 4 is the surface to be measured in the same device. FIG. 5 is a diagram showing the light-receiving characteristics of the same device as above; FIG. 6 is a diagram explaining an image area measuring device improved from the device shown in FIG. 3; 7 is a diagram showing the positional relationship of light shielding plates in the same device as above, FIG. 8 is a diagram showing light receiving characteristics in the same device, FIG. 9 is a diagram showing an embodiment of the image area measuring device of the present invention, and FIG. is a diagram showing the arrangement relationship between the printing plate and the optical system in the same device as above,
Figures 11 and 12 are diagrams showing the photoelectric conversion section, and Figure 13 is a diagram showing the photoelectric conversion section.
The figure is a diagram for explaining polarization characteristics. 22...Stepping motor, 25A...Scanning mirror, 25B...Scanner, 26...Photomultiplier tube, 2
7... Light shielding plate, 30... Image to be measured, 32... Optical scanning section, 33... Photoelectric conversion section, 34... Analyzer, 3
5... Arithmetic unit, 41... Linearly polarized He-Ne laser, 42... 1/4 wavelength plate, 43... Polarizer. Agent Patent attorney Minoru Kinoshita (and 1 other person) Figure 1□ Figure 6 Figure 7 1゜Figure 8

Claims (9)

[Claims] (1) An image to be measured having two regions with different reflectances, a light source, a light scanning section that scans light from the light source onto the image to be measured, and a receiver that receives reflected light from the image to be measured. a photoelectric conversion unit that converts the received light into an electrical signal according to the amount of received light; and a photoelectric conversion unit that processes the photoelectrically converted electrical signal to calculate the area of at least one of the two regions of the image to be measured. a first polarizing means for converting light from the light source into circularly polarized light, and a first polarizing means synchronized with the scanning of the optical scanning section, between the light source and the optical scanning section; and a second polarizing means that is displaced to convert the light from the first polarizing means into linearly polarized light. An image area measuring device characterized by being provided with an analyzer that transmits only light having a polarization plane perpendicular to the polarization plane. (2) In claim 1, the light scanning section includes a scanning mirror that irradiates light from the light source onto the image to be measured, and the scanning mirror is arranged orthogonal to the optical axis of the light from the light source. a main scanner that rotates around an axis to scan the light from the light source in the X direction on the image to be measured;
and a sub-scanner that rotates the scanning mirror around the optical axis of the light from the light source to scan the light from the light source in the Y direction on the image to be measured. measuring device. (3) In claim 2, the image to be measured is curved in an arc shape centered on the scanning mirror and toward one of the directions scanned by a main scanner and a sub-scanner. An image area measuring device characterized by: (4) In claim 3, the photoelectric conversion section is provided between a photomultiplier tube and an image to be measured, and is arranged in a direction perpendicular to a curvature direction of the image to be measured. An image area measuring device comprising: a light shielding plate that attenuates reflected light from the image to be measured as the angle of incidence of light from the image to be measured to the photomultiplier tube decreases during scanning. (5) An image area measuring device according to any one of claims 1 to 4, characterized in that the light source is a linearly polarized laser. (6) An image area measuring device according to any one of claims 1 to 4, characterized in that the light source includes a non-polarized laser and a polarizing filter. (7) An image area measuring device according to any one of claims 1 to 6, characterized in that the first polarizing means is a quarter wavelength plate. (8) An image area measuring device according to any one of claims 1 to 7, characterized in that the second polarizing means is a polarizer. (9) An image area measuring device according to any one of claims 1 to 8, characterized in that the image to be measured is an offset printing plate.