JPH0259923B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image area measuring device for determining the area occupied by each region and its ratio for an image having two types of regions with different reflectances (hereinafter referred to as a binary image). .

Conventionally, as a device for calculating the area of a binary image,
For example, a so-called picture area ratio measurement device is known that calculates the ratio of the area of the part to which ink adheres (image area) to the area of the area to which ink does not adhere (non-image area) from the printing plate of an offset printing machine. There is. As shown in FIGS. 1 and 2, this picture area ratio measuring device has 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 produced by offset printing are usually
The size is about 0.5m x 0.5m to 1.2m x 1.4m. 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, since a fluorescent lamp is used as a linear light source, it is difficult to keep the amount of light emitted stable and uniform for a long time, and it is difficult to maintain the sensitivity of multiple photoelectric conversion elements at the same level. Since it is difficult to achieve this, 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. 3, the surface to be measured is
Two optical deflectors 13 and 14 controlled by an optical deflector control device 12 and one photoelectric converter 15 are arranged close to each other at an arbitrary point on a normal line set at the center of A laser beam from a laser 17 driven by a laser driving device 16 is directed to one optical deflector 13.
to scan the surface to be measured 11 in the X direction and the other optical deflector 14 to scan the surface to be measured 11 in the Y direction, while the reflected light from the surface to be measured 11 is received by the photoelectric converter 15. After converting it into an electrical signal, the calculation unit 18 calculates the image area of the surface to be measured 11 based on the electrical signal, and the result is outputted to the magnetic card 20 or the like via the output unit 19. It is something. 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 beam spot in the X direction when the laser beam 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 a 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 point where it intersects with is the origin O of the X direction, and from the origin O
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,
When the distance from the light receiving surface 15A 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, and the angle that the light receiving surface 15A 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 2, the solid angle α is approximately (α≪
1) α≒2/r・cosθ ...(1) In this equation (1), cosθ=z/r,
Since r ² = z ² + x ² , the amount of received light I is: I∝2/r・cosθ=2z/r ² =2z/z ² +x ²
...(2) becomes. If this is illustrated using x as a variable, it will be as shown in FIG. 5. For example, if x is about the same as z, the amount of light received at the central portion (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. As shown in FIG.
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 of the central axis of the curvature. An optical deflector 25 and a photomultiplier tube 26, which are operated by an optical deflector control device 24, are respectively attached to the mounting frame 23, and the photomultiplier tube 26 is
A light shielding plate 2 is placed between the light receiving surface 26A and the surface to be measured 11.
7 is provided, and an electric signal received and converted by a photomultiplier tube 26 is provided to a microcomputer 29 via an A/D converter 28.

Here, the scanning mirror 25A of the optical deflector 25 is positioned at the intersection of the central axis and the normal to the center of the surface to be measured 11, and the photomultiplier tube 25
When placed close to the scanning mirror 25A, 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 stepping motor 22, the surface to be measured 11 can be scanned at any position in the Y direction of the surface to be measured 11. Since the distance from the photomultiplier tube 26 to the light receiving surface 26A of the photomultiplier tube 26 is approximately constant, the amount of received light can be constant at any position in the Y direction. On the other hand, the light shielding plate 27
As shown in FIG. 7, when the light spot is located on a perpendicular line drawn from the center of the light-receiving surface 26A of the photomultiplier tube 26 to the surface to be measured 11, the amount of light shielded is maximum when the position of the light spot is at the origin o. It can be seen that the amount of light shielding decreases as the distance from the origin o increases. Therefore,
Height z from the surface to be measured 11 to the light receiving surface 26A
When the height z ₁ from the surface to be measured 11 to the light shielding plate 27 is changed, the amount of light received is as follows: As shown in Figure 8, when z ₁ = 260 mm, the line is broken, and when z ₁ = 280 mm, it is the solid line.
By changing z ₁ , the distribution of the amount of received light can be made equivalently uniform in scanning in the X direction. Incidentally, similar results can be obtained by using, in place of the light shielding plate 27, an optical filter having a concentration distribution in which the transmittance increases from the origin o toward the periphery. 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 solves the problems of the conventional example, but there may be another problem. Normally, in the case of 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, in order to prevent the hydrophilicity of non-image areas from being impaired due to oxidation due to contact with air or hand marks, the surface of the plate is coated with a transparent coating after the image area is formed by development. Covering with a rubber film (called gumming) is performed. When the surface to be measured, whose surface is protected by a transparent film, is measured using the apparatus shown in FIG. 6, when the laser beam is located at the center in the Since the portion becomes specularly reflected light from the surface of the transparent protective film, there is a problem that information corresponding to the image area of the object to be measured cannot be obtained.

In order to prevent this, for example, the scanning mirror 25A and the photomultiplier tube 25 must be
The distance between the scanning mirror 25A and the measured object may be set to be approximately the same as the distance from the scanning mirror 25A to the object to be measured. However, the maximum size of printing plates for offset printing machines is 1200 mm.
×1360mm, so in order to accurately measure the entire image area of such a large surface to be measured, the distance from the scanning mirror 25A to the surface to be measured must be
Since it needs to be about 1200mm, it is not a practical method because it is structurally unreasonable.

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 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 detected. By receiving 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 allows only light with a polarization plane perpendicular to the linearly polarized light incident on the image to be measured to pass through. The above objective is achieved by removing the reflected light from the image to be measured and having the photoelectric conversion section receive only the light parallel to the transmission axis of the analyzer from among 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 explaining the same example, the sixth
Components that are the same as those in the figures are given the same reference numerals, and their explanations will be omitted or simplified.

In this embodiment, a light source section 31 that emits linearly polarized light
and a light scanning section 3 that scans the linearly polarized light from the light source section 31 onto the printing plate 30 curved in an arc shape.
2, and 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.
, an analyzer 34 disposed on the light-receiving surface side of the photoelectric conversion section 33, and a calculation section 35 that calculates the image area of the printing plate 30 based on the signal from the photoelectric conversion section 33. .

The light source section 31 includes a linearly polarized He-Ne laser 41 and a linearly polarized He-Ne laser 41.
A quarter-wave plate 42 converts the linearly polarized light from It is composed of a polarizer 43 that makes the light incident on the scanning mirror 25A. The laser 4
The 1 and 1/4 wavelength plates 42 are arranged along the same axis as the rotation axis of the stepping motor 22 so as to share an optical axis with each other. 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). It is rotatably mounted integrally with the scanning mirror 25A.

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 scanning section 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 25A is attached to the center point P of the circular arc, and the photoelectric conversion section 33 is attached close to the 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 in the X direction of the printing plate 30 as the scanning mirror 25A is rotated about an axis perpendicular to the optical axis by the operation of the scanner 25B. As the scanning mirror 25A is rotated about the optical axis by the operation of the stepping motor 22, the printing plate 30 is scanned in the Y direction.

Further, the photoelectric conversion section 33 is connected to the mounting frame 23.
It consists of a photomultiplier tube 26 attached via a holder 61 to the photomultiplier tube 26, and a light shielding plate 27 for equalizing the amount of light received by the photomultiplier tube 26 when scanning the printing plate 30 in the X direction. ing. As shown in FIGS. 11 and 12, the holder 61 has a light receiving hole 62 formed at a position corresponding to the light receiving surface of the photomultiplier tube 26, and is located on the opening surface side of the light receiving hole 62. The fixing screw 6 is used to adjust the distance g between the light shielding plate 27 and the holder 61.
It is attached by 3.

Further, the analyzer 34 is shown in FIGS.
As shown in FIG. 2, the holder 6 is adjusted so that its transmission axis is perpendicular to the transmission axis of the polarizer 43.
It is attached to the opening surface of the light receiving hole 62 of No. 1. Therefore, the reflected light from the printing plate 30 is subjected to a uniform positive effect by the light shielding plate 27, and then enters the analyzer 34. Then, this analyzer 34 detects the printing plate 30.
Only reflected light having a polarization plane perpendicular to the polarization plane of the incident light is transmitted and photoelectrically converted by the photomultiplier tube 26.

Further, the calculation unit 35 includes the photomultiplier tube 2
6, the A/D converter 28 converts the photoelectrically converted signal into a digital signal, and operates the stepping motor 22 and the scanning section 25B according to a predetermined program. A microcomputer 29 calculates the image area of the printing plate 30 based on information given from the device 28. The microcomputer 29 causes the light from the light source section 31 to scan the printing plate 30 in the X direction through the operation of the scanner 25B, and in the scanning in the X direction, the photoelectric conversion section 33
The device sequentially captures data given from the computer at predetermined timing and sequentially stores it in a predetermined storage area. 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 section 33 is They are sequentially captured at predetermined timings and sequentially added to designated storage areas. By repeating this process, the entire surface of the printing plate 30 is scanned. This allows the storage area to contain
The cumulative value in the Y direction is stored for each predetermined unit along the X direction.

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

Next, the operation of this embodiment will be explained. Laser light emitted from the linearly polarized laser 41 is converted into light having circularly polarized characteristics by passing through the 1/4 wavelength plate 42 . The light that passed through the 1/4 wavelength plate 42 is
The polarizer 43 converts the light into linearly polarized light again. At this time, the polarization plane of the light from the polarizer 43 is
However, since the incident light from the 1/4 wavelength plate 42 is circularly polarized, the polarizer 4
The linearly polarized light extracted in step 3 is uniform at any angle. The linearly polarized light from the polarizer 43 is reflected by the scanning mirror 25A and irradiated onto the printing plate 30, and as the scanning mirror 25A is rotated by the scanner 25B and the stepping motor 22, the printing plate 30 is reflected in the X direction and the Y direction. scanned in the direction. At this time, the polarizer 43 and the scanning mirror 25
Since it is rotated together with A, the polarizer 43
The polarization plane of the linearly polarized light after passing through the scanning mirror 25
The relative angle between A and the plane of incidence (the plane containing the incident light and reflected light) is always constant at any angular position of the rotation of the scanning mirror 25A in the Y direction. Therefore, at any position of the printing plate 30 in the Y direction, the plane of polarization and the plane of incidence of the irradiated light are always kept constant.

Now, as shown in FIG. 13, the surface is a transparent film 30.
When reflected light from the scanning mirror 25A is incident on the printing plate 30 covered with A, the incident light is separated into reflected light and refracted light on the surface of the transparent film 30A. This reflected light is linearly polarized light with the same polarization plane as the incident light, and 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 first passes through the light shielding plate 27.
After receiving the uniform light reception correction effect, the analyzer 34
reach. Since the transmission axis of the analyzer 34 is adjusted to be perpendicular to the transmission axis of the polarizer 43, that is, the polarization plane of the light incident on the printing plate 30, the specularly reflected light from the surface of the transparent film 11A is absorbed, and the printing Of the light reflected from the surface of the plate 30, only light having a polarization plane parallel to the transmission axis of the analyzer 34 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 scanned between the photomultiplier tube 26 and the printing plate 30 on the light receiving side. Since the analyzer 34 that transmits only light having a polarization plane perpendicular to the incident light on the plate 30 is provided, when measuring the printing plate 30 whose surface is covered with the transparent film 30A, the transparent film 30
The specularly reflected light from the surface of A is removed, and the printing plate 30
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, without being affected by the light reflected from the surface of the transparent film 30A. Image area can be measured accurately. Moreover, 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 laser 41
The linearly polarized light emitted from the 1/4 wavelength plate 42 converts the linearly polarized light into light having circularly polarized light characteristics, and the transmitted light is incident on the printing plate 30 by the polarizer 43 that rotates integrally with the scanning mirror 25A. When the scanning mirror 25A scans the printing plate 30 in the X and Y directions, the transmitted light is converted into linearly polarized light with a plane of polarization parallel to the plane of incidence. The plane of polarization of the incident light can be kept parallel to the plane of incidence, 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 incident angle, but is also related to the angle between the polarization plane of the incident light and the incident plane. 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, it is desirable to adjust the polarizer 43 so that the plane of polarization of the light incident on the printing plate 30 is parallel to the plane of incidence.

In addition, in the above-mentioned embodiment, the case where the linearly polarized laser 41 was used as the light source was explained.
Similar effects can be obtained by using, for example, a combination of a non-polarized laser and a polarizing filter as a light source, 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; FIG. 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,
FIG. 10 is a diagram showing the arrangement relationship between the printing plate and the optical system in the above apparatus, FIGS. 11 and 12 are diagrams showing the photoelectric conversion section, and FIG. 13 is a diagram for explaining the light shielding characteristics. 22... Stepping motor, 25A... Scanning mirror, 25B... Scanner, 26... Photomultiplier tube, 27... Light shielding plate, 30... Image to be measured, 32
...Light scanning unit, 33...Photoelectric conversion unit, 34...Analyzer, 35...Arithmetic unit, 41...Linearly polarized He
-Ne laser, 42...1/4 wavelength plate, 43...polarizer.

Claims (1)

[Scope of Claims] 1. A device for measuring the image area of an image to be measured having two regions with different reflectances, comprising: a light source; and a light scanning unit that scans light from the light source onto the image to be measured. a photoelectric conversion unit that receives reflected light from the image to be measured and converts it into an electrical signal according to the amount of received light; and a photoelectric conversion unit that processes the electrical signal photoelectrically converted by the photoelectric conversion unit to convert the reflected light from the image to be measured. a calculation unit that calculates the area of at least one of the two regions, and a first polarized light that converts the light from the light source into light having circular polarization characteristics, between the light source and the light scanning unit. and a second polarizing means that is displaced in synchronization with the scanning of the optical scanning section and converts the light from the first polarizing means into linearly polarized light, and on the light receiving surface side of the photoelectric conversion section. An image area measuring device comprising: an analyzer that transmits only light having a polarization plane perpendicular to the polarization plane of the linearly polarized light incident on the image to be measured. 2. In claim 1, the optical scanning unit includes a scanning mirror that irradiates light from the light source onto the image to be measured, and an axis perpendicular to the optical axis of the light from the light source. a main scanner that rotates around the center to scan light from the light source in the X direction on the image to be measured; and a main scanner that rotates around the optical axis of the light from the light source to scan the light from the light source on the image to be measured. An image area measuring device comprising: a sub-scanner that scans light in the Y direction on the image to be measured. 3. In claim 2, the image to be measured is curved in an arc shape centered on the scanning mirror and in one of the directions scanned by the main scanner and the sub-scanner. An image area measuring device characterized by: 4. In claim 3, the photoelectric conversion unit is provided between a photomultiplier tube and an image to be measured, and is scanned in a direction orthogonal 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 incident angle of light from the image to be measured to the photomultiplier tube is smaller. 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. In any one of claims 1 to 4, the light source is a non-polarized laser;
An image area measuring device comprising: 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.