JP4581763B2 - Image input device and image evaluation device - Google Patents

Description

  The present invention relates to an image input apparatus for evaluating a two-dimensional image and an image evaluation apparatus using the same, and in particular, evaluates a monochrome image and color image information output by an image output apparatus such as a monochrome copy or a color hard copy. The present invention relates to an image input apparatus and an image evaluation apparatus using the same.

  When evaluating image quality, there are psychological evaluation for quantifying the degree of image quality perceived by humans and physical characteristics for evaluating physical characteristics of the image itself with a measuring machine. Psychological evaluation is widely used for final inspections of products, but has disadvantages such as different inspectors and changes in test results due to fatigue of the inspectors.

  On the other hand, as an image quality evaluation method, for example, there is an image evaluation method and apparatus described in Patent Document 1. This image evaluation apparatus converts image information including two-dimensional position information and optical information into color information, and converts the converted two-dimensional information into two-dimensional spatial frequency information by frequency analysis. After the spatial frequency information is made one-dimensional, correction corresponding to the spatial frequency characteristic of human vision is applied, and not only density (lightness) information but also saturation information and hue information as color information can be detected. it can.

  Conventionally, the image information of the inspection image was quantified using a photomultiplier, a spectral filter, etc., but since a measurement time is required, a method for quantifying the image information using a line sensor or an area sensor has been devised recently. Yes.

  With the recent improvement in image quality of image output devices, high resolution is also required for imaging resolution when performing image evaluation. A high-resolution lens is used to capture the evaluation image at a high resolution. However, there is a disadvantage that the depth of focus becomes shallow as the resolution of the lens increases, and if the optical adjustment is not performed properly, the captured image will be blurred. There was a problem that it would occur. For example, in order to observe an image with high resolution, an image quality measuring device converts a minute area into an image signal using a CCD or the like. As an example, when an optical resolution is 10 μm, the lens has an area of 10 μm square. An image is formed on one pixel of a CCD, and the lens has a shallow depth of focus in order to capture an image with a sufficient resolution in an area of 10 μm square, and the distance between the measurement target and the lens needs to be kept constant.

  On the other hand, there is a method of measuring the distance from the evaluation image and performing feedback. For example, it is possible to irradiate the evaluation image with laser light and measure the distance from the evaluation image using a method such as a change in the light receiving position of the reflected light, a phase difference of the laser light, or a reflection time of the laser light. For example, in order to capture an image with high MTF characteristics in a scanner, a method has been proposed in which a distance from a document placed on a document table is measured and focus adjustment is performed according to the measurement result (see, for example, Patent Document 2). ).

  However, since the image evaluation apparatus needs to capture the evaluation image with high resolution and high gradation, a desired amount of reflected light from the evaluation image is required for one pixel of the image sensor, and a sufficient amount of light is given even in a minute region. Therefore, a large amount of light is required for the light source that illuminates the evaluation image. For this reason, when distance measurement using a laser is performed under illumination of an evaluation image, illumination light may be disturbed and distance measurement may become unstable.

  The frequency of occurrence of this phenomenon also depends on the contents of the evaluation image. In other words, there are unique parts such as high-density images in the evaluation image.For example, the high-density part is less likely to cause false detection of distance measurement due to less laser reflected light, There was a problem that a distance sensing error occurred due to attached dust or the like. This phenomenon will be described with reference to FIG.

  First, FIG. 7a shows an example of an overall view of an evaluation image used for image evaluation. In the image evaluation, various evaluation images 206 are arranged in order to perform image measurement of line image quality and surface image quality. FIG. 7b shows a partially enlarged view of FIG. 7a. When the distance to the evaluation image 206 is measured by the triangulation method using the light emitting element 208 and the light receiving element 209, the laser light is reflected when the dark portion of the evaluation image is measured. Less light. On the other hand, the evaluation image is irradiated with strong illumination light in order to quantize the evaluation image for each fine area by the image sensor, and the reflected light of the illumination light is also incident on the light receiving element 209 for distance measurement. The light intensity distribution on the CCD provided for detecting the light receiving position as the light receiving element 209 cannot accurately calculate the light receiving position of the reflected light of the laser light when the illumination light is incident in addition to the laser light.

  On the other hand, as shown in FIG. 7c, a method of suppressing disturbance caused by illumination light by providing a narrowband interference filter 210 or the like that transmits only the wavelength of laser light on the front surface of the light receiving element 209 is generally used. When the intensity of light is high and the wavelength of the laser light is included in the illumination light itself used for image evaluation, the effect is limited because the illumination light passes through the interference filter 210, and the laser light receiving position is determined. It becomes impossible to calculate accurately. Of course, there is also known a method of increasing the detection level at the light emitting / receiving portion of the distance measuring system such as the sensitivity / integration time change of the light receiving element 209 or the laser intensity / irradiation time change, but it does not lead to reliable distance detection. . That is, the distance measurement becomes unstable when the intensity of the illumination light is larger than the reflected light from the evaluation image of the laser light used for the distance measurement.

  The above-mentioned problem has been described with the triangulation method as an example, but it is not a problem that occurs only in the triangulation method, but also with a method using a method such as a phase difference of laser light or a reflection time of laser light. Needless to say, this is a problem that can occur in all distance measurement methods using laser light. To solve this problem, a laser line generator such as a cylindrical lens or a rod lens is used to convert the laser light for distance measurement into a line shape and expand the reflection area for distance measurement to irradiate the reflected light with a cylindrical lens, etc. A method has been proposed in which an image is formed on a light receiving element by using a light to smooth a weak portion and a strong portion of reflected light, and measure from the change in the light receiving position.

  FIG. 8a shows an example in which laser light is converted into a line shape using a cylindrical lens or the like. The laser beam from the semiconductor laser 208 is converted into a line shape using a laser line generator such as a cylindrical lens 212 and irradiated to an evaluation image for distance measurement. The linear reflected light from the evaluation image enters the cylindrical lens 212, forms an image on the surface of the CCD element that is the light receiving element 209, the reflected light position is calculated using a control circuit (not shown), and the triangulation method is performed from the reflected light position. Is used to calculate the distance.

  However, because the laser radiation angle is limited, it is smaller than the captured image in the evaluation image. Especially when the line image evaluation direction matches the direction converted by the laser line generator when performing line image evaluation etc. There is no effect at all. Furthermore, since the laser light is converted into a line shape, the desired area of the evaluation image can be smoothed, which is effective for distance measurement stability, but the laser intensity per unit area of the evaluation image is reduced. For this reason, if the reflected light is used as it is, the reflected light intensity is small and weak against disturbance, and even if the reflected light is collected using a cylindrical lens or the like, the disturbance is also collected, so that no effect is obtained. Of course, it is possible to measure the distance without illuminating the evaluation image with the illuminating light as disturbance light, save the distance measurement result in the storage means, and perform the image evaluation based on the result. There is a problem that it takes very much.

  In addition, as shown in FIG. 8b, it is possible to perform multipoint distance measurement by providing a plurality of semiconductor lasers 208 and a light receiving element 209 paired with a laser instead of converting the laser into a line shape. It becomes expensive and has practical problems. Although it is conceivable to split the laser beam with a beam splitter or the like here, the intensity of the laser beam is lowered for the above-described reason, and therefore the influence of the disturbance of the illumination beam is caused. Although it is possible to reduce the number of CCDs by using, large area CCDs are expensive, and thus cost problems remain.

An object of the present invention is to provide an image input device capable of adjusting the focus by stably measuring the distance between the evaluation image and the imaging device even when there is a disturbance such as the surface state of the evaluation image or the evaluation image illumination light. An object of the present invention is to provide a used image evaluation apparatus.
JP-A-5-284260 JP-A-4-56564

  In consideration of the above-described facts, the present invention provides an image input device capable of performing focus adjustment by stably measuring the distance between an evaluation image and an imaging device even when there is a disturbance such as a surface state of the evaluation image or evaluation image illumination light. It is another object of the present invention to provide an image evaluation apparatus using the same.

The image input apparatus according to claim 1, an imaging unit that captures an object to be imaged, an illuminating unit that illuminates the object to be imaged, and a distance measuring unit that measures a distance between the object to be imaged and the imaging unit. A focal length adjusting unit that adjusts a focal length of the imaging unit based on a measurement result of the distance measuring unit, wherein the distance measuring unit applies a two-dimensional laser beam to the object to be imaged. A laser beam scanning unit that scans automatically, and a light receiving unit that receives laser light diffusely reflected by the object to be imaged, and measures the distance from the light receiving position information on the light receiving unit to the surface of the object to be imaged It is characterized by doing.

  In the invention having the above-described configuration, the object to be imaged is two-dimensionally scanned with the laser beam used for distance measurement, so that reliable distance measurement can be performed regardless of the contents of the object to be imaged, and a clear image can be captured.

  The image input apparatus according to claim 2, wherein the object to be imaged is an evaluation image.

  In the invention with the above-described configuration, it is possible to reliably measure the distance regardless of the contents of the evaluation image by scanning the laser beam used for distance measurement two-dimensionally, and it is possible to capture a clear image necessary for image evaluation.

  According to a third aspect of the present invention, the light receiving element of the light receiving means is a CCD element.

  In the invention having the above-described configuration, a general CCD can be used as the light receiving unit, whereby an image input apparatus with high accuracy and low cost can be obtained.

  According to a fourth aspect of the present invention, the light receiving element of the light receiving means is an optical position detecting element.

  In the invention with the above configuration, by using the optical position detection element as the light receiving element, it is possible to obtain a highly accurate image input device having excellent position resolution and responsiveness.

The image input device according to claim 5 is characterized in that the laser beam scanning means uses a laser light source that emits laser light and a polygon mirror .

In the invention having the above configuration, by deflecting the laser beam using the polygon mirror, it is possible to perform reliable distance measurement using a normal laser light source, and it is possible to capture a clear image necessary for image evaluation.

The image input apparatus according to a sixth aspect is characterized in that the laser beam scanning means is a surface emitting laser.

  In the invention with the above configuration, the use of a surface emitting laser eliminates the need for a deflecting device, enables reliable distance measurement with a simple configuration, and enables imaging with a clear image.

In the first aspect 7, the sharpness by using the image input apparatus according to any one of claims 1 to 6, graininess, and for any or a plurality of items of gradation The evaluation image is evaluated .

  In the invention with the above-described configuration, the evaluation image is two-dimensionally scanned with the laser beam used for distance measurement, thereby enabling reliable distance measurement regardless of the content of the evaluation image, and taking a clear image necessary for image evaluation. Is possible.

  Since the present invention has the above-described configuration, an image input device capable of stably adjusting the focus by stably measuring the distance between the evaluation image and the imaging device even in the presence of disturbance such as the surface state of the evaluation image or the evaluation image illumination light. And an image evaluation apparatus using the same.

  Hereinafter, an image evaluation apparatus according to the present invention will be described with reference to the drawings.

<First Embodiment>
FIG. 1 is a block diagram showing a hardware configuration example of an image evaluation apparatus according to the first embodiment of the present invention.

As shown in FIG. 1, the image evaluation apparatus 10 according to the present embodiment includes a drive device 11 (corresponding to “focal length adjusting unit” according to claim 1 ) and an illumination device 12 (with “illumination according to claim 1”). Means ” , a distance measuring device 13 (corresponding to“ distance measuring means ”described in claim 1), and an imaging device 14 including an imaging element 21 and a lens 22 (“ imaging means ”described in claim 1). and equivalent) to performs a control device 15 is constituted from the arithmetic unit 16, imaging evaluation image 25, the evaluation. The drive device 11 changes the relative positional relationship between the imaging device 14 and the evaluation image 25, and the illumination device 12 illuminates the evaluation image with a desired illuminance. The imaging device 14 includes an imaging element 21 and captures an evaluation image 25 and the like. The distance measuring device 13 measures the distance between the evaluation image 25 and the imaging device 14 and the like. The control device 15 controls the drive device 11, the illumination device 12, and the imaging device 13 based on the result of the arithmetic device 16, and in particular, drives the drive device 11 from the measurement result of the distance measurement device 13 and evaluates the evaluation image in the imaging device 14. The focus adjustment is performed so that the focal length of the imaging device 14 becomes equal to the measurement result at the time of 25 imaging.

  Next, the operation of the image evaluation apparatus of the present embodiment configured as described above will be described with reference to the flowchart shown in FIG.

  First, in step S101, the image evaluation apparatus is initialized and the origin is returned to grasp the positional relationship within the image evaluation apparatus 10. Next, in step S102, the illumination device 12 is turned on in order to obtain a light amount necessary for image input of the evaluation image 25. Next, in step S103, a white reference plate, a light shielding state signal, and the like that are provided in advance to perform gain adjustment of the image sensor 21 after the light amount of the illumination device 12 is stabilized are input.

  In step S104, the shading correction coefficient of the image sensor 21 is determined based on the result obtained in step S103. The shading correction method is not described in detail because various correction methods are generally known, but the correction coefficient of the image sensor 21 is determined by shading correction that is not particularly limited. In step S105, the evaluation image 25 is placed on the stage 23 and the stage 213 is driven in one direction. Next, in step S106, the distance to the evaluation image 25 is captured using two-dimensional information.

  Next, in step S107, in order to capture an image with the image sensor 21 that is a one-dimensional line sensor, the distance to the imaged position is calculated from the result of step S106 by interpolation of two-dimensional position information. Although a detailed description of the interpolation method is omitted, a generally known interpolation method such as a spline may be used, and the interpolation method is not particularly limited.

Next, in step S108, the focal length adjustment unit performs focal length adjustment based on the distance measurement result obtained by interpolation in step S107. Next, in step S109, a signal from a linear scale that is linked to the driving device 11 that drives the stage 23 is input, and it is determined whether or not the stage 23 has moved to the location where the image sensor 21 captures an image. If not, the stage 23 is further driven until the imaging position is reached.

  In this embodiment, the position of the stage 23 is detected from a signal from a linear scale provided along with the stage 23 to determine whether or not it is an imaging position. However, the signal processing speed and the stability during driving of the stage 23 are determined. In consideration, the imaging timing may be calculated from the stage drive speed asynchronously with the linear scale signal.

  Next, in step S110, the evaluation image 25 is captured. Next, in step S111, the image signal captured by image capturing is corrected using the shading correction coefficient calculated in step S104. In this embodiment, the shading correction is performed after step S110. However, when the processing speed does not follow, the shading correction may be performed after all the evaluation image data is captured.

  Next, in step S112, it is determined whether or not imaging of all desired regions of the evaluation image 25 has been completed. If not completed, the process returns to step S105, and imaging of the evaluation image 25 is continued until completion. Next, in step S113, the illumination device 12 is turned off.

  Next, in step S114, the captured image is evaluated. Although details of the evaluation method are omitted, for example, sharpness, graininess, gradation, and the like are evaluated. Although detailed description regarding image evaluation items, evaluation algorithms, and the like is omitted, a general image evaluation algorithm may be used, and the image evaluation method and contents are not particularly limited.

  In step S115, the image evaluation result is stored. Here, in addition to the evaluation result, items such as the imaging data of the evaluation image 25 and the imaging date and time may be stored together.

  FIG. 3 shows the configuration of the image evaluation apparatus according to this embodiment.

  As shown in FIG. 3, the image evaluation apparatus 10 arranges the evaluation image 25 on the document table 23, illuminates the evaluation image 25 with the illumination devices 12 a and 12 b, and reflects the reflected light to the image sensor 21 via the lens 22. An image is formed and an evaluation image 25 is captured.

  Since the image pickup device 21 is a line CCD, an evaluation image is picked up while the image pickup device 21, the lens 22, and the illumination devices 12a and 12b are driven in a direction substantially perpendicular to the CCD arrangement of the line CCD (arrow in the figure). The imaging is repeated until the imaging of the area is completed. At this time, distance measurement is performed by the distance measuring device 13 as described above.

  FIG. 4 shows details of the distance measuring apparatus according to this embodiment.

  As shown in FIG. 4, the laser light emitted from the semiconductor laser 28 is deflected into a two-dimensional surface by the polygon mirror 20 and then irradiated onto the evaluation image, and the reflected light is received by the light receiving element 29 which is a two-dimensional CCD. To do.

At this time, a reflected light position on the light receiving element 29 is calculated using a control circuit (not shown), and a distance from the reflected light position to the evaluation image 25 is calculated using a triangulation method. Based on the calculation result, the focal length at the time of shooting is properly maintained by the focal length adjusting means ( not shown).

  Here, a laser irradiation method to a two-dimensional surface by a polygon mirror will be described with reference to FIG.

  FIG. 5 shows a distance measuring method according to this embodiment.

  As shown in FIG. 5, the mirror surface 20a of the polygon mirror 20 is intentionally tilted or distorted so that the laser beam L scans a desired region of the evaluation image 25 two-dimensionally as the polygon mirror 20 rotates. Is provided. As a result, the laser beam L can be two-dimensionally irradiated within the range where distance measurement is required as the polygon mirror 20 rotates, and distance measurement can be performed while avoiding unstable portions of distance measurement.

  FIG. 5 b shows the locus of laser light on the evaluation image 25. Here, as an example of the trajectory of the laser beam L, an example of the trajectory of the laser beam L by a four-sided mirror is shown. The laser beam L reflected by the mirror surface 20a of the polygon mirror 20 irradiates the evaluation image two-dimensionally by irradiating the surface of the evaluation image 25 vertically and horizontally as shown in FIG. 5b.

  By receiving the laser beam L irradiated on the two-dimensional surface, it is possible to measure the distance of the evaluation image 25 in two dimensions, and it is possible to reliably perform the measurement without being affected by disturbances such as a high density portion or dust in the evaluation image 25. In addition, the distance between the evaluation image 25 and the imaging device 14 can be measured. Further, since the laser light L is not converted into splits or lines, sufficient laser intensity can be secured, and stable distance measurement can be performed even in an environment where disturbance such as illumination light exists.

  In the embodiment described above, the laser light L from the polygon mirror 20 is directly applied to the evaluation image 25. However, the laser light L may be collimated by a collimator lens or the like after passing through the polygon mirror 20 in order to perform more accurate distance measurement. In the above embodiment, the polygon mirror 20 having the distorted mirror surface 20a is used as a method of irradiating the two-dimensional surface of the laser beam L. However, the deflection method of the laser beam L is not limited to the polygon mirror 20, and for example, Needless to say, a galvanometer mirror may be used, or the semiconductor laser itself may be two-dimensionally vibrated by a vibration device such as a piezoelectric element, and the method of changing the laser beam is not limited.

<Second Embodiment>
A second embodiment according to the present invention will be described with reference to FIG.

  FIG. 6 shows a distance measuring device according to the second embodiment of the present invention.

  In the present embodiment, a surface emitting laser 35 is used as a semiconductor laser for measuring the distance from the evaluation image 25. As an example, the evaluation image 25 is irradiated with laser light L from a surface-emitting laser 35 constituted by a 100 × 100 two-dimensional array, the reflected light is received by a light receiving element 29, and evaluation is performed from the calculation result of the light receiving position of the laser light L. The distance to the image 25 is measured, and the focus control of the image pickup system is performed as in the first embodiment.

  As a result, by receiving the laser beam L irradiated to the two-dimensional surface of the evaluation image 25, it becomes possible to measure the distance to the evaluation image 25 in two dimensions, and disturbances such as high-density portions and dust in the evaluation image 25 Thus, the distance between the evaluation image 25 and the imaging device 14 can be reliably measured without being affected by the above.

  As described above, according to the image evaluation apparatus according to each embodiment of the present invention, even if there is a disturbance such as illumination light intensity, density of the evaluation image portion, unevenness of the evaluation image, dust attached to the evaluation image, etc. Therefore, it is possible to accurately measure the distance from the evaluation image, and it is possible to capture a clear and focused image.

It is a block diagram which shows the hardware structural example of the image evaluation apparatus which concerns on the 1st Example of this invention. It is a process flowchart of the image evaluation apparatus which concerns on the example of 1st Embodiment of this invention. It is a perspective view which shows the structure of the image evaluation apparatus which concerns on the 1st Example of this invention. It is a perspective view which shows the structure of the distance measuring device which concerns on the example of 1st Embodiment of this invention. It is a figure which shows operation | movement of the distance measuring device which concerns on the example of 1st Embodiment of this invention. It is a perspective view which shows the structure of the distance measuring device which concerns on 2nd Example of this invention. It is a figure which shows operation | movement of the conventional distance measuring apparatus. It is a figure which shows operation | movement of the conventional distance measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image evaluation apparatus 11 Drive apparatus 12 Illumination apparatus 13 Distance measuring apparatus 14 Imaging apparatus 15 Control apparatus 16 Arithmetic apparatus 20 Polygon mirror 21 Imaging element 22 Lens 23 Stage 25 Evaluation image 28 Semiconductor laser 29 Light receiving element 35 Surface emitting laser

Claims (7)

Imaging means for imaging an object to be imaged;
Illumination means for illuminating the object to be imaged;
Distance measuring means for measuring the distance between the object to be imaged and the imaging means;
A focal length adjusting unit that adjusts a focal length of the imaging unit to be equal to the measurement result based on a measurement result of the distance measuring unit;
The distance measuring means is a laser light scanning means for two-dimensionally scanning the object to be imaged with laser light;
Light receiving means for receiving laser light diffusely reflected by the object to be imaged, and
An image input apparatus for measuring a distance from light receiving position information on the light receiving means to a surface of the object to be imaged.   The image input apparatus according to claim 1, wherein the imaged object is an evaluation image.   3. The image input device according to claim 1, wherein the light receiving element of the light receiving means is a CCD element.   3. The image input device according to claim 1, wherein the light receiving element of the light receiving means is an optical position detecting element.   5. The image input apparatus according to claim 1, wherein the laser light scanning unit uses a laser light source that emits laser light and a polygon mirror. 6.   6. The image input device according to claim 1, wherein the laser beam scanning unit is a surface emitting laser.   An image evaluation apparatus that evaluates an evaluation image for any one or a plurality of items of sharpness, graininess, and gradation using the image input apparatus according to claim 1.

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