JP2007104575A - Image evaluation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide techniques for suppressing deterioration in the service life of a lamp while adopting a scheme of enhancing light emission wavelength property by increasing a light emission intensity of the lamp for illumination in an image evaluation apparatus. <P>SOLUTION: A controller 401 determines whether or not an image evaluation mode selected by a user via a UI unit 404 is a mode paying attention to coloring. In the case of the mode paying attention to coloring, a lamp voltage control circuit 403 is instructed to apply a voltage of a predetermined high level to a lamp 402 and a relative intensity of a B (blue) component in the light emission of the lamp 402 is improved. In the case of a mode not paying attention to coloring, on the other hand, even if the B component is weak, there is no problem, thereby instructing the lamp voltage control circuit 403 to apply a voltage of a predetermined low level to the lamp 402. Since a high level is not required at all the time, deterioration in the service life of the lamp can be relaxed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image evaluation apparatus for evaluating monochrome image and color image information output by an image output apparatus such as a monochrome copy or a color hard copy.

  When evaluating image quality, there are psychological evaluation for quantifying the degree of image quality perceived by humans and physical evaluation 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 a physical evaluation method of image quality, for example, there is an image evaluation 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 has been quantified using a precise device configuration such as a photomultiplier tube and a spectral filter. However, since measurement requires time and cost, recently, image data using a line sensor or area sensor has been used. Methods for quantifying information have been devised. As such a method, there is one disclosed in Patent Document 2. In the method of this document, color information of a color image is obtained together with two-dimensional position information by reading the measurement object using an inexpensive scanner, and the image quality of the measurement object is evaluated based on the information. .

  With the recent improvement in image quality of image output devices, high resolution is also required for imaging when performing image evaluation. In order to capture an evaluation image with high resolution, it is possible to improve the measurement accuracy by obtaining an output with a high S / N ratio so that the output from each minute pixel of the image sensor, which is a light receiving element, is sufficiently large against noise. It becomes extremely important for. For this purpose, it is necessary that the amount of light emitted from the illumination light source to the measurement object is sufficiently large.

  In addition, in order to evaluate a color image, not only the amount of light but also the spectral emission characteristics of the light source are important. If there is wavelength discontinuity or lack of light quantity as spectral emission characteristics within the visible wavelength range of 400 to 700 nm, color information cannot be accurately measured. Thus, considering both the light quantity and the spectral emission characteristics, it can be said that a heat radiation light source such as a halogen lamp is suitable as the type of light source. In the case of other light sources such as fluorescent lamps and discharge lamps, strong light emission (bright line) appears at a specific wavelength due to the light emission principle, which tends to cause a problem in terms of wavelength continuity, and it is difficult to obtain a large amount of light.

  A halogen lamp is a light source that is excellent in terms of wavelength continuity and light emission intensity, but has a property that a short wavelength component has a lower intensity than a long wavelength component. For this reason, among the red (R), green (G), and blue (B) components included in the emission wavelength, the B component on the shortest wavelength side is relatively weak. Further, the spectral sensitivity of a CCD as an image sensor is high on the long wavelength side and low on the short wavelength side. Due to these synergistic effects, the SN ratio of the B component of the image sensor output is relatively deteriorated.

  Therefore, Patent Documents 3 and 4 show examples of controlling the light amount in order to correct the RGB balance of the light source, so-called white balance. An example of optimizing the B component image sensor electrification accumulation time in order to correct the RGB sensitivity difference caused by the spectral sensitivity of the image sensor is disclosed in Patent Document 5.

JP 05-284260 A Japanese Patent Laid-Open No. 10-023191 JP 05-316519 A JP 05-328386 A Japanese Patent Laid-Open No. 08-307601

  As described above, conventionally, various corrections have been performed using an additional mechanism in order to prevent a relative decrease in the SN ratio of the B component. However, since these mechanisms are provided, the mechanism is complicated and the cost is increased.

  As a means for increasing the B component, which is a short wavelength, while avoiding such a complicated mechanism and an increase in cost, a measure of increasing the filament temperature by increasing the voltage applied to the lamp can be considered. However, as the applied voltage increases, the lamp life tends to decrease. When the rated voltage of the lamp is exceeded, there is a problem that the lamp life significantly decreases.

  The present invention provides a technique for suppressing deterioration of lamp life while adopting a method of improving emission wavelength characteristics by increasing the emission intensity of an illumination lamp.

  An image evaluation apparatus according to the present invention is an image evaluation apparatus that illuminates an evaluation target image with a heat radiation type light source, detects reflected light from the evaluation target image, and evaluates the evaluation target image. And a control means for controlling the level of power supplied to the light source according to the mode determined by the determination means.

  In a preferred aspect of the present invention, the determination unit determines whether or not the image evaluation mode is a mode that focuses on color, and the control unit determines that the mode is an evaluation mode that focuses on color. The level of power supplied to the light source is set to a first level, and the level of power supplied to the light source is set to a second level lower than the first level in an evaluation mode not paying attention to color.

  In another preferred aspect, the determination means determines whether or not the image evaluation mode is an evaluation mode for evaluating an image of a yellow color material, and the control means determines that the mode is a yellow color material. If the evaluation mode is to evaluate an image, the level of power supplied to the light source is set to the first level. If the evaluation mode is not to evaluate the image of the yellow color material, the level of power supplied to the light source is lower than the first level. The second level.

  In still another preferred aspect, the determination unit determines whether or not the image evaluation mode is a mode in which a blue component of reflected light from the evaluation target image is used for evaluation, and the control unit determines that the mode is blue. If the mode uses the component for evaluation, the level of power supplied to the light source is set to the first level. If the mode does not use the blue component for evaluation, the level of power supplied to the light source is set to a second level lower than the first level. Level.

  In still another preferred aspect, the determination unit receives a selection of an image evaluation mode from a user, and determines the mode based on the selection result.

  In still another preferred aspect, the discrimination means discriminates the type of the evaluation target image by pre-scanning the evaluation target image, and discriminates the image evaluation mode based on the type.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, a schematic configuration of hardware of the image evaluation apparatus is shown in FIG. In this apparatus, an evaluation object original 104 is placed on an original platen 105, the evaluation object original 104 is illuminated by the illumination devices 103a and 103b, and reflected light is imaged on the image sensor 101 via the lens 102 to evaluate the object. The original 104 is imaged. In this example, the image sensor 101 is a line CCD, and the evaluation target document 104 is imaged while the image sensor 101, the lens 102, and the illumination devices 103a and 103b are driven substantially perpendicular to the CCD array of the line CCD. The imaging is repeated until the imaging of the area is completed.

  An example of the structure of the lighting devices 103a and 103b is shown in FIG. One lighting device is a combination of a line-shaped halogen lamp tube 201 and a condensing reflecting plate 202 accommodated in a housing 203. An air cooling fan 204 is installed on the back side of the reflecting plate 202 so as to cool the heat generated by light emission. A heat ray absorption filter 205 for removing infrared rays is installed on the light emitting surface side.

  As shown in FIG. 3, the line-shaped halogen lamp tube 201 is generally constructed by stretching a tube 301 in which a gas containing a halogen gas is sealed, in which a plurality of filaments 302 are connected. . Examples of the halogen gas include iodine (I), bromine (Br), chlorine (Cl), and fluorine (F). Tungsten is generally used for the filament 302, and tungsten evaporated from the filament reacts with the halogen gas, and returns to the filament again through a series of reactions called a so-called halogen cycle. As described above, since the halogen gas is effective for preventing evaporation of tungsten, as a result, the efficiency and life of the lamp can be improved. As characteristics of the halogen lamp, a relatively large amount of light can be easily obtained compared to other light sources such as a discharge tube and a fluorescent lamp, and since the emission spectral characteristics are continuous, it is desirable from the viewpoint of color measurement.

  Although it is a halogen lamp having such excellent characteristics, although its emission wavelength distribution is continuous, as shown in FIG. 4, the emission intensity of the short wavelength component is relatively weak compared to the long wavelength. Have. This is because the light emitted from the halogen lamp uses thermal radiation. As shown by the Planck radiation law, the temperature of the filament, which is the light emitter, increases from the infrared region to the visible wavelength region, that is, from the long wavelength side to the short wavelength side. This is because the intensity increases relatively in the wavelength side direction. However, in a tungsten filament used in a general halogen lamp, the color temperature is as low as about 3000 K, and the short wavelength component is actually relatively weak.

  For this reason, among the red (R), green (G), and blue (B) components included in the emission wavelength, the B component on the shortest wavelength side is relatively weak. Further, the spectral sensitivity of a CCD as an image sensor is high on the long wavelength side and low on the short wavelength side. Due to these synergistic effects, the SN ratio of the B component of the image sensor output is relatively deteriorated.

  FIG. 5 shows a system response by a combination of a typical halogen lamp and a color CCD. It can be seen that the relative sensitivity of the B component is lower than that of the R and G components. Here, as a practical problem, a system response when passing through an IR cut filter for removing unnecessary infrared light emission components is shown.

  One method for increasing the ratio of the B component contained in the emission wavelength of the halogen lamp is to increase the applied voltage. This is because the ratio of the short wavelength component can be increased from the Planck radiation law by increasing the temperature of the filament that is the light emitter. FIG. 6 shows how the emission spectral characteristics of the halogen lamp change when the applied voltage is changed. In this case, an IR cut filter is also used, and a wavelength component of 700 nm or more is removed. For comparison, the data is normalized with each peak value being 100%. As can be seen from the figure, the intensity ratio of the short wavelength component included in the emission wavelength increases as the applied voltage increases. However, since the absolute amount of the total amount of light is also proportional to the applied voltage, when performing wavelength control with the applied voltage, it is necessary to consider not only the ratio of the wavelength components but also the amount of light. For example, since the ratio of the long wavelength component is inherently high, the evaluation can be performed using the G component or the R component that is advantageous in terms of the amount of light when it is not particularly necessary to consider the balance of all RGB components. The measurement accuracy is maintained even when the applied voltage is relatively low.

  As a problem in increasing the applied voltage, there is a concern about the influence on the lamp life. FIG. 7 shows the relationship between the lamp applied voltage (relative ratio to the rated voltage) and the lamp life. The lamp life strongly depends on the applied voltage, and the lamp life is significantly reduced by exceeding the rated voltage value that is optimally designed as a lamp use condition. Generally, the standard condition is within ± 10% of the rated voltage, and it has been found that the life at the rated voltage + 10%, which is also the upper limit, is reduced to 1/3 of the life at the rated voltage. Therefore, increasing the applied voltage in order to increase the B component ratio of the emission wavelength must be considered in view of the lamp life.

  Based on the above considerations, in this embodiment, it is determined whether or not to increase the B component ratio according to the difference in the image evaluation mode executed by the image evaluation apparatus, thereby improving the measurement accuracy and extending the lamp life. We decided to make it compatible.

  That is, in this embodiment, when it is necessary to accurately measure all the RGB wavelength ranges including the short wavelength B component, such as evaluation of color information, a relatively high voltage is applied to increase the color temperature. Thus, the colorimetric accuracy is improved by increasing the ratio of the B component contained in the emission wavelength. On the other hand, in the case where evaluation is performed only with the density of an image without color information such as a line image or a character image, it is not necessary to measure the B component with high accuracy, and therefore the evaluation may be performed using the G component or the R component. . Since the G component or the R component is advantageous in terms of the amount of light, the lamp life is extended by lowering the color temperature by lowering the applied voltage than in the case of evaluating color information.

  FIG. 8 shows a functional configuration for such lamp control in the image evaluation apparatus of the present embodiment. In the configuration of FIG. 8, the controller 401 is a control unit that controls the entire image evaluation apparatus. For example, the controller 401 controls the drive mechanism of the image sensor 101 and the illumination devices 103a and 103b to read the evaluation target. Do. The controller 401 can be realized, for example, by causing a processor such as a CPU to execute a program. This program includes a control routine for the voltage applied to the lamp as will be described later.

  The lamp voltage control circuit 403 is a circuit that controls the voltage applied to the lamp 402 of the illumination devices 103a and 103b. The lamp voltage control circuit 403 has a function of switching the voltage applied to the lamp 402 between two levels (voltage values) of high and low. Voltage values of two levels, high and low, are registered in advance in the lamp voltage control circuit 403 or the controller 401. When the applied voltage is set to a high level, the color temperature of the light emitted from the lamp 402 increases, so that the proportion of the short wavelength component becomes larger than that at the low level. As a result, the B component of the illumination is strengthened, so that the colorimetric accuracy can be improved. On the other hand, if the applied voltage is at a low level, the life of the lamp 402 is longer than that at a high level, although the color measurement accuracy is inferior to that at a high level. The voltage value of each level of the applied voltage is not particularly limited. For example, the high level may be about several percent higher than the rated voltage of the lamp 402 and the low level may be the rated voltage, or the high level may be about the rated voltage and the low level may be a lower voltage.

  The level of the voltage applied to the lamp 402 is switched based on, for example, an image evaluation mode instructed by the user.

  The image evaluation mode is a type of image evaluation that can be executed by the image evaluation apparatus. For example, image characteristics caused by a combination of color and frequency components, such as a mode for obtaining the color value of the target image (for example, the CIE L * a * b * value) and the granularity of the colored image ("grainy" feeling). Examples include a mode for obtaining a value, a mode for obtaining characteristics (for example, sharpness of an edge) such as a line image and a character image, and a mode for obtaining the resolution of a grayscale image. Among these image evaluation modes, in a mode in which attention is paid to a color such as a mode for obtaining a color value or granularity of a colored image, the measurement accuracy improves when the B component of illumination is strong. Therefore, it is preferable to set the applied voltage to a high level in such a mode. On the other hand, the intensity of the B component does not have to be strong in a mode that does not focus on color, such as a mode in which a line image, a character image, or a gray image is evaluated. In particular, when a black and white image is used as an evaluation target, the intensity of the B component is not so important because only the G component or the R component can be evaluated. Therefore, in the mode not paying attention to the color, even if the applied voltage is set to a low level for extending the lamp life, the measurement can be performed with sufficient accuracy.

  In the present embodiment, the controller 401 has determination information indicating whether each image evaluation mode included in the image evaluation apparatus is a mode in which attention is paid to color (in other words, a mode corresponding to a high-level applied voltage). Then, as shown in FIG. 9, the controller 401 accepts selection of an image evaluation mode from the user via a UI (user interface) unit 404 having a display screen, a keyboard, and the like (S1), and the selected image evaluation is performed. It is determined with reference to the above-described determination information whether the mode corresponds to a mode that focuses on color (S2). If it is determined that the mode is focused on color, the controller 401 instructs the lamp voltage control circuit 403 to set the applied voltage to the lamp 402 to a high level (S3). Execute processing for reading. On the contrary, if it is determined that the mode is not the mode in which attention is paid to the color, the controller 401 instructs the lamp voltage control circuit 403 to set the applied voltage to a low level and executes the reading process (S4). When the applied voltage is set to a low level, image evaluation may be performed using the G or R component (preferably G component) of the read image, or both.

  Instead of the procedure shown in FIG. 9 described above, the procedure shown in FIG. 10 can be used. In the procedure of FIG. 10, when the execution of image evaluation is instructed, the controller 401 pre-scans the evaluation target document 104 before the main scan (imaging) for actual image evaluation (S11). Thus, it is determined whether the evaluation target document 104 is a color image or a monochrome image (S12). This determination may be performed by a known method. As a result of this determination, the lamp voltage control circuit 403 is instructed to set the applied voltage to the lamp 402 to a high level (S13) if it is a color image, and to a low level (S14) otherwise. Run a scan.

  Since it is only necessary to determine whether the image has color in the pre-scan, a low-resolution image read in a short scan time is sufficient, and illumination may be weaker than in the case of precise colorimetry. In this way, since pre-scanning may be performed for a short time at a relatively low intensity, the influence on the lamp life is not so great.

  As described above, in the example of FIG. 10, the type of the document to be evaluated is determined by pre-scanning. This is whether or not the image evaluation mode performed on the document to be evaluated focuses on color. It is equivalent to discriminating.

  When it is necessary to accurately measure the short wavelength B component, such as evaluation of color information, by the mechanism of the embodiment as described above, a relatively high voltage is applied to raise the color temperature and include it in the emission wavelength. In order to improve the colorimetric accuracy by increasing the ratio of the B component that is generated, and on the other hand, when evaluating only the shade of the image without color information such as line images and character images, the applied voltage is lowered to lower the color temperature. This makes it possible to extend the lamp life. As a result, while avoiding an increase in the cost of the image evaluation apparatus due to the addition of the B component correction mechanism and avoiding or mitigating the problem of an increase in the cost due to the shortening of the lamp life, etc. Image evaluation can be performed.

  The embodiment described above is merely an example. For example, the light source of the image evaluation apparatus may be a halogen lamp having another shape such as a spot shape instead of a linear halogen lamp. It will be easily understood that the system of the present embodiment can be applied even when a heat radiation type lamp other than the halogen lamp is used. In the above example, the illumination light source is of a type that condenses with a reflector. However, the present invention is not limited to this, and even when other condensing means are used, condensing is unnecessary. Even so, the method of this embodiment can be applied. The method of this embodiment is applicable not only when the line sensor is used for reading the evaluation target image but also when another type of detector such as an area sensor is used. In the above example, the light emission intensity of the lamp is controlled by the applied voltage, but the light emission intensity may be controlled by current control. That is, if the mode requires the relative intensity of the B component to be increased, the current supplied to the lamp may be set to a high level, and if not, the level may be set to a low level lower than the high level. Regardless of voltage control or current control, the level of power supplied to the lamp may be switched according to the image evaluation mode.

  In the above example, the level of the applied voltage is switched according to the presence or absence of the color of the document to be evaluated. However, for example, when evaluating an evaluation target original of Y (yellow) color, the light reception signal of the B component that is the complementary color is important, and it is desirable that it has sufficient intensity. Therefore, when the mode for evaluating the Y color is selected, or when it is determined by prescan that the document to be evaluated is a single Y color, it is preferable to set the applied voltage to a high level.

  In the above, an example in which the applied voltage to the lamp 402 is set to two levels of high and low is shown. However, it is of course possible to set this to three or more levels and switch according to the image evaluation mode.

It is a figure which shows roughly the hardware constitutions of an example of the image evaluation apparatus with which control of embodiment is applied. It is a figure which shows roughly an example of a structure of the illuminating device with which an image evaluation apparatus is provided. It is a figure for demonstrating schematic structure of a line-shaped halogen lamp tube. It is a figure which shows an example of the light emission spectral characteristic of a halogen lamp. It is a figure which shows an example of the system response in the combination of a halogen lamp and color CCD. It is a figure which shows the applied voltage dependence of the light emission spectral characteristic of a halogen lamp. It is a figure which shows the relationship between a halogen lamp applied voltage and a lamp life. It is a figure which shows the function structure for the lamp control in the image evaluation apparatus of embodiment. It is a figure which shows an example of the process sequence for lamp application voltage control. It is a figure which shows another example of the process sequence for lamp application voltage control.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 Image pick-up element, 102 Lens, 103a, 103b Illuminating device, 104 Document for evaluation, 105 Document stand, 401 Controller, 402 lamp, 403 Lamp voltage control circuit, 404 UI (user interface) part.

Claims (6)

An image evaluation apparatus that illuminates an evaluation target image with a heat radiation type light source, detects reflected light from the evaluation target image, and evaluates the evaluation target image,
A discriminating means for discriminating an image evaluation mode to be executed for the evaluation target image;
Control means for controlling the level of power supplied to the light source according to the mode determined by the determination means;
An image evaluation apparatus comprising: The image evaluation apparatus according to claim 1,
The determining means determines whether or not the image evaluation mode is a mode for paying attention to a color,
The control means sets the level of power supplied to the light source to the first level if the mode is an evaluation mode that focuses on color, and sets the level of power supplied to the light source to be the first level if the mode is evaluation mode that does not focus on color. A second level lower than the level of
An image evaluation apparatus characterized by that. The image evaluation apparatus according to claim 1,
The determining means determines whether the image evaluation mode is an evaluation mode for evaluating an image of a yellow color material,
If the mode is an evaluation mode for evaluating a yellow color material image, the control means sets the level of power supplied to the light source to a first level, and if the mode is not an evaluation mode for evaluating a yellow color material image, the light source A level of power supplied to the second level lower than the first level;
An image evaluation apparatus characterized by that. The image evaluation apparatus according to claim 1,
The determination unit determines whether the image evaluation mode is a mode in which a blue component of reflected light from the evaluation target image is used for evaluation,
The control means sets the level of power supplied to the light source as a first level if the mode uses a blue component for evaluation, and sets the level of power supplied to the light source if the mode is not a mode that uses a blue component for evaluation. A second level lower than the first level,
An image evaluation apparatus characterized by that. The image evaluation apparatus according to claim 1,
The determination unit receives a selection of an image evaluation mode from a user, and determines a mode based on a result of the selection.
An image evaluation apparatus characterized by that. The image evaluation apparatus according to claim 1,
The determining means determines the type of the evaluation target image by pre-scanning the evaluation target image, and determines the image evaluation mode based on the type.
An image evaluation apparatus characterized by that.

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