JP2005352789A - Shading correction data acquiring method for electronic camera, and image processing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shading correction data acquiring method, and an image processing device capable of correcting shading of an image taken by a camera by acquiring shading correction data for the camera on the basis of a virtual uniform light source. <P>SOLUTION: The image processing device 100 is characterized by that the camera 110 and a computer 120 are connected, a moving mechanism 130 is provided for moving the camera 110, the virtual light source is provided by approximating an image pickup lens 111 of the camera 110 to a light source by the moving mechanism 130, shading correction of the camera 110 is carried out on the basis of the light source to acquire the shading correction data, and shading of the image taken by the camera 110 can be corrected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electronic camera shading correction data acquisition method and an image processing apparatus for correcting shading of an image captured using an electronic camera such as an analog or digital camera.

  In the following description, a digital electronic camera will be described. The “electronic camera” is simply abbreviated as “camera”.

  In an image processing apparatus using a camera, shading occurs due to the influence of an imaging lens, a charge-coupled device (CCD = Charge Coupled Device, hereinafter abbreviated as “CCD”), a prism, and the like, and the surrounding luminance of the captured screen is reduced. To do.

  When an image processing apparatus using a camera is used, it is necessary to acquire shading correction data and correct a captured image in order to cancel the shading.

Conventionally, as a method of acquiring shading correction data,
(1) For example, a method for imaging a light source having uniform brightness such as an integrating sphere, (2) a method for imaging a light source having previously subdivided luminance data, and (3) a method for correcting shading correction data for each imaging lens. Yes, the correction data is acquired using any one of these methods.

These methods have the following problems. That is,
In the case of the method (1),
1) It is difficult to prepare a uniform light source 2) It is difficult to maintain a uniform light source Depending on the angle of view of the camera (which varies depending on the subject), a large light source is required 3) Large When a light source is used, a large dark room is required.
1) It is difficult to obtain fragmented luminance data (time and accuracy are problems)
2) It is difficult to maintain the brightness of the light source (the brightness data must be re-measured when the state changes)
3) Depending on the angle of view of the camera, a large light source is required, and it is difficult to acquire luminance data. 4) When a large light source is used, a large dark room is required. For the method,
1) In the case of a color camera, particularly a 3CCD camera, the shading data differs for each of red, green, and blue (hereinafter referred to as R, G, and B, respectively) due to the influence of the prism optical system in the camera, and therefore cannot be corrected accurately. about. Further, even in the case of a 1 CCD color camera, there is a problem that shading of R, G, and B filters must be taken into consideration.

  The present invention is intended to solve these problems, and creates a virtual uniform light source, obtains camera shading correction data based on the light source, and performs camera shading correction data. It is an object of the present invention to provide an acquisition method and an image processing apparatus capable of correcting shading of an image of an object to be inspected captured by the camera subjected to the shading correction.

  Therefore, the shading correction data acquisition method for the camera according to the present invention is characterized in that a virtual uniform light source is obtained by bringing the imaging lens of the electronic camera close to the light source and the shading correction data of the electronic camera is acquired.

  It is desirable to dispose a diffusion plate in front of the light source. In addition, if the luminance value does not change by moving the electronic camera with respect to the virtual uniform light source, it is determined that the virtual uniform light source is uniform.

  The electronic camera shading correction data acquisition method of the present invention is characterized in that, if the electronic camera is a color electronic camera, the color electronic camera shading correction data for each color of red, green and blue is created.

  Furthermore, the image processing apparatus of the present invention is characterized in that an electronic camera and a computer are connected, and a moving mechanism is provided to bring the imaging lens of the electronic camera closer to a virtual uniform light source. This image processing apparatus is provided with a shading correction data acquisition unit for the electronic camera and a luminance unevenness inspection unit for the object to be inspected.

  Further, in the luminance inspection method for an object to be inspected according to the present invention, a virtual uniform light source is obtained by bringing the imaging lens of the electronic camera close to the light source, shading correction data of the electronic camera is generated, and the shading correction data is obtained. It is used to inspect the uniformity of luminance of an object to be inspected.

  Furthermore, according to the method for inspecting the luminance of an object to be inspected according to the present invention, if the electronic camera is a color electronic camera, the shading correction data of the color electronic camera for each color of red, green, and blue is created, and the shading correction data thereof is generated. Is used to inspect the luminance uniformity of the object to be inspected.

  Therefore, according to the present invention, it is possible to easily acquire shading correction data by using a virtual uniform panel with the same image processing apparatus, and the shading of the object to be inspected can be inspected using the shading correction data.

According to the camera shading correction data acquisition method of the present invention,
1. 1. It is not necessary to prepare a uniform light source and a light source having multi-point luminance data, and it is inexpensive. 2. It is not necessary to manage the light source such as the luminance distribution and luminance value used to acquire shading correction data. 3. A light source used for acquiring shading correction data can be easily obtained. It is possible to obtain an effect that the space for obtaining the shading correction data may be a narrow space.

Further, according to the image processing apparatus of the present invention,
1. 1. It is possible to provide a function of acquiring shading correction data without changing the size of the image processing apparatus. 2. When the image processing apparatus has a shading correction data acquisition function, the operator can acquire shading correction data. It is possible to obtain an effect that the shading correction data can be acquired in the image processing apparatus and can be performed in a short time.

Furthermore, according to the luminance inspection method of the object to be inspected according to the present invention,
1. The effect is obtained that the shading correction data of the camera obtained by using the image processing apparatus of the present invention is used, and the luminance of the object to be inspected can be inspected by using the same image processing apparatus.

  As described above, conventionally, in order to perform shading correction, it is necessary to prepare a uniform light source or a light source having multi-point luminance data. However, in the present invention, a virtual uniform light source is created.

  In an image processing device that performs luminance measurement using a camera, shading correction is an indispensable correction because optical elements such as the camera's imaging lens, CCD, prism, etc. overlap and lower the peripheral brightness. The correction method is also standardized.

  When the aperture or focus of the imaging lens is moved, the optical characteristics of the imaging lens change, so that the shading correction data also changes. In a state where the imaging lens and the focus are fixed, the shading correction data does not change. Before performing shading correction using this characteristic, the camera distance (angle of view) with respect to a subject such as a flat panel display (hereinafter referred to as “FPD”), a cathode ray tube (hereinafter referred to as “CRT”), etc. ) Determine the focus and aperture, and fix in this state. Then, as it is, the front end of the imaging lens of the camera is brought close to the subject. Then the camera image is very out of focus.

  By bringing the camera closer to the subject, the field of view of the camera becomes a local part of the subject, and the focus is considerably blurred. In this state, the subject is caused to emit light (usually white), and a milky white diffusion plate is further provided in front of the subject, so that the image captured by the camera becomes a uniform light source.

  To determine whether this uniform light source is really uniform, the camera is moved up and down and left and right, and shading correction data is acquired at each position. If there is no difference in the acquired data, it can be determined that the light source is uniform.

  Here, in the obtained shading correction data, assuming that the maximum luminance is 100%, the uniformity of the light source may be regarded as 99% or more if the difference when the camera is moved is within 1%.

  In a camera using a prism such as a 3CCD color camera, since the optical characteristics of R, G, and B of the prism are different, it is necessary to acquire shading correction data for each of R, G, and B. Further, even with a 1 CCD color camera, there may be shading in the color filter of the camera, so it is also necessary to acquire shading correction data for each of R, G, and B.

  The method of actually correcting using the shading correction data acquired as described above is performed using a general method of lifting a portion where the luminance level has fallen due to shading.

  As in the image processing apparatus of the present invention, when a computer and a camera are electrically connected and a camera position adjustment mechanism (distance between the camera and the object to be measured) is added, the object to be measured (FPD, CRT, etc.) Even when the camera settings such as the focus position and aperture position of the imaging lens change due to the change in the shading, the shading correction data can be easily obtained. That is, there is no need to perform the shading correction data acquisition operation at another location.

  In addition, since the change in the shading correction data due to the focus movement of the imaging lens is very gradual, if the shading correction data is obtained by thinning out to some extent, the correction data for the entire focus variable range is obtained. If the aperture position is added to a matrix state, shading correction data for all the imaging lenses can be acquired.

  Further, if the imaging lens and iris of the camera can be automatically controlled from a computer, shading correction data can be acquired automatically. Furthermore, even when the image processing apparatus is actually used, it is possible to use it without being aware of the shading correction of the camera.

  Furthermore, if the image processing apparatus of the present invention is used, not only the shading correction data of the camera can be obtained, but also the luminance uniformity of the object to be inspected can be easily inspected.

  The camera shading correction data acquisition method and image processing apparatus of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram of an image processing apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram of the image processing apparatus shown in FIG. 1, and FIG. 4 is a diagram showing the positional relationship, FIG. 4 is a diagram showing the positional relationship when a diffusion plate is interposed between the camera and the subject of the image processing apparatus shown in FIG. 1, and FIG. 5 is a diagram showing the image processing shown in FIG. FIG. 6 is a flowchart of a method for acquiring shading correction data of a camera, and FIG. 7 is a case where an image processing apparatus is used based on shading correction data. It is a brightness nonuniformity measurement flowchart.

  1 and 2, reference numeral 100 indicates an image processing apparatus of the present invention. The image processing apparatus 100 includes an imaging device (hereinafter referred to as “camera”) 110 such as a monochrome camera and a color camera, a computer 120 capable of controlling various parameters of the camera 110 and displaying imaging results, and a camera 110. Is composed of a moving mechanism 130 for bringing the light source close to the light source, a display 140, a keyboard 150, a mouse 160 and the like.

  The camera 110 includes an imaging lens 111 having a focus and an aperture function, and the camera 110 is connected to a camera interface board 124 of the computer 120 via a cable 112. The camera 110 is supported by the moving mechanism 130 and approaches or separates from a subject P described later.

  The moving mechanism 130 has a horizontal surface, a base 131 on which the subject Pa or the object Pb to be inspected is supported, a support column 132 that is established perpendicular to the base 131, and an arrow in the support column 132. In this way, the arm 133 is supported so as to be movable up and down and is extendable and retractable. The camera 110 is fixed to the tip of the arm 133.

  The computer 120 includes a central processing unit (hereinafter referred to as “CPU”) 121, a memory 122, a hard disk 123, an interface board 124, etc., and the memory 122, hard disk (HDD) 123, and interface board 124 are centralized through a bus line 125. It is connected to the device 121. In addition, a display 140, a keyboard 150, and a mouse 160 are connected to the bus line 125. The interface board 124 is for capturing information data captured by the camera 110 into the computer 120.

  Next, a method for obtaining shading correction data of a camera using the image processing apparatus 100 will be described with reference to FIGS.

  3, 4, and 5 are schematic diagrams illustrating the positional relationship between the camera 110 of the image processing apparatus 100 and the subject Pa. Although not described here, the camera 110 and the subject Pa are in a dark room state so that no external light source enters.

  In addition, in order to form a virtual uniform light source, as shown in FIG. 3, an FPD with good luminance unevenness is selected as the subject Pa. Also, as shown in FIG. It is desirable to interpose a milky white diffusion plate D immediately before the subject Pa, and to use the subject Pa alone or the subject Pa and the diffusion plate D in combination.

  First, an FPD, which is a subject Pa with little luminance unevenness, is installed on a base 131 below the camera 110.

  Next, the angle of view of the imaging lens 111, that is, the distance to the FPD that is the subject Pa is determined (FIG. 2).

  Then, the focus and aperture of the imaging lens 111 are determined.

  Subsequently, as shown in FIG. 5, the camera 110 attached to the arm 133 is moved so that the distance from the tip of the imaging lens 111 to the subject Pa is as close as possible to about 1 mm, for example.

  In such a state, shading correction data is acquired. This shading correction data is stored in the HDD 123 of the computer 120.

  Next, shading correction of the camera 110 is performed based on the shading correction data.

  Then, when the camera 110 is returned to its original position and the diffusion plate D is used, the diffusion plate D is removed.

  Next, a luminance inspection method for the object Pb to be inspected using the image processing apparatus 100 of the present invention will be described with reference to the flowchart of FIG. In practice, the inspection object Pb is measured and inspected by a display device such as a liquid crystal panel, a plasma display, a cathode ray tube TV, or a monitor.

  First, in step S1, the camera 110 of the image processing apparatus 100 is returned to the original position shown in FIG. 3 (upward in the illustrated example), and the object Pb is placed and fixed on the base 131. Then, the image processing apparatus 100 including the camera 110 is operated, and the inspected object Pb emits light in white, red, green, and blue, and the whole is imaged and taken into the CCD.

  Next, after capturing the captured image, the captured image is captured into the interface board 124, classified into R, G, and B data, corrected, and stored in the memory 122 of the computer 120 (step S2).

  In the next step S3, the edge of the inspection object Pb is detected. The following image processing is performed within this edge. In this step S3, the position of the inspection object Pb is shown in the camera 110.

  In the next step S4, the black level of the camera 110 is corrected. The CPU 121 corrects the black level of the CCD of the camera 110 in order to remove the slight output from the camera 110 even when no light enters the camera 110. That is, the slight output is subtracted.

  In addition, the shading data of the image pickup lens 111 and the shading data of the CCD are both taken for the black level correction, and the shading correction is performed based on the correction data previously obtained (step S5).

  Next, in step S6, crosstalk correction is performed. The spectral characteristics of R, G, and B of the object Pb to be inspected and R, G, and B of the color filter of the camera 110 are actually slightly shifted. For example, when only the R single color is illuminated, it is actually sufficient to output only R, but actually there is also leakage of G, and both outputs are also output. Since an error occurs if the crosstalk is included in the image data, excess data for the crosstalk is removed.

Next, in step S7, the luminance value is corrected. This is a digital value, and what is actually captured is a digital value from 0 to 255, but the digital value of each object Pb is converted into a luminance value (cd / m ² ) of data that is actually handled.

  Next, luminance unevenness is calculated from the luminance value (step S8).

  In step S9, the luminance unevenness is displayed on the display 140 of the computer 120.

  When the image processing apparatus 100 is actually used, the shading correction data is obtained by the flow as described above, the shading correction data is read from the HDD, and the R, G, B data stored in the memory 122 is corrected.

  Then, after this correction, another inspection object Pb is continuously photographed. At that time, the image is captured by performing correction according to the flow as described above.

  Actually, the luminance unevenness of each RGB color of the object Pb to be inspected may be inspected, but RGB may be simultaneously emitted to inspect the luminance unevenness in the white state.

  In the conventional image processing apparatus, in order to obtain the shading correction data of the camera, the camera is removed and brought to the camera manufacturer to obtain the shading correction data. In the processing apparatus 100, there is no such trouble, and the moving mechanism 130 that can move the camera 110 as described above is provided, and calibration can be performed immediately on the moving mechanism 130. The inspection object Pb can be immediately inspected with the same image processing apparatus 100.

  As long as the focus and the diaphragm are not moved, it is not necessary to recalibrate the imaging lens 111. When the type of the display panel, which is the object to be inspected Pb, changes and becomes brighter and the aperture needs to be reduced a little, the aperture is reduced, measured, and data is acquired. This operation can actually be performed by the image processing apparatus 100 itself. There is no need to calibrate by removing the camera as in the prior art described above.

  Further, the focus movement of the imaging lens is normally used while being fixed, but the focus needs to be slightly moved when the size of the display panel is changed. Therefore, shading correction is previously taken according to the position of the focus ring, and if the focus ring position has a certain value, the data can be used.

  Further, when the display panel that is the object to be inspected Pb becomes brighter or darker, it is necessary to change the aperture. If the aperture is changed, the shading correction data will also change, so if you create shading correction data in advance using the focus and aperture matrix, the focus and aperture values will remain on that matrix without having to recalibrate each time. Can be determined to use this shading correction data. These measurement data values may be stored in advance in the HDD. If the measurement data is stored in the HDD in a matrix in this way, when the next object to be measured is measured, for example, 1 of 3 on the matrix, the shading correction data is read out, and based on it. It can be easily corrected.

  The present invention can be widely used for correcting shading of an electronic camera.

1 is a configuration diagram of an image processing apparatus according to an embodiment of the present invention. It is a block diagram of the image processing apparatus shown in FIG. FIG. 2 is a positional relationship diagram in a state where a camera and a subject of the image processing apparatus illustrated in FIG. 1 are separated from each other. FIG. 2 is a positional relationship diagram in a state where a diffusion plate is interposed between a camera and a subject of the image processing apparatus illustrated in FIG. 1. FIG. 2 is a positional relationship diagram in a state where an imaging lens of a camera of the image processing apparatus illustrated in FIG. 1 is brought close to a subject. It is a brightness nonuniformity measurement flowchart in the case of using an image processing apparatus based on shading correction data.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Image processing apparatus of one Example of this invention, 110 ... Electronic camera, 111 ... Imaging lens, 112 ... Cable, 120 ... Computer, 121 ... Central processing unit, 122 ... Memory, 123 ... CCD, 124 ... Camera interface board , 125 ... bus line, 130 ... moving mechanism, 131 ... base, 132 ... support, 133 ... arm, 140 ... display, 150 ... keyboard, 160 ... mouse, Pa ... subject, Pb ... subject to be inspected, D ... diffusion plate

Claims (8)

  A method for obtaining shading correction data of an electronic camera, wherein a virtual uniform light source is obtained by bringing an imaging lens of the electronic camera close to the light source, and shading correction data of the electronic camera is obtained.   2. The method for obtaining shading correction data of an electronic camera according to claim 1, wherein a virtual uniform light source is obtained by disposing a diffusion plate in front of the light source.   The shading of an electronic camera according to claim 1, wherein if the luminance value does not change by moving the electronic camera with respect to the virtual uniform light source, it is determined that the virtual uniform light source is uniform. Correction data acquisition method.   When the electronic camera is a color electronic camera, a shading correction data acquisition method for an electronic camera, wherein shading correction data of the color electronic camera for each color of red, green and blue is created.   An image processing apparatus comprising: a moving mechanism that connects an electronic camera and a computer and moves an imaging lens of the electronic camera closer to a virtual uniform light source.   6. The image processing apparatus according to claim 5, further comprising a shading correction data acquisition unit for the electronic camera and a luminance unevenness inspection unit for the object to be inspected.   Obtaining a virtual uniform light source by bringing the imaging lens of the electronic camera close to the light source, creating shading correction data of the electronic camera, and inspecting the luminance uniformity of the object to be inspected using the shading correction data A method for inspecting luminance of an object to be inspected. If the electronic camera is a color electronic camera, create shading correction data of the color electronic camera for each color of red, green, and blue, and use the shading correction data to inspect the luminance uniformity of the object to be inspected. A characteristic luminance inspection method for an object to be inspected.

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