JP2004088190A - Camera system using parallel output solid state imaging device, and its correction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the variation of the characteristics of amplifiers in a multi-amplifier read type solid state imaging device causes the image quality to be deteriorated. <P>SOLUTION: The camera system uses an imaging device (10) having an imaging section divided into a plurality of horizontally arranged blocks and reading amplifiers corresponding to the blocks. It images a correcting object (20) having such a gradation pattern that the incident light quantity is constant in the horizontal direction but varies at a fixed rate in the vertical direction. Using gradation data of at least series of pixels adjacent to the blocks boundaries of the imaging section among the imaging results, it forms cumulative histograms about the number of events per gradation for the individual blocks (45, 55), forms correction data showing the corresponding relation of the gradations before and after the correction about blocks to be corrected to reduce the difference between these cumulative histograms (46, 56), and corrects the imaging results of a desired object using the correction data (47, 57). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a camera system using a parallel output solid-state imaging device and a correction method therefor.
[0002]
[Prior art]
There is a technique for increasing the speed of reading by providing a plurality of reading amplifiers of a solid-state imaging device for the purpose of realizing high-resolution moving image shooting, continuous shooting with a digital still camera, and the like. That is, a parallel output solid-state imaging device having an imaging unit divided into a plurality of blocks and a readout amplifier for each block is employed in the camera system. When this parallel output solid-state imaging device is used, it is necessary to correct the variation in the gradation level in the outputs of the plurality of read amplifiers. Moreover, non-linear level correction is required.
[0003]
According to a conventional technique, a white object is imaged by a CCD solid-state imaging device, and the gain of an amplifier circuit is adjusted so that the amplifier output level at that time becomes equal (Japanese Patent Laid-Open No. 1-114174).
[0004]
However, this conventional technique can achieve linear correction, but cannot achieve non-linear level correction.
[0005]
Therefore, in a camera system using an imaging unit divided into a plurality of blocks arranged in the horizontal direction and a parallel output solid-state imaging device having a readout amplifier for each block, a pixel column adjacent to each block boundary of the imaging unit is used. A technique has been proposed in which a cumulative histogram relating to the number of events (the number of pixels) for each gradation is created for each block using the gradation data, and a nonlinear correction process for each gradation is performed so as to reduce the difference between these cumulative histograms. (Japanese Patent Application No. 2002-113041).
[0006]
[Problems to be solved by the invention]
However, according to the amplifier correction technique using the cumulative histogram, when a natural image is taken, there may be a large difference in the gradation data of the boundary pixel between adjacent blocks, which causes an error in the cumulative histogram. Therefore, do not use gradation data having a difference larger than a predetermined value between adjacent blocks for creating a cumulative histogram, or forcibly remove the focus position from the solid-state imaging device while creating correction data. It performs focus control, accumulates and uses gradation data obtained by a plurality of imagings, and controls an aperture or an electronic shutter in each of a plurality of imagings so that a wide range of gradation data can be used. Was necessary for the creation of a proper cumulative histogram.
[0007]
SUMMARY OF THE INVENTION It is an object of the present invention to efficiently create an appropriate cumulative histogram by devising a correction subject, thereby realizing non-linear correction of amplifier characteristics.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention employs a correction subject having a gradation pattern such that the incident light amount is constant in the horizontal direction and the incident light amount changes at a constant rate in the vertical direction. Things.
[0009]
More specifically, the present invention relates to a camera system using a parallel output solid-state imaging device having an imaging unit divided into a plurality of blocks arranged in a horizontal direction and a readout amplifier for each block, and an input device in a horizontal direction. A correction subject having a gradation pattern in which the light amount is constant and the incident light amount changes at a constant rate in the vertical direction is imaged by the parallel output solid-state image sensor, and at least each of the block boundaries of the image pickup unit among the imaging results A cumulative histogram relating to the number of events for each gradation is created for each block using the gradation data of the pixel row adjacent to the pixel row, and the gradation before and after the correction related to the correction target block is reduced so as to reduce the difference in the created cumulative histogram. Correction data representing the correspondence between the two is created, and the arbitrary output from the parallel output solid-state imaging device is generated using the created correction data. In which it was decided to correct the characteristics of the read amplifier for each block by correcting the imaging result of the body.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0011]
FIG. 1 is an example of a CCD solid-state imaging device that performs reading with a plurality of amplifiers. The parallel output solid-state imaging device 10 of FIG. 1 includes imaging units 11, 14, 17 divided into three blocks arranged in the horizontal direction, horizontal CCDs 12, 15, 18 for each block, and amplifiers 13, 16 and 19. That is, the three areas divided by the dotted lines in FIG. 1 are read by different amplifiers (channels). Each of the imaging units 11, 14, and 17 has a two-dimensionally arranged photodetector (photodiode) and a vertical CCD for each column.
[0012]
FIG. 2 is an example of a correction subject. In the correction subject 20 in FIG. 2, the light intensity gradually becomes brighter at a fixed rate from the bottom to the top. Dotted lines are drawn for convenience, and the portions divided by the dotted lines in FIG. 2 correspond to the image pickup units 11, 14, and 17 that perform reading with separate amplifiers of the solid-state image sensor 10 shown in FIG. Irradiated. By imaging the correction subject 20 and reading data of one screen, the number of horizontal pixels of the imaging units 11, 14, and 17 divided according to the amplifier has the same output, and the amount of light gradually decreases in the vertical direction. Changing gradation data can be obtained for each channel.
[0013]
FIG. 3 shows the principle of correcting the amplifier characteristics from the gradation data obtained by imaging the correction subject 20 in FIG. The correction subject 20 in FIG. 2 has a uniform light amount distribution in the horizontal direction, and what is _denoted by N0 in FIG. 3A corresponds to the number of horizontal pixels of the divided block. FIG. 3B shows three amplifiers having different characteristics. When the subject having the characteristics A, B, and C shown in FIG. 3B is imaged with the subject shown in FIG. 3A, the histograms shown in FIG. 3C are obtained. When a cumulative histogram is taken for FIG. 3C, a graph of monotonically increasing as shown in FIG. 3D is obtained. In this graph, the graph obtained by exchanging the vertical and horizontal axes is the graph of FIG. 3 (e), which is a graph reflecting the amplifier characteristics shown in FIG. 3 (b). To understand this more simply, a graph obtained by integrating FIG. 3A with the light amount L indicates that the cumulative number of events (the number of events having a light amount equal to or less than L) N and the light amount L are proportional to each other. If the L in the graph of FIG. 3B is replaced with N, the graph of FIG. 3E is obtained.
[0014]
According to the principle shown in FIG. 3, the correction subject 20 of FIG. 2 is imaged, and a cumulative histogram is created from the read gradation data. Then, as shown in FIG. 4A, the characteristics are matched with the reference amplifier. Specifically, by correcting the input signal (the output value of the analog / digital conversion) according to the conversion table in FIG. 4B, the amplifier characteristics can be matched over the entire digital range where the analog / digital conversion has been performed.
[0015]
FIG. 5 shows an example of a system configuration for realizing the above principle. When capturing the correction subject 20 through the lens 25, the drive circuit 30 drives the parallel output solid-state imaging device 10. The gradation data read from the solid-state imaging device 10 is switched via CDS (correlated double sampling) 41, 51, gain / offset adjustment units 42, 52, and ADC (analog / digital conversion) 43, 53. Units 44 and 54 input the data to cumulative histogram creating units 45 and 55 to create the graph shown in FIG. The created graph is written into the correction data holding memories 46 and 56. It is desirable that the amount of incident light in the vertical direction of the correction subject 20 be changed in a range wider than the input ranges of the ADCs 43 and 53.
[0016]
Next, the gradation data read out of the solid-state imaging device 10 by capturing an image of an arbitrary subject is sent to the switching units 44 and 54 via the CDSs 41 and 51, the gain / offset adjustment units 42 and 52, and the ADCs 43 and 53. The signals are sent to the correction units 47 and 57. The correction units 47 and 57 convert the input data with reference to the correction data written in the correction data holding memories 46 and 56. Since it is not necessary to add correction to the reference amplifier, it is not necessary to have circuits such as a switching unit, a cumulative histogram creation unit, a correction data holding memory, and a correction unit.
[0017]
The corrected data is sent to the one-screen memory 60 to be made into one image, subjected to image processing by the circuit 61, and output. As a result, an image in which the characteristics are corrected between the amplifiers and where no boundary appears can be obtained.
[0018]
FIG. 5 shows an example of a system configuration when the correction subject 20 is placed outside the camera. For example, the correction is performed by imaging the correction subject 20 at the time of factory inspection.
[0019]
FIG. 6 is an example of a system configuration when a correction subject is provided inside the camera. According to FIG. 6, when the shutter 26 is closed, the illumination of the correction subject 21 provided inside the camera is turned on, the correction subject 21 is imaged via the mirror 22, and the result of this imaging is used. Make corrections. By providing the correction subject 21 inside the camera in this way, real-time correction can be performed by the user, and there is an advantage that the case where the amplifier characteristic of the parallel output solid-state imaging device 10 changes over time due to temperature or the like can be achieved.
[0020]
In the above example, the CCD-type parallel output solid-state imaging device 10 has been described. However, as long as the solid-state imaging device performs reading with a plurality of amplifiers, the principle of correcting the amplifier characteristics is effective.
[0021]
【The invention's effect】
As described above, according to the present invention, in the correction of a camera system using a parallel output solid-state imaging device having an imaging unit divided into a plurality of blocks arranged in the horizontal direction and a readout amplifier for each block, Since a correction subject having a gradation pattern in which the incident light amount is constant in the horizontal direction and the incident light amount changes at a constant rate in the vertical direction is adopted, an appropriate cumulative histogram should be efficiently created. By correcting non-linear variations in amplifier characteristics, high-quality image capturing is possible.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration example of a CCD-type parallel output solid-state imaging device included in a camera system according to the present invention.
FIG. 2 is a plan view showing an example of a subject used for correcting an amplifier characteristic in the camera system of the present invention.
FIGS. 3A to 3E are diagrams illustrating the principle of correcting the amplifier characteristics in the camera system of the present invention.
FIGS. 4A and 4B are diagrams illustrating a process of correcting amplifier characteristics in the camera system of the present invention.
FIG. 5 is a block diagram illustrating an overall configuration example of a camera system according to the present invention.
FIG. 6 is a block diagram illustrating another configuration example of the camera system of the present invention.
[Explanation of symbols]
10 parallel output solid-state imaging devices 11, 14, 17 imaging units 12, 15, 18 horizontal CCD
13, 16, 19 Amplifier 20 Correction subject 21 Illumination + Built-in correction subject 22 Mirror 41, 51 CDS (correlated double sampling)
42, 52 Gain / offset adjustment units 43, 53 ADC (analog / digital conversion)
44, 54 Switching unit 45, 55 Cumulative histogram creation unit 46, 56 Correction data holding memory 47, 57 Correction unit 60 Single screen memory

Claims (4)

An imaging unit divided into a plurality of blocks arranged in a horizontal direction, and a correction method for a camera system using a parallel output solid-state imaging device having a readout amplifier for each block,
Imaging the correction subject having a gradation pattern such that the incident light amount is constant in the horizontal direction and the incident light amount changes at a constant rate in the vertical direction, using the parallel output solid-state imaging device;
Creating a cumulative histogram for each block of the number of events for each tone using tone data of a pixel row adjacent to each block boundary of at least the imaging unit among the results of the imaging,
A step of creating correction data representing a correspondence relationship between gradations before and after correction on the correction target block so as to reduce the difference between the created cumulative histograms;
Correcting the characteristic of the readout amplifier for each block by correcting an imaging result of an arbitrary object by the parallel output solid-state imaging device using the generated correction data. Correction method. The correction method for a camera system according to claim 1,
A step of employing a correction subject in which the amount of incident light in the vertical direction changes in a range wider than an input range of a converter for converting an output of the readout amplifier into a digital value for each block. Camera system correction method. An imaging unit divided into a plurality of blocks arranged in a horizontal direction, and a camera system using a parallel output solid-state imaging device having a readout amplifier for each block,
A correction subject having a gradation pattern such that the incident light amount is constant in the horizontal direction and the incident light amount changes at a constant rate in the vertical direction,
A cumulative histogram relating to the number of events for each gradation is created for each block using at least gradation data of a pixel column adjacent to each block boundary of the imaging unit in the imaging result of the correction subject by the parallel output solid-state imaging device. Means for generating correction data representing the correspondence relationship between the gradation before and after the correction for the correction target block so as to reduce the difference between the created cumulative histograms,
Means for correcting the characteristics of the read amplifier for each block by correcting an imaging result of an arbitrary object by the parallel output solid-state imaging device using the created correction data. Camera system. The camera system according to claim 3,
A camera system further comprising a memory for holding the created correction data.

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