JP4533440B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus that captures a subject image.

  A configuration example of a conventional digital still camera will be described with reference to FIG.

  In this figure, when a photographer operates a camera operation switch 201 (consisting of a camera main switch, a release switch, etc.), the overall control CPU 200 detects a change in the state of the camera operation switch 201 and supplies power to other circuit blocks. Start supplying.

  A subject image within the photographing screen range is formed on the image sensor 204 through the main photographing optical systems 202 and 203 and converted into an analog electric signal. An analog electrical signal from the image sensor 204 is processed in an analog manner by the CDS / AGC circuit 205 and converted into a predetermined signal level, and further converted into a digital signal by the A / D converter 206 in order of each pixel. The

  Note that the image sensor 204 outputs an image signal when the driver circuit 207 controls the horizontal drive and the vertical drive of the image sensor 204 in a predetermined manner based on a signal from the timing generator 208 that determines the overall drive timing.

  Similarly, the CDS / AGC circuit 205 and the A / D converter 206 also operate based on the timing from the timing generator 208.

  Reference numeral 209 denotes a selector that selects a signal based on a signal from the overall control CPU 200, and an output from the A / D converter 206 is input to the memory controller 215 via the selector 209, and all signals are input to the frame memory 216. The output is transferred. Therefore, in this case, all the pixel data of each photographing frame is temporarily stored in the frame memory 216. Therefore, in the case of continuous photographing, all the pixel data of the photographed image is written into the frame memory 216.

  After completion of the writing operation to the frame memory 216, the contents of the frame memory 216 storing the pixel data are transferred to the camera digital signal processing unit (DSP) 210 via the selector 209 under the control of the memory controller 215. The camera DSP 210 generates RGB color signals based on the pixel data of each image stored in the frame memory 216.

  In a state before normal shooting, the generated RGB color signals are transferred to the video memory 211 periodically (for each frame), so that the monitor display unit 212 performs finder display and the like.

  On the other hand, when the photographer instructs photographing (that is, image recording) by operating the camera operation switch 201, each pixel data for one frame is read from the frame memory 216 by a control signal from the overall control CPU 200. The image data is processed by the camera DSP 210 and then temporarily stored in the work memory 213.

  Subsequently, the data in the work memory 213 is compressed by the compression / decompression unit 214 based on a predetermined compression format, and the compressed data is stored in the external nonvolatile memory 217 (usually using a nonvolatile memory such as a flash memory). .

  Conversely, when observing image data that has already been taken, the data compressed and stored in the external memory 217 is expanded to normal pixel-by-pixel data through the compression / decompression unit 214, and the expanded pixel-by-pixel data is obtained. Is transferred to the video memory 211, and the captured image can be observed through the monitor display unit 212.

  As described above, the normal digital camera is configured to convert the output from the image sensor 204 into actual image data through a signal processing circuit in almost real time and output the result to a memory or a monitor circuit.

  On the other hand, in the digital camera system as described above, in particular, in the case of an interchangeable lens single-lens reflex camera, compatibility with a silver salt film, for example, a 135 format film camera system is important.

  The lens can be used if a common mount is used, but there is a difference in size between the imaging element and the film with respect to the shooting angle of view, that is, the focal length.

  At present, an image pickup device is naturally limited in size that can be manufactured at a time due to the relationship between manufacturing apparatuses, so-called steppers, and is generally smaller than a film from the viewpoint of cost. However, considering the same shooting feeling as a film, in particular, depiction with a wide-angle lens, an image pickup device having the same size as a silver salt film is desirable.

  FIG. 8 simply shows a case where one image pickup device such as a CCD is connected by three-division exposure (hereinafter referred to as “connecting exposure”) as one of countermeasures.

  FIG. 8 shows an example in which the image is divided into three regions such as left, center, and right, each is exposed with an individual mask, and finally configured as one image sensor. In the figure, each of the vertical structures composed of a semiconductor layer, an on-chip color filter layer, and an on-chip microlens layer is subjected to stitching exposure to form an image sensor having the same size as the film.

  FIG. 9 is an explanatory diagram of the semiconductor layer when FIG. 8 is a CCD. In this CCD, the charges of the pixels generated in the photodiode unit 190 are transferred to the vertical CCD 191 all at a predetermined timing, and the next timing is shown. Then, the charges of the vertical CCD 191 of all lines are transferred to the horizontal CCDs 192, 193 and 194.

  In the configuration shown in FIG. 9, the horizontal CCDs 192, 193, and 194 both transfer their charges toward the common amplifier 195 for each transfer clock, and the output after the amplifier is read out through the common CDS / AGC circuits 196 and 198. It will be a thing.

Accordingly, if the connection exposure can be performed without any problem, it can be used in the same manner as a normal image sensor.
JP-A-11-220116 Japanese Patent Laid-Open No. 64-141881 JP 2002-252808 A JP 2002-125156 A Japanese Patent Application No. 2002-154407 (Japanese Patent Laid-Open No. 2003-348604)

  Even in the CCD of FIG. 9 that looks like nothing changes, there is actually a considerable shift due to splicing exposure in each of the vertical structures composed of the semiconductor layer, on-chip color filter layer, and on-chip microlens layer, and the output level is high. There is a problem that the three regions vary.

  In particular, the on-chip color filter layer and the on-chip microlens layer are easily displaced, and the influence appears as a step in the gain direction. In particular, since the on-chip color filter layer is exposed for each color, there is a problem that the shifts are different and the steps in each color are different.

  Furthermore, as shown in FIG. 10, each of them may be twisted planarly (two-dimensionally), resulting in a considerably complicated shift.

In order to achieve the above object, a first divided exposure region and a second divided exposure region that are different from the first divided region are manufactured in a plurality of divided exposures on a semiconductor substrate, and are different from the first divided region. at least Yes, and corrects an image sensor that have a plurality of channels for reading out a signal, the signal read out in the same channel from the first divided exposure region and the second divided exposure regions of the imaging device A correction unit; and a control unit that writes a signal multiplied by a correction value by the correction unit into a frame memory. The correction unit includes a signal from the first divided exposure area read from the same channel and the first signal. the difference between the output level due to the divided exposure of a signal from the second divided exposure regions corrected, Chan for signals read out the correction in the plurality of channels Provided is an imaging device which is characterized in that each Le.

  According to the present invention, it is possible to obtain a high-quality image without variation between imaging regions.

  Hereinafter, a method for correcting an imaging signal and an imaging apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram of an imaging apparatus (digital camera) according to the first embodiment of the present invention.

  Basically, a block correction unit 6 and a correction nonvolatile memory 7 for storing the correction value are added to FIG.

  In FIG. 1, reference numeral 1 denotes an image pickup device, which performs the same drive and control as a normal device even if it is constituted by continuous exposure. The image sensor 1 is driven by a driver 2 and operates at a predetermined frequency. The timing generator 3 is a timing generating circuit that outputs a vertical synchronizing signal VD and a horizontal synchronizing signal HD, and simultaneously supplies timing signals to each circuit block.

  The pixel signal from the image pickup device 1 is input to the CDS / AGC circuit 4, and by performing processing such as known correlated double sampling, reset noise and the like included in the output of the CCD or the like are removed, and a predetermined signal is obtained. Amplifies the output up to the signal level. The amplified pixel signal is converted into a digital signal by the A / D converter 5 to obtain a digitized pixel signal.

  The digitized pixel signal is sent to the block correction unit 6 to correct a shift due to joint exposure. The block correction unit 6 reads the correction value for each block from the correction non-volatile memory according to an instruction from the overall control CPU, and performs the correction described later on the digital pixel signal according to the timing signal from the timing generator 3.

  Information on the taking lens 20 is transmitted to the overall control CPU 18 through the mount 19 (camera and lens mount). Therefore, when the correction value for each block is switched by the photographic lens, an instruction is issued from the overall control CPU 18 to the block correction unit 6. This will also be described later.

  The corrected pixel signal is input to the memory controller 10 via the selector 8, and all signal outputs are transferred to the frame memory 11. Accordingly, in this case, all the pixel data of each shooting frame are temporarily stored in the frame memory 11, and therefore, in the case of continuous shooting, all the pixel data of the shot images are written into the frame memory 11.

  After the writing operation to the frame memory 11 is completed, the contents of the frame memory 11 storing the pixel data are transferred to the camera digital signal processing unit (DSP) 9 via the selector 8 under the control of the memory controller 10. The camera DSP 9 generates RGB color signals based on the corrected pixel data of each image stored in the frame memory 11.

  When the photographer instructs shooting (that is, image recording) by operating the camera operation switch 17, each pixel data for one frame is read from the frame memory 11 by the control signal from the overall control CPU 18, and the camera The image is processed in the DSP 9 and then temporarily stored in the work memory 13.

  Subsequently, the data in the work memory 13 is compressed by the compression / decompression unit 15 based on a predetermined compression format, and the compressed data is stored in the external nonvolatile memory 17 (usually using a nonvolatile memory such as a flash memory). .

  When observing captured image data, the data compressed and stored in the external memory 16 is expanded to normal pixel data through the compression / decompression unit 15, and the expanded pixel data is converted into video data. By transferring the image to the memory 12, the photographed image can be observed through the monitor display unit 14.

  The configuration in FIG. 1 is a configuration on the premise that the load of signal processing in the camera DSP 9 is not increased. If the signal processing by the camera DSP 9 has a system margin, it is of course possible to correct the deviation by the camera DSP.

  Next, correction of deviation caused by continuous exposure will be described.

  As described above, the on-chip color filter layer and the on-chip microlens layer are easily displaced, and the influence appears as a step in the gain direction. In particular, since the on-chip color filter layer is exposed for each color, there is a problem that the shifts are different and the steps in each color are different.

  Therefore, in the present embodiment, correction is performed with a correction value obtained by storing or calculating in advance a correction value for each block composed of a plurality of pixels that subdivide the exposure division area.

  FIG. 2 is an explanatory diagram of division in block units.

  When the image sensor is connected and exposed at two joints on the left and right as shown in FIG. 6A, and one image sensor is formed by connecting three areas of the left, center, and right, the image shown in FIG. In this way, the image sensor is divided into a plurality of blocks which are one of the boundaries dividing the left and right joints. Here, 6 vertical divisions and 11 horizontal divisions are used. Therefore, the entire image pickup device has a number of blocks as shown in FIG. 3C, which becomes the correction value table itself. However, since the present embodiment has correction values corresponding to the colors of the on-chip color filter, for example, in the case of a general Bayer filter, a correction value table consisting of four surfaces as shown in FIG. .

  Although it is considered that the larger the number of blocks, the better the accuracy, but the storage area on the system increases accordingly, so it should be determined in balance with the effect.

  Next, the format of the correction value will be specifically described.

  The correction value is a correction value in the gain direction, and the correction value is applied to the pixel signals on both sides of the joint so that there is no step between the left and right joints.

  In this embodiment, as a correction value to be obtained, a division exposure area including the optical axis of the photographing optical system, that is, a center area signal in this embodiment is used as a reference, and correction values in the right and left areas are obtained. did.

  This is because priority is given to using the center of the screen as it is. After all, the central part of the screen is likely to be an object of appreciation, and it is based on the judgment that it is natural to take out the performance of the imaging optical system sufficiently.

  Furthermore, the correction of the shift is aimed at eliminating the step at the connecting portion, and the achievement of the purpose is regarded as the first priority. On the other hand, it is assumed that other corrections are left to other corrections, and the same correction value as that of the boundary end is used as it is in the direction orthogonal to the boundary direction, independently in the boundary direction of the joint.

  One correction value table from the above viewpoint is as shown in FIG.

  In FIG. 3, the correction values in the central area are all 1, and the right and left areas are optimal values for individual blocks in the blocks along the joints. The vertical direction (horizontal direction in the figure) of the joints The correction value is the same as the correction value. As a result, a natural change is maintained in the peripheral portion even if, for example, there is a change in the peripheral light amount.

  On the other hand, if the correction value is inevitably changed due to, for example, the pupil distance or aperture value of the photographing lens, the correction value is switched for each target lens.

  FIG. 4 is an explanatory diagram, and particularly in an interchangeable lens for a single-lens reflex system, the pupil distance varies mainly depending on the focal distance. Accordingly, for example, three types of correction values for standard, wide-angle, and telephoto are prepared, all stored in the nonvolatile memory for correction values, and when the photographic lens 20 is attached to the camera, the mount 19 Through the lens identification information (lens ID) obtained through the above, an optimum correction value table is sent to the correction calculation area of the block correction unit 6 so that a satisfactory deviation can always be corrected.

  The attached lens information may be used by changing or calculating the correction value based on the pupil distance or aperture value information itself, instead of changing the lens ID.

(Second Embodiment)
In the above embodiment, the readout system of the image sensor 1 has one channel. In the present embodiment, a case will be described in which the readout system capable of high-speed readout has two channels.

  FIG. 5 is a block diagram of an image pickup apparatus (digital camera) in which the readout system of the image pickup device 1 has two channels.

  In order to emphasize high speed, two CDS / AGC circuits 4-1 and 4-2 and two A / D conversion units 5-1 and 5-2 are added to the block diagram of FIG.

  There are various ways of reading out the two systems by the image sensor 1, and it is not limited to the left / right distribution at the center of the element surface as shown in Japanese Patent Laid-Open No. 2000-253305 as shown in FIG. (B in the same figure), and further, it may be read out in a more finely divided manner inside the image sensor, and multiplexed to two channels when going outside (FIG. (C)).

  In these cases, it is necessary to cope with a deviation caused by a difference in readout system.

  Although this differs depending on the combination with the configuration of the on-chip color filter, for example, when a Bayer arrangement is adopted, (A) and (B) in FIG. 6 are possible even with one set of block correction tables.

  On the other hand, in the case of FIG. 5C, two sets of block correction values are required if the misalignment between a plurality of systems is not corrected by some method. This is because there are two readout channels for the same on-chip color filter color.

  As described above, according to the first and second embodiments, when the imaging region of the imaging element in the imaging device is formed by joint exposure, the sensitivity is uneven in the two-dimensional direction. It becomes possible to correct a signal difference between regions.

  Further, even when the non-uniformity differs depending on optical factors of the photographing optical system, such as the exit pupil position and the aperture value, it is possible to correct the signal difference more appropriately.

  Further, even when readout is performed by multiple systems, it is possible to correct signal differences between a plurality of regions including deviation amounts due to a plurality of readout channels.

1 is a configuration explanatory diagram of a digital camera according to Embodiment 1 of the present invention. FIG. It is explanatory drawing of the block division | segmentation in Embodiment 1 of this invention. It is explanatory drawing of the correction value table in Embodiment 1 of this invention. It is explanatory drawing of the extended correction value table in Embodiment 1 of this invention. FIG. 6 is a configuration explanatory diagram of a digital camera according to Embodiment 2 of the present invention. It is explanatory drawing of the correction value table which concerns on Embodiment 2 of this invention. It is a block diagram explaining the structure of a conventional digital camera. It is explanatory drawing of connection exposure. It is explanatory drawing of the semiconductor image pick-up element by connection exposure. It is explanatory drawing of an example of the shift | offset | difference by a joining exposure.

Explanation of symbols

1 Image sensor 2 Driver 3 TG / SSG
4,4-1,4-2 CDS / AGC circuit 5,5-1,5-2 A / D conversion circuit 6 Block correction circuit 7 Non-volatile memory for block correction 8 Memory selector 9 Camera DSP
DESCRIPTION OF SYMBOLS 10 Memory controller 11 Frame memory 12 Video memory 13 Work memory 14 Monitor display part 15 Compression / decompression part 16 Non-volatile memory 17 Camera operation switch 18 Overall control CPU
19 Camera / Lens Mount 20 Lens

Claims (4)

Produced by a plurality of divided exposure on a semiconductor substrate, the second divided exposure regions of the first divided exposure region and the first divided area different from the area at least chromatic in the imaging area, and reads out the signal an image sensor that have a plurality of channels for,
Correction means for correcting a signal read out in the same channel from the first divided exposure region and the second divided exposure region of the image sensor;
Control means for writing a signal multiplied by a correction value by the correction means to a frame memory;
The correction unit corrects a difference in output level caused by the divided exposure between the signal from the first divided exposure area read from the same channel and the signal from the second divided exposure area, and performs the correction. An image pickup apparatus that performs the processing for each channel with respect to signals read by the plurality of channels .   The imaging apparatus according to claim 1, wherein correction is performed using a separate correction value for each lens.   3. The imaging apparatus according to claim 1, wherein correction is performed using separate correction values for each exit pupil position of the optical system. 4.   4. The imaging apparatus according to claim 1, wherein correction is performed using a separate correction value for each aperture value. 5.

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