JP2006121173A - Pixel arrangement method for imaging pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pixel arrangement method of imaging elements which can the image quality improved. <P>SOLUTION: The imaging device has the primary color filters of red, green and blue, and the filters are arranged in the Bayer system. The element has a thinning operation mode for thinning the pixels of a vertical direction, and reading the pixels in addition to a mode for reading all the pixels and has pixels read at only the thinning operation mode. The thinning operation mode is a mode, in which a pixel obtained compositing one read pixel with some unread pixels, is considered as a single pixel, and electrical signals are read for composite pixels read in the thinning operation mode, with a timing in which the number of pixels to be composited of composite pixels to be read at odd-numbered position differs from that of composite pixels to be read at even-numbered position. In this imaging element, the method decides the arrangement of columns of filters of red, green and blue of the imaging element. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pixel arrangement method of an image sensor used when capturing a still image or a moving image.

  An image sensor such as a CCD image sensor used in a digital camera generally has three primary color filters of red (R), green (G), and blue (B), and the arrangement is determined by a method called a Bayer method. Has been made. As shown in FIG. 2A, this is a method in which G is arranged in a checkered pattern and RB is arranged in the remaining portion. Strictly speaking, when the Bayer method is considered in terms of coordinates, four types of arrangements can be combined as shown in FIGS.

  In the image pickup apparatus, the light collected by the lens passes through one of the RGB filters of the image pickup element and is then irradiated to a passive element called a photodiode. At this time, light energy is converted into electrical energy, and charges are accumulated in the photodiode. This signal charge is converted into a voltage and then subjected to video processing by a subsequent A / D converter, a signal processing circuit, etc., and a still image or a moving image is reproduced.

  There are roughly two types of methods for reading the signal charge of the image sensor. There are an all-pixel mode for reading out signal charges corresponding to all the pixels of the image sensor and a thinning-out operation mode for reading out signal charges corresponding to some pixels by thinning out the vertical direction. The description of the all pixel mode is omitted in the present invention, and the thinning operation mode is described.

  The thinning-out operation mode is an operation mode in which one column is read out for every number of pixels of the image sensor. Most display devices such as LCD panels of digital cameras have only about one-tenth the number of pixels of the image sensor. For this reason, when a scene being photographed is shot (referred to as EVF) or when a photographed image is displayed, an image using all pixels of the image sensor cannot be used. Therefore, it is necessary to thin out the image to reduce the number of pixels, but a method of thinning out and reading out the signal charge itself from the image sensor is adopted. Further, since it takes time to read out information of all pixels of one screen, an equivalent afterimage phenomenon occurs in which an image appears to be cut off during EVF or moving image shooting. Since the thinning-out operation mode is thinned out and read out, the time for reading out information on one screen is shortened, and the equivalent afterimage phenomenon is suppressed to an inconspicuous level. Therefore, for these reasons, in the EVF or moving image shooting, a thinning-out operation mode in which some pixels are thinned and read out is used.

  A reading method in the thinning operation mode will be described. In the photodiode that performs energy conversion, one photodiode corresponds to one pixel of the image sensor, and when irradiated with light, an amount of charge is generated and accumulated. Further, vertical transfer electrodes (φV1, φV2) are connected to the respective photodiodes and are alternately arranged in the vertical direction. Some of the vertical transfer electrodes φV1 and φV2 are vertical transfer electrodes that operate in the thinning-out operation mode, and are denoted as φV1A and φV2A. The other electrodes are denoted as φV1B and φV2B (FIG. 3). After a charge is stored in the photodiode, when a pulse voltage called a readout pulse is applied only to the vertical transfer electrodes of φV1A and φV2A, the negative charge stored in the photodiode is transferred to φV1A and φV2A by electrical action. Moving. After the movement, other charges stored in the photodiode are discarded in the substrate and are not used. Next, the voltage of the electrode is moved in the vertical direction by alternately switching between a state in which charges are attracted (+) and a state in which charges are not attracted (−). The voltages applied to φV1A and φV1B, and φV2A and φV2B are the same except for the read pulse voltage. The ratio of the total of φV1A and φV2A with respect to all the vertical transfer electrodes is generally 1/4 or less, and this is the thinning ratio of the thinning operation mode. Note that the positive electrode (charge allowable electrode) to which charges are attracted includes an electrode to which signal charges are actually attracted and an electrode in which no charges are present (referred to as color charges). In addition, although detailed description is avoided, charges are not mixed or reversely flowed by reading and vertical transfer.

  In addition, as shown in FIG. 3, an electrode called a horizontal transfer path is connected to the end of the vertical transfer electrode, and the electric charge moved one step in the vertical direction from the end is transferred to this horizontal transfer path. Also in the horizontal transfer path, the electrodes of φH1 and φH2 are alternately arranged, and the vertical electrodes arranged in a line in the vertical direction correspond to one horizontal transfer electrode. The horizontal electrode is also moved in the horizontal direction by alternating ++. Charge mixing and backflow will not occur in the same way as the vertical transfer electrode, although it will be avoided.

  An output amplifier is connected to the end of the horizontal transfer electrode. In the output amplifier, the charge is converted into a voltage based on the principle of capacitor charge and output. This voltage is serially transferred to the A / D converter as shown in the figure, and then transferred to the video information processing system for image processing.

  When the charge moves from the vertical transfer path to the horizontal transfer path, one charge allowable region moves and horizontal transfer is not performed, but one signal charge and a plurality of color charges are moved to the horizontal transfer path to perform horizontal transfer. Begins. This is shown in FIG. This figure shows the voltage state of a certain vertical transfer electrode and the time course of the attracted electric charge. The white squares are color charges, and the other squares are charges. In these two states, a positive voltage is applied to the electrode. In the case of-, it is assumed that a voltage of-is applied to the electrode. To explain with this table, in the horizontal transfer electrode, the color charge is delivered at time t2, but the charge is delivered and synthesized at time t4. At time t5, charges are transferred in the horizontal direction. In this way, when the signal is transferred to the horizontal transfer electrode, the signal charge and the color charge are combined (the combined charge is referred to as a charge packet). This is because the color charge contains almost no charge, so there is no effect on the image even if it is combined, and horizontal transfer processing for one charge allowable area increases processing time and power consumption. By connecting to. FIG. 5 is a timing chart showing these vertical transfer timing and horizontal transfer timing.

  The ratio of the sum of φV1A and φV2A to all the vertical transfer electrodes, that is, the thinning ratio in the thinning-out operation mode of the image sensor differs for each image sensor, but care must be taken in the case of an odd number. This is because, in the case of an odd number, the number of color charges to be synthesized is different between the odd-numbered packet and the even-numbered packet. In the case of the decimation rate of 1/4, one color charge is synthesized for each packet. However, in the case of decimation of 1/5, one and two are synthesized.

  In the CCD image sensor, a false signal called smear is generated due to light leaking into the vertical transfer path. Smear generates a false charge in proportion to the amount of light leaking. As a result, almost the same amount of electric charge is added in the vertical direction, and an appearance and a band of light are generated vertically. In addition, when smear occurs, not only signal charges but also color charges that conventionally have no charge are generated. Smear is a problem that cannot be avoided due to the structure of the CCD image sensor.

  Here, in an image pickup device that performs odd-number thinning in the thinning-out operation mode, the color of the pixel filter corresponding to a packet with a large amount of color charge is the amount of color charge synthesized due to a difference in color charge synthesis amount in the charge packet. Only emphasis will be given and smear will be colored. As a result, EVF and moving images become very ugly images.

  Since smear is proportional to the intensity of light, it stands out in places where strong light such as sunlight is generated outdoors. In addition, since the human eye is more likely to see red light with a lower frequency than green / blue light with higher frequencies, the charge corresponding to a packet with a large amount of color charge is the charge of the red filter. Furthermore, smear becomes more noticeable. The arrangement of the pixels of the conventional image sensor is not considered such a smear red tendency and varies.

In addition, the filters of the respective colors of the image sensor may have a difference in spectral sensitivity level. This level difference is processed in the video processing circuit so that the gain is adjusted to the same amount. However, since smear is signal charge generated without passing through the filter, gain adjustment is performed for the same amount of charge, and signals of different sizes are actually handled. However, although it is possible to arrange the pixels so as to cancel out the difference in charge magnitude due to this gain adjustment and the difference in charge magnitude due to the difference in color charge synthesis, this is actually considered. Absent.
JP 10-155100 A

  Therefore, in the image pickup element having a thinning-out operation mode for thinning out by an odd number, when smear occurs, 4 possible in FIGS. 2A to 2D so as to eliminate the smear red tendency that is conspicuous for humans. We propose an arrangement method for R, G, and B that is suitable for the arrangement of various types of filters.

With respect to claim 1, in the image pickup device having the primary color filters of red, green, and blue and arranged by the Bayer method,
In addition to the mode to read out all pixels, it has a thinning-out operation mode to read out by reading out pixels in the vertical direction,
There are pixels that are read out only in the thinning operation mode,
The thinning-out operation mode is a mode in which one pixel that is read out and a combination of several pixels that are not read out are regarded as one pixel.
The charge signal is read at a timing such that the number of synthesized pixels of the odd-numbered synthesized pixels and the even-numbered synthesized pixels are different from the synthesized pixels read in the thinning-out operation mode. for,
It is characterized by a method for determining the arrangement of red, green and blue filter rows of an image sensor.

Further, in claim 2, in the image pickup device having primary color filters of red, green, and blue and arranged by the Bayer method,
In addition to the mode to read out all pixels, it has a thinning-out operation mode to read out by reading out pixels in the vertical direction,
There are pixels that are read out only in the thinning operation mode,
The thinning-out operation mode is a mode in which one pixel that is read out and a combination of several pixels that are not read out are regarded as one pixel.
The charge signal is read out at a timing such that the number of synthesized pixels of the odd-numbered synthesized pixels and the even-numbered synthesized pixels are different from the synthesized pixels read out in the thinning operation mode,
Further, the present invention is characterized in that the arrangement of the red, green, and blue filter rows of the image sensor is determined for these features in which the spectral sensitivity characteristic of red is smaller than two of green and blue.

  As described above, according to the present invention, by determining an appropriate pixel arrangement in the CCD image sensor, a smear that is colored when smear occurs does not occur in the captured moving image and EVF. Video can be provided.

(First embodiment)
Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of an imaging apparatus according to the present invention. This imaging apparatus includes a lens barrel 1 including a lens and a diaphragm, a lens barrel control driver 2 that drives the lens barrel 1, a solid-state imaging device 3 that converts light collected by the lens barrel 1 into electrical energy, and a solid-state imaging device 3 A timing generator 4 that controls the image signal, an A / D conversion circuit 5 that performs A / D conversion on the pixel signal output from the solid-state imaging device 3, and a video processing circuit that receives the A / D converted pixel signal and performs video processing 6 and system control circuit 7.

  FIG. 3 shows a simple configuration of the solid-state imaging device 3. A portion indicated by a square 31 represents a pixel filter and a photodiode. The pixel filter is one of red (R), green (G), and blue (B), and can store charges proportional to the amount of light by the photodiode. Reference numeral 32 denotes a vertical transfer electrode, and charges stored in the photodiode 31 are moved by a read pulse. Reference numeral 33 denotes a horizontal transfer electrode, which is an electrode for transferring charges transmitted through the vertical transfer electrode. Reference numeral 34 denotes an output amplifier unit which converts charges into voltage on the principle of capacitor charging and outputs the voltage to the A / D conversion circuit 5. The solid-state imaging device 3 is a Bayer array CCD image sensor having primary color filters red, green, and blue as shown in FIG. 2A, and the thinning-out operation mode is a mode in which 1/5 pixels are thinned out in the vertical direction and read out. It shall be. The thinning-out mode can take four types as shown in FIGS.

Now, in order to extract the pixel signal from the solid-state imaging device 3, it is assumed that the signal of the timing generator is arbitrary, but the following conditions are strictly observed. (1) It is assumed that φV1 * and φV2 * are alternately arranged in the vertical direction, and φV1A and φV2A are arranged at regular intervals. In the horizontal direction, φV1A, φV1B, φV2A, and φV2B determined here are arranged in the same manner (* is A or B).

  (2) The charge transfer from the photodiode to the vertical transfer electrode in the thinning-out operation mode is first performed from φV1A, and then φV2A is performed later. The read pulse is generated only during the period when the voltage is in the + state.

  (3) There are two types of voltages for vertical transfer operation applied to φV1 * and φV2 *: a state where voltage is attracted (+) and a state where voltage is not attracted (−). It has become.

  The following will be described with reference to FIG. First, according to the condition (1), φV1A, φV1B, φV2A, and φV2B corresponding to the photodiodes are arranged. Any arrangement may be used, but since the thinning operation mode is 1/5 thinning, two φV1A and φV2A are arranged in ten vertical transfer electrodes. Next, the readout timing of the thinning operation is determined.

  Time t1: φV1 * is set to +, and φV2 * is set to −.

  Time t2: Further, it is assumed that a read pulse voltage is applied to φV1A, and charge is transferred from the photodiode to φV1A. At this time, one of the five electrodes is charged in the + electrode, and no charge is present in the remaining four electrodes (color charge is present).

  Time t3: Next, a voltage of − is applied to φV1 * and a voltage of + is applied to φV2 *, and the read charges are moved by one stage.

  Time t4: φV2A is read out. In the vertical transfer electrode, two charges exist in five +, and three color charges exist.

  Time t5: The signal charge is transferred vertically to the horizontal transfer electrode until it moves. When the charge moves, horizontal transfer is performed (time t8).

In addition, when moving to the horizontal transfer electrode, the signal charge and the color charge are combined. Of the 5 positive electrodes that can be transferred, 2 are the charge and 3 are the color charge. Distribute color charge to That is, (1) two color charges and one charge (2) one color charge and one charge are delivered to the charge packet delivered to the horizontal transfer electrode.

  At this time, the amount of charge synthesized when two colored charges are combined also increases the amount of charge synthesized when smear occurs. In particular, in the case of a charge corresponding to a red filter, red is more noticeable to human eyes. Therefore, a red pixel filter is arranged so that one color charge is combined with the charge corresponding to the red filter. That is, red and green are arranged in the pixel 2 corresponding to φV1A in FIG. 6, and green and blue are arranged in the pixel 1.

  Here, even when the thinning-out operation mode is 1/7, 1/9, etc. other than 1/5, the color charges to be synthesized are 2, 3, 3, and 4, and are synthesized in the same manner as in 1/5. There is no problem as long as the charge with less color charge corresponds to red. Further, the reading order is φV1A and φV2A, but even if this order is changed, there is no problem because there is no influence thereafter. In addition, in the case of distributing color charges, there is a possibility that the distribution is not nearly equal, such as 0 and 3, but the red charge may be combined with the smaller color charge. There is no problem because the method does not change.

(Second embodiment)
The configuration of the solid-state imaging device according to the second embodiment is the same as that of the first embodiment as shown in FIG. Further, the RGB possible arrangement of the solid-state imaging device is also as shown in FIGS. 3A to 3D, as in the first embodiment.

  First, spectral sensitivity characteristics as shown in FIG. 6 are obtained for the solid-state imaging device. Here, it is assumed that R is the smallest. The magnitude of this spectral sensitivity is adjusted by the video processing circuit so that it has the same magnitude, but the smear is a signal that does not pass through the filter, so the signal of the same magnitude is only gain adjusted. Will not be the same amount. Therefore, the largest pixel filter whose gain is adjusted by the video processing circuit, that is, the pixel filter having the smallest spectral sensitivity, is arranged on the charge synthesized by one color charge. That is, red and green are arranged in the pixel 1 in FIG. 7, and green and blue are arranged in the pixel 2. As a result, the smear red color generated by the color charge synthesis and the smear red color generated by the gain adjustment are canceled out and become inconspicuous.

It is a block diagram which shows the structure in one Embodiment of this invention. (A)-(d) is the arrangement | sequence of the pixel filter of the solid-state image sensor in this embodiment. It is a structure of the solid-state image sensor in this invention. It is the figure which showed a mode that an electric charge was combined when passing to a horizontal transfer path. It is a figure of an example of the timing of a vertical and a horizontal transfer electrode in 1/5 thinning-out operation mode. It is an example of the spectral sensitivity characteristic of the CCD image sensor in this embodiment. It is an example of the pixel arrangement | positioning method in this embodiment.

Explanation of symbols

1 Lens barrel (lens, aperture, etc.)
2 barrel control driver 3 solid-state imaging device 31 pixel, photodiode 32 vertical transfer electrode 33 horizontal transfer electrode 34 output amplifier 71 pixel, photodiode 72 vertical transfer electrode 73 horizontal transfer electrode

Claims (2)

In the image sensor that has the primary color filters of red, green, and blue and is arranged by the Bayer method,
In addition to the mode to read out all pixels, it has a thinning-out operation mode to read out by reading out pixels in the vertical direction,
There are pixels that are read out only in the thinning operation mode,
The thinning-out operation mode is a mode in which one pixel that is read out and a combination of several pixels that are not read out are regarded as one pixel.
The charge signal is read at a timing such that the number of synthesized pixels of the odd-numbered synthesized pixels and the even-numbered synthesized pixels are different from the synthesized pixels read in the thinning-out operation mode. for,
A method for determining the arrangement of red, green, and blue filter columns of an image sensor. In the image sensor that has the primary color filters of red, green, and blue and is arranged by the Bayer method,
In addition to the mode to read out all pixels, it has a thinning-out operation mode to read out by reading out pixels in the vertical direction,
There are pixels that are read out only in the thinning operation mode,
The thinning-out operation mode is a mode in which one pixel that is read out and a combination of several pixels that are not read out are regarded as one pixel.
The charge signal is read out at a timing such that the number of synthesized pixels of the odd-numbered synthesized pixels and the even-numbered synthesized pixels are different from the synthesized pixels read out in the thinning operation mode,
Further, a method of determining the arrangement of the red, green, and blue filter rows of the image sensor for those features having red spectral sensitivity characteristics smaller than two of green and blue.

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