JP2007214772A - Image signal processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus employing a region-divided reading type imaging element wherein the image quality of a composite image can be enhanced. <P>SOLUTION: An image signal processing apparatus improves the image quality of a composite image by including: a signal difference correction means for correcting signal differences of image signals outputted from a plurality of output terminals of the imaging element; and a black level correction means for correcting a black level for output signals from the signal difference correction means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image signal processing apparatus that divides and reads an image output of a solid-state imaging device and corrects a signal difference between a plurality of read output signals.

  In recent years, with the advancement of digital signal processing technology and semiconductor technology, a digital video camera in which a recording / playback device for digitally recording a moving picture signal of a standard television system, for example, NTSC system or PAL system, and an imaging device has been commercialized. Some digital video cameras have a still image recording function by taking advantage of the feature of digital recording. Some have a digital I / F for connection with a computer or the like, and have a function of taking a captured image into the computer. Furthermore, there are some which have a plurality of recording media and can select the recording media according to the purpose of use of the image.

  In such an apparatus, when a recorded image is reproduced by connecting to a television, the image size is determined by the digital video standard, for example, 720 × 480 pixels, but there is no problem, but the digital I / F is not used. When transferring an image to other media via a network, a larger number of pixels may be required due to image quality problems.

  Accompanying the increase in the number of pixels of the image sensor, it is necessary to drive the image sensor at a higher frequency in order to read out information of all the pixels of the image sensor, leading to S / N degradation and increased power consumption.

  As one method for increasing the data rate of imaging information while keeping the driving frequency of the imaging device low, the imaging surface is divided into a plurality of regions, and independent charge transfer units, amplifiers, and output terminals are provided in each region. There is a method of reading the imaging signals in parallel. An example of such an image sensor is shown in FIG. In the same figure, the imaging surface of the imaging device 1400 is divided into two areas, left and right, 1401 and 1402 are photoelectric conversion and vertical transfer units, 1403 and 1404 are horizontal transfer units, 1405 and 1406 are amplifiers, and 1407 and 1408 are outputs. Terminal. By using the imaging device having such a structure, there is an advantage that imaging information having a data rate twice as high as the driving frequency of the imaging device can be obtained.

For example, Patent Document 1 and Patent Document 2 can be cited as conventional examples.
JP 2002-252808 A JP 2002-320142 A

  However, the disadvantage of this method is that image quality degradation such as the occurrence of a boundary line due to signal differences between regions when images are generated by combining multiple regions due to non-uniform characteristics of the charge transfer unit or amplifier in each region. There was a problem that occurred.

  Usually, in an imaging apparatus, there is a black level correction unit that corrects an optical black level (hereinafter referred to as an OB level) output from an imaging device to a constant value. There was a problem that the OB level fluctuated.

  An object of the present invention is to improve the image quality of a composite image by correcting a black level after correcting a signal difference between regions in an imaging device using an area division readout type imaging device.

  In order to solve the above-described problem, an image signal processing apparatus according to claim 1 of the present invention includes a signal difference correction unit that corrects a signal difference between image signals output from a plurality of output terminals of an image sensor, and a signal difference correction. A black level correcting means for correcting the black level with respect to the output signal of the means;

  According to the present invention, in an imaging apparatus using an area-divided readout image sensor, the image quality of a composite image can be improved by correcting a black level after correcting a signal difference between areas.

(Example 1)
FIG. 1 is a drawing that best represents the features of the present invention, and is a block diagram of an imaging apparatus equipped with the detection apparatus of the present invention. In the figure, an image passing through a lens 101 is formed on an image sensor 103. In this embodiment, the image sensor is a CCD area sensor. The image signal imaged on the CCD area sensor 103 is converted into an electric signal, divided into left and right parts and read out, and the left half is added to the buffer 105A and the right half is added to the buffer 105B.

  A specific example of the CCD area sensor 103 is shown in FIG. The left half of the area sensor portion is 201A, and the right half is 201B. There are optical black portions 203A and 203B at both ends of the area sensor portion. The images that are sequentially vertically transferred from the area sensor parts 201A and 201B are respectively added to the horizontal transfer units 205A and 205B. The left horizontal transfer unit 205A is the same in the left direction of the figure and the right horizontal transfer unit 205B is the same. The signals are horizontally transferred to the right in the figure, converted into voltages by the read amplifiers 207A and 207B, respectively, and output to the output terminals 209A and 209B.

  The timing of the output image signal will be described with reference to FIG. 301A and 301B indicate one horizontal period in the left and right image signals, respectively. The horizontal axis is time. The left and right image signals in the same horizontal period are read out in the same horizontal period, and as an order, they are read out from the outside to the inside, so the optical black portion is read first, and then from both sides toward the center. Dummy data is read by continuously applying the horizontal transfer pulse for a while even after all the images have been read. FIG. 3B is an enlarged view of the dummy data portion in FIG. In this embodiment, a primary color filter will be described as an example. In the case of the primary color checkered filter, the GBGB color filter and the RGRG color filter are alternately attached to each line. In the figure, an example in the case of the GB line is shown, and after the signal 303A on the left screen is sequentially read as GBGB, the dummy pixels are read as DM1A, DM2A,. Since the signal 303B on the right screen is read from the right end, the order of G and B is reversed, and after reading BGBG, the dummy pixels are read as DM1B, DM2B.

  Returning to FIG. The outputs of the buffers 105A and 105B are applied to the CDS 109A and 109B. The CDS 109A, 109B removes low frequency noise by applying correlated double samples to the left and right CCD output waveforms, respectively, and then the analog signals are converted into digital signals by the A / D 111A, 111B, and the result is a dummy clamp means 112A , 112B.

  The dummy clamp means 112A and 112B are composed of dummy readout means 1120A and 1120B and subtraction means 1121A and 1121B. The dummy readout means 1120A and 1120B read out the pixel value of the dummy part of the CCD area sensor and output the result to the subtraction means 1121A and 1121B for each channel. Add. As shown in FIG. 2, in the CCD area sensor with two-channel reading on the left and right sides, charges are horizontally transferred to both the left and right sides, so that they are read out from the outside toward the center. If the horizontal drive pulse is continuously applied after reading the pixels, so-called dummy levels are read from both channels. This dummy level represents a potential in the vicinity of the center, and the offset of the left and right two screens can be adjusted by aligning the dummy levels read to both channels.

  The outputs of the dummy clamp means 112A and 112B are applied to the linearity correction means 123A and 123B. The linearity correction unit 123A corrects the linearity. Since the linearity differs for each CCD and analog front end, the linearity is measured using the exposure control means 157 at the time of shipment from the factory and stored in the storage means 163 externally attached to the calculation means 145. The linearity is corrected by reading from the storage unit 163 and setting it in the linearity correction units 123A and 123B.

  The outputs of the linearity correction means 123A and 123B are applied to the black level correction means 125A and 125B. The black level correction means 125A, 125B includes OB reading means 1250A, 1250B and subtraction means 1251A, 1251B. The OB reading means 1250A and 1250B calculate the average value of the pixels in the OB portion shown by 203A and 203B in FIG. 2 for each channel, and output the result to the computing means 145. The calculation means 145 calculates the average value of the OB levels of both channels, adds the result to the OB subtraction means 1251A and 1251B for each channel, subtracts the OB level, and adds the result to the gain correction means 129A and 129B.

  The gain correction means 129A and 129B (for the right channel not shown) have two roles. One is to increase the gain electrically when the brightness is insufficient even when the aperture is opened, and the other is to adjust the left and right gains. In the past, there was an analog amplifier in the analog front end, and gain was increased by setting a decibel gain from the microcomputer to the analog amplifier. However, in the case of a divided readout CCD as in this embodiment, gain is increased by the analog amplifier. Since the gain between channels cannot be guaranteed with respect to temperature, voltage, aging, etc., the analog amplifier is abolished, and instead, the A / D conversion accuracy in the analog front end is increased, for example, the conventional 12-bit The gain is increased by digital multiplication.

  The left and right images whose gains have been corrected by the gain correcting means 129A and 129B are synthesized by the synthesizing means 147 and are added to the camera signal processing 149 as a single-screen signal similar to the conventional one. Various processes such as a reduction process, a camera shake correction process, a γ correction, a color separation, and a luminance edge enhancement in accordance with the DVC digital video standard are performed and output to the terminal 151 as an image signal.

1 is a block diagram illustrating an imaging apparatus according to a first embodiment. Schematic diagram of CCD area sensor Timing diagram of output image signal Schematic diagram of image sensor

Explanation of symbols

103 CCD area sensor
112A, 112B Dummy clamp means
123A, 123B linearity correction means
125A, 125B Black level correction means
129A, 129B Gain correction means
145 Calculation means
147 Synthesis means
163 Memory means

Claims (4)

  A signal difference correction unit that corrects a signal difference between image signals output from a plurality of output terminals of the image sensor and a black level correction unit that corrects a black level with respect to an output signal of the signal difference correction unit are provided. An image signal processing device.   2. The image signal processing apparatus according to claim 1, wherein the signal difference correction means includes dummy clamp means for correcting an offset difference at a dummy level of the image signal.   2. The image signal processing apparatus according to claim 1, wherein the signal difference correction means includes linearity difference correction means for correcting a linearity difference of the image signal.   2. The image signal processing apparatus according to claim 1, wherein the black level correction means is a clamp means for correcting the optical black (OB) level of the image signal to be constant, and the correction amount is output from the signal difference correction means. An image signal processing apparatus characterized by being identical to a plurality of output signals.

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