JP2012090177A - Camera system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a camera system in which gain variation is reduced in gain switch of multiple amplifiers.SOLUTION: This camera system in which gain switch is possible comprises: an image sensor capable of varying a shutter speed by changing a storage time; a first amplifier in which a gain division step is large; and a second amplifier in which a gain division step is small. In accordance with the gain switch level of one of the amplifiers, in the gain switch of the amplifier, the shutter speed is varied first, the shutter speed is returned to original speed next, and a gain of the other amplifier is switched.

Description

  The present invention relates to a camera system having a plurality of amplification means.

  In order to realize a camera capable of photographing under low illuminance, it is desired to apply more gain. For this purpose, a plurality of amplifying means are provided to improve the low illuminance performance by increasing the total amplification factor (see, for example, Patent Document 1). Such a conventional technique will be described with reference to FIG.

  The imaging element 401 converts an optical image formed on the imaging surface via a lens (not shown) into an electrical signal and outputs it as an image signal. The image signal output from the image sensor 401 is amplified by two-stage amplifying means including an amplifier A402 having a large gain dividing step and an amplifier B403 having a small gain dividing step. Then, the gain is controlled by the camera control circuit 404 while switching the respective amplifiers in combination. The image processing circuit 405 performs predetermined signal processing on the image signal amplified by the amplifier A 402 and the amplifier B 403 and outputs the processed signal.

  Here, the gain switching of the two types of amplifiers takes into account the gain switching of the amplifier A402 having a large gain dividing step, and the two types of amplifiers are combined by changing the gain of the amplifier B403 having a small gain dividing step. The gain change has a linear characteristic.

Japanese Patent Registration No. 0573442

  However, when gain switching control is performed by the method disclosed in the above-mentioned patent document, variation (error) of each gain (amplification factor) of two types of gains to be combined is generated as a step, and the two types of gains are By switching at the same time, it appears as a step in the total gain. That is, there is a problem in that a linear shock cannot be obtained with a gain change, and a luminance shock occurs in which the brightness varies when the gain is switched. This will be described with reference to FIG.

  In FIG. 5, (a) is a gain switching step of the amplifier B403 with a small division step, and (b) is a gain switching step of the amplifier A402 with a large division step. (C) is a total gain switching step in which these two types of amplifiers are combined. As described above, each amplifier has a gain variation, so that a step is generated when the gains of the two types of amplifiers are switched simultaneously.

  An object of the present invention is to provide a camera system that eliminates a step at the time of gain switching that occurs when using a plurality of amplifying means, and that can realize a linear total gain characteristic without a step.

  The present invention has been made to achieve the above object, and the camera system of the present invention includes an image sensor that converts an optical image of a subject into an image signal and outputs the image signal, and changes the gain in the first division step. A first amplifying means for amplifying the image signal; and a second amplifying means for amplifying the image signal by changing the gain in a second division step finer than the first division step, A camera system for amplifying the image signal with a desired gain by combining the gain of the first amplifying means and the gain of the second amplifying means, wherein either one of the first and second amplifying means When the gain is increased by a predetermined gain, the other gain is decreased and the shutter speed of the image sensor is decreased by an amount corresponding to the predetermined gain. The gain and having a control means for the control such shutter speed increases the amount corresponding the image sensor corresponding to the predetermined gain with increasing the predetermined gain.

  According to the present invention, it is possible to provide a camera system having a linear gain characteristic as a total when an image signal output from an imaging sensor is amplified using a plurality of amplifying means.

The block diagram of the camera system of an Example. The figure for demonstrating the gain switching method of an Example. The flowchart for demonstrating the gain switching method of an Example. The figure for demonstrating a prior art example. The figure for demonstrating a prior art example.

(Example)
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a camera system according to an embodiment of the present invention.

  In FIG. 1, an image sensor 101 converts an optical image of a subject received by an image sensor surface through a lens (not shown) into an electrical signal, and amplifies the image to a predetermined signal level by an amplifier in the sensor (not shown). Output as a signal. A sensor drive circuit (timing generator) 102 generates a drive signal for driving the image sensor 101. An electrical signal converted in the imaging sensor 101 is output as an image signal at a timing synchronized with the drive signal. Further, by controlling this drive signal, the accumulation time (shutter speed) in which charges are accumulated is changed according to the optical image received by the image sensor 101.

  The analog amplification circuit 103 (first amplification means) amplifies the image signal output from the imaging sensor 101 by changing the gain (amplification factor) in the first division step. Here, since the image signal output from the imaging sensor 101 is an analog image signal, the analog amplifier circuit 103 amplifies the image signal with an analog amplifier. The A / D conversion unit 104 converts the analog image signal into a digital image signal.

  The digital amplifying circuit 105 (second amplifying means) amplifies the digital image signal output from the A / D converter 104 by changing the gain in a finer division step than the first division step. Here, since the image signal from the A / D converter 104 is a digital image signal, the digital amplification circuit 105 amplifies the image signal by multiplying the digital image signal by a magnification.

  In this embodiment, the analog gain by the analog amplifier circuit 103 (first amplifier means) and the digital gain by the digital amplifier circuit 105 (second amplifier means) are combined and output from the image sensor 101 with a desired gain. The image signal is amplified. By combining digital gain and analog gain, a larger gain can be applied as a total gain.

  The image processing circuit 106 performs various signal processing such as gamma correction processing, color correction processing, and noise reduction on the digital image signal amplified by the digital amplification circuit 105. The camera control circuit 107 outputs shutter speed (accumulation time) information to the sensor drive circuit 102. Also, gain information is output to the analog amplifier circuit 103 and the digital amplifier circuit 104. Controls such as a zoom operation, a focus focusing operation, and an aperture control operation by a lens unit (not shown) are also performed.

  The memory circuit 108 stores in advance analog gain variation (error) data from the analog amplifier circuit 103 and digital gain variation (error) data from the digital amplifier circuit 104, respectively. In addition, the image memory circuit 109 is written with an image signal subjected to various signal processing by the image processing circuit 106. The D / A converter 110 converts the digital image signal output from the image processing circuit 106 into an analog image signal and outputs the analog image signal to an external monitor or the like.

  Next, gain variations in the analog gain of the analog amplifier circuit 103 and the digital gain of the digital amplifier circuit 105 will be described. Table 1 shows variations in the number of division steps and gain (amplification factor) of gain switching per 6 dB in each of the analog gain of the analog amplifier circuit 103, the digital gain of the digital amplifier circuit 105, and the accumulation time (shutter speed) of the image sensor 101. It is a table | surface which shows (error).

  As is apparent from Table 1, the digital gain has a larger number of division steps when switching the gain and the gain (amplification factor) variation (error) is smaller than the analog gain. In addition, when the shutter speed (accumulation time) of the image sensor is converted to a gain in dB and compared with both the analog gain and the digital gain, the shutter speed (accumulation time) has a higher gain than both the analog gain and the digital gain. The number of division steps when switching is large, and variation (error) in gain (amplification factor) is small.

  The variation in analog gain due to the analog amplifier circuit 103 depends on the circuit characteristics of the analog amplifier, and the variation in digital gain due to the digital amplifier circuit 105 depends on the bit width for digital processing. On the other hand, the variation in shutter speed (accumulation time) depends on the accuracy of the clock frequency of the timing signal for driving the image sensor, but this accuracy is generally several tens of ppm (parts per million). The variation is relatively smaller than analog gain and digital gain.

  In this embodiment, the shutter speed (accumulation time) of the image sensor by the sensor drive circuit is changed when the analog gain by the analog amplifier circuit 103 and the digital gain by the digital amplifier circuit 105 are switched. Then, variations (errors) between the analog gain and the digital gain are absorbed by fine adjustment of the shutter speed (accumulation time), and gain control is possible so that there is no gain step as a total and the amplification factor is linear.

  FIG. 2 is a diagram for explaining a gain (amplification factor) switching method under the control of the camera control circuit 107 in the embodiment of the present invention. 2A shows switching of digital gain by the digital amplifier circuit 105. FIG. Since the digital amplification circuit 105 has a smaller gain division step than the analog amplification circuit 103 that can be set as shown in Table 1, it is possible to change the gain in fine division steps. (B) shows the switching of the analog gain by the analog amplifier circuit 103. Since the analog amplification circuit 103 has a larger gain division step than the digital amplification circuit 105 that can be set as shown in Table 1, the gain is changed with a larger width than the digital gain. (C) shows switching of the shutter speed (accumulation time) of the image sensor 101 by the sensor driving circuit 102. (D) shows the total gain of the digital gain, the analog gain, and the shutter speed (accumulation time).

  In this embodiment, the gain variation generated in each of the analog gain and the digital gain is absorbed as follows, and a linear total gain without a step is realized.

  First, when the analog gain by the analog amplifier circuit 103 is increased by one step from 0 dB to 6 dB, the digital gain by the digital amplifier circuit 105 is decreased from 6 dB to 0 dB prior to that. At the same time, the shutter speed of the image sensor 101 is controlled to decrease from 1/60 seconds to 1/30 seconds. Here, as the digital gain is lowered from 6 dB to 0 dB, the shutter speed is switched from 1/60 seconds to 1/30 seconds and lengthened by 1/30 seconds, so that the gain for 6 dB is compensated by the shutter speed. .

  Here, when a variation (error) of 0.1 dB occurs in the digital gain, even if the digital gain is controlled to decrease from 6 dB to 0 dB, it is actually not 0 dB but only 0.1 dB. become. Therefore, in this embodiment, the digital gain error of 0.1 dB is absorbed at the shutter speed. Specifically, the shutter speed is controlled to be {1 / 30− (the number of shutter seconds corresponding to a gain of 0.1 dB)} seconds. If the gain of 0.1 dB is converted into shutter speed, it becomes 0.00038 seconds. Therefore, if the shutter speed is controlled to be (1 / 30-0.00038) seconds, the digital gain error is absorbed and totaled. The gain is 6 dB.

  Next, the analog gain by the analog amplifier circuit 103 is increased from 0 dB to 6 dB, and at the same time, the shutter speed of the image sensor 101 is controlled from 1/30 seconds to 1/60 seconds so as to increase. Here, as the analog gain is increased from 0 dB to 6 dB, the shutter speed is switched from 1/30 seconds to 1/60 seconds and shortened by 1/30 seconds, thereby reducing the gain by 6 dB at the shutter speed. .

  Here, if the analog gain has a variation (error) of 0.5 dB, even if control is performed to increase the analog gain from 0 dB to 6 dB, it actually increases to 6.5 dB instead of 6 dB. It will be. Therefore, in this embodiment, in addition to the above-described variation of 0.1 dB of the digital gain, the variation of 0.5 dB of the analog gain is absorbed at the shutter speed. Specifically, the shutter speed is controlled to be {1 / 60− (the number of shutter seconds corresponding to a gain of 0.1 dB + 0.5 dB)} seconds. When the shutter speed is 1/60 seconds, the gain of 0.6 dB is converted into the shutter speed, which is 0.0012 seconds. Therefore, if the shutter speed is controlled to be (1 / 60-0.0012) seconds, Absorbing digital gain and analog gain errors, the total gain is 6 dB.

  As described above, in this embodiment, when the analog gain by the analog amplifier circuit 103 and the analog gain by the digital amplifier circuit 105 are switched, the shutter speed control of the image sensor 101 by the sensor driving circuit is combined. By such control, variations in analog gain and digital gain are absorbed, and linear gain control with no step as a whole becomes possible.

  Next, the flow of the gain (amplification factor) switching method in the embodiment of the present invention will be described with reference to the flowchart of FIG. The flowchart in FIG. 3 is executed under the control of the camera control circuit 107. A conversion table for converting the variation of each gain of analog gain and digital gain from dB to shutter speed is stored in the memory circuit 108, and the excess or deficiency of gain when gain is increased / decreased is used as the shutter speed. Control to convert and absorb.

  In step 301, a gain change routine is started. In step 302, it is determined whether the gain to be changed is the analog gain by the analog amplifier 103 or the digital gain by the digital amplifier circuit 105. If the analog gain by the analog amplifier circuit 103 is to be changed, the process proceeds to step 303.

  In step 303, analog gain variation data (conversion table) stored in advance in the memory circuit 108 is read out and temporarily stored as a correction parameter. In step 304, the analog gain by the analog amplifier circuit 103 is changed by a predetermined gain (for example, 6 dB).

  If the digital gain by the digital amplifier circuit 105 is to be changed in step 302, the process proceeds to step 305. In step 305, digital gain variation data (conversion table) stored in advance in the memory circuit 108 is read out and temporarily stored as a correction parameter. In step 306, the digital gain is changed by a predetermined gain (for example, 6 dB).

  When each gain is changed in step 304 or 306, the process proceeds to step 307, and the shutter speed is changed to absorb the gain variation based on the gain variation data (conversion table) read in step 303 or 305. To do. In step 308, the gain change routine ends.

  By performing a series of these controls, variations in the analog gain and the digital gain are absorbed, and linear gain control without gain steps and variations as the total gain becomes possible. Here, the above control is desirably performed within one period, but may be performed over a plurality of periods.

(Other examples)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

DESCRIPTION OF SYMBOLS 101 Image sensor 102 Sensor drive circuit 103 Analog amplifier circuit 105 Digital amplifier circuit 106 Image processing circuit 107 Camera control circuit 108 Memory circuit 109 Image memory circuit

Claims (4)

An imaging sensor that converts an optical image of a subject into an image signal and outputs the image signal, a first amplification unit that amplifies the image signal by changing a gain in a first division step, and finer than the first division step A second amplifying means for amplifying the image signal by changing the gain in a second division step, and combining the gain of the first amplifying means and the gain of the second amplifying means with a desired gain. A camera system for amplifying the image signal,
When the gain of either one of the first and second amplifying means is increased by a predetermined gain, the other gain is decreased by the predetermined gain and the shutter speed of the image sensor is decreased by an amount corresponding to the predetermined gain. Then, a control means for controlling the one of the gains to increase the predetermined gain and to increase the shutter speed of the imaging sensor by an amount corresponding to the predetermined gain;
A camera system comprising:   2. The camera system according to claim 1, wherein the first amplifying unit amplifies an analog image signal, and the second amplifying unit amplifies the digital image signal.   3. The camera system according to claim 1, wherein an error in gain of one or both of the first and second amplifying units is absorbed by the shutter speed. 4.   4. The camera system according to claim 3, further comprising storage means for previously storing gain error data of the first and second amplification means.

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