JP2010088019A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus for reducing a luminance step phenomenon caused by a difference in storage time between lines of an imaging device. <P>SOLUTION: The imaging apparatus includes: a synchronization signal generating section 106 for generating vertical synchronization signals at predetermined intervals and generating the predetermined number of horizontal synchronization signals while two vertical synchronization signals are generated; the imaging device 102 for storing electric charge while shifting a term for each area in accordance with the vertical synchronization signals and the horizontal synchronization signals; and a control section 105 for setting the intervals of horizontal synchronization signals in accordance with a target value to decide a term during which the interval of horizontal synchronization signals is set to a value different from the target value if a term required until generating the predetermined number of horizontal synchronization signals is not matched with the predetermined interval of vertical synchronization signals. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging apparatus, and more particularly to an imaging apparatus characterized by a technique for generating a synchronization signal for an imaging element.

  In an imaging device such as a digital video camera, an image sensor such as a CMOS sensor and a CCD stores and reads signals from each pixel in accordance with a vertical synchronization signal indicating a vertical synchronization period and a horizontal synchronization signal indicating a horizontal synchronization period.

  The vertical synchronization period operates so as to have a fixed interval determined in advance by a moving picture standard such as NTSC or PAL. On the other hand, since the period required for the horizontal synchronization period differs depending on the number of pixels read from the image sensor and the readout method, an integral multiple of a certain horizontal synchronization period does not necessarily match the vertical synchronization period.

For example, as shown in FIG. 5, when the vertical synchronization period is V, the horizontal synchronization period is H, and the number of horizontal synchronization periods with respect to the vertical synchronization period is N, V = N × H + α
Thus, a fractional period of α may occur.

  Conventionally, a synchronizing signal generator that generates a vertical synchronizing signal and a horizontal synchronizing signal absorbs a fractional period with H + α as one of the horizontal synchronizing periods in the vertical synchronizing period, and generates a synchronizing signal so that the other periods become H. By generating, the vertical synchronization period V operates to be constant.

  Hereinafter, for convenience, a period in which the horizontal synchronization period is changed so as to absorb the fraction period is referred to as a fraction adjustment period.

  In recent years, as represented by a CMOS sensor in an imaging device used in an imaging apparatus, each line of pixels of the imaging device sequentially starts and reads out in synchronization with a horizontal synchronization signal. The rolling shutter type is increasing.

  The rolling shutter system is characterized in that the accumulation time differs for each line as compared to a global shutter system such as a CCD in which all pixels of the image sensor are simultaneously accumulated and read out.

Patent document 1 is mentioned as a prior art relevant to the above.
JP 2001-69406 A

  However, in an image pickup apparatus using a rolling shutter type image pickup device, there are the following problems when the image pickup device is driven by a horizontal synchronization signal having a fraction adjustment period as described above.

  FIG. 5 is a timing chart showing how each line of the image sensor is stored and read out by the rolling shutter method in accordance with the synchronization signal.

  VD is a vertical synchronization signal, HD is a horizontal synchronization signal, HCNT is a line number, RST is an accumulation start timing of each line, and RD is a readout timing of each line.

  According to the horizontal synchronization signal HD, the accumulation start timing RST and the read timing RD of each line are sequentially switched. In a certain line, the time from the accumulation start timing RST to the read timing RD corresponds to the accumulation time of the line.

  When the horizontal synchronization period is constant, the accumulation time of each line is equal, but in the horizontal synchronization signal HD, if the uniformity of the horizontal synchronization period is lost due to the fraction adjustment period, the fraction adjustment period is included in the accumulation time. There is a difference in the accumulation time between the line where the signal exists and the line where it does not.

  For this reason, in the image signal output from the image sensor, a luminance step phenomenon occurs in which the signal level varies depending on the accumulation time difference above and below a certain line.

For example, the length of the vertical synchronization period is V, the length of the horizontal synchronization period is H, and the length of the fraction adjustment period is H + α. The number of horizontal synchronization periods for one vertical synchronization period is N lines, the effective pixel readout line from the image sensor is the Ps line to the Pe line, and the accumulation time corresponding to the accumulation start RST to the readout RD is M lines. In this case, the accumulation time T1 in the normal period is
T1 = M × H
On the other hand, the accumulation time T1 of the line read in the accumulation time M line period after the fraction adjustment is
T2 = M × H + α
The accumulation time fluctuates. Hereinafter, the period of the accumulation time M line after the fraction adjustment is referred to as an accumulation time fluctuation period.

  Consider a state in which a fraction adjustment period is generated on the (Ps-1) th line. Since the accumulation time is M lines, the accumulation time fluctuation period is from the Ps line to the (Ps + M−1) line. In this state, since the accumulation time variation period is during the effective pixel readout period, a luminance step phenomenon occurs in the output image.

The level X of the luminance step phenomenon is the level ratio of the image signal read during the accumulation time variation period to the image signal read during the normal period,
X = T2 / T1 = (M × H + α) / M × H
It is represented by

  Therefore, the shorter the accumulation time, the shorter the accumulation time fluctuation period, but the greater the level difference phenomenon. On the other hand, if the accumulation time is long, the level of the luminance step phenomenon becomes small, but the accumulation time fluctuation period becomes long.

  An object of the present invention is to provide an imaging apparatus capable of reducing a luminance step phenomenon caused by a difference in accumulation time of each line of an imaging element.

  In order to achieve the above object, the imaging device according to claim 1 generates a vertical synchronization signal at a predetermined interval and generates a predetermined number of horizontal synchronization signals while the two vertical synchronization signals are generated. In accordance with the target value, the synchronization signal generating means for generating the image sensor, the image pickup device that accumulates charges by shifting the period for each region according to the vertical synchronization signal and the horizontal synchronization signal, and the interval between the horizontal synchronization signals, If the period required to generate the predetermined number of horizontal synchronization signals does not match the predetermined interval of the vertical synchronization signals, the interval of the horizontal synchronization signals is set to a value different from the target value. And a control means for determining the period.

  According to the imaging apparatus of the present invention, it is possible to reduce the luminance step phenomenon caused by the difference in the accumulation time of each line of the imaging element.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block configuration diagram of an imaging apparatus according to an embodiment of the present invention.

  In FIG. 1, the imaging apparatus includes a lens group 101 and a rolling shutter type imaging element 102 that performs accumulation start and readout processing for each line in accordance with horizontal and vertical synchronization signals. The image sensor 102 accumulates charges while shifting the period for each region in accordance with the vertical synchronization signal and the horizontal synchronization signal.

  The image pickup apparatus also includes an analog front end (hereinafter abbreviated as AFE) 103 that amplifies the output of the image sensor 102 and performs A / D conversion, and a setting unit 104 that sets the accumulation time and the number of readout lines of the image sensor 102. Prepare.

  The imaging apparatus also controls the control unit 105 that controls the interval of a predetermined number of horizontal synchronization signals according to the setting of the accumulation time and the number of readout lines, and generates a synchronization signal that generates horizontal / vertical synchronization signals according to the settings from the control unit 105. Part 106 is provided.

  Further, the imaging apparatus includes a camera signal processing unit 107, a recording signal processing unit 108, a display device 109 such as a liquid crystal panel, and a recording medium 110 such as a DVD disk or a memory card.

  Next, the operation of the imaging apparatus will be described.

  The setting unit 104 sets the accumulation start / read timing of each pixel, that is, the accumulation time for the image sensor 102. In addition, a driving method related to a reading period, such as an addition / decimation method, is set for a reading range for pixels.

  Similarly, information on the accumulation time and the readout period is also input to the control unit 105. The control unit 105 determines the interval of the horizontal synchronization signal according to the input accumulation time and readout period. A specific determination method will be described later.

  The synchronization signal generation unit 106 generates a synchronization signal according to the vertical synchronization signal at a predetermined interval and the horizontal synchronization signal interval determined by the control unit 105.

  When an optical image is formed on the light receiving surface of the image sensor 102 through the lens group 101, the photodiode of each pixel on the image sensor 102 corresponds to the accumulation start / read timing at each pixel and the amount of incident light. Photocharge is generated.

  In accordance with the input horizontal synchronization signal, the start and readout of each line are performed by a rolling shutter system in which processing is performed sequentially shifted.

  The generated photoelectric charge is output as an output video voltage signal in a predetermined order from the output terminal. The output video voltage signal is amplified by the AFE 103 and converted into digital data.

  After the processing as described above is performed, predetermined camera signal processing is performed by the camera signal processing unit 107, and data of the processing result is displayed on the display device 109, while passing through the recording signal processing unit 108. The recorded image is recorded on the recording medium 110.

  In the present invention, the control unit 105 sets the interval of the horizontal synchronization signal according to the target value, so that the period required to generate the predetermined number of horizontal synchronization signals does not match the predetermined interval of the vertical synchronization signal. In this case, control is performed as follows. That is, the control unit 105 determines a period during which the horizontal synchronization signal interval is set to a value different from the target value.

  Further, the control unit 105 sets a horizontal synchronization signal interval in an effective area for generating image data for recording in the image sensor 102 to a target value, and a horizontal synchronization signal in at least a part of the area outside the effective area. Set the interval to a value different from the target value.

  In addition, when the effective area for generating the recording image data in the image sensor 102 changes, the control unit 105 sets the horizontal synchronization signal interval to a value different from the target value in accordance with the change in the effective area. Change the period set in.

  Further, the control unit 105 changes the period for setting the interval of the horizontal synchronization signal to a value different from the target value after a certain period with respect to the horizontal synchronization period in which the last line of the effective area of the image sensor 102 is read.

  In addition, when the accumulation time for accumulating charges in the image sensor 102 changes, the control unit 105 changes the period for setting the horizontal synchronization signal interval to a value different from the target value according to the change in the accumulation time. .

  In addition, the control unit 105 sets the interval of the horizontal synchronization signal to a value different from the target value and a value different from the target value so that the ratio or difference between the target value and the value different from the target value is equal to or less than the threshold value. Control the width.

  Hereinafter, each embodiment will be described.

(First embodiment)
FIG. 2 is a timing chart showing how the lines of the image sensor are stored and read out by the rolling shutter method in accordance with the synchronization signal generated by the synchronization signal generator in FIG. 1 (1).

  VD is a vertical synchronization signal, HD is a horizontal synchronization signal, HCNT is a line number, RST is an accumulation start timing of each line, and RD is a readout timing of each line.

  According to the horizontal synchronization signal HD, the accumulation start timing RST and the read timing RD of each line are sequentially switched. The time from the accumulation start timing RST to the read timing RD in a certain line corresponds to the accumulation time of that line.

  For example, the length of the vertical synchronization period is V, the length of the horizontal synchronization period is H, the length of the fraction adjustment period is H + α, and the number of horizontal synchronization periods for one vertical synchronization period is N lines. The effective pixel readout line is changed from the Ps line to the Pe line.

  Further, when the accumulation time corresponding to the accumulation timing from the accumulation start timing RST to the read timing RD is M lines, the synchronization signal generator 106 operates so as to generate the fraction adjustment period on the Pe + K line.

  When the setting of the number of effective pixel readout lines for the image sensor 102 changes and Pe changes, the generation line of the fraction adjustment period can also change accordingly. Since the accumulation time is M lines, the accumulation time fluctuation period is from the (Pe + K + 1) line to the (Pe + K + M) line.

  If the accumulation time variation period is between the Pe line of a certain vertical synchronization period and the Ps of the next vertical synchronization period, the luminance step phenomenon does not occur for the read effective image. Even if the accumulation time M becomes longer and exceeds Ps, the degree X of the luminance step phenomenon becomes smaller as M increases, so that the influence of the luminance step phenomenon on the image can be relatively reduced.

  Since it is desirable to take as long as possible the accumulation time M until Ps is exceeded, it is optimal that K is 1.

  As described above, in the present embodiment, the interval of horizontal synchronization signals in the effective area for generating image data for recording in the image sensor 102 is set to the target value. The interval of the horizontal synchronization signal in at least a part of the area outside the effective area is set to a value different from the target value. When the effective area changes, the period for setting the horizontal synchronization signal interval to a value different from the target value is changed according to the change in the effective area.

  By controlling in this way, it is possible to reduce the luminance step phenomenon caused by the difference in accumulation time of each line of the image sensor 105 and improve the image quality of the captured image.

(Second Embodiment)
FIG. 3 is a timing chart showing how the lines of the image sensor are stored and read out by the rolling shutter method in accordance with the synchronization signal generated by the synchronization signal generator in FIG. 1 (2).

  VD is a vertical synchronization signal, HD is a horizontal synchronization signal, HCNT is a line number, RST is an accumulation start timing of each line, and RD is a readout timing of each line.

  According to the horizontal synchronization signal HD, the accumulation start timing RST and the read timing RD of each line are sequentially switched. The time from the accumulation start timing RST to the read timing RD in a certain line corresponds to the accumulation time of that line.

  For example, the length of the vertical synchronization period is V, the length of the horizontal synchronization period is H, the length of the fraction adjustment period is H + α, and the number of horizontal synchronization periods for one vertical synchronization period is N lines. The effective pixel readout line is changed from the Ps line to the Pe line.

  Further, when the accumulation time corresponding to the accumulation timing from the accumulation start timing RST to the read timing RD is M lines, the synchronization signal generator 106 operates to generate a fraction adjustment period on the Ps-MK line.

  When the setting of the accumulation time for the image sensor 102 changes and M changes, the fraction adjustment period generation line can also change accordingly. Since the accumulation time is M lines, the accumulation time fluctuation period is from the (Ps−M−K + 1) th line to the (Ps−K) line.

  If the accumulation time variation period is between the Pe line of a certain vertical synchronization period and the Ps of the next vertical synchronization period, the luminance step phenomenon does not occur for the read effective image. Even if the accumulation time M becomes longer and before Pe, the degree X of the luminance step phenomenon decreases as M increases, so that the influence of the luminance step phenomenon on the image can be relatively reduced.

  Since it is desirable that the accumulation time M until exceeding Pe is as long as possible, it is optimal that K is 1.

  As described above, according to the present embodiment, the interval of horizontal synchronization signals in the effective region for generating image data for recording in the image sensor 102 is set to the target value. Then, the interval of the horizontal synchronizing signal in at least a part of the area outside the effective area is set to a value different from the target value. Further, when the accumulation time changes, the period for setting the horizontal synchronization signal interval to a value different from the target value is changed according to the change in the accumulation time.

  By controlling in this way, it is possible to reduce the luminance step phenomenon caused by the difference in accumulation time of each line of the image sensor 102 and improve the image quality of the captured image.

(Third embodiment)
FIG. 4 is a timing chart showing how each line of the image sensor is stored and read out by the rolling shutter method in accordance with the synchronization signal generated by the synchronization signal generator in FIG. 1 (3).

  VD is a vertical synchronization signal, HD is a horizontal synchronization signal, HCNT is a line number, RST is an accumulation start timing of each line, and RD is a readout timing of each line.

  According to the horizontal synchronization signal HD, the accumulation start timing RST and the read timing RD of each line are sequentially switched. The time from the accumulation start timing RST to the read timing RD in a certain line corresponds to the accumulation time of that line.

  For example, the length of the vertical synchronization period is V, the length of the horizontal synchronization period is H, the number of horizontal synchronization periods for one vertical synchronization period is N lines, and the effective pixel readout line from the image sensor is Pe line.

  Further, when the accumulation time corresponding to the accumulation timing from the accumulation start timing RST to the read timing RD is M lines, the synchronization signal generator 106 sets the length of the horizontal synchronization period of the (α / β) line to H + β. Operate.

The accumulation time T1 in the normal period is
T1 = M × H
On the other hand, the accumulation time T3 when all the horizontal synchronization periods within the accumulation time are H + β is
T3 = M × (H + β)
become.

The degree X of the luminance step phenomenon is expressed as a ratio when all horizontal synchronization periods within the accumulation time are H + β and H.
X = T3 / T1 = M × (H + β) / M × H = (H + β) / H
It becomes. In this case, it does not depend on the accumulation time M.

  Since the level of the luminance step phenomenon is not detected within a certain level, a level TH that can be detected is set in advance, β is determined so that X is smaller than TH, and the fraction adjustment period H + β and the fraction adjustment period The α / β line, which is a period for generating, is set.

  Since the degree X of the luminance step phenomenon is preferably as small as possible, β = 1 is optimal.

  As described above, according to the present embodiment, the horizontal synchronization signal interval is set to a value different from the target value so that a ratio or difference between the target value and the target value is less than or equal to a threshold value. The width of the area set to a value different from the target value is controlled.

  By controlling in this way, it is possible to reduce the luminance step phenomenon caused by the difference in accumulation time of each line of the image sensor 102 and improve the image quality of the captured image.

It is a block block diagram of the imaging device which concerns on embodiment of this invention. It is a timing chart which shows a mode that each line of an image pick-up element is accumulate | stored and read by a rolling shutter system according to the synchronizing signal generated by the synchronizing signal generation part in FIG. It is a timing chart which shows a mode that each line of an image pick-up element is accumulate | stored and read by a rolling shutter system according to the synchronizing signal generated by the synchronizing signal generation part in FIG. It is a timing chart which shows a mode that each line of an image pick-up element is accumulate | stored and read by a rolling shutter system according to the synchronizing signal generate | occur | produced by the synchronizing signal generation part in FIG. It is a timing chart which shows a mode that each line of an image pick-up element is accumulate | stored and read by a rolling shutter system according to the synchronizing signal which the synchronizing signal generation part in the imaging device which concerns on a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Lens group 102 Image pick-up element 103 Analog front end 104 Setting part 105 Control part 106 Synchronization signal generation part 107 Camera signal processing part 108 Recording signal processing part 109 Display apparatus 110 Recording medium

Claims (6)

Synchronization signal generating means for generating a vertical synchronization signal at a predetermined interval and generating a predetermined number of horizontal synchronization signals while the two vertical synchronization signals are generated;
In accordance with the vertical synchronization signal and the horizontal synchronization signal, an image sensor that accumulates charges by shifting a period for each region;
By setting the interval of the horizontal synchronization signal according to a target value, if the period required to generate the predetermined number of horizontal synchronization signals does not match the predetermined interval of the vertical synchronization signal, Control means for determining a period for setting a horizontal synchronization signal interval to a value different from the target value;
An imaging apparatus comprising:   The control means sets an interval of the horizontal synchronizing signal in an effective area for generating image data for recording in the image sensor to the target value, and the horizontal in at least a part of the area outside the effective area. The imaging apparatus according to claim 1, wherein the interval of the synchronization signal is set to a value different from the target value.   When the effective area for generating image data for recording of the image sensor changes, the control means changes the interval of the horizontal synchronization signal from the target value according to the change of the effective area. The imaging apparatus according to claim 2, wherein a period set for the value is changed.   The control means changes the period for setting the interval of the horizontal synchronization signal to a value different from the target value after a certain period with respect to the horizontal synchronization period in which the last line of the effective area of the image sensor is read. The imaging device according to claim 3.   When the accumulation time for accumulating charges in the image sensor changes, the control unit changes a period for setting the interval of the horizontal synchronization signal to a value different from the target value according to the change in the accumulation time. The imaging apparatus according to claim 2, wherein:   The control means sets the interval of the horizontal synchronization signal to a value different from the target value and a value different from the target value so that a ratio or difference between the target value and a value different from the target value is equal to or less than a threshold value. The image pickup apparatus according to claim 1, wherein the width of the area to be controlled is controlled.

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