JP3483899B2 - Electronic imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic image pickup apparatus, and more particularly, to an electronic image pickup apparatus having an autofocus function using an image pickup device. 2. Description of the Related Art Conventionally, various auto-focusing methods have been proposed. For example, a memory addition method in which a video signal is added in units of fields to reduce random noise is known. This memory addition method generally uses a recursive filter to add information (image signal) newly obtained to the information (image signal) up to that time by 1 / K (K is a coefficient) and to add a plurality of information. This is a method of averaging information to reduce random noise and improve the S / N ratio. [0003] However, in the above-mentioned memory addition method, since a large number of images are added, that is, the images are added for a long time, so-called motion blur occurs. Therefore, it is inconvenient for use in an autofocus mechanism. On the other hand, there is known a mechanism for increasing the gain of an image sensor by using a long-time shutter. However, this long-time shutter system causes a reduction in sampling grade for auto focus and a motion blur similar to the memory addition system described above. And so on, which makes it difficult to put it to practical use. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an electronic image pickup apparatus which solves the above-mentioned problems and dramatically improves the limit of the image pickup device on the low luminance side. And In order to achieve the above object, an electronic imaging apparatus according to the present invention comprises a line of an image sensor.
Driving means capable of performing addition driving;
And a video memory for storing a field image to be read.
When the brightness is low, the field signal with line addition is
Used for AE, AF and AWB,
Frame signals that have been field-interpolated using video memory
It is used for display and recording. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to description of embodiments of the present invention, an outline of the present invention will be described. The present invention provides: Field intermittent line addition drive is performed for the image sensor. According to the line addition drive (details will be described later), the vertical resolution is reduced, but the sensitivity is improved. Therefore: The image information from the odd field by the line addition drive is used for autofocus, and the image information from the even field by the normal drive (normal drive) is used as image information of a monitor such as an EVF and a recording system. That is, at the time of auto focus, odd information gained equivalently by line addition is added, and at the time of monitoring and recording, the ordinary field interpolated with the field memory is used for the odd field.
By using the respective information, the autofocus can be performed while securing 30 samples / second, for example.
The sensitivity can be improved by a factor of 0 or more.
Note that the above numerical value, 30 samplings / second, is a sufficient value for an autofocus of a video camera or the like. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a main configuration of an electronic image pickup apparatus according to a first embodiment of the present invention. In the first embodiment, as shown in the figure, an image sensor 2 for generating an image signal of a subject (not shown) formed by a photographing lens 1a, and a subject image signal from the image sensor 2 A pre-processing circuit 3 which performs processing such as sample & hold, gain control, etc. to convert it into a normal video signal; an imaging main process 4 which performs various image processing on the video signal from the pre-processing circuit 3; A video memory 5 which receives an output signal from the process 4 and stores the video signal and outputs the video signal to an external recording system or an EVF (Electronic View Finder), etc .; a BPF; a detection circuit; an integration circuit; A high frequency component relative to the video signal from the pre-processing circuit 3;
That is, a contrast extraction circuit 6 for detecting a contrast signal corresponding to an imaging contrast, a contrast signal output from the contrast extraction circuit 6 are input, the signal is selected at a timing described later, and the focus actuator 1 is selected based on the signal. Controller 7 for controlling focus and controlling the focus, and writing / writing of the video memory 5 under the control of the system controller 7.
A memory controller 8 for controlling the reading operation and an image sensor driver SSG9 controlled by the system controller 7 to control the driving of the image sensor 2 constitute a main part. The system controller 7 is constituted by a CPU or the like, and monitors the increase or decrease in the value of the contrast signal based on the contrast signal output from the contrast extraction circuit 6, so that the maximum value is obtained. The photographing lens 1a is controlled by controlling the focus actuator 1.
Is driven. The SSG 9 controls the driving of the image sensor 2 as will be described later, in accordance with an instruction from the system controller 7, in addition to the normal function as a driver of the image sensor 2. Here, the line addition driving will be described. The line addition drive is performed by applying a gate to a horizontal transfer pulse sent from the SSG 9 (see FIG. 1) to the image pickup device 2 (see FIG. 1) (into a so-called "missing state"), and Is a technical means for adding the electric charges of the lines in the image sensor 2. Hereinafter, this will be described in detail with reference to FIG. FIG. 2 is a time chart showing pulses for driving the image sensor. The imaging device in this case is an interline CCD as an example. In FIG. 2A, reference symbol VD indicates a vertical drive signal for representing one field unit, and reference symbol HD indicates an example of a horizontal drive signal. In the figure, reference numeral 1
H indicates one horizontal effective scanning period. When the horizontal pulse signal HD is at the "L" level, the period 1H 'is at the time of switching the horizontal line. In general, in the case of an interline CCD, data stored in each pixel of the CCD is first transferred to a vertical transfer register simultaneously for all pixels, and thereafter, is transferred to the vertical transfer register for one period 1H '.
Shifted vertically by lines. At this time, of the pixel data stored in the vertical transfer register, one line of data located at a position adjacent to the horizontal transfer register is transferred to the horizontal transfer register. During the horizontal effective scanning period 1H, the pixel data of the one line is sequentially shifted in the horizontal direction by one pixel at a time, and is read from the end of the horizontal transfer register. In the figure, φ1 and φ2 indicate the horizontal transfer pulses, and the horizontal transfer pulses are set to “H” at an early period corresponding to the shift of one pixel at a time during a period indicated by a cross in the figure. The level and the “L” level are repeated, and the pixel data is read out one pixel at a time in synchronization with this cycle, as described above.
As shown in FIG. 2B, the horizontal transfer pulses .phi.1 and .phi.2 correspond to the horizontal pulse signal H in the one horizontal scanning period 1H.
In the period 1H 'in which D is at the "L" level,
The horizontal transfer pulse φ1 is at “H” level, and the horizontal transfer pulse φ2 is at “L” level. When the horizontal pulse signal HD becomes "H" level, the horizontal transfer pulses .phi.1 and .phi.2 alternately repeat "H" level and "L" level at the above-mentioned early period. The CCD employed in the first embodiment performs horizontal transfer using two-phase pulses, and is shown by two-phase pulses φ1 and φ2 in the drawing. Now, for a system that performs charge transfer by the above-described mechanism, a horizontal transfer pulse that repeats the "H" level and the "L" level in the above-described early period during the one horizontal scanning period 1H is generated. The line addition drive is a driving method of adding pixel data during one horizontal scanning period 1H or a plurality of horizontal scanning periods to add pixel data during these periods.
According to this line addition driving, the output is doubled by adding the pixel data for 2 horizontal scanning periods 2H. That is, since the charge amount is increased and the sensitivity is improved, it is possible to cope with a low-luminance image. By the way, when the line addition driving is performed in this manner, when the horizontal transfer pulse for the line addition is stopped, the corresponding image signal does not output the data as the original image signal. The actual output image of one field is in a so-called "missing tooth" state (interdigital) and is not formed as an image, but can be used sufficiently for autofocus or automatic exposure. In FIG. 2 (a), the symbol HON is a signal which becomes "L" level during line addition as described above, and is constant "H" in a normal state as shown in FIG. In the "level" state, for example, when two lines are added, four lines are added, and eight lines are added, the waveforms are as shown in FIG. In this case, in the case of the above two-line addition, it is doubled,
In the case of the line addition, the sensitivity is improved about four times, and it becomes possible to cope with an image with lower luminance every time the degree of the line addition is increased. Further, the applicant has confirmed through experiments and the like that the resolution, contrast and the like are reduced each time the degree of the line addition is increased, but it is sufficiently practical at least up to several tens of lines added. Next, the signal waveform of each part in the first embodiment will be described with reference to a time chart shown in FIG. Note that the VD signal is added for each period of one vertical scanning period for convenience of expression of timing. FIG. 3A shows an image pickup device 2 (see FIG. 1).
3 is a time chart showing the output of the CCD. In the figure, in the periods indicated by A1, A2, and A3 (one vertical scanning period), image signals obtained by normal image processing are output, and 1 in the diagram is indicated by B1, B2, and B3.
In the vertical scanning period, an image signal by the above-described line addition is output. FIG. 3D is a time chart showing the CCD output signal used for the auto-focus AF operation. The auto-focusing operation is performed using pixel data obtained by line addition in the periods indicated by B1, B2, and B3. This indicates that a focus operation is performed. In the drawing, the output from the CCD during the period indicated by the mark x is not used for the autofocus operation. FIG. 3B is a time chart showing an image output to a recording system, a monitor, and the like. As shown in the figure, first, the first vertical scanning period (period A1)
1), after the image signal from the CCD (image pickup device 2, see FIG. 1) undergoes image processing in the pre-processing circuit 3, the image pickup main process 4 (see FIG. 1), the video memory 5 (see FIG. 1). ) And output. At this time, the image signal from the image sensor 2 in the period A1 is stored in the video memory 5 (see FIG. 1), and the video signal from the video memory 5 in the next one vertical scanning period is equivalent to that in the period A1. An image signal is output. Similarly,
The image signal output in the scanning period every two horizontal scanning periods is equivalent to the image signal in the immediately preceding scanning period. That is, the same image signal is repeated over two vertical scanning periods. As described above, by using a video memory to supplement an image in a scanning period during which a normal image output cannot be obtained, it is possible to use a substantial increase in sensitivity by pixel addition without any problem. Next, a modification of the first embodiment will be described. FIG. 3C is a time chart showing an image output to a recording system, a monitor, and the like, as in FIG. 3B. The image memory is added by a video memory in units of fields. This is an example of the case. That is, the three normal image signals obtained from the immediately preceding six vertical scanning periods using the video memory, that is, a so-called “missing” image signal, and the latest normal image signal are added to each pixel independently and averaged. The image signal is output as an image signal for two vertical scanning periods. This makes it possible to deal with low-luminance images with a lot of noise. Conventionally, an image processing method of reducing noise by averaging such an image having much noise is well known. However, in a conventional technique which simply performs this processing on an image with much noise and low luminance, It has been difficult to perform an autofocus operation in consideration of the movement of a subject. On the other hand, in the present modified example, even if the image has a low luminance, the autofocus operation can be performed by generating the image data for the autofocus using the image signal obtained by using the line addition. Next, an electronic imaging apparatus according to a second embodiment of the present invention will be described. FIG. 4 is a block diagram showing a main configuration of the second embodiment. In the second embodiment, a mode changeover switch 10 is added to the first embodiment, and as shown in FIG.
The other configuration is the same as that of the first embodiment, and the description is omitted here. The mode changeover switch 10 is a mode changeover switch for switching between the normal mode and the time-division mode, and makes it possible to externally switch to the mode. With the addition of the mode changeover switch 10, the image sensor driver SSG9 is controlled by the system controller 7 to switch and control the driving of the image sensor 2 in accordance with the mode selected by the mode changeover switch 10. . The mode changeover by the mode changeover switch 10 is normally set to the normal mode, and may be configured to automatically switch to the time division mode at low luminance. FIG. 5 is a flowchart showing a subroutine operation for automatically switching to the time division mode. As shown in the figure, first, it is determined whether or not the brightness is low when performing the auto focus operation (step S).
101) If the brightness is low, the mode changeover switch 10 is set to the time division mode (step S102), and if the autofocus operation can be sufficiently performed, the mode is set to the normal mode (step S103). Next, a third embodiment of the present invention will be described. FIG. 6 is a time chart for explaining the operation of the third embodiment. 3, reference numerals A1 and A2 indicate periods during which image signals are output by normal image processing as in the case shown in FIG. 3, and reference numerals B0, B1, and B2 also indicate pixels obtained by line addition similarly to FIG. Indicates the period during which data is output. In addition, for convenience of timing expression, a VD signal is added for each period of one horizontal scanning period 1H. The configuration of the third embodiment is the same as that of the first embodiment. At least in the time-division mode, the driving rate of the image sensor is changed to the image signal output rate and the video memory 5 (FIG. 1).
) Is set higher than the output rate of the output from As shown in the figure, when the image signal output rate (shown by the normal rate in the figure) is, for example, 60 Hz, the drive rate of the image sensor (shown by the imager drive rate in the figure) is doubled to 120 Hz. I have to. At this time,
It is assumed that the rates of all the image sensor drive signals are also doubled. In this case, since it cannot be used as an image signal as it is, the video memory 5 converts it to a rate of 60 Hz that can be output as an image signal.
The capacity of the buffer memory in the video memory 5 is sufficient for the purpose. According to the third embodiment, the first,
An image output signal having a higher dynamic resolution than in the second embodiment can be obtained. That is, in the first and second embodiments, since the normal image signal and the line-added image signal can be obtained only alternately, only the signal of the sampling rate required by the signal output rate can be obtained. For this reason, the moving resolution (moving image resolution) as a moving image must be slightly reduced. On the other hand, in the third embodiment, although the charge storage time per pixel is １ ／ of the normal, the normal image signal and the line added image signal are output at the same sampling rate as the signal output rate requires. Are obtained, it is possible to obtain an image signal without a decrease in dynamic resolution, and in this case, information of up to 60 Hz can be used as a sampling rate of the autofocus. In the above description of the embodiment, two types of driving are performed by "field intermittent". However, this is only a typical form of the preferred embodiment, and the present invention is not limited to this. First, the two types of driving can be switched and used at an arbitrary timing.
Whether to assign to n is completely arbitrary. Further, the image information of the line addition may be used for various functions other than the autofocus, for example, AE and AWB. As described above, according to the present invention, it is possible to provide an electronic image pickup apparatus which dramatically improves the limit on the low luminance side of the image pickup element.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a main configuration of an electronic imaging apparatus according to a first embodiment of the present invention. FIG. 2 is a time chart showing pulses for driving an image sensor in the first embodiment. FIG. 3 is a time chart showing a signal waveform of each unit in the first embodiment. FIG. 4 is a block diagram showing a main configuration of an electronic imaging apparatus according to a second embodiment of the present invention. FIG. 5 is a flowchart showing a subroutine operation for automatically switching to a time division mode in the second embodiment. FIG. 6 is a time chart showing main operations of an electronic imaging apparatus according to a third embodiment of the present invention. [Description of Signs] 1 ... Focus actuator 2 ... Imaging element 3 ... Pre-processing circuit 4 ... Imaging main process 5 ... Video memory 6 ... Contrast extraction circuit 7 ... System controller 8 ... Memory controller 9 ... SSG

Claims (1)

(57) [Claims] [Claim 1] Drive capable of line addition driving of an image sensor
Means for storing a field image output from the image sensor
A video memory, and when the luminance is low, the field signal added with the line is AE
Video, AF and AWB
Displays frame signals that have been field-interpolated using memory.
An electronic imaging device characterized by being used for display and recording .