JP6416034B2 - Imaging apparatus and focus control method - Google Patents

Description

  The present invention relates to an imaging apparatus and a focus control method.

  Conventionally, in a focus detection circuit that applies only a differential signal component in the horizontal direction, a 1H delay circuit (line memory, FIFO (First-In, First-Out), etc.) is unnecessary, and the circuit scale is relatively small. There is an advantage that it can be realized, but since the differential signal component in the vertical direction is zero, in the case of a subject where the horizontal change rate of the luminance value such as a horizontal line is zero (the horizontal component is zero) or very small, It is difficult to detect the maximum point of the AF (Autofocus) evaluation value, and the normal operation of the autofocus function is difficult in principle. In addition, a 1H delay circuit (line memory, FIFO, etc.) is required to generate a differential signal in the vertical direction, the memory circuit scale in an FPGA (Field Programmable Gate Array) device increases, and the memory mounting is limited. There is an upper problem.

  As a prior art document, for example, Patent Document 1 discloses a technique for avoiding a decrease in focus detection accuracy in a focus detection apparatus having a function of dividing and controlling a line sensor into a plurality of blocks. .

Japanese Patent No. 5576664

  An object of the present invention is to focus a lens even on a subject whose contour component in the horizontal direction is zero or very low.

  An imaging apparatus according to the present invention is an imaging apparatus that is coupled to a lens unit having a focus function. The imaging apparatus includes an imaging unit, a video signal processing unit, a video signal output unit, and a signal processing unit. Means for generating a first AF evaluation value by differentiation and intraframe integration from the luminance signal output from the signal processing unit; and means for generating a second AF evaluation value by integration of one line and interframe integration from the luminance signal And a maximum value detecting means for detecting a maximum value from the first AF evaluation value or the second AF evaluation value, and the maximum value detecting means generates a focus control signal for the lens unit.

  The imaging apparatus according to the present invention is the above-described imaging apparatus, wherein the maximum value detecting unit generates a focus control signal based on focus position information from the lens unit.

  Furthermore, the focus control method for an image pickup apparatus according to the present invention is a focus control method for an image pickup apparatus combined with a lens unit having a focus function, the step of differentiating a luminance signal, and the step of converting the differentiated signal into an absolute value Integrating a frame to generate a first AF evaluation value, integrating a luminance signal by one line, selecting a maximum value and a minimum value by intra-frame comparison, a maximum value and a minimum value A step of making the difference an absolute value, a step of generating a second AF evaluation value by inter-frame integration, a step of comparing the first AF evaluation value with a predetermined value, a first AF evaluation value and a predetermined value The second AF evaluation value is selected if the first AF evaluation value is the same, the first AF evaluation value is selected if the first AF evaluation value is different from the predetermined value, and the focus position information of the lens unit Take And having the steps of, detecting a maximum value of the first AF evaluation value or the second AF evaluation value, and outputting a focus control signal.

  According to the present invention, the lens can be focused even on a subject whose contour component in the horizontal direction is zero or very low.

It is a block diagram for demonstrating the imaging device which is one Example of this invention. It is a figure for demonstrating operation | movement of the imaging device which is one Example of this invention. 6 is a flowchart for explaining the operation of the imaging apparatus according to the embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram for explaining an imaging apparatus according to an embodiment of the present invention.
In FIG. 1, the imaging device 100 is coupled to a lens unit 150 having a focus function.
The imaging apparatus 100 includes an imaging unit 101, a video signal processing unit 102, a video signal output unit 103, and a signal processing unit 120.
The imaging apparatus 100 photoelectrically converts the incident light collected by the lens unit 150 by the imaging unit 101, performs level adjustment of the video signal by the video signal processing unit 102, and the signal of a predetermined format by the video signal output unit 103. Convert to and output.

The signal processing unit 120 generates a focus control signal for controlling the lens unit 150 with a focus function from the luminance (Y) signal output from the video signal processing unit 102.
The signal processing unit 120 includes an HPF (High-Pass Filter) unit 121, an absolute value processing unit 122, a gate signal generation unit 123, an in-frame integration unit 124, a predetermined value generation unit 125, a comparison unit 126, and a one-line integration unit 127. , An intra-frame comparison unit 128, a difference extraction unit 129, and a CPU (Central Processing Unit) unit 140.
The CPU unit 140 includes a selection unit 141, a maximum value detection unit 142, and an inter-frame integration unit 143.
Note that the CPU unit 140 may constitute all or part of the signal processing unit 120.

Next, the operation of the image pickup apparatus according to an embodiment of the present invention will be described with reference to FIGS.
FIG. 2 is a diagram for explaining the operation of the imaging apparatus according to the embodiment of the present invention.
FIG. 2 shows a state in which the imaging apparatus 100 is imaging a subject whose horizontal temporal variation such as a horizontal line is zero or close to zero within the focus detection area frame.

The HPF unit 121 differentiates only the luminance (Y) signal in the horizontal direction to generate dY / dt.
The focus control method of the lens which is an embodiment of the present invention is a contrast difference method. Therefore, in order to extract the magnitude of the differential signal component dY / dt, the absolute value is converted into an absolute value by the absolute value processing unit 122 and output as | dY / dt |.

The gate signal generation unit 123 generates a gate signal for selecting a period that can be used for the focus control signal in the Y signal. For example, the gate signal generation unit 123 generates a gate signal for deleting a blanking period.
The intra-frame integrating unit 124 integrates the same frame while the gate signal is valid, and outputs the first AF evaluation value to the CPU unit 140 for each frame period.

  Here, the frame video signal when the focus position is the in-focus position is assumed to be the kth frame 1 (hereinafter referred to as frame k). With respect to the frame, the frame video signals before and after one frame period are (k−1) and (k + 1) th frames (hereinafter referred to as frame (k−1) and frame (k + 1)), respectively. To do. The maximum and minimum luminance signal values in frame k are Yk_max and Yk_min, respectively, and the luminance in the line in frame k (the signal obtained by averaging the luminance value of each pixel in the same line per pixel). Value) is set to Lk_max and Lk_min, respectively.

In outdoor daytime, etc., the brightness of the subject is high, and the gain control signal of the video signal processing unit 102 is zero (no or little noise, gain of 1 time) or close to zero (gain of about 1 time), the brightness in the horizontal direction Therefore, Yk_max = Lk_max and Yk_min = Lk_min are satisfied.
On the other hand, in nighttime darkness and the like, the luminance of the subject is low, and the gain control signal of the video signal processing unit 102 is increased, so that the noise is also increased. That is, Yk_max ≠ Lk_max and Yk_min ≠ Lk_min.

If only one pixel with the same coordinates is detected in the video signal, it is feared that a luminance signal value deviating from the original contrast level such as noise particles and white scratches may be detected.
Therefore, the maximum value (Lk_max) 2 and the minimum value (Lk_min) 3 of the luminance value for the same line in the frame of FIG. 2 are detected.

From the above, the difference between the maximum and minimum luminance values increases as the focal point is approached, and conversely, the difference between the maximum and minimum luminance values decreases as the subject is out of focus. (referred to as fp) is the in-focus position in the kth frame, the following relationship holds.
| Lk-2_max -Lk-2_min | <| Lk-1_max -Lk-1_min | <| Lk_max -Lk_min |
| Lk_max -Lk_min |> | Lk + 1_max -Lk + 1_min |> | Lk + 2_max -Lk + 2_min |

  While the lens unit 150 is operating and the focus position is constantly changing, a frame period from a frame a to a frame b (a <b.s. | ab |> 1) (a plurality of frames) Frame) The horizontal differential signal | dY / dt obtained by making the value integrated by the inter-frame integration unit 143 in the internal calculation processing of the CPU 140 a new AF evaluation value and absolute-valued by the absolute-value processing unit 122 in the same frame When it is determined that | H = 0, the output of the comparison unit 126 becomes “true”, and the selection unit 141 causes the selection unit 141 to calculate Σ | Lfp_max−Lfp_min | And the maximum value detection unit 142 detects it.

The maximum value detection unit 142 outputs a focus control signal fp corresponding to the detected maximum point to the lens unit 150.
The maximum value detection unit 142 detects the maximum integral value between the frames as the in-focus position. As a result, the integral value Σ | Lfp_max−Lfp_min | of the difference between the line maximum value and the line minimum value in the same frame including the in-focus position (fp = k) is maximized.
However, as a precaution, if the value of | a−b | is too high (for example, the number of frames to be integrated is too large), the processing load increases or the characteristics become dull and the maximum point detection accuracy Therefore, it is necessary to select an appropriate value.

At the next sampling (sampling interval for each frame), | Lfp_max-Lfp_min | of each frame is integrated in the interval [a + 1, b + 1], and is output as the second AF evaluation value.
Similarly, a value obtained by integrating | Lfp_max-Lfp_min | by shifting the integration interval for each sampling period is output as the second AF evaluation value.

The imaging apparatus 100 according to the embodiment of the present invention detects only the maximum line and the minimum line in the same frame (for example, ignores the signal value in the intermediate line), thereby controlling the gain of the video signal processing unit 102. When the signal is high gain (high gain), it is possible to reduce erroneous detection of the contrast difference when the noise increases, and the erroneous detection of the integrated value is reduced. That is, noise resistance is improved.
Note that the imaging apparatus 100 according to the embodiment of the present invention inputs the focus position information (Near end to Far end) from the lens unit 150 to the maximum value detection unit 142, so that convergence of the focal point is accelerated.

Next, the detailed operation of the imaging apparatus according to the embodiment of the present invention will be described with reference to FIG.
FIG. 3 is a flowchart for explaining the operation of the imaging apparatus according to the embodiment of the present invention.
In FIG. 3, the signal processing unit 120 differentiates the luminance (Y) signal to generate a dY / dt signal (S301), and converts the dY / dt signal into an absolute value to generate a | dY / dt | signal. (S302).

In the process of S303, it is determined whether the | dY / dt | signal is within the valid period of the gate signal. If it is within the valid period (YES), the process proceeds to S303, and if not within the valid period (NO). The process returns to S301.
In the process of S304, the first AF evaluation value is generated by integrating the inside of the frame.

  Next, the signal processing unit 120 integrates the luminance (Y) signal by one line (S305), selects L, max and L, min by intra-frame comparison (S306), and the difference between L, max and L, min | L, max-L, min | is extracted (S307) and integrated between frames to generate a second AF evaluation value (S308).

Next, the signal processing unit 120 determines whether or not the first AF evaluation value and the second AF evaluation value are the same in the process of S309. If they are the same (YES), the process proceeds to S310 and is not the same. In this case, the process proceeds to S311.
In the process of S310, the second AF evaluation value is selected and the process proceeds to S312.
In the process of S311, the first AF evaluation value is selected and the process proceeds to S312.

  Next, the signal processing unit 120 acquires focus position information from the lens unit 150 (S312), detects the maximum value of the first AF evaluation value or the second AF evaluation value (S313), and generates a focus control signal fp. The image is output to the lens unit 150 (S314).

  The imaging apparatus according to the embodiment of the present invention can focus a lens even on a subject whose contour component in the horizontal direction is zero or very low.

  Although the present invention has been described in detail above, it is needless to say that the present invention is not limited to the imaging apparatus described here, and can be widely applied to imaging apparatuses other than those described above.

  Since either the horizontal differential signal within the same frame of the luminance signal or the difference information between frames can be selected, the lens can be focused even on a subject whose horizontal contour component is zero or very low. .

  100: imaging device, 150: lens unit, 101: imaging unit, 102: video signal processing unit, 103: video signal output unit, 120: signal processing unit, 121: HPF unit, 122: absolute value processing unit, 123: Gate signal generation unit, 124: intra-frame integration unit, 125: predetermined value generation unit, 126: comparison unit, 127: 1 line integration unit, 128: intra-frame comparison unit, 129: difference extraction unit, 140: CPU unit, 141 : Selection unit, 142: maximum value detection unit, 143: inter-frame integration unit.

Claims (3)

In an imaging device combined with a lens unit having a focus function,
The imaging apparatus includes an imaging unit, a video signal processing unit, a video signal output unit, and a signal processing unit,
The signal processing unit is configured to generate a first AF evaluation value by performing differentiation and intraframe integration from the luminance signal output from the video signal processing unit, and from the luminance signal to a first line integration and an interframe integration. Means for generating two AF evaluation values, and maximum value detecting means for detecting a maximum value from the first AF evaluation value or the second AF evaluation value,
The maximum value detection unit generates a focus control signal for the lens unit. The imaging device according to claim 1,
The imaging apparatus according to claim 1, wherein the maximum value detecting unit generates a focus control signal based on focus position information from the lens unit. In a focus control method of an imaging device combined with a lens unit having a focus function,
Differentiating the luminance signal, converting the differentiated signal to an absolute value, integrating the frame to generate a first AF evaluation value,
Integrating a luminance signal by one line; selecting a maximum value and a minimum value by intra-frame comparison; converting a difference between the maximum value and the minimum value to an absolute value; Generating an AF evaluation value;
Comparing the first AF evaluation value with a predetermined value, selecting the second AF evaluation value if the first AF evaluation value is the same as the predetermined value, and the first AF evaluation. Selecting the first AF evaluation value if the value is different from the predetermined value;
Obtaining focus position information of the lens unit;
Detecting a maximum value of the first AF evaluation value or the second AF evaluation value; outputting a focus control signal;
A focus control method for an imaging apparatus, comprising:

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