JPH02234577A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To eliminate the need for provision of an additional parts to an image pickup section except a lens drive motor by declining a threshold level properly and adjusting a focus lens so as to maximize the picture element number with higher brightness (or lower) than the threshold level. CONSTITUTION:A focus adjustment lens of an image pickup section 1 is matched to the nearest point as soon as the focus adjustment is started. Then a lens drive motor 2 moves the lens continuously in a direction to focus the lens in the remoter position. A picture element comparison integration circuit 6 compares a threshold level calculated from a picture of a preceding frame at a threshold level calculating circuit 3 with the brightness of each picture element and counts the number of picture elements having the larger brightness than the threshold level over several frames. A frame comparator circuit 7 compares the picture element numbers integrated by a picture element comparison integration circuit 5 and when the picture element number calculated newly is smaller than the picture element number calculated precedingly, a stop signal is given to the lens drive motor 2, which stops the movement of the lens.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an imaging device, and particularly to an automatic focusing device 1 thereof. [Prior Art] Conventional automatic focusing devices 1 include devices that utilize reflection of sound waves, etc., devices that optically double an out-of-focus image, and utilize the fact that the double images overlap. there were. [Problems to be solved by the invention] In the conventional automatic focusing device described above, it was necessary to add a part of the device near the optical section to the lens drive motor.
Another drawback was that it was difficult to focus on any point in the image. An object of the present invention is to provide an automatic focusing device that solves the above problems. [Means for Solving the Problems] In order to achieve the above object, an automatic focusing device according to the present invention includes a circuit that determines a threshold value, compares the brightness of each pixel with the threshold value, and compares the brightness of each pixel with the threshold value, and It has a circuit that counts pixels with (or low) brightness, a circuit that compares the counted pixels between frames, and a lens drive motor that receives the output signal and drives the lens for focusing. [Example] Hereinafter, an example of the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, l is an imaging unit, 2 is a lens drive mode controller, 3 is a threshold calculation circuit that determines a threshold value, 4 is an average value calculation circuit, 5 is a maximum brightness detection circuit, 6 is a pixel comparison integration circuit,
7 is a frame comparison circuit. In addition, in the figure, N in the average value calculation circuit 4 means the total number of pixels in one frame, and K means O<K.
<1 range. At the same time as the focus adjustment starts, the focus adjustment lens of the imaging unit 1 focuses on the closest point. Next, the lens drive motor 2 continuously moves the lens in a direction that focuses on a distant object. The threshold value calculation circuit 3 has an average value calculation circuit 4 and a maximum brightness detection circuit 5, and calculates the average brightness value of one frame (V) and the maximum brightness (V) of the same frame from the A/D converted image signal. Detect. From these values, the threshold value ■7 is V7=VA
It is calculated as (Vll VA )・K (0kuK<
1). The pixel comparison/accumulation circuit 6 compares the brightness of each pixel with the threshold value calculated from the image of the previous frame by the threshold calculation circuit 3, and counts the number of pixels having a brightness greater than the threshold value over several frames. The frame comparison circuit 7 compares the number of pixels accumulated by the pixel comparison and accumulation circuit 5, and generates a stop signal to the lens drive motor 2 when the newly calculated number of pixels becomes smaller than the previously calculated number of pixels. , the lens drive motor 2 stops the movement of the lens. Figure 2 shows an example of the brightness distribution of a horizontal line in an in-focus image, and Figure 3 shows an example of the brightness distribution in an out-of-focus image of the same object as in Figure 2. By setting an appropriate value higher (lower) than the average brightness of the image as a threshold, the total number of pixels with brightness higher (lower) than the threshold is maximized in an in-focus image. The present invention determines an appropriate threshold value and adjusts the lens so that the number of pixels having luminance greater (or lesser) than the threshold value is maximized. [Effects of the Invention] As explained above, the present invention appropriately determines the threshold value and adjusts the focusing lens so that the number of pixels with luminance higher (or lower) than the threshold value is maximized. The lens position can be determined by the lens drive motor, and there is no need to attach any additional parts to the imaging unit other than the lens drive motor.Also, by specifying the area where pixels are sampled, it is possible to focus on any position in the image. has.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an in-focus image, and FIG. 3 is a diagram showing an out-of-focus image. 1... Imaging unit 2... Lens drive motor 3... Threshold value calculation circuit 4... Average value calculation circuit 5
... Maximum brightness detection circuit 6 ... Pixel comparison integration circuit 7
... Frame Comparison Circuit 111 Example Patent Applicant: NEC Corporation Representative Patent Attorney: Sugano
Naka・r (N111)

Claims (1)

[Claims] (1) A circuit that determines a threshold value, a circuit that compares the brightness of each pixel with the threshold value, and counts pixels with a brightness higher (or lower) than the threshold value, and a circuit that compares the counted pixels between frames. An automatic focusing device comprising: a circuit; and a lens drive motor that receives an output signal from the circuit and drives a lens for focusing.