JP2007279694A - Automatic focusing device and photographing device - Google Patents

Abstract

An in-focus position is accurately obtained without being affected by a change in luminance.
An AF evaluation value calculation circuit 19 divides an image pickup signal output from a distance measurement area into blocks according to a plurality of areas constituting the distance measurement area; First and second frequency component extraction units 31 and 32 that extract low-order frequency components, and first and second frequency components extracted by the first and second frequency component extraction units 31 and 32 are integrated for each block. 2 from the integrated value for each block obtained by the second integrating unit 34, the maximum value detecting unit 35 for detecting the maximum value from the integrated value for each block obtained by the first integrating unit 33, and the integrated value for each block obtained by the second integrating unit 34. An average value calculation unit 36 that calculates an average value and a difference calculation unit 37 that calculates a difference between the maximum value and the average value. The CPU controls the lens driving unit using the difference value calculated by the difference calculation unit 37 as an AF evaluation value.
[Selection] Figure 2

Description

  The present invention relates to a contrast detection type automatic focusing device used in a photographing apparatus such as a digital camera and a photographing apparatus including the same.

  2. Description of the Related Art In recent years, digital cameras that convert a subject image captured by an image sensor such as a CCD (Charge Coupled Device) image sensor into digital image data and record it have become widespread. Most digital cameras have an auto focus (AF) function so that even beginners can easily focus.

  As this AF function, a high frequency component (contrast value) is extracted from an image pickup signal output from the image pickup device, and the focus lens is driven and focused so that an integrated value (AF evaluation value) of the high frequency component becomes maximum. A so-called contrast detection method for detecting the position is known. This contrast detection method has the disadvantage that the subject cannot be focused when the subject has no contrast or is dark, but has the advantage that the mechanism can be simplified because the imaging device itself is also used as a distance measuring sensor. It is widely used in small digital cameras.

However, this contrast detection method is known to cause a problem even when the subject has contrast and the subject is sufficiently bright. For example, if there is a high-luminance subject other than the main subject in the distance measurement area, or if a subject other than the main subject enters or exits the distance measurement area due to camera shake, the AF evaluation value is affected. As a result, the AF operation becomes unstable (see, for example, Patent Documents 1 and 2). In the inventions of Patent Documents 1 and 2, the AF evaluation value component is weighted for the area where the unnecessary subject is located, and the influence of the unnecessary subject on the AF evaluation value is reduced, thereby stabilizing the AF operation. ing.
JP-A-8-321985 JP 2004-191892 A

  However, even the automatic focus adjustment device that performs weighting on the AF evaluation value as described above cannot cope with the case where the luminance in the distance measurement area varies as a whole. In other words, when the brightness suddenly decreases during AF operation (so-called hill-climbing search), a pseudo peak is generated in the AF evaluation value as shown in FIG. 8, and the position of the pseudo peak different from the true peak is adjusted. There is a problem that it is erroneously detected as a focal position.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an automatic focus adjustment device and an imaging device capable of accurately obtaining a focus position without being affected by a change in luminance. To do.

  In order to achieve the above object, the automatic focus adjustment apparatus of the present invention includes a block dividing unit that divides an image pickup signal output from a distance measuring area of an image pickup device into blocks according to a plurality of small areas constituting the distance measuring area. A first frequency component extracting means for extracting high-order frequency components from each block divided by the block dividing means; and a second frequency component extracting means for extracting low-order frequency components from each block divided by the block dividing means. Frequency component extraction means, first integration means for integrating the frequency components extracted by the first frequency component extraction means for each block, and frequency components extracted by the second frequency component extraction means for each block A second integration means; a maximum value detection means for detecting a maximum value from the integrated values for each block obtained by the first integration means; An average value calculating means for calculating an average value from the integrated values for each block obtained by the second integrating means, a maximum value detected by the maximum value detecting means, and an average value calculated by the average value calculating means Difference calculating means for calculating the difference and drive means for driving the focus lens to the in-focus position using the value calculated by the difference calculating means as an evaluation value.

  The automatic focus adjustment apparatus of the present invention includes a block dividing unit that divides an imaging signal output from a ranging area of an imaging device into blocks according to a plurality of small areas constituting the ranging area, and the block dividing unit. First frequency component extracting means for extracting high-order frequency components from each block divided by the above, and second frequency component extracting means for extracting low-order frequency components from each block divided by the block dividing means; First integrating means for integrating the frequency components extracted by the first frequency component extracting means for each block; second integrating means for integrating the frequency components extracted by the second frequency component extracting means for each block; The integrated value obtained by the first integrating means and the integrated value obtained by the second integrating means are used as a weighting coefficient for each block. Weighted addition means for weighted addition, maximum value detecting means for detecting a maximum value from the integrated value for each block obtained by the first integrating means, and weighted addition value for each block obtained by the weighted adding means Average value calculating means for calculating an average value from the above, difference calculating means for calculating a difference between the maximum value detected by the maximum value detecting means and the average value calculated by the average value calculating means, and the difference calculating means Driving means for driving the focus lens to the in-focus position using the value calculated by the above as an evaluation value.

  In addition, it is preferable to provide weighting coefficient calculation means for calculating the weighting coefficient used by the weighting addition means based on the imaging conditions.

  Further, it is preferable that the first frequency component extracting means is for extracting the highest frequency component.

  In addition, a photographing apparatus according to the present invention includes any one of the above automatic focusing devices.

  In the automatic focus adjustment apparatus of the present invention, the imaging signal output from the ranging area of the imaging element is divided into blocks according to a plurality of areas constituting the ranging area, and the maximum integrated value of the higher-order frequency components From this, the evaluation value is calculated by subtracting the average value of the integrated values of the low-order frequency components, and when the focus lens is moved, the average value is the maximum value at a rate of change smaller than the maximum value. It shows the characteristic of following. As a result, the evaluation value is not easily affected by fluctuations in luminance and the like, and only a true peak is generated. Therefore, the focus lens can be accurately set at the in-focus position.

  Also, by subtracting the maximum value of the integrated value of the higher-order frequency component from the maximum value of the added value obtained by weighted addition of the integrated value of the higher-order frequency component and the integrated value of the lower-order frequency component, The followability of the average value with respect to the maximum value can be changed according to the weighting coefficient. When the ratio of weighting to the integrated value of higher-order frequency components is increased, the followability is increased, and the pseudo peak can be effectively canceled out.

  In FIG. 1, a digital camera 10 according to the first embodiment of the present invention is centrally controlled by a CPU (main control circuit) 11. The CPU 11 controls the operation of each unit in response to an operation signal input from the operation unit 12 including a shutter button, a menu button, a selection key, and the like. Note that the shutter button is a two-stage press switch. When the shutter button is half-pressed, shooting preparation processing such as an AF operation is performed, and when the shutter button is fully pressed after half-pressing, a shooting operation is performed.

  The imaging lens 13 includes a focus lens that moves along the optical axis. The lens driving unit 14 includes a lens motor and a motor driver, and drives the focus lens in the imaging lens 13. The lens driving unit 14 is controlled by the CPU 11.

  A CCD image sensor 15 is disposed on the optical axis of the imaging lens 13. The subject light that has passed through the imaging lens 13 enters the light receiving surface of the CCD image sensor 15, undergoes photoelectric conversion by each light receiving element in the light receiving surface, and is output as an electrical imaging signal from the output amplifier after charge transfer. The

  A CDS (Double Correlation Sampling) / AGC (Auto Gain Control) circuit 16 samples and holds the imaging signal output from the CCD image sensor 15 and at the same time performs amplification with an appropriate gain. The A / D converter 17 converts the imaging signal output from the CDS / AGC circuit 16 into digital image data, and inputs the image data to a DSP (digital signal processing circuit) 18 and an AF evaluation value calculation circuit 19.

  The DSP 18 performs predetermined image processing such as color interpolation, YC conversion, gamma correction, contour correction, and white balance correction on the input image data. The image data that has been subjected to image processing by the DSP 18 is displayed as a through image on the LCD 21 by an LCD (liquid crystal display) driver 20.

  The compression / decompression processing circuit 22 operates when the shutter button is fully pressed, acquires image data from the DSP 18, and performs predetermined compression processing (for example, JPEG compression) on the image data. The card I / F 23 writes the image data compressed by the compression / decompression processing circuit 22 to a memory card 24 that is detachably connected.

  The card I / F 23 reads image data from the memory card 24 when a predetermined operation is performed in the reproduction mode. This image data is decompressed by the compression / decompression processing circuit 22 and reproduced and displayed on the LCD 21 via the LCD driver 20.

  The AF evaluation value calculation circuit 19 operates when the shutter button is half-pressed, calculates an AF evaluation value based on the image data input from the A / D converter 17, and inputs this to the CPU 11. . The CPU 11 uses the AF evaluation value obtained by the AF evaluation value calculation circuit 19 to control the lens driving unit 14 in accordance with a “mountain climbing control method” as described in JP-A-6-268896. . The lens driving unit 14 moves the focus lens to a position (focus position) where the AF evaluation value is maximized in accordance with an instruction from the CPU 11. This AF operation is performed at regular intervals not only when the shutter button is half-pressed but also when a through image is displayed.

  FIG. 2 shows the configuration of the AF evaluation value calculation circuit 19. Ranging area setting information is input to the block dividing unit 30 from the CPU 11. As shown in FIG. 3, the distance measuring area 40 is set in the imaging screen 41 of the CCD image sensor 15, and is divided into small areas A1 to A16. The range of the distance measuring area 40 within the imaging screen 41 is set by the operation unit 12. The block dividing unit 30 extracts only the portion corresponding to the distance measuring area 40 from the image data input from the A / D converter 17, and extracts the extracted image data into 16 blocks according to the small areas A1 to A16. Divide into B1 to B16. The blocks B1 to B16 are input to the first frequency component extraction unit 31 and the second frequency component extraction unit 32, respectively. That is, the block dividing unit 30 distributes image data.

  The 1st and 2nd frequency component extraction parts 31 and 32 are provided for every block of B1-B16, respectively, and extract the frequency component of image data for every block. The first and second frequency component extraction units 31 and 32 are so-called bandpass filters (BPF). The first frequency component extraction unit 31 extracts higher-order frequency components than the second frequency component extraction unit 32. For example, the first frequency component extraction unit 31 extracts the highest-order frequency component (difference between adjacent pixels), and the second frequency component extraction unit 32 extracts a lower-order frequency component lower than that. The frequency components extracted by the first and second frequency component extraction units 31 and 32 are input to the first and second integration units 33 and 34, respectively.

  The first and second integration units 33 and 34 perform integration after converting the frequency components extracted by the first and second frequency component extraction units 31 and 32 into absolute values, and the integration value for each block of B1 to B16. Is calculated. The first and second integrating units 33 and 34 are so-called digital integration circuits. The integrated value of the higher-order frequency component calculated by the first integrating unit 33 is input to the maximum value detecting unit 35 for each block. The integrated value of the low-order frequency component calculated by the second integrating unit 34 is input to the average value calculating unit 36 for each block.

  The maximum value detection unit 35 detects the maximum value from the 16 integrated values that have been input, and inputs this to the difference calculation unit 37. On the other hand, the average value calculation unit 36 calculates an average value of the 16 input integrated values, and inputs this to the difference calculation unit 37. The difference calculation unit 37 calculates a difference between the input maximum value and the average value, and inputs a positive value obtained by converting the difference into an absolute value to the CPU 11 as an AF evaluation value.

  In FIG. 4A, the curve A shows the maximum value output from the maximum value detection unit 35 with respect to the focus lens position, and the curve B shows the average value output from the average value calculation unit 36. These are shown with respect to the focus lens position. Since the curve B is based on a low-order frequency component and is averaged, the curve B follows the change of the curve A with a smaller change rate than the curve A. Therefore, even if it is affected by the decrease in luminance as described above, the pseudo peak does not occur in the difference value between the curves A and B, that is, the AF evaluation value, as shown in FIG. Only occurs.

  As described above, the AF evaluation value output from the AF evaluation value calculation circuit 19 is not easily affected by luminance fluctuations that affect the entire distance measurement area, and only a true peak giving the maximum value is generated. Can be accurately set to the in-focus position. Therefore, the digital camera 10 can perform a stable AF operation even in a shooting environment where the light source is blinking.

  Next, a second embodiment of the present invention will be described. The present embodiment is different from the first embodiment in the average value calculation method in the AF evaluation value calculation circuit. In FIG. 5, the AF evaluation value calculation circuit 50 is provided with a weighting addition unit 51. Note that portions having the same functions as those in the first embodiment are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

  The weighted adder 51 receives the integrated values from the first and second integrating units 33 and 34, and the weighted adding unit 51 adds the integrated value from the first integrating unit 33 and the first integrated value for each block B1 to B16. 2 The integrated value from the integrating unit 34 is added at a predetermined rate, and the added value is input to the average value calculating unit 36.

  Specifically, as shown in FIG. 6, the weighting addition unit 51 includes a coefficient storage unit 52 that stores two weighting coefficients w1 and w2 and an integrated value S1n for each block output from the first integration unit 33. A multiplier 53 that multiplies (n = 1 to 16) by a weighting coefficient w1, and a multiplier that multiplies the integration value S2n (n = 1 to 16) for each block output from the second integration unit 34 by a weighting coefficient w2. 54 and an adder 55 for adding the multiplication results of the multipliers 53 and 54 to obtain an added value Tn (= w1 · S1n + w2 · S2n). The weighting coefficients w1 and w2 satisfy the relationship of w1 + w2 = 1, and are set to w1 = 0.25 and w2 = 0.75, for example. The average value calculation unit 36 averages the addition value Tn (n = 1 to 16) output from the addition value Tn.

  According to the present embodiment, the followability of the average value with respect to the maximum value can be changed with respect to the average value and the maximum value input to the difference calculation unit 37. By increasing the ratio of the weighting coefficient w1, the followability with respect to the maximum value of the average value is increased, and the pseudo peak can be effectively canceled out. However, if the ratio of the weighting coefficient w1 is too large, it is difficult for a true peak to appear in the AF evaluation value output from the difference calculation unit 37. The values of the weighting factors w1, w2 are preferably determined in consideration of these.

  Next, a third embodiment of the present invention will be described. This embodiment is different from the second embodiment in that the weighting coefficients w1 and w2 are changed according to a predetermined condition. In FIG. 7, the AF evaluation value calculation circuit 60 is provided with a weighting coefficient calculation unit 61. Note that portions having the same functions as those of the second embodiment are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

  The weighting coefficient calculation unit 61 calculates appropriate weighting coefficients w1, w2 based on the imaging conditions set by the CPU 11 (imaging conditions determined for each shooting mode), and weights the calculated weighting coefficients w1, w2. This is input to the coefficient storage unit 52 in the addition unit 51. For example, when there are “landscape shooting mode” and “portrait shooting mode” with different exposure settings as the imaging mode and the landscape shooting mode is set, there are few high-frequency noise components in the image data. The ratio of the weighting coefficient w2 to the frequency component is increased. On the other hand, when the portrait shooting mode is set, since the high frequency noise component increases in the image data, the ratio of the weighting coefficient w1 to the high frequency component is increased.

  According to the present embodiment, an appropriate AF evaluation value is obtained according to the shooting mode, and a true peak can be detected more reliably.

  In each of the above embodiments, the highest frequency is extracted by the first frequency component extraction unit 31, but the present invention is not limited to this, and the extraction frequency may be changed as appropriate.

  Moreover, in each said embodiment, the 1st frequency component extraction part 31, the 1st integrating | accumulating part 33, the 2nd frequency component extracting part 32, and the 2nd integrating | accumulating part 34 are each provided for every said block, and the process of each block is parallelly performed. Although the present invention is executed, the present invention is not limited to this, and the first frequency component extraction unit 31, the first integration unit 33, the second frequency component extraction unit 32, and the second integration unit 34 are each set as one set. Block processing may be executed in a time-sharing manner.

  Further, in each of the above embodiments, as shown in FIG. 3, the number of divisions of the ranging area is set to 16, but the present invention is not limited to this, and the number of divisions and the size and shape of the small area are appropriately changed. It's okay.

  In each of the above embodiments, the image sensor is a CCD image sensor. However, the present invention is not limited to this, and another image sensor such as a CMOS image sensor may be used as the image sensor. The image sensor may include a color filter. In this case, it is preferable to input the luminance component after YC conversion of the image data to the AF evaluation value calculation circuit. Alternatively, only one color component constituting the image data (for example, a green component in the case of a primary color filter) may be input to the AF evaluation value calculation circuit.

  In each of the above embodiments, a digital camera is used as an example of the photographing apparatus. However, the present invention is not limited to this, and can be applied to other photographing apparatuses such as a digital video camera.

It is a figure which shows the electrical constitution of a digital camera. It is a figure which shows the structure of AF evaluation value calculation circuit. It is a figure which shows the ranging area set in an imaging screen. (A) is a figure which shows the maximum value output from a maximum value detection part, and the average value output from an average value calculation part, (B) shows AF evaluation value output from a difference calculating part. FIG. It is a block diagram of AF evaluation value calculation circuit which shows the 2nd Embodiment of this invention. It is a figure which shows the structure of a weighting addition part. It is a block diagram of AF evaluation value calculation circuit which shows the 3rd Embodiment of this invention. It is a figure which shows AF evaluation value obtained by the conventional automatic focus adjustment apparatus.

Explanation of symbols

10 Digital camera 11 CPU
DESCRIPTION OF SYMBOLS 13 Imaging lens 14 Lens drive part 15 CCD image sensor 19, 50, 60 AF evaluation value calculation circuit 30 Block division part 31 1st frequency component extraction part 32 2nd frequency component extraction part 33 1st integration part 34 2nd integration part 35 Maximum value detection unit 36 Average value calculation unit 37 Difference calculation unit 40 Distance measurement area 50 AF evaluation value calculation circuit 51 Weighted addition unit 61 Weighting coefficient calculation unit

Claims (5)

Block dividing means for dividing an image pickup signal output from the distance measuring area of the image sensor into blocks according to a plurality of small areas constituting the distance measuring area;
First frequency component extracting means for extracting high-order frequency components from each block divided by the block dividing means;
Second frequency component extraction means for extracting low-order frequency components from each block divided by the block dividing means;
First integrating means for integrating the frequency components extracted by the first frequency component extracting means for each block;
Second integrating means for integrating the frequency components extracted by the second frequency component extracting means for each block;
Maximum value detecting means for detecting a maximum value from the integrated value for each block obtained by the first integrating means;
Average value calculating means for calculating an average value from the integrated value for each block obtained by the second integrating means;
Difference calculating means for calculating a difference between the maximum value detected by the maximum value detecting means and the average value calculated by the average value calculating means;
Driving means for driving the focus lens to the in-focus position using the value calculated by the difference calculating means as an evaluation value;
An automatic focusing apparatus characterized by comprising: Block dividing means for dividing an image pickup signal output from the distance measuring area of the image sensor into blocks according to a plurality of small areas constituting the distance measuring area;
First frequency component extracting means for extracting high-order frequency components from each block divided by the block dividing means;
Second frequency component extraction means for extracting low-order frequency components from each block divided by the block dividing means;
First integrating means for integrating the frequency components extracted by the first frequency component extracting means for each block;
Second integrating means for integrating the frequency components extracted by the second frequency component extracting means for each block;
Weighting addition means for weighting and adding the integrated value obtained by the first integrating means and the integrated value obtained by the second integrating means according to a weighting coefficient for each block;
Maximum value detecting means for detecting a maximum value from the integrated value for each block obtained by the first integrating means;
An average value calculating means for calculating an average value from the weighted addition value for each block obtained by the weighted addition means;
Difference calculating means for calculating a difference between the maximum value detected by the maximum value detecting means and the average value calculated by the average value calculating means;
Driving means for driving the focus lens to the in-focus position using the value calculated by the difference calculating means as an evaluation value;
An automatic focusing apparatus characterized by comprising:   The automatic focus adjustment apparatus according to claim 2, further comprising weighting coefficient calculation means for calculating a weighting coefficient used by the weighting addition means based on an imaging condition.   4. The automatic focus adjustment apparatus according to claim 1, wherein the first frequency component extracting unit extracts a highest-order frequency component. 5.   An imaging apparatus comprising the automatic focusing apparatus according to any one of claims 1 to 4.

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