JP3310324B2 - Automatic focusing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing apparatus, and more particularly to an automatic focusing apparatus which detects a focusing position based on contrast data based on a video signal.

[0002]

2. Description of the Related Art Conventionally, as one of automatic focusing methods of an image pickup apparatus using an image pickup device, contrast data of an object for evaluating the degree of focusing based on a video signal at the time of extending or retracting a focusing lens. Then, there is a method in which the lens position at which the value shows a peak is determined as the focus position, and the focusing lens is driven to this position. This method is referred to as a “hill climbing method”, and is described in the NHK Technical Research Report (1965, Vol. 17, No. 1, pp. 86
No.), pp. 21-37). In the focus control device to which the “hill-climbing method” is applied, a luminance signal before gamma correction (hereinafter referred to as γ correction) for correcting a photoelectric conversion characteristic of luminance is used as a video signal from which contrast data is extracted. There are cases where Y is used and cases where a γ-corrected luminance signal Yγ is used.

[0003]

However, in the above-mentioned conventional focusing control device, in which a gamma-corrected luminance signal Yγ is used as a video signal from which contrast data is extracted, a high-luminance subject is located at the center. A defect occurs on a certain screen. That is, as shown in FIG. 5A of the subject screen G20, when there is a burning candle B1, which is a high-brightness subject, in the center of the screen, and the periphery of the burning candle B1 is a peripheral part B2 with a dark background. In the luminance section, since the luminance signal is compressed for γ correction, the increase / decrease of the contrast value, which is the contrast data for the center subject, is reduced, and accurate focusing cannot be performed. Also,
In the case of using the luminance signal Y without γ correction, as shown in FIG. 5B of the subject screen G30, when the main subject C1 in the backlight state is to be focused on, Contrast data is drawn to the peripheral portion C2 of the high-luminance background, and accurate focusing cannot be performed. That is,
Since the DC (direct current) component of the luminance signal of the high luminance object in the peripheral portion C2 increases, the contrast value also increases, and accurate focusing on the main object C1 cannot be performed. In any of the above cases, the luminance signal for obtaining the contrast data includes the luminance signal Y before the γ correction.
Alternatively, only the γ-corrected luminance signal Yγ is used alone, and no contrivance has been made to obtain appropriate contrast data.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and in an automatic focusing apparatus using contrast data of a subject, the contrast data is converted into luminance data according to a specific area and a peripheral area in a screen. It is an object of the present invention to provide an automatic focusing device that can perform weighting adjustment with high precision on a subject in a specific area even if a luminance difference is present between the specific area and a peripheral area by giving weight.

[0005]

An automatic focusing apparatus according to the present invention comprises a first contrast data based on a gamma-corrected video signal and a second contrast data based on a non-gamma-corrected video signal.
A contrast data generating unit that obtains the luminance level of the specific area in the screen in a first state lower than the luminance level of the peripheral area of the specific area, or the luminance level of the specific area. Identifying means for identifying whether the level is in a second state higher than the luminance level of the peripheral area of the specific area, and identifying the first contrast data and the second contrast data for each of the first contrast data and the second contrast data A focus adjustment means for performing a focus adjustment operation based on third contrast data obtained by adding weights according to the identification result by the means and adding the weights.

[0006]

Prior to the detection of the in-focus position, whether the subject is in the first state or the second state is determined based on the luminance difference between the specific area and the peripheral area, and gamma correction is performed based on the result of the identification. First contrast data based on a video signal;
Appropriate weighting is applied to each of the second contrast data based on the video signal that is not gamma-corrected and added to obtain third contrast data for focusing. Then, focusing adjustment is performed based on the contrast data.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a main block configuration diagram of an electronic imaging apparatus having a built-in automatic focusing apparatus according to an embodiment of the present invention. As shown in the figure, the present apparatus mainly includes a focusing lens 301 driven to be focused by a focusing motor 311, a captured object light, and a photometric element 312 side and an imaging element 303.
A half mirror 302 that divides the image into an object, an image pickup device 303 that converts a subject image into an electric signal, an image pickup processing circuit 304 that performs image signal amplification and sample hold processing, and further performs γ correction of a luminance signal, and a video (not shown). An output terminal unit 314 that outputs a video signal to a recording / reproducing system; and first contrast data based on high-frequency components of a luminance signal Yγ, which is information for evaluating the degree of focusing and is subjected to γ correction related to photoelectric conversion characteristics. A first BPF circuit (band-pass filter) 305 of the contrast data generating means for extracting the second contrast data, and a second BPF circuit of the contrast data generating means for extracting the second contrast data based on the high-frequency component of the luminance signal Y not subjected to the γ correction 307, and first and second A / D conversion circuits for performing analog / digital conversion on the contrast data, respectively. And 06,308, photometric device 312 for metering the subject light divided by the half mirror 302
And 3A for converting the photometric output from analog to digital
It comprises a / D conversion circuit 313, an arithmetic processing circuit 309 composed of a CPU, a ROM, a RAM and the like, and a motor drive circuit 310 for driving the same motor as a focusing motor 311 as focusing adjustment means.

The arithmetic processing circuit 309 includes a peak value recognizing means for a contrast value, which is contrast data, a gain setting means for amplifying an image pickup signal, an identifying means for identifying a luminance state of a subject, and Third contrast data is calculated by adding a weighted value described later to the contrast data of the first and second contrast data, and the focusing lens 301 is driven by the focusing motor 311 via the motor drive circuit 310 based on the third value. Focus adjusting means for adjusting the focus. Also, the ROM incorporated in the arithmetic processing circuit 309 stores the weighting coefficients α and β corresponding to the luminance state of the subject, or
Basic data for calculating the coefficients α and β are stored. Further, the photometric element 312, which is an identification means for identifying the brightness state of the subject, is a photometric element having a sun-shaped photometric area shown on the screen G1 of FIG. 3, and the central area is defined as the specific area A1, Further, the peripheral area is defined as a peripheral area A2.
To correspond to.

The focusing operation of the present imaging apparatus having the above-described configuration will be described. First, the light intensity of each of the specific area A1 and the peripheral area A2 of the subject light taken in through the focusing lens 301 is measured by the photometric element 312. Detect and third
The data is taken into the arithmetic processing circuit 309 via the A / D conversion circuit 313 as a digital value. Then, the brightness level of the specific subject is determined and identified based on the light amount of the central specific area A1. Further, the arithmetic processing circuit 309 identifies two states based on the light amount of the peripheral area A2. That is, the brightness of the specific area A1 is standard or low, and
When the luminance level of the second area is higher than the luminance level of the specific area A1, that is, in the backlight state as shown in FIG. 5B, it is identified as the first state. When the luminance of the central specific area A1 is high and the luminance level of the peripheral area A2 is lower than the luminance level of the specific area A1, that is, as shown in FIG. When there is a tall subject, it is identified as the second state. In addition, the first,
State 2 is not the state, that is, the brightness of the specific area is high,
The state where the luminance of the peripheral area is high or standard, the state where the luminance of the specific area is standard or low, and the state where the luminance of the peripheral area is high are similarly identified. The first state, the second state, and the luminance of the subject identified as described above;
The weighting coefficients α and β respectively corresponding to the other states are read from a ROM incorporated in the arithmetic processing circuit 309, or
Obtained by calculation.

On the other hand, the output signals of the luminance signals Y.gamma.
07 and the first and second A / D conversion circuits 306 and 308, and digital values of contrast values, which are first and second contrast data based on the signal Yγ and the signal Y, are taken into the arithmetic processing circuit 309. Therefore, weighting is performed by multiplying the contrast values based on the Y signal and the Yγ signal by weighting coefficients α and β respectively corresponding to the first state, the second state, and the other states. A third contrast value is obtained by adding the weighted contrast values. The number of lens driving steps indicating the peak of the third contrast value is obtained by focusing adjustment means incorporated in the imaging processing circuit 309, and focusing is performed by a motor drive circuit 310 and a focusing motor 311 which are also focusing adjustment means. The lens 301 is moved to the number of focusing steps.

The weighting coefficients α and β for the first and second contrast data are values corresponding to the first state, the second state, and the other states, respectively. For example, assuming that the weighting coefficients for the first state are α3 and β3, a value of α3> β3 is obtained. That is,
In the backlight state, the contrast value based on the Yγ signal is greatly weighted to reduce the contrast in the peripheral area. If the weighting coefficients for the second state are α2 and β2, the value of α2 <β2 is obtained. That is,
When there is a high-luminance subject in the dark, the contrast value based on the Y signal is greatly weighted to emphasize the contrast of the specific area. In addition, the first
Weighting coefficients α1, β1, α4, β4 are given to states other than the second state, respectively. In addition,
The weighting coefficient may be determined by the sensitivity of the image sensor 303, the aperture value, and the BPF circuits 305 and 30 in addition to the brightness information of the subject.
The value changes depending on the characteristic of No. 7, the shutter speed, and the like. The calculation for obtaining the coefficients α and β may be based on fuzzy inference or may be performed using ROM table data storing values obtained by experiments.

On the basis of the third contrast value obtained as described above, the arithmetic processing circuit 309 detects the above-mentioned contrast peak position, and reaches the peak position via the motor drive circuit 310 and the focusing motor 311. Then, the focusing lens 301 is moved at a high speed to end the focusing operation.

Next, the above-described focusing operation of the automatic focusing apparatus of the present embodiment will be described in more detail with reference to the flowchart of FIG. When the focus processing command is output, the arithmetic processing circuit 309 starts the processing operation.
In step S2, the luminance level of the specific area A1 on the screen of the subject is checked based on the output of the photometric element 312.
Jump to 3. In step S2, the peripheral area A of the subject screen is similarly determined based on the output of the photometric element 312.
The luminance level of No. 2 is checked, and if the luminance level is high or normal, the process proceeds to step S4. For the contrast value of the first BPF circuit 305 which processes the luminance signal Yγ corrected for γ, the weighting coefficient α1 is changed by γ correction. A weighting coefficient β1 is set for the contrast value of the second BPF circuit 307 which processes the luminance signal Y not to be processed. Also,
If it is determined in step S2 that the luminance level of the peripheral area A2 is low, the process jumps to step S5 assuming that the subject is in the second state. The weighting coefficient α2 is applied to the contrast value of the first BPF circuit 305 for processing the luminance signal Yγ with γ correction, and the weighting coefficient α2 is applied to the contrast value of the second BPF circuit 307 for processing the luminance signal Y without γ correction. The coefficient β2 is set respectively.

In step S3, the peripheral area A2 of the screen of the subject is determined based on the output of the photometric element 312.
And if the luminance level is high, it is determined that the backlight state is the first state, and the process proceeds to step S6. The weighting coefficient α3 for the contrast value from the first BPF circuit 305 for processing the luminance signal Yγ corrected for γ, and the weighting coefficient for the contrast value of the second BPF circuit 307 for processing the luminance signal Y without γ correction are used. Set β3 respectively. If it is determined in step S3 that the brightness level of the peripheral area A2 is normal or low, the process jumps to step S7. Then, the contrast value of the first BPF circuit 305 that processes the luminance signal Yγ corrected for γ is weighted by α4
Is weighted by β4 for the contrast value of the second BPF circuit 307 which processes the luminance signal Y without γ correction.
Are set respectively.

Subsequently, the process proceeds to step S8 and the subsequent steps, where the contrast value is fetched under the conditions set in the above steps, and the number of peak steps is detected. That is, the third contrast data obtained by multiplying the first and second contrast data acquired at the stage number n of the focusing lens 301, that is, the first and second contrast data at the first stage by the set weighting coefficients α and β, respectively, is added. The contrast value is taken into Cn (step S8). And the focusing lens 30
1 is driven forward by one step (step S9), and the value of the weighted third contrast data at that position is changed to Cn +
1 (step S10). Subsequently, the contrast values Cn and Cn + 1 are compared, and it is determined that the contrast value is increasing until the value Cn becomes larger (step S11). Then, n is incremented (step S13), and the process returns to step S9. When the contrast value Cn becomes larger, it is determined that the peak has been exceeded, the focusing lens 301 is driven to rotate in reverse by one stage, and the routine ends with the focusing state.

As described above, in the automatic focusing apparatus according to the present embodiment, in the case of a backlit subject, the contrast value is drawn toward the surrounding high-luminance background only by the luminance signal Y without gamma correction, and false focusing is performed. Since there is a possibility of focusing, when calculating a contrast value for focus detection, the γ-corrected luminance signal Yγ
Is multiplied by a larger weighting factor. The contrast value obtained from the luminance signal Y without γ correction is multiplied by a smaller weighting coefficient. Then, the contrast value obtained by adding both is used as the focus position detection information, so that the contrast of the surrounding high-luminance subject is weakened, the contrast of the dark central specific subject is emphasized, and the On the other hand, highly accurate focus position detection is performed. On the other hand, when the periphery is dark and there is a high-luminance subject in the center, the luminance signal
If only γ is used, the change amount of the contrast in the central high-luminance portion is small, and there is a possibility of false focusing. Therefore, when calculating the contrast value for focus detection, the contrast value based on the γ-corrected luminance signal Yγ Multiplies by a smaller weighting factor. The contrast value obtained from the luminance signal Y without γ correction is multiplied by a larger weighting coefficient. Since the contrast value obtained by adding the two is used as the focus position detection information, the contrast of the bright central specific subject is emphasized, and the focus position of the specific subject is detected with high accuracy. . As described above, according to the automatic focusing apparatus of the present embodiment, it is possible to perform processing for obtaining good contrast data for subjects in various luminance states.

In the apparatus of the above-described embodiment, the first and second BPs are used as a contrast data extracting circuit system.
Although two systems of the F circuit system are provided, the present invention is not necessarily limited to this configuration, and BPF circuit systems of other systems having different filter characteristics are separately provided, and weights are given to the respective BPF circuit systems. It is also possible to configure an automatic focusing device that further improves focusing accuracy by obtaining data. In the embodiment, the imaging processing circuit 30
4, a first and second BPF circuit and an A / D conversion circuit 3
05 to 308 are provided so that contrast data, which is a digital signal, is taken into the arithmetic processing circuit 309. As a modified example, the imaging processing circuit 304 is provided therein with a Yγ signal or Y signal digitizing section. Processing such as taking in the Yγ signal and the digital signal of the Y signal into an arithmetic processing circuit 309, performing digital filtering inside the processing circuit, calculating a contrast value, and further multiplying by a weighting coefficient. Is performed by digital processing, the BPF circuit and the A / D conversion circuits 305 to 308 become unnecessary, and the circuit is simplified.

In the embodiment, the luminance information for setting the gain of the photographing processing circuit is fetched via the photometric element 313. The gain is set based on the image signal of the image sensor 303. It is also possible to configure the automatic focusing device of the present invention. Further, as a modified example of the photometric element used in the automatic focusing apparatus of the above-described embodiment, the image sensor 3
It is also possible to propose a device that obtains photometric information using the imaging signal of No. 03. That is, in the above-described embodiment, the luminance information is captured via the dedicated photometric element 312 having two photometric areas, but the photometric information of each area may be captured based on the image signal of the image sensor 303. It is possible to configure the automatic focusing device of the present invention. For example, the imaging screen G10 of the imaging element 303 is divided into nine photometric areas as shown in FIG. The two areas A15 and A18 correspond to the specific area A1, and the areas A11 to A14, A16, A17,
The seven areas of A19 correspond. The sum of the light amounts of the divided areas is applied to the luminance of each of the specific and peripheral areas. The brightness level of the subject is specified and the brightness of each surrounding area is determined in the same manner as in the above-described embodiment, and the first state and the second state are identified. The following processing is the same as that of the first embodiment. When determining the difference in luminance between the specific and peripheral regions, the light amount ratio of each region may be obtained, and the first state and the second state may be identified based on the ratio value.

In the above embodiment, a "hill climbing system" is used.
However, the automatic focusing apparatus of the present invention is not limited to this. The entire lens drive range, or contrast information of a predetermined drive range,
Once, capture and focus on the focus system based on the information, based on the gist of the present invention,
Of course, it is applicable. The gist of the present invention is:
The present invention can be applied not only to an electronic camera but also to a movie camera and a camera using a silver halide film.

[0020]

As described above, the automatic focusing device of the present invention
When obtaining contrast data to be used at the time of focus position detection, the brightness state of the subject is compared with the first contrast data based on the gamma-corrected luminance signal and the second contrast data based on the non-gamma-corrected luminance signal. The contrast data obtained by assigning weighting coefficients according to the above is added to correspond to the third contrast data for detecting the in-focus position, so that a subject against backlight, a subject having a high-luminance subject at the center, etc. However, it is possible to provide an automatic focusing apparatus having a remarkable effect such that an accurate focusing position can be detected irrespective of the brightness state of the surroundings.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electronic imaging apparatus having a built-in automatic focusing apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart of a focusing process of the electronic imaging apparatus of FIG. 1;

FIG. 3 is a view showing a pattern of a photometry area of a photometry element used in the electronic imaging apparatus of FIG. 1;

FIG. 4 is a diagram showing a pattern of a photometric area of a modification of the automatic focusing apparatus of FIG. 1 in which an output of an image sensor is used instead of the photometric element.

5A is a diagram showing a state of luminance of a subject on a shooting screen, and FIG. 5A shows a high-luminance subject in a central specific area;
(B) The specific area in the center is dark,
The surrounding area shows a screen in a bright backlight state.

[Explanation of symbols]

304: imaging processing circuit (contrast data generation means) 305: first BPF circuit (contrast data generation means) 306: first A / D conversion circuit (contrast data generation means) ) 307 Second BPF circuit (contrast data generation means) 308 Second A / D conversion circuit (contrast data generation means) 309 Operation processing circuit (subject brightness level) Identification means, contrast data generation means, focus adjustment means) 310 motor drive circuit (focus adjustment means) 311 ... focus motor (focus adjustment means) 312 ……………………………………………………………………………………………………………………………………………………………………………… ······························································ ...........................
... Specified area A2, A11 to A14, A16, A17, A19.
……… Surrounding area α, β, α2, β2, α3, β3, α4, β4 ... weighting coefficient (value giving weight)

Claims (1)

(57) [Claims] 1. A contrast data generating means for obtaining both first contrast data based on a gamma-corrected video signal and second contrast data based on a non-gamma-corrected video signal, and brightness relating to a specific area in the screen. The level is in a first state lower than the luminance level of the peripheral area of the specific area, or the luminance level of the specific area is in a second state higher than the luminance level of the peripheral area of the specific area. Identification means for identifying whether the first contrast data and the second contrast data are weighted according to the identification result by the identification means, and added. And a focus adjustment means for performing a focus adjustment operation based on the following.