JP2932537B2 - Automatic focus adjustment device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus adjustment device for automatically adjusting an optical imaging distance of an object by driving an optical system provided in an imaging device.

<Prior Art> For example, in an image pickup apparatus for object recognition, in order to obtain an image of good image quality, an operator manually drives an optical system to perform focus adjustment by trial and error, or performs a target adjustment from the optical system. The focus adjustment is performed by measuring the distance to an object, calculating the optimum focus position according to the measured value, and the like.

<Problems to be solved by the invention> However, in the former method, when the object is changed,
Since the same focus adjustment work is required each time, it is impossible to expect speeding up of work and improvement of work efficiency at all.

Also, the latter method requires a distance measurement system,
There is a disadvantage that the entire apparatus becomes expensive, and the apparatus becomes large-sized and installation space is limited. Also, since the formula for calculating the focal position differs depending on the type of lens used in the optical system, the versatility of the device is lacking, and if there is another object behind the object, the focus adjustment is performed on that object. May be performed.

The present invention has been made in view of the above problem, and utilizes an image quality histogram that quantitatively expresses image quality for focus adjustment of an optical system, thereby achieving optimal and quick focus adjustment without the need for a distance measurement system. It is an object of the present invention to provide an automatic focus adjustment device that is enabled.

<Means for Solving the Problems> The invention described in claim 1 variably sets a focus adjustment amount in order to automatically adjust an optical imaging distance by driving an optical system provided in an imaging apparatus. Adjustment amount setting means for driving, driving means for driving the optical system according to the set focus adjustment amount to change the optical imaging distance, and changing the optical imaging distance by the driving means. A histogram adjusting unit for generating an image quality histogram for image evaluation for each input image obtained while determining, and a determining unit for determining an optimal focus adjustment amount using a peak value of each of the generated image quality histograms. And a brightness level and a binary level obtained by binarizing the input image based on the brightness level as the histogram for image evaluation.
A histogram indicating the relationship with the frequency data indicating the degree of smoothness of the value image is generated.

According to a second aspect of the present invention, the discriminating means includes a comparing means for comparing the peak values of the respective image quality histograms, and the optimum focus adjustment amount is discriminated based on the comparison result.

According to the third aspect of the present invention, in addition to the adjustment amount setting means, the driving means, and the histogram generating means as in the first aspect, a designation means for designating an object of focus adjustment based on brightness, and a designation of each image quality histogram An automatic focus adjustment device is configured by a determination unit that determines an optimal focus adjustment amount using a peak value corresponding to the brightness of the target object.

<Operation> An image quality histogram of each input image is generated while variably setting a focus adjustment amount to change an optical image forming distance of the optical system, and an optimum focus adjustment amount is determined using a peak value of each image quality histogram. Therefore, it is possible to perform the optimal and quick focus automatic adjustment, and to obtain an image with the optimal image quality.

When the image having the optimum image quality is subjected to the binarization processing, the smoothest binary image is obtained when the image is binarized at a brightness level corresponding to the peak value of the image histogram obtained for the image. Therefore, it is possible to obtain an image having an optimum image quality and, at the same time, obtain an optimum binarization threshold value for binarizing the image.

In addition, if an object to be adjusted is designated with reference to brightness, even if a plurality of objects exist in the field of view of the imaging device, a desired object can be focused.

<Embodiment> FIG. 1 shows a schematic configuration of an automatic focus adjustment apparatus according to an embodiment of the present invention, which comprises an imaging device 1, a lens drive mechanism 2, and a drive control device 3.

The imaging device 1 is a television camera that captures a target object 5 and generates a grayscale image. The imaging device 1 includes an optical system 4 that can perform focus adjustment. The lens drive mechanism 2 is for changing the optical imaging distance of the optical system 4 by rotating the optical system 4 forward and backward within a predetermined angle range by a motor (not shown).

The drive control device 3 changes the optical imaging distance of the optical system 4 by generating a variable focus adjustment amount (for example, a voltage value) to the lens drive mechanism 2 to generate an image quality histogram of the input image each time. The amount of focus adjustment that minimizes the peak value of the image quality histogram is determined as the optimum value, and the optical imaging distance of the optical system is determined based on the amount of focus adjustment.

FIG. 2 shows a specific example of the image quality histogram.
The horizontal axis represents the binarization level, and the vertical axis represents poor image quality.
In the figure, the solid line indicates the image quality histogram 6 obtained from the in-focus input image, and the broken line indicates the image quality histogram 7 obtained from the out-of-focus input image. The peak value of the former image quality histogram 6 is shown. p ₁ is a value smaller than the peak value p ₂ of the latter quality histograms 7.

Therefore, when the image quality histogram with the minimum peak value is obtained, the focus adjustment amount for the input image is determined as the optimum value.

The above-mentioned image quality histogram is generated by using a known example (Japanese Patent Laid-Open No. 64-51586) proposed by the applicant before, and FIG. 3 shows a specific configuration of the drive control device 3 according to the known example. It is shown in

The drive control device 3 in the illustrated example includes a microcomputer 10
The window scanning unit 11, the illegal pattern detection unit 12, the illegal pattern histogram generation unit 13, the brightness histogram generation unit 14, the image quality histogram generation unit 15, the histogram smoothing unit 16, and the peak value search unit 17 I have it.

The window scanning unit 11 controls the microcomputer 10
Address generator 19 connected via U bus 18
And an image memory 24 connected to the address generator 19 via an image bus 20, and a first shift register 25 of a FIFO (first-in first-out) system connected to a data bus 23 of the image bus 20. And the first group of latch circuits 26 to
29 and the same FIFO connected to this last-stage latch circuit 29
A second shift register 30 and a second group of latch circuits 31 to 34 are provided.

The window scanning unit 11 in the illustrated example is for setting a rectangular window 35 as shown in FIG. 4 on the grayscale image stored in the image memory 24 and performing raster scanning. Predetermined pixels A _{0 to} A _{7 for} the image in
Brightness data d ₀ to d ₇ is adapted to be taken out simultaneously. In the figure, the crosses indicate pixels that are not to be processed.

That is, the address generator 19 sequentially generates the address of each pixel in the image memory 24, and outputs the brightness data of the pixel corresponding to the address to the first shift register 25 via the image bus 20. In the image bus 20, an address bus 21 transmits an address, a data bus 23 transmits brightness data, and a control bus 22 transmits an address strobe signal and a read / write signal. Assuming that the number of pixels in the horizontal direction of the image memory 24 is n (see FIG. 4), the first shift register 25 has a first group of latch circuits 26 based on this n.
An operation of delaying the output of the brightness data by the number of stages (n-4) obtained by subtracting the number of stages of ~ 29 is executed. The first group of four-stage latch circuits 26 to 29 perform the operation of the shift register as a whole, and the output of the last-stage latch circuit 29 is output to the second shift register 30.
The second shift register 30 also has (n-4) stages, and outputs the brightness data to the second group of four-stage latch circuits 31 to 34 by delaying the output by the number of stages.

Thus, the first-stage and second-stage latch circuits 26 to 29, 31
34 and the second shift register 30 simultaneously extract brightness data, and the outputs of the first group of latch circuits 26 to 28 output the brightness data d of the pixels A _{0 to} A ₂ in the window 35. ₀ to d ₂ gives also the output of the second shift register 30 and the second group of latch circuits 31 to 34 to give the brightness data d ₃ to d ₇ of the pixel a ₃ to a ₇ in the window 35 become.

Brightness data d ₀ to d ₇ of the respective pixels A ₀ to A ₇ together with the output to the illegal pattern detecting section 12, illegal pattern histogram generation unit 13 and the brightness for the brightness data d ₁ of the specific pixel A ₁ It is also output to the histogram generation unit 14.

Illegal pattern detector 12 fetches these brightness d ₀ to d _7, after binarizing the pixels in the window 35 brightness data d ₁ specific pixel A ₁ as a threshold value, the binary It is determined whether the pattern corresponds to a legal pattern or an illegal pattern. If the pattern is an illegal pattern, a detection flag “1” is output, and the frequency of occurrence of the illegal pattern for each brightness (threshold) is counted in the illegal pattern histogram generation unit 13 to generate an illegal pattern histogram. Is done. Similarly, brightness histogram generator
At 14, the frequency of each brightness is counted and a brightness histogram is generated.

Here, the legal pattern means a binary pattern that frequently appears on a smooth image as exemplified in FIG.
An illegal pattern means a binary pattern that frequently appears on a non-smooth image as exemplified in FIG. In FIGS. 5 and 6, hatched portions are pixels having binary data of “1”, and in the binary pattern of FIG. 6, a hole 36 of “0” is formed inside the pixel region of “1”. I have.

As described above, the illegal pattern histogram generation unit 13 stores the illegal pattern histogram f _hist on a memory (not shown).
(K) is generated. Here, f _hist (k) means the frequency of occurrence of illegal patterns at the threshold value k. In this embodiment, by evaluating the pattern by the illegal pattern detecting unit luminance data d ₀ other pixel brightness data d ₁ of the specific pixel as the threshold at 12 and d ₂ to d _7, as a result Is represented by the flag flag, the illegal pattern histogram f
_hisk (k) is formed according to the following equation:

f _hist (k) = f _hist (k) + flag ‥‥ However, it is assumed that each element of the illegal pattern histogram is initialized to zero.

The brightness histogram generation unit 14 generates a brightness histogram hist (k) on a memory (not shown). here
hist (k) means the frequency of occurrence of a pixel of brightness k, and this brightness histogram hist (k) is similarly generated according to the following equation.

hist (k) = hist (k) + 1 ‥‥ Returning to FIG. 3, the image quality histogram 15 generates an image quality histogram q _hist (k) after the generation of the illegal pattern histogram and the brightness histogram is completed. The image quality histogram q _hist (k) provides an evaluation standard for image quality, in this embodiment, a standard indicating poor image quality, and is generated according to the following equation.

(1) When hist (k) = 0 q _hist (k) = Q ₀ ‥‥ (2) When hist (k) ≠ 0 In the above equation, Q ₀ is a constant (maximum value).

Next, the histogram smoothing processing section 16 in FIG. 3 is for smoothing the image quality histogram q _hist (k) as necessary. As a result, as shown in FIG. Is generated.

In FIG. 2, the horizontal axis represents the binarization level (threshold k), and the vertical axis represents the image quality. The image quality is peaked when the binarization level is L.

The peak value search unit 17 searches for the peak values p ₁ and p ₂ ,
The search result is notified to the microcomputer 10 through the CPU bus 18.

FIG. 7 shows a control procedure of the focus adjustment by the above-described apparatus example.

In step 1 of the figure (indicated by “ST1” in the figure),
The microcomputer 10 of the drive control unit 3 sets an initial value F ₁ as the focus adjustment amount F _0, and outputs the value to a level drive mechanism 2 (Step 2). The level drive mechanism 2 drives the optical system 4 based on the input value to set the optical imaging distance.

In the next step 3, the image pickup apparatus 1 picks up an image of the object 5 based on the optical image forming distance, and stores the grayscale image in the image memory 24.
Is stored in Next, in step 4, the drive control device 3
Generates an image quality histogram for this input image, and obtains a peak value (image quality evaluation value) of the image quality history column.
The image quality evaluation value is stored in that time being taken into the microcomputer 10 as the minimum image quality evaluation value H ₀ to a memory (not shown).

Next, in step 5, the microcomputer 10
It adds the predetermined minute value ΔF to the focus adjustment amount F ₀ to calculate a new focus adjustment amount F _0, the optical system 4 and rotated and outputs the value to the lens driving mechanism 2, thereby a new An optical imaging distance is set (step 6).

Next, in step 7, the image pickup apparatus 1 picks up an image of the object 5 based on the optical imaging distance, and the grayscale image is stored in the image memory 24.
Is stored in Step 8 In the drive control unit 3 of the following produces a quality histogram per the input image, obtains the peak value of the image quality histogram as an image quality evaluation value H _1,
It is stored in the memory of the microcomputer 10.

Next Step 9 microcomputer 10 in the has determined whether the quality evaluation value H ₁ is less than the minimum image quality evaluation value H _0, the smaller the better the image quality evaluation value H ₁ that if obtained in step 8 The determination of “H ₀ > H ₁ ” in step 9 is “YE
S ", and this with an image quality evaluation value H ₁ is stored in the memory instead placed a minimum of image quality evaluation value H ₀ in step 10.

In the next step 11, the microcomputer 10 focus adjustment amount F ₀ to by adding a predetermined small value ΔF to calculate a new focus adjustment amount F ₀ of the next, the lens driving mechanism 2 that value
To drive the optical system 4 to rotate, thereby setting a new optical imaging distance (step 12).

Next, the image pickup apparatus 1 picks up an image of the object 5 based on the optical image formation distance, and the grayscale image is stored in the image memory 24 (step 13). In the next step 14, the drive control device 3
Generates a quality histogram per the input image, obtains the peak value of the image quality histogram as an image quality evaluation value H _1, is stored in the memory of the microcomputer 10.

Then the microcomputer 10 in step 15 is determined whether the quality evaluation value H ₁ is the minimum image quality evaluation value H ₀ is less than, the smaller the better the image quality evaluation value H ₁ that if obtained in step 14 The determination of “H ₀ <H ₁ ” in step 15 is “NO”
Then, the process returns to step 10 and the same procedure is performed.

If If greater than the image quality evaluation value H ₀ image quality evaluation value H ₁ is the minimum determined at step 14, the image quality evaluation value H ₀ of the minimum could be formed into a minimum value, the determination in step 15 the "YES" Become. In the next step 16, the microcomputer 10
Subtracts a predetermined small value ΔF than the current focus adjustment amount F ₀ calculates the focus adjustment amount F ₀ of the previous, the optical system 4 and rotated by the output to the lens driving mechanism 2 that value as the determined value ,
This fixes the optical imaging distance (step 17).

If in step 9 above, is greater than the minimum image quality evaluation value H ₀ is better image quality evaluation value H ₁ obtained in step 8, a determination is "H _0> H _1" in step 9 becomes "NO" proceeds to step 18, the microcomputer 10 calculates the focus adjustment amount F ₀ of the last by subtracting a predetermined minute value ΔF than the current focus adjustment amount F _0. Further microcomputer 10
Calculates the next new focus adjustment amount F ₀ by further subtracting a predetermined small value ΔF from the focus adjustment amount F ₀ in the next step 19, outputs the value to the lens drive mechanism 2, and rotates the optical system 4. Drive, thereby setting a new optical imaging distance (step 20).

In the next step 21, the imaging apparatus 1 images the object 5 based on the optical imaging distance, and the grayscale image is stored in the image memory 24.
Is stored in Then the drive control unit 3 in step 22 generates an image quality histogram per the input image, and stores the peak value of the image quality histogram memory of the microcomputer 10 obtained as the image quality evaluation value H _1.

The next step 23 the microcomputer 10 in the has determined whether the quality evaluation value H ₁ is less than the minimum image quality evaluation value H _0, the smaller the better the image quality evaluation value H ₁ that if obtained in step 22 The determination of “H ₀ <H ₁ ” in step 23 is “N
O ", go to step 24, microcomputer
10 This after storing in the memory instead placed a minimum of image quality evaluation value H ₀ with the image quality evaluation value H _1, a similar procedure is performed following the process returns to step 19.

If If greater than the image quality evaluation value H ₀ image quality evaluation value H ₁ is the minimum determined at step 22, the image quality evaluation value H ₀ of the minimum could be formed into a minimum value, the determination in step 23 is a "YES" Become. The microcomputer 10 in the next step 25 by adding a predetermined small value ΔF than the current focus adjustment amount F ₀ calculates the focus adjustment amount F ₀ of the last, is output to the lens driving mechanism 2 that value as the determined value To rotate the optical system 4 to fix the optical imaging distance (step 17).

FIG. 8 shows a field of view 37 of the imaging apparatus 1, in which a plurality of objects 5A and 5B having different brightness exist.

When it is assumed that one object 5A is darker than the other object 5B, when an image quality histogram is obtained from an input image obtained by imaging including both objects 5A and 5B, a curve as shown in FIG. 9 is obtained. Become.

In the figure, the solid line shows the image quality histogram 38 obtained from the input image in which the darker object 5A is in focus, and the broken line shows the image quality histogram 39 obtained from the input image out of focus on the darker object 5A, Each is shown. According to the figure, two peaks appear in each of the image quality histograms 38 and 39 corresponding to the number of objects, but the peak having the smaller brightness has the peak value p ₁ of the former image quality histogram 38. There has been a value smaller than the peak value p ₂ of the latter quality histogram 39.

Therefore, after specifying which object to focus on, for example, when focusing on the darker object 5A, when an image quality histogram in which the peak value is the smallest for the smaller peak of brightness is obtained, the The focus adjustment amount for the input image is determined as the optimum value.

In this case, the object of the focus adjustment can be designated by an external input device based on the visual judgment of the worker using the brightness of the object as a criterion, but in the case of this embodiment, the input image obtained in an appropriate focus adjustment state The brightness of both objects 5A and 5B is measured by the microcomputer 10 and the focus adjustment target is specified based on the measurement result.

FIG. 10 shows a measurement procedure by the microcomputer 10. After setting a predetermined window at the position of each of the objects 5A and 5B of the input image in step 1, the next step 2 is executed.
The average brightness a, b of the pixels contained in each window
Is being measured. In the next step 3, the average values a and b of the brightness are compared in magnitude. If a <b, step 4 is "YES", the object A is designated as a target of focus adjustment, and the brightness of the object A is adjusted. the initial value F ₁ of focus adjustment amount is selected in the vicinity of the (step 5). If a> b, step 4 is “NO”, the object B is designated as the object of focus adjustment, and the initial value F ₁ of the focus adjustment amount is selected near the brightness of the object B ( Step 6).

<Effect of the Invention> As described above, the present invention generates the image quality histogram of each input image while variably setting the focus adjustment amount and changing the optical imaging distance of the optical system, and then sets the peak value of each image quality histogram. Since the optimum focus adjustment amount is determined by using this function, it is possible to automatically and optimally adjust the focus automatically without the need for a distance measurement system, and to obtain an image of the optimum image quality. An optimum binarization threshold can be obtained from the obtained image quality histogram.

Further, in the invention according to the third aspect, an object to be focused is specified based on brightness, even when a plurality of objects are present in the field of view of the imaging device, it is possible to focus on a desired object. It has a remarkable effect achieved for the purpose of the invention.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of an automatic focus adjustment device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a specific example of an image quality histogram, and FIG. 3 is an example of a circuit configuration of a drive control device. FIG. 4 is an explanatory diagram showing a window set on a grayscale image, FIG. 5 is an explanatory diagram showing an example of a legal pattern, FIG. 6 is an explanatory diagram showing an example of an illegal pattern, FIG. FIG. 8 is a flowchart showing a control procedure of focus adjustment, FIG. 8 is an explanatory diagram showing an object in the field of view of the imaging apparatus, FIG. 9 is an explanatory diagram showing a specific example of an image quality histogram,
FIG. 10 is a flowchart showing a procedure of measuring brightness by the microcomputer. DESCRIPTION OF SYMBOLS 1 ... Image pick-up device, 2 ... Lens drive mechanism 3 ... Drive control device, 4 ... Optical system 10 ... Microcomputer

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G06T 1/00

Claims (3)

(57) [Claims] 1. A focus adjustment device for automatically adjusting an optical imaging distance by driving an optical system provided in an imaging device, comprising: an adjustment amount setting means for variably setting a focus adjustment amount. A driving unit for driving the optical system according to the focus adjustment amount to change the optical imaging distance, and an image evaluation for each input image obtained while changing the optical imaging distance by the driving unit. Histogram generating means for generating an image quality histogram, and determining means for determining an optimal focus adjustment amount using a peak value of each generated image quality histogram, wherein the histogram generating means includes a brightness level, A histogram indicating the relationship between the binary image obtained by binarizing the input image based on the brightness level and frequency data indicating the degree of smoothness of the binary image is stored in the image quality evaluation image for image evaluation. Automatic focus adjustment device formed by generating a chromatogram. 2. The automatic focus adjustment apparatus according to claim 1, wherein said determination means includes a comparison means for comparing peak values of the respective image quality histograms, and determines an optimum focus adjustment amount based on the comparison result. 3. A focus adjustment device for automatically adjusting an optical imaging distance by driving an optical system provided in an imaging device, comprising: an adjustment amount setting means for variably setting a focus adjustment amount. A driving unit for driving the optical system according to the focus adjustment amount to change the optical imaging distance, and an image evaluation for each input image obtained while changing the optical imaging distance by the driving unit. Histogram generation means for generating an image quality histogram, designation means for designating an object of focus adjustment with reference to brightness, and using the generated image quality histograms and the brightness of the object designated by the designation means. Determination means for determining an optimal focus adjustment amount, wherein the histogram generation means obtains a brightness level and binarizes the input image based on the brightness level. A histogram indicating a relationship with frequency data indicating a degree of smoothness of the binary image as an image quality histogram for the image evaluation, wherein the determination unit determines whether the brightness of the designated object in each image quality histogram is high. An automatic focus adjustment device that determines the optimal focus adjustment amount using the corresponding peak value.