JPS6243590B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus adjustment method in an imaging device using an image sensor, and particularly to a method that allows a synchroscope to adjust focus without using a finder or the like.

Conventionally, in imaging devices using image sensors, the focus has been adjusted by observing the output waveform of the image sensor using a synchroscope or by using a viewfinder like a camera. However, this method required a relatively expensive synchroscope and had problems such as a complicated optical system.

It is an object of the present invention to solve these conventional problems and to enable accurate focus adjustment with simple operations without using a synchronizer, a viewfinder, or the like.

That is, the present invention gradually changes the focus of the imaging device in an arrangement such that the boundary between the subject and the background or the clear boundary between the bright and dark areas on the subject is projected on the image sensor of the imaging device, On the other hand, the bright area discrimination level is set to a value slightly darker than the pixel output level obtained from the image sensor corresponding to the bright area bordering the boundary, and the bright area discrimination level is set to a value slightly darker than the pixel output level obtained from the image sensor corresponding to the dark area. The dark area discrimination level is set to be a value slightly brighter than the pixel output level that is set, and the pixel output that has a value intermediate between the two discrimination levels among the series of pixel outputs output from the image sensor for each scan is set. This system is characterized in that it discriminates the number of pixels, counts the number of pixels, and determines whether the object is in focus based on the counting result.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a diagram showing an example of the arrangement of an imaging device, a subject, and a light source when implementing the method according to the present invention. In this example, a light source 2 is arranged behind the subject 1 to illuminate the subject 1 from behind, and an imaging device 3 is arranged in front of the subject 1, and the image sensor element 4 in the imaging device 3 receives the image. It is configured such that an image near the edge of the subject 1, that is, the boundary between the subject 1 and its background, is projected at the center of the surface via an optical system (not shown). Further, as the image sensor element 4 shown in this example, a line sensor using a charge coupled device (CCD), a photodiode array (PDA), etc. is used.

FIG. 2 shows an example of an electric circuit that determines focus based on the output of the image sensor element 4.

On the light-receiving surface of the image sensor element 4, photoelectric elements (hereinafter referred to as pixel elements) that convert the amount of light at each point into an electrical signal proportional to the amount of light are arranged in a row. When a scanning signal of a predetermined frequency is applied, the outputs of adjacent pixel elements (hereinafter simply referred to as pixel outputs) are sequentially output in series in synchronization with this scanning signal, and are amplified by an amplifier 5. Then, a series of pixel output pulse trains as shown in FIG. 4 are obtained.

In the amplifier output waveform shown in FIG. 4, the high level portion on the right side of the pulse train of each period is located on the light receiving surface of the image sensor element 4 in the configuration shown in FIG.
This corresponds to the pixel output in the bright area, which is caused by the light rays from the light source 2 reaching the object 1 unobstructed, while the low-level area on the left side is caused by the light rays from the light source 2 being blocked by the object 1. This corresponds to the pixel output of the dark area that occurs.

Further, the amplifier output pulse train of each period shown in FIG. 4 shows an output waveform obtained while gradually changing the focus by adjusting the optical system of the imaging device 3, and among others, a high level corresponding to a bright area. Pulse trains P ₁ to _{P 4} that change rapidly from pulses to low-level pulses corresponding to dark areas show the output waveforms when in focus, while pulse trains that change gradually
_P5 to _P8 show output waveforms when the image is out of focus. In addition, P ₃ , P ₄ , P ₇ , and P ₈ , which have relatively high values in the low-level portions of each pulse train, represent output waveforms when slightly transparent paper or the like is used as the object 1 .

OP amplifiers A ₁ and A ₆ that constitute a sample and hold circuit are connected to the output side of the amplifier 5 through analog gates 6 and 7, respectively, and the analog gates 6 and 7 are connected to each other via analog gates 6 and 7, respectively, as shown in FIG. Gate pulses G ₁ and G ₂ are supplied. Therefore, in response to the gate pulse _G1 , the output of several pulses from the end of the amplifier output of each period, that is, the output corresponding to the bright part, is held at the input side of the OP amplifier _A1 , and in the same way. On the input side of OP amplifier A ₆ , the output of several pulses from the beginning of the amplifier output of each period,
In other words, the output corresponding to the dark area is held. Then, on the output side of OP amplifiers A ₁ and A ₆ , a fourth
As shown in the figure, hold outputs E ₁ and E ₆ corresponding to each of the above hold inputs are obtained.

Two amplifying OP amplifiers A ₂ and A ₃ with different gains are connected in parallel to the output side of OP amplifier A ₁ , and the gain of OP amplifier A ₂ is set to be larger than that of A ₃ . has been done. Therefore, the OP amp
On the output side of A ₂ and A ₃ , there are two heights as shown in Fig. 4 E ₂ and E ₃ .
Two voltages are output, and the higher voltage is used for bright area discrimination, which will be described later, and the lower voltage is used for dark area discrimination. That is, the bright area or dark area discrimination reference level determined based on the intensity of the light source 2 shown in FIG. 1 is output to the output side of the OP amplifiers A ₂ and A ₃ .

A ₄ and A ₅ are OP amplifiers that constitute an adder circuit, and the output E ₂ of the OP amplifier A ₂ and the output E ₆ of the OP amplifier A ₆ are supplied in parallel to the input side of the OP amplifier A ₄ . The input side of OP amplifier A ₅ is the output E ₃ of OP amplifier A ₃ and the output of OP amplifier E ₆ .
E ₆ is supplied in parallel. Therefore, each input is connected to the output side of OP amplifier _A4 as shown in Figure 4.
Output voltage V ₁ corresponding to the sum of E ₂ and E ₆ is obtained, and
An output voltage V ₂ corresponding to the sum of each input E ₃ and E ₆ is obtained on the output side of the OP amplifier A ₅ . In other words, the output side of the OP amplifier A ₄ outputs the bright area discrimination reference level V ₁ determined based on the intensity of the light source 2 shown in FIG. 1 and corrected according to the transmittance of the subject 1. On the other hand, a dark area discrimination reference level V ₂ determined based on the intensity of the light source 2 and corrected according to the transmittance of the subject 1 is outputted to the output side of the OP amplifier A ₅ . A ₇ and A ₈ are OP amplifiers each forming a comparator, and the reference voltage input terminal of OP amplifier A ₇ is connected to the output V ₁ of the OP amplifier A ₄ .
At the same time, the output V ₂ of the OP amplifier A ₅ is supplied to the reference voltage input terminal of the OP amplifier A ₈ , and the output V 2 of the OP amplifier A 5 is also supplied to the input terminals of the discriminated signals of the OP amplifiers A ₇ and A ₈ . 5 outputs are supplied in parallel. In the pulse train from the amplifier 5, the output of the OP amplifier _A7 becomes "H" for pulses with a level higher than the bright area discrimination level _V1 , and becomes "H" for pulses with a level lower than that. It becomes "L". On the other hand, the output of the OP amplifier _A8 becomes "H" for pulses with a level higher than the dark area discrimination level _V2 in the pulse train from the amplifier 5, and becomes "H" for pulses with a level lower than that. It becomes "L".

Therefore, if the output of the OP amplifier A ₇ is inverted by the inverter 8 and this inverted output and the output of the OP amplifier A ₈ are supplied to the NAND element 9, the output of the NAND element 9 will be the pulse train from the amplifier 5. It becomes "L" only for pulses at an intermediate level between _V1 and _V2 .

10 is a counter that counts "L" pulses output from the NAND element 9;
As shown in FIG. 4, the reset signal is reset by a reset signal that is slightly delayed from the periodic signal that is generated every time a scan is started. A latch circuit 11 latches the output of the counter 10 in response to a periodic signal, and the output of the latch circuit 11 is displayed on a display device 12.

Therefore, the display device 12 displays the following information in each scanning period.
In the pulse train output from the amplifier 5, the number of pulses at an intermediate level between the bright area discrimination level _V1 and the dark area discrimination level _V2 is displayed. Here, as mentioned above, it has been confirmed that the number of pulses at this intermediate level decreases as the focus is adjusted, so the numerical value displayed on the display device 12 while gradually changing the focus of the imaging device 3. Once you find the point where the minimum value is reached, you can easily focus without using any synchroscope or finder.

FIG. 3 shows another embodiment of the present invention, in which a light emitting diode is automatically turned on when the output of the counter 10 reaches a preset value at the time of focus alignment. be. That is, 13 is a digital comparator that compares the count value of the counter 10 and the set value of the digital register 14. This comparator 13 performs a comparison operation in response to the periodic signal, and when the two values match. A predetermined output pulse is generated only when the This output pulse is then transmitted to the timer circuit 15 (for example,
(mono-multi, etc.) until the end of the next scanning cycle. On the other hand, transistors 16 and 17 are connected to the output side of the timer circuit 15 and switch in response to the outputs "H" and "L" of the timer circuit, respectively, and light emitting diodes 18 and 19 are turned on via these transistors. is configured to do so.

Therefore, if the value at the time of focus adjustment is set in advance in the digital digit register 14, the counter 10
One of the light-emitting diodes 18 and 19 lights up in accordance with the count output, and based on this, it is possible to more easily determine that the subject is in focus.

In the above embodiments, it is determined that the focus is achieved through the operator's visual sense, but an automatic focus adjustment mechanism is provided in the imaging device 3, and the counting output of the counter 10 is applied to the automatic focus adjustment mechanism for automatic control. You can also adjust the focus by

As is clear from the above explanation, according to the method according to the present invention, it is possible to accurately adjust the focus of an imaging device using an image sensor without using a synchroscope or a finder, and with simple operations. For example, when inspecting steel plates, roll paper, or the like on an automatic conveyance line using this type of imaging device, it is possible to enable an on-site operator to adjust the focus.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the arrangement of an imaging device, a subject, and a light source when implementing this method, Fig. 2 is an electric circuit diagram implementing this method, Fig. 3 is another electric circuit diagram, FIG. 4 is a diagram showing waveforms at various parts in FIG. 2. 1...Subject, 3...Imaging device, 4...Image sensor, 10...Counter, A7, A8...Comparator, _V1 ...Bright area discrimination level, _V2 ...Dark area discrimination level.

Claims (1)

[Claims] 1 In an arrangement where the boundary between the subject and the background or the clear boundary between the bright and dark areas on the subject is projected on the image sensor of the imaging device, the focus of the imaging device is gradually changed, while the boundary is The bright area discrimination level is set to be a value slightly darker than the pixel output level obtained from the above image sensor corresponding to the bright area, and the bright area discrimination level is set to a value slightly darker than the pixel output level obtained from the above image sensor corresponding to the dark area. The dark area discrimination level is set so as to have a slightly bright value, and among a series of pixel outputs output from the image sensor for each scan, a pixel output having a value intermediate between the above two discrimination levels is discriminated, and the number of pixels is determined. 1. A focus adjustment method for an imaging device using an image sensor, the method comprising counting the number of pixels and determining whether the focus is achieved based on the counting result.