JPH0711617B2 - Image detection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image detection method for an autofocus device that performs focus determination using an image sensor such as a CCD line sensor.

(Technical background of the invention) Various autofocus methods using an image sensor such as a CCD line sensor have been proposed. However, this autofocus operation is premised on that the projection light of the image area suitable for the operation is input to the image sensor. For example, a correct autofocus operation cannot be performed in an image area having a single lightness or an area in which the density changes less frequently, which causes a malfunction.

Therefore, a method of determining whether or not the image area is suitable for autofocus prior to the autofocus operation has been proposed. For example, there is a method in which the output signal of the line sensor is binarized at a predetermined binarization level, the number of times of polarity reversal, in other words, the number of black and white reversals is calculated, and if there is a predetermined number of times or more, an image exists. However, this method prepares different binarization levels for negative and positive when the negative and positive film is used for the original image like a micro reader printer, and sets the type of negative and positive manually. It was necessary to select one of the binarization levels, and the operation was troublesome.

(Object of the Invention) The present invention has been made in view of such circumstances, and it is possible to automatically determine an area including an appropriate image even if the original image is either negative or positive, and negative·
It is an object of the present invention to provide an image detection method for an autofocus device that does not require a positive setting.

(Constitution of the Invention) According to the present invention, an object of the present invention is to detect an image of an autofocus device that controls a projection lens to a focus position by using an output signal of the image sensor obtained by scanning an image projection light with the image sensor. In the method, the output signal of the image sensor is binarized by each of the negative and positive binarization levels to obtain each polarity reversal number, and each polarity change frequency is further compared with each negative and positive constant value. Is performed in parallel, and an autofocus operation is performed by detecting an image area in which at least one of the polarity inversion times is equal to or more than the predetermined value, and the image detection method is achieved.

(Embodiment) FIG. 1 is an overall schematic view of a reader printer which is an embodiment of the present invention, FIG. 2 is a block diagram of its autofocus control device, FIG. 3 is a flow chart of operation, and FIG. 4 is a line. The output signal V of the sensor and the output waveform of each part are shown in FIG.
Corresponds to a negative film and (B) corresponds to a positive film.

In FIGS. 1 and 2, reference numeral 10 is an original image of a micro photograph such as a micro fish or a micro roll film.
Reference numeral 12 denotes a light source, and the light from the light source 12 is guided to the lower surface of the original image 10 via a condenser lens 14, a heat insulating filter 16, and a reflecting mirror 18. In the reader mode, the transmitted light (image projection light) of the original image 10 is guided to the transmissive screen 28 by the projection lens 20, the reflecting mirrors 22, 24 and 26, and the original image 10 is displayed on the screen 28.
To form an enlarged projection image of. In printer mode,
The reflecting mirror 24 is rotated to the position shown by the phantom line in FIG.
22、30、32 by PPC type slit exposure type printer 3
Guided by 4. The reflecting mirrors 22 and 30 move in synchronization with the rotation of the photosensitive drum 36 of the printer 34, and a latent image is formed on the photosensitive drum 36. This latent image is visualized with toner charged to a predetermined polarity, and this toner image is transferred to the transfer paper 38.

Reference numeral 40 denotes a zone setting means, which includes a mark 42 indicating a focus zone and a manual knob 44 for moving the mark 42 on the screen 28. The position a of the zone is detected by the position detector 46 and sent to the control means 48.

A focus control optical system 50 includes a semi-transparent mirror 52 arranged on the optical axis of the image projection light, a projection lens 54, a CCD line sensor 56 as an image sensor, and a servo motor 58.
With. A part of the projection light that has passed through the projection lens 20 is guided to the line sensor 56 through the projection lens 54 by the semitransparent mirror 52. The line sensor 56 is movable by a motor 58 in a direction orthogonal to the optical axis. The projection lens 54
When the projection lens 20 is placed at a position where the projection light is focused on the projection surface of the screen 28 or the photosensitive drum 36, its focal length is determined so that it is accurately focused on the light receiving surface of the line sensor 56. ing.

The autofocus mechanism includes a servomotor 60 that moves the projection lens 20 back and forth in the optical axis direction, and the projection light is projected on the screen 28.
Alternatively, the focus is controlled by the control means 48 so that an image is correctly formed on the projection surface of the photosensitive drum 36.

The control means 48 is constructed as shown in FIG. That is, the CCD driver 64 drives the line sensor 56 in synchronization with the clock pulse output from the clock 62. The line sensor 56 outputs a pulse voltage that changes in voltage corresponding to the amount of incident light of each pixel for each scanning. This pulse voltage varies from pixel to pixel even if the same amount of light is projected due to variations in the characteristics of each pixel. The signal processing circuit 66 corrects the variation of this characteristic of each pixel and shapes the waveform to make the fourth signal.
The output signal V in FIGS.

The output signal V thus signal-processed is converted into a digital signal by the A / D converter 68 and input to the CPU 72 via the input interface 70. In FIG. 2, 74 is a ROM for storing the control program of the CPU 72, 76 is a RAM, 78 is an output interface, 80 and 82 are D / A converters, and 84 and 86 are drivers for driving the motors 58 and 60, respectively. .

In FIG. 2, reference numerals 100 and 102 denote comparators. The output signal V is input to the non-inverting input terminals of the comparators 100 and 102, and the negative inputs are respectively set by the variable resistors 104 and 106 at the inverting input terminals. And the binarization levels a and b for positive are input (see FIG. 4). Therefore, the outputs of these comparators 100 and 102 are shown in FIG.
As shown in, the level becomes H level in the range of V> a and V> b.
It is of course possible to set the binarization levels a and b here as fixed fixed values, but it is desirable to set them based on the density histogram.

FIG. 5 is a principle diagram for obtaining these binarization levels a and b using a histogram, in which the output waveform of the image output signal V is a constant value.
Of the two points l and m intersecting with h ₀ , the constant value α is added to the larger one l to make the negative constant value a = (l + α), and the smaller one m
The constant value β for positive is subtracted from the constant value b = (m-β)
Can be set.

In FIG. 2, 108 and 110 are monostable multivibrators, which output polarity inversion pulses e and f having a constant time width in synchronization with the rising edges of the waveforms of the outputs c and d of the comparators 100 and 102.
These polarity inversion pulses e and f are integrated by the counters 112 and 114 for each scanning of the line sensor 56. These count values Nn, Np respectively indicate the number of polarity reversals, and the constant values Mn, Mp set by the setters 116, 118 and the comparators 120, 122, respectively.
Are compared in. When the count values Nn, Np reach the constant values Mn, Mp, the comparators 120, 122 determine that there is an image and H
It outputs level signals g and h. Signals g and h are OR circuit 124
When any one of the signals g or h becomes H level, the H level signal g or h is read into the CPU 72.

Next, the operation of this embodiment will be described. The control means 48 first reads the position of the zone set by the zone setting means 40,
The servo motor 58 is controlled so that the projection light of the area corresponding to this zone enters the line sensor 56. The user selects the reader mode with the reflecting mirror 24 in the position shown by the solid line in FIG. 1, and projects the target original image on the screen 28 (step 20).
0). A part of this projection light is guided to the line sensor 56 by the semi-transparent mirror 52.

The control means 48 then reads and stores the output signal V of the line sensor 56 (step 202), while measuring the exposure amount based on this output signal V (step 204). That is, the output signal V of the signal processing circuit 66 is read into the CPU 72 through the interface 70, and the CPU 72 controls the exposure amount.
If the exposure amount is not proper (step 206), the light amount is changed (step 208), and the exposure amount is measured again. The adjustment of the exposure amount is performed by, for example, selecting the voltage of the pixel corresponding to the background area from the output signal voltage of each pixel of the line sensor 56 and adjusting the light amount of the light source 12 so that the voltage becomes a predetermined voltage. Be seen.

Next, the control means 48 determines whether or not the projection light input to the line sensor 56 includes an image suitable for autofocus. When the binarization levels a and b are obtained as shown in FIG. 5, the density histogram of the output signal V is obtained by the first scanning, and the above calculation a = l + α and b = m−β.
Thus, the binarization levels a and b for negative and positive are obtained.
Then, while moving the line sensor 56, it is binarized by each of the binarization levels a and b (step 210), and the number of polarity inversions Nn and Np is accumulated by the counters 112 and 114 (step 2).
12). If the count values Nn, Np are larger than the constant values Mn, Mp, the comparators 120, 122 determine that an image is present and the H-level signal g
Alternatively, h is output to the OR circuit 124 (step 214). Therefore, the count value Nn using the binarization level a is set for the negative film and the binarization level b is set for the positive film.
If the count value Np using is valid and there is an appropriate image regardless of the negative / positive of the original image,
A level signal g or h is obtained. Since the positive film has a characteristic that an accumulated error due to dust is large, it is preferable to set the positive constant value Mp to a value obtained by adding an error due to dust in advance to the negative constant value Mn.

If neither of the signals g and h goes to the H level, the CPU 72 issues an alarm such as a buzzer or a lamp as no image and requests a change of the focus zone (step 216). The user operates the knob 44 while looking at the screen 28 so that the mark 42 is overlapped with another position where the projected image is present.
Move 42. The CPU 72 moves the line sensor 56 to this new area and repeats the operation of step 102 and subsequent steps. If either of the signals g and h is at the H level, it is determined that there is an appropriate image (step 218), and the control means 48 scans the line sensor 56 once again and performs autofocus control based on the output at that time (step 220). ).

Various autofocus control methods can be applied. For example, the position of the projection lens 20 having the maximum contrast is obtained from the output signal V and the position is focused (steps 222 and 224).

If the printer mode is set in this focused state (step 22
6), the reflecting mirror 24 is rotated to the phantom line position in FIG.
The image is transferred to and a hard copy is obtained.

In this embodiment, the focus zone is set by the user on the screen 28.
The line sensor 56 was configured to move along with the manual change by the knob 44 while looking at the mark 4.
2, manual zone setting means such as the knob 44 may be omitted, and the motor 58 may be driven by the instruction of the CPU 72 to automatically change the focus zone when there is no image.

The image sensor is not limited to the CCD line sensor, but may be a MOS type line sensor or an area sensor.

(Effect of the Invention) As described above, the present invention binarizes the output signal of the image sensor according to each binarization level for negative and positive,
When one of the integrated values of the respective polarity inversion times is equal to or more than a certain value set for negative and positive, it is determined that an appropriate image exists. Since the autofocus operation is performed, it is possible to automatically determine the presence or absence of an appropriate image regardless of whether the original image is negative or positive, and it is possible to perform the appropriate autofocus operation.

[Brief description of drawings]

FIG. 1 is an overall schematic view of a reader printer which is an embodiment of the present invention, FIG. 2 is a block diagram of its autofocus control device, FIG. 3 is a flow chart of operation, and FIG. 4 is an output signal of an image sensor and FIG. 5 is a diagram showing the output waveform of each part, and FIG. 5 is an explanatory diagram of the principle of obtaining the binarization level. 10 …… Original image, 20 …… Projection lens, 56 …… One-dimensional solid-state image sensor, 112,114 …… Counter, a, b …… Binarization level, Nn, Np …… Count value (number of polarity reversals), Mn, Mp: a constant value.

Claims (2)

[Claims] 1. An image detection method for an autofocus device for controlling a projection lens to a focus position by using an output signal of an image sensor obtained by scanning image projection light with an image sensor, wherein the output signal of the image sensor is used. Is binarized by each binarization level for negative and positive to obtain the number of polarity inversions, and the operation of comparing each number of polarity inversions with each constant value for negative and positive is performed in parallel, An image detection method, wherein an autofocus operation is performed by detecting an image area in which at least one of the polarity inversion times is equal to or more than the predetermined value. 2. The image detecting method according to claim 1, wherein the constant value is set to a value larger than the constant value for the negative and the constant value for the positive.