JPH0612375B2 - Image detection method for optical device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image detection method applied to an optical device such as a reader printer having an autofocus mechanism.

(Technical background of the invention) Conventionally, there have been microphoto readers and printers for forming projection light (image projection light) of an original microphotograph on a screen or a photoconductor, or reader printers in which both are combined. In the case of providing an autofocus (hereinafter referred to as AF) mechanism for automatically focusing in this type of optical device, first, an area in which AF is performed after selecting an appropriate exposure amount is selected, and projection light in the area is projected on a screen or The optical system is controlled so that an image is accurately formed on the projection surface of the photoconductor or the like. However, at this time, when there is no image in the selected area, for example, when the selected area corresponds to the background area of the original image of a single color, it is not possible to connect the image on the projection surface. Therefore, there is a problem that the AF mechanism does not operate properly.

Further, prior to this AF control, it is necessary to adjust the exposure amount so as to determine the optimum exposure amount. A light amount detection element such as cadmium sulfide (CdS) has been widely used for this exposure adjustment. However, since this conventional method obtains the average amount of light in a wide photometric region, there is a problem in that the amount of detected light varies depending on the area ratio between the background portion and the image portion, and accurate exposure adjustment cannot be performed.

(Object of the Invention) The present invention has been made in view of such circumstances, and an area including an image having a sufficiently large contrast that can always be adjusted to an appropriate exposure amount even if the average light amount of the photometric area changes. It is an object of the present invention to provide an image detection method in an optical device capable of properly operating the AF mechanism by selecting.

(Structure of the Invention) According to the present invention, an object of the present invention is to form projection light of an image recorded on a film on a projection surface and perform autofocus control on a partial region selected from the projection image. In an optical device with an autofocus mechanism, the pulse voltage of the image sensor obtained by scanning the projection light of the selected area with the image sensor is compared with a predetermined reference voltage to determine the number of pulses corresponding to the background portion of the image. After counting and determining the appropriate exposure amount by adjusting the light amount of the light source so that this count value falls within the set range, the number of times the continuous pulse voltage of the image sensor changes in height with respect to the reference voltage is counted. However, since this count value is greater than or equal to the set value, it is determined that there is an image suitable for autofocus control, while when the count value is less than or equal to the set value, the image is This is achieved by an image detecting method for an optical device, which is characterized by determining that there is no image, selecting another area, and selecting an area having an image suitable for autofocus control.

That is, the exposure amount is determined by detecting not the average light amount of the photometric area but the light amount of the background portion, and if the number of black and white reversals is less than or equal to the set value, it is determined that there is no suitable image and the same determination is made for another area. Repeatedly, an area including an image suitable for autofocus is selected.

(Embodiment) FIG. 1 is an overall schematic view of a microphotograph reader printer which is an embodiment of the present invention, FIG. 2 is a block diagram of an autofocus mechanism, FIG. 3 is a flow chart of operation, and FIG. It is a waveform diagram.

In FIG. 1, reference numeral 10 is an original image of a micro photograph such as a micro fish or a micro roll film. 1
2 is a light source, and the light from the light source 12 is the condenser lens 1
4, it is guided to the lower surface of the original image 10 through the heat insulating filter 16 and the reflecting mirror 18. In the reader mode, the transmitted light of the original image 10 is guided to the transmissive screen 28 as a projection surface by the projection lens 20 and the reflecting mirrors 22, 24 and 26,
An enlarged projection image of the original image 10 is formed on the screen 28. In the printer mode, the reflecting mirror 24 is rotated to the imaginary line position in FIG. 1, and the projection light is guided by the reflecting mirrors 22, 30, 32 to the PPC printer 34. Therefore, a latent image is formed on the photosensitive drum 36 of the printer 34.
This latent image is visualized with toner charged to a predetermined polarity, and this toner image is transferred to the transfer paper 38.

The autofocus mechanism includes a rotatable reflecting mirror 40, a projection lens 42, a CCD line sensor 44 as an image sensor, a servomotor 46, and the like, and the projection light passing through the projection lens 20 passes through the projection lens 42 by the reflecting mirror 40. It is guided to the line sensor 44. The line sensor 44 can be moved by a motor 46 in a direction orthogonal to the optical axis. In addition, the projection lens 42 projects the projection light onto the screen 2
8 or the focal length is determined so that when the projection lens 20 is placed at a position where it is focused on the projection surface of the photosensitive drum 36, an image is accurately formed on the light receiving surface of the line sensor 44.

During focus control, the servo motor 48 moves the projection lens 20 back and forth in the optical axis direction so that the projection light is properly imaged on the projection surface of the screen 28 or the photosensitive drum 36.

Reference numeral 50 denotes a control circuit, which sequentially performs exposure amount adjustment, image detection, and focus control based on the output of the line sensor 44.

The exposure amount adjustment is performed as follows. First, the CPU 52 outputs a signal to the output port 56 according to a program previously stored in the ROM 54 when the power switch is turned on, operates the driver 58 so that the reflecting mirror 40 is present in the projection optical path, and directs the projection light to the line sensor 44. Lead. Also CPU
Reference numeral 52 controls the power supply 60 via the output port 56 so as to turn on the light source 12 in the darkest state. Further, the CPU 52 outputs the data selector 6 via the output port 56.
The selector signal "0" is sent to 2 (step 100 in FIG. 3). The data selector 62 guides the output of the comparator 64 to the counter 68 when the selector signal is "0", and the output of the single-shot multivibrator (hereinafter referred to as single shot) 66 which can be re-triggered when the selector signal is "1". . Further, the CPU 52 initializes the count value N of the counter 68 to 0 (step 102).

Next, the CPU 52 activates the drive circuit of the line sensor 44. In synchronization with the drive pulse p, the line sensor 44 sequentially outputs a pulse voltage q corresponding to the amount of light incident on the pixel in accordance with the pixel array. That is, the projection light on the light receiving surface of the line sensor 44 is scanned. This pulse voltage q is
Even if the same amount of light is projected due to variations in the characteristics of each pixel, it varies for each pixel. The signal processing circuit 70 corrects variations in the characteristics of each pixel and shapes the waveform to obtain a rectangular wave a as shown in FIG. In this figure, G indicates the reference black level voltage, and the pulse voltage V _a on the positive side with respect to the reference black level voltage G indicates the exposure amount incident on each pixel. The pulse on the negative side is the feedthrough of the reset clock.

This rectangular wave a is input to the positive phase input terminal of the comparator 64.
Further, a setter (variable resistance) 7 is provided at the negative phase input terminal of the comparator 64.
The reference voltage V _c set by 2 is input. Therefore, the comparator 64 compares V _a with V _c (FIG. 3, step 104) and outputs the pulse b shown in FIG. 4 (B) when V _a > V _c . This pulse b is input to the counter 68 through the data selector 62, 1 is added to the count value N of the counter 68 (step 106), and otherwise the count value N is not changed.
Then, this operation is repeated for all pixels (steps 108 and 110). Therefore, this count value N is the number of pixels for which V _a > V _c in the light amount of the light source 12 at that time,
In other words, in the case of a positive original image, the background area (white) indicates the number of projected pixels.

Generally, in a negative manuscript in which texts and the like are made micro, the image portion is much smaller than the background area, and is usually about 6%. Therefore, the number of pulses that become the pulse voltage V _{a of} each pixel corresponding to the background region is very large.

The CPU 52 reads the count value N of the counter 68 via the input port 74 and compares it with the set value α previously input to the RAM 76 (step 112). Now, since the light source 12 is initially set to the darkest state, N <α. Therefore, the CPU 52 sends a signal to the power source 60 via the output port 56 to raise the voltage of the light source 12 by one step and increase the light amount thereof (step 114). And steps 102-114
If Yuke increasing the quantity of light of the light source 12 stepwise by repeating the operation, the number of pixels pulse voltage V _a exceeding the reference voltage V _c starts to rapidly increase, if its count value N is more than the set value α Judge that the exposure is appropriate. Therefore, when the exposure amount of a predetermined number of pixels corresponding to the background area exceeds a certain level, it is determined that the exposure is appropriate. The reference voltage V _c is set in advance so that the optimum exposure amount can be obtained at this time.

Next, the control circuit determines whether or not projection light including an image suitable for autofocus control is incident on the line sensor 44. That is, image detection is performed. First, the CPU 52 sends a selector signal "1" to the data selector 62 to make the output of the retriggerable single shot 66 ready for input to the counter 68 (step 116). Further, the content N of the counter 68 is cleared to 0 (step 118).
The single shot 66 is the pulse b output by the comparator 64.
Triggered by the rising edge of, a positive rectangular wave c is output for a fixed time T thereafter. This time T is set to be longer than the period interval t of the pulse output by the line sensor 44 and shorter than 2t. Therefore, when the pulse b is continuous, the single shot 66 is re-triggered by each pulse b, so that it becomes a continuous positive rectangular wave, and when the pulse b is interrupted, the positive rectangular wave disappears. As a result, Fig. 4 (C)
, The continuous pulse voltage V _a is changed to the reference voltage V _c.
The output of the single shot 66 changes each time the level changes. This output is input to the counter 68,
The counter 68 changes V _a to V in synchronization with the rising of this waveform.
_The number of times the height changes with respect to _c is counted (step 12
0,122). This operation is performed for all the pixels (steps 124 and 126), and when all the pixels are finished, the counter 68
The count value N of is compared with the set value β (step 128).
As a result, if N <β, the CPU 52 drives the motor 46 via the driver 78 to move the line sensor 44 so that the projection light of another region is incident on the line sensor 44 (step 130).

In this way, if the count value N of the counter 68 exceeds the set value β, it is determined that there is an image having a sufficient contrast in which the black-and-white change of the image is focus controllable.

The CPU performs the exposure amount adjustment (step 100
To 114) and image detection (steps 116 to 130), focus control is performed. Various algorithms for this focus control are possible, and for example, the in-focus position of the projection lens 20 can be obtained by the so-called "mountain climbing method". In this method, as shown in FIG. 3, first, the projection lens 20 is moved to the most recent or farthest focal position (here, x = 0) (step 132), and the pulse voltage V output from the signal processing circuit 70 is outputted. _{Let a be} the exposure amount signal I of each pixel, and obtain the maximum value I (M) and minimum value I (m) of this exposure amount signal I (step 1
34). For example, the exposure amount signal I of a pixel in the line sensor 44 is temporarily stored in the RAM 76, and the magnitude comparison with the exposure amount signal I of the next pixel is made. The larger one is I (M) and the smaller one is I (m ), And this operation is sequentially repeated for all pixels (step 130) to RAM 76.
I (M) and I (m) can be stored. The CPU 52 then calculates the visibility V (x) represented by the following equation, for example, as a reference of the contrast of the image and stores it in the RAM 76 (step 138).

V (x) = {I (M) -I (m)} / {I (M) + I (m)} The projection lens 20 is moved by Δx to obtain V (x + Δx) in the same manner, and V (x) The projection lens 20 is moved in increments of Δx until the rate of increase of 0 becomes negative or negative (step 140) (step 142). In this way, the focus position of the projection lens 20 is obtained.

At this in-focus position, the projection lens is moved once so that it crosses the in-focus point, and the in-focus point is obtained from the half-value width of the change characteristic curve of the visibility V (x) at that time (half-value width method). It is also possible to move the projection lens over the range and obtain the position where the visibility V (x) at that time is maximum as the focus (full scan method).

The CPU 52 then causes the reflecting mirror 40 to exit the projection optical path,
Operates as a normal reader or printer.

In the above-described embodiment, the line sensor 44 is moved by the motor 46 when there is not sufficient contrast during image detection, but the present invention can also move the original image 10.

As described above, the present invention compares the pulse voltage of the image sensor obtained by scanning the partial area of the image recorded on the film with the image sensor with the reference voltage, and corresponds to the background portion. The number of pulses to be counted is controlled, and the light source light quantity is controlled so that this count value falls within the setting range.On the other hand, the number of consecutive pulse voltage changes relative to the reference voltage is higher or lower than the set value. Determine.

Therefore, the exposure amount is adjusted by the pulse voltage output from the pixels in the background area, and the average light amount in a partial area is not detected. The amount can be adjusted.

Further, before performing the AF operation, the exposure amount is optimized and the presence or absence of an image is determined. The presence or absence of an image is determined by comparing the pulse voltage of each pixel of the image sensor with the reference voltage, and if the number of times the continuous pulse voltage changes between high and low with respect to the reference voltage is greater than or equal to the set value Judge that there is. If it is equal to or less than the set value, it is determined that there is no image suitable for autofocus, and the same determination is repeated for other areas, and an area including an image suitable for autofocus is selected. Therefore, AF control can always be performed in an area having sufficient contrast, and the operation accuracy of the AF mechanism is improved.

[Brief description of drawings]

FIG. 1 is an overall schematic diagram of a microphotograph reader printer which is an embodiment of the present invention, FIG. 2 is a block diagram of the image detecting apparatus, FIG. 3 is a flow chart of operation, and FIG. 4 is an output waveform diagram of each part. is there. 10 ...... original screen as a 28 ...... projection surface, 44 ...... line sensor as an image sensor, _{V a} ...... pulse voltage, _{V c} ...... reference voltage.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G03B 27/32 C 9017-2K

Claims (1)

[Claims] 1. An optical device with an autofocus mechanism for forming an image of projection light of an image recorded on a film on a projection surface and performing autofocus control on a partial area selected from the projection image. , The number of pulses corresponding to the background portion of the image is counted by comparing the pulse voltage of the image sensor, which is obtained by scanning the projected light of the selected area with the image sensor, with the predetermined reference voltage, and this count value is set within the set range. After determining the appropriate exposure amount by adjusting the light amount of the light source so as to enter, the number of times the continuous pulse voltage of the image sensor changes to high or low with respect to the reference voltage is counted, and this count value is equal to or more than a set value. Therefore, while it is determined that there is an image suitable for autofocus control, when the count value is equal to or less than the set value, it is determined that there is no image and another area is set. Image detection method for an optical device, which comprises selecting an area having an image suitable for the constant and autofocus control.