JPS63135910A - Auto focusing method - Google Patents

Abstract

PURPOSE:To always perform accurate discrimination for focusing, by finding the entire length of an output signal in one scan of an image sensor, and the area of a part sandwiched between the minimum level or the maximum level of the output signal and the output signal, and setting the position of a projecting lens where a quotient obtained by the division of the square of the entire length by the area becomes maximum as a focal position. CONSTITUTION:A control means 48 performs auto focus control based on the output of a line sensor 56. A CPU72, after initializing a memory to zero for an L representing the length of the output signal of the line sensor 56 and an S representing the area, reads in the voltage of the output signal in order. And the CPU finds the absolute value of the difference between the output signals of adjacent picture elements, and adds the absolute value on the L, and substitutes an added result for the L, then stores it. The CPU72 finds a complexity degree (e) stipulated in an equation (e)=L2/S by using the L and the S. The CPU72 repeats an operation by moving the projecting lens 20 by a prescribed quantity, and finds the position of the projecting lens 20 where the complexity degree (e) becomes maximum, and sets the position as the focal position. In such a way, it is possible to perform the discrimination for the focusing with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an autofocus method for determining focus using an image sensor such as a CCD line sensor.

(Technical Background of the Invention) Various autofocus devices using image sensors such as CCD line sensors have been proposed. For example, a method has been considered in which the contrast of an image is determined from the output signal of each pixel of an image sensor, and the position where this contrast is maximum is determined as the focal position. in this case,
Conventionally, the sharpness of the output signal has been determined by inputting the output signal to a band-pass filter and differentiating the output of the band-pass filter (see, for example, Japanese Patent Laid-Open No. 132313/1983). However, in this case, due to the inherent characteristics of the differentiating circuit, there is a problem that it is sensitive to noise and its operation tends to become unstable. Furthermore, the difference in output signal voltage between the reference level pixel and the effective pixel of the line sensor is excessively detected due to differentiation, resulting in a problem of poor reliability.

Therefore, focusing on the fact that the output signal of the image sensor becomes smoother as the degree of out-of-focus increases, the fine brightness and darkness of the image disappears, and the complexity of the output signal is used to determine focus. . Here, complexity is defined as the quotient of the total length of the output signal divided by the area of the output signal.

However, in this case, the output signal of the image sensor is.

If the image includes a solid black area, the output signal in this solid black area will not be zero, but will be at a partial level, so as the area of the solid black area increases, the complexity value will decrease. There was a problem that highly accurate focus determination could not be made.

(Purpose of the Invention) The present invention has been made in view of the above circumstances, and when determining focus based on the complexity of the output signal, even if there is a solid black area in the image, it will be affected by it. The purpose of the present invention is to provide an autofocus system that can always perform highly accurate focus determination without any trouble.

(Structure of the Invention) According to the present invention, this object is achieved in an O:focus method in which a projection lens is controlled to a focusing position using an output signal of an image sensor obtained by scanning image projection light with an image sensor. The total length of the output signal during one scan of the image sensor and the area of the portion sandwiched between the lowest level or highest level of this output signal and the output signal are determined, and the quotient obtained by dividing the square of the total length by the area is calculated. This is achieved by an autofocus method characterized by setting the maximum projection lens position as the in-focus position.

(Example) Fig. 1 is an overall schematic diagram of a league printer that is an embodiment of the present invention, Fig. 2 is a block diagram of its autofocus control device, Fig. 3 is a flowchart of operation, and Fig. 4 is an output It is a figure which shows a signal and the area part which is calculated|required.

In FIG. 1.2, reference numeral 10 is an original image of a microphotograph such as microfiche or microroll film. 12 is a light source, and the light from the light source 12 passes through a condenser lens 14, a heat shielding filter 16, and a reflecting mirror 18 to the original image lO.
guided to the underside of

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 and the reflecting mirrors 22, 24, 26.
8, an enlarged projected image of the original image 10 is formed. In the printer mode, the reflecting mirror 24 is rotated to the imaginary line position in FIG.
The projection light is guided to a PPC type slit exposure type printer 34 by reflecting mirrors 22, 30, 32. printer 34
The reflecting mirrors 22 and 30 move in synchronization with the rotation of the photosensitive drum 36, and a latent image is formed on the photosensitive drum 36. This latent image is made visible by toner charged to a predetermined polarity, and this toner image is transferred onto the transfer paper 38.

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

Reference numeral 50 denotes a focus control optical system, which includes a semi-transparent mirror 52 disposed on the optical axis of image projection light, a projection lens 54, a CCD line sensor 56 as an image sensor, and a servo motor 58.

A portion of the projection light that has passed through the projection lens 20 is guided by a semi-transparent mirror 52 to a line sensor 56 through a projection lens 54 . The line sensor 56 is movable by a motor 58 in a direction perpendicular to the optical axis. Furthermore, when the projection lens 20 is placed at a position where the projection light is focused on the screen 28 or the projection surface of the photosensitive drum 36,
The focal length of the line sensor 56 is determined so that the image is accurately formed on the light receiving surface of the line sensor 56.

The autofocus mechanism includes a servo motor 60 that moves the projection lens 20 forward and backward in the optical axis direction, and the focus is controlled by the control means 48 so that the projection light is correctly focused on the screen 28 or the projection surface of the photosensitive drum 36.

The control means 48 is constructed as shown in FIG. In other words, in synchronization with the clock pulse output by the clock 62, C
The OD driver 64 drives the line sensor 56. This line sensor 56 outputs a pulse signal whose voltage changes in accordance with the amount of light incident on each pixel for each scan. This pulse signal 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 this variation in the characteristics of each pixel and shapes the waveform to produce the output signal V shown in FIG. 5A.

The output signal V processed in this way is sent to the A/D converter 6.
8 is converted into a digital signal, and the input interface 7
0 to the CPU 72. In FIG. 2, 74 is a ROM that stores control programs for the CPU 72, and 76
is RAM, 78 is output interface, 80 and 8
2 is a D/A converter, 84.86 is a motor 58.
This is a driver that drives 60.

Next, the operation of this embodiment will be explained. The control means 48 first reads the position a of the zone set by the zone setting means 40, and controls the servo motor 58 so that the projected light of the area corresponding to this zone is incident on the line sensor 56.

The user selects the reader mode with the reflecting mirror 24 positioned at the solid line position in FIG. .

The control means 48 then measures the exposure amount based on the output of the line sensor 56 (step 102).

That is, the output signal V of the signal processing circuit 66 is read into the CPU 72 via the interface 70, and the exposure amount is controlled by the CPU 72. If the exposure amount is not appropriate (step 104) and the light amount is changed (step 106), the exposure amount is measured again. This adjustment of the exposure amount can be done, for example, by adjusting the background area of the output signal of each pixel of the line sensor 56. This is done by selecting the signal of the corresponding pixel and adjusting the light amount of the light source 12 so that the signal has a predetermined value.

Next, the control means 48 determines whether or not the projection light input to the line sensor 56 includes an image (step 108
), this judgment is made based on whether or not the number of black and white inversions of the image is greater than or equal to a predetermined value, and if it is greater than or equal to the predetermined value, the image is judged to be weak (step 110). The control means 48 issues an alarm such as a buzzer or lamp to request a change in the focus zone (step 112).The user operates the knob 44 while looking at the screen 28, and the mark 42 overlaps the position where the projected image is located. Move the mark 42 as shown.

Next, the control means 48 performs autofocus control based on the output of the line sensor 56.

The CPU 72 first initializes the memory of L indicating the length of the output signal of the line sensor 56 and S indicating the area to O (step 114), and then sequentially reads the output signal voltage V following the scanning. (Step 116). The CPU 72 stores the output signal (2) for one scan in the RAM 76, and stores the output signal (V) of the adjacent pixel. and V. The absolute value of the difference from -1 is determined (step 118). Then, this absolute value is added to the above value, and this addition result is newly replaced with L and stored (
Step 120).

On the other hand, the CPU 72 outputs the lowest level V of the output signal V during one scan.
To detect @in (step 122), the difference between the output signal vn of each pixel (Vn - Vain) is multiplied by a constant Δy corresponding to the pixel interval, and this multiplied value is calculated as the part sandwiched between the output signal and the lowest level. The microsurface v1 of In other words, S = Δ y × (vn − vain ) (
Step 124). The CPU 72 adds this microsurface v1 to the S, replaces this addition result with a new S, and stores it (step 126). The CPU 72 outputs the output signal ■ already stored in step 116. are sequentially read and the operations of steps 118 to 126 are repeated (step 128
). This result shows the total length of the output waveform, and S is the fourth
The area indicated by diagonal lines in the figure is shown.

The CPU 72 calculates the complexity e defined by the following equation using S, and stores it in the RAM 76 (step 130
).

e=L2/5 The CPU 72 moves the projection lens 20 by a predetermined amount ΔX and repeats the same operation as described above (step 132), finds the position of the projection lens 20 where the complexity e is maximum (step 134), and selects this position. is the in-focus position (step 136
).

Various algorithms are possible for control to obtain the maximum value of this complexity e. For example, by moving the projection lens 20 by a predetermined amount Δχ in the direction in which the complexity e increases,
Since the rate of increase in e is O, a "hill-climbing method" is used to detect the position of the projection lens 20 where the complexity e is maximum. Alternatively, the projection lens 20 may be moved once across the focused point, and the focused point may be determined from the half-width of the characteristic curve of change in complexity e at that time (half-width method), or the projection lens 20 may be moved once across the focused range. It is also possible to move it and find the position where the complexity e is maximum (full scan method).

If you switch to printer mode in this focused state (step 13)
8) The reflecting mirror 24 is rotated to the imaginary line position in FIG. 1, and the image is transferred to the transfer paper 38 to obtain a hard copy.

In this embodiment, - the lowest level V of the output signal V during scanning
The area of the portion sandwiched between Sin and the output signal is calculated. However, the present invention may use the area of the portion sandwiched between the output signal and the highest level v wax of the output signal (d) during -scanning, as shown by diagonal lines in FIG.

Note that the image sensor is not limited to a CCD line sensor, but may be an MO3 type line sensor, an area sensor, or the like.

(Effects of the Invention) As described above, the present invention can be obtained by dividing the square of the total length of an image sensor output signal during one scan by the area of the portion sandwiched between the lowest level or highest level of the output signal and the output waveform. This method calculates the degree of complexity of the image and focuses on the position of the projection lens where this degree of complexity is maximum, so even if there is a solid black area in the image, the degree of complexity can be calculated without being affected by it. , enabling highly accurate focus determination.

[Brief explanation of the drawing]

Fig. 1 is an overall schematic diagram of a league printer that is an embodiment of the present invention, Fig. 2 is a block diagram of its autofocus control device, Fig. 3 is a flowchart of its operation, and Fig. 4 is its output signal and required area. FIG. 5 is a diagram showing the output signal and the area to be determined in another embodiment. lO... Original picture, 20... Projection lens, 56... Line sensor. ■...Output signal, VIIin...lowest level, V intestine ax...highest level, L...total length, S...area, e...complexity. Patent Applicant Fuji Photo Film Co., Ltd. Agent Patent Attorney Yama 1) Yu Akira Figure 1 Figure 1 ^ Figure 4 Figure 5 Procedural Amendment Form Stamp January 20, 1986 Commissioner of the Patent Office Kuro 1) Yu Akira 1. Indication of the case 1986 Patent Application No. 280686 2. Name of the invention Autofocus method 3. Person making the amendment Relationship to the case Patent applicant address 210 Nakanuma, Minamiashigara City, Kanagawa Prefecture Name (520)
) Fuji Photo Film Co., Ltd. Representative: Sho Ohnishi 4, Agent address: 6-21-1 Nishi-Shinbashi, Minato-ku, Tokyo Number of inventions increased by the amendment: 07, Subject of the amendment: 8, Contents of the amendment: (1) ) In the second line of page 7 of the specification, "output signal of Fig. 5A" is corrected to "output signal of Fig. 4". (that's all:

Claims (1)

[Scope of Claims] An autofocus method in which a projection lens is controlled to a focus position using an output signal of an image sensor obtained by scanning image projection light with an image sensor, comprising: an output signal of the image sensor during one scan; Find the total length of the signal and the area of the part sandwiched between the lowest level or highest level of this output signal and the output signal, and focus on the projection lens position where the quotient of the square of the total length divided by the area is maximum. An autofocus method characterized by determining the position.