JPS6370812A - Automatic focusing method - Google Patents

Abstract

PURPOSE:To always exactly adjust the focus to the surface of an original picture by dividing an image sensor into plural areas, deriving an aggregation excluding a focused position by the reverse side of the original picture, among the focused positions of every area, and determining the final focused position of a projection lens, based on this aggregation. CONSTITUTION:A CPU 78 derives the maximum value of variation curves A1-A4 of a contrast signal C to a lens position (x) in each area I1-I4, based on a data of a RAM 82, and derives a position of a projection lens 20 at this time, as focused positions x1-x4 of each area I1-I4. The CPU 78 derives an aggregation of focused positions, in which the largest number of focused positions are contained, and also, adjacent to each other, among thee respective focused positions x1-x4. In this case, x1, x2 and x4 are contained in this aggregation. The CPU 78 derives an arithmetic average of this aggregation, and sets it as a focused position xF of the projection lens 20. When the projection lens 20 is moved to this position xF, focusing is obtained.

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 COD line sensor.

(Technical Background of the Invention) Various autofocus devices have been proposed using image sensors such as COD line sensors. A method is being considered in which the position where the maximum value is reached is set as the in-focus position.

However, if at least a part of the original painting is transparent or semi-transparent, and there is dust, scratches, or dirt on the back side of this transparent or semi-transparent part, you may want to focus on the dust, etc. on the back side. For example, in league printers, the film base of the original image is usually about 100 g, and when the back side of the original image is focused, the front side image becomes blurred.

(Objective of the Invention) The present invention was made in view of the above circumstances, and it is an object of the present invention to always correctly focus on the front side of an original painting without focusing on the back side, even if there is dust, scratches, or dirt on the back side of the original painting. The purpose of the present invention is to provide an autofocus method that enables automatic focusing.

(Structure of the Invention) According to the present invention, this object is to provide an autofocus method for controlling a projection lens to a focusing position using an output signal of an image sensor obtained by scanning image projection light with an image sensor. Contrast signals are obtained for each of the plurality of regions of the image sensor, and the projection lens position at which each of these contrast signals is maximized is determined as the in-focus position for each region. This is achieved by an autofocus method characterized in that the focus position of the projection lens is determined using a set of focus positions.

(Principle) If the line sensor is divided into a plurality of regions (for example, four) and the contrast signal C of each region is determined with respect to the change in the projection lens position χ, the result will be as shown in FIGS. 5A1 to A4. The contrast signal C based on the image on the surface of the original is AI, A2.
As shown in A4, the projection lens position (focus position) χ approaches χF when it reaches its maximum. On the other hand, the contrast signal C due to dust, scratches, or dirt on the back side of the original image becomes as shown in A3, and the maximum projection lens position (focus position) χ is a position χ far away from χF.Reposition χ
The difference between F and χf corresponds to the thickness of the original film base.

The present invention uses the former set, that is, a set of focus positions that include the focus positions of the largest number of regions and are close to each other.
Find the final focus position χF.

For example, the focus position χ1, χ2 of each area included in this set
, the arithmetic mean of χ4 χ■=(χ1+χ2+χ4)/3,
The median value χ2 is set as the in-focus position.

(Embodiment) Fig. 1 is an overall schematic diagram of a league printer which is an embodiment of the present invention, Fig. 2 is a block diagram of its autofocus control device, and Fig. 3 is a flowchart of its operation.

Further, FIG. 4 is a diagram showing the output waveform, and FIG. 5 is a diagram showing the change in contrast signal with respect to the lens position.

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 is transmitted to the original image 10 via a condenser lens 14, a heat shielding filter 16, and a reflecting mirror 18.
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 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 . Line sensor 56 is motor 58
This makes it possible to move in a direction perpendicular to the optical axis. Further, the projection lens 54 is arranged so that when the projection lens 20 is stirred to a position where the projection light is focused on the screen 28 or the projection surface of the photosensitive drum 36, an image is accurately formed on the light receiving surface of the line sensor 56. Its focal length is determined.

The autofocus mechanism includes a motor 60 that moves the projection lens 20 forward and backward in the optical axis direction, and the projection light is directed to the screen 28.
Alternatively, the focus is controlled by the control means 48 so that the image is correctly formed on 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 that 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. Signal processing circuit 6
6 corrects the variation in the characteristics of each pixel and performs waveform shaping to obtain the output signal V shown in FIG.

The output signal V subjected to signal processing in this way is passed through the bandpass filter 6
8 and becomes the output W shown in FIG.

70 is a distributor, and 72 (72a to 72d) is a peak hold circuit.The distributor 70 counts the clock pulses of the clock 62, and divides the total length of the line sensor 56 by 4.
The output signal W of each area ll-I4 is divided into
are sequentially sent to the respective peak hold circuits 72a to 72d. This peak hold circuit 72 detects the maximum value of the output signal W, and this maximum value becomes the contrast signal C (C, to C4) of each area.

These contrast signals C are converted into digital signals by the A/D converter 74 and input to the CPU 78 via the input interface 76.

In FIG. 2, 80 is a ROM that stores control programs for the CPU 78, 82 is a RAM, 84 is an output interface, 86 and 88 are D/A converters, and 90.92 are drivers that drive the motors 58 and 60, respectively. .

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 motor 58 so that the projection light of the area corresponding to this zone is incident on the line sensor 56. The user places the reflecting mirror 24 at the solid line position in FIG. 1 and selects the image mode to project the target original image onto the screen 28 (step 1oo). A portion of this projected light is guided to the line sensor 56 by the semi-transparent mirror 52.

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

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 output signal of the corresponding pixel and adjusting the amount of light from the light source 12 so that the output signal becomes 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 determination is made, for example, based on whether the number of times the image is inverted between black and white is equal to or greater than a predetermined value. If it is equal to or greater than a predetermined value, it is determined that an image exists (step 110). issues an alarm such as a buzzer or lamp to request a change in focus zone (step 112). The user operates the knob 44 without looking at the screen 28, and moves the mark 42 so that it overlaps the position where the projected image is located.

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

The CPU 78 first initializes the memory indicating the contrast signals 01 to C4, which are the outputs of the respective peak hold circuits 72, to O (step 114).

The distributor 70 is configured so that the scanning of the line sensor 56 is 1/1/2 of its total length.
4, the output W of the bandpass filter 68 is sequentially input to the peak hold circuits 72a to 72d. The peak hold circuits 72a to 72d calculate the maximum value of the output signal W of the bandpass filter 68 within the four regions 1 to I4 of the line sensor 56 by combining them with contrast signals C and -C. C.P.
U78 reads this contrast signal Cl-C4 through A/D converter 74 and input interface 76 in accordance with the progress of scanning, and stores it in RAM 82 together with the position χ of projection lens 20 at that time. That is, C+ (
χ)1, ... Ca (χ) (step 120), the CPU 78 adjusts the projection lens 20 by a predetermined amount Δχ
The operation of step 120 is repeated over the entire movement range of the projection lens 20 (steps 122 and 124).
), and as a result, the RAM 82 stores the contrast signals of each region 11 to I4 for the positions of all the projection lenses 20: C
+ (χ)1~Ca (χ), C+ (χ+Δχ)~Ca (χ+Δχ), C+
(χ+2Δχ) to Ca (χ+2Δχ) are stored.

Based on the data in the RAM 82, the CPU 78 determines change curves A1 to A4 of the contrast signal C with respect to the lens position χ in each region 11 to step 4, as shown in FIG. The CPU 78 determines the maximum value of each curve Al-As, that is, the maximum value of the contrast signal C of each region A to I, and determines the position of the projection lens 20 at this time as the focus position χ1 to χ4 of each region II to A4 ( Step 126).

The CPU 78 determines each of these focus positions χ! A set of focus positions that include the largest number of focus positions and that are close to each other from among ~χ4 are determined. In this embodiment, χ1, χ2, and χ4 are included in this set. The CPU 78 calculates the arithmetic mean χ of this set (step 128), and uses this position χ- as the projection lens 20.
The in-focus position is χF. Then, if the projection lens 20 is moved to this position χF (step 130), it will be in focus (
Step 132).

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

In this example, the arithmetic mean χ of the obtained set is calculated as the focus position χ
However, the present invention is not limited to this, and the median value χ of the set is
2 may be taken as the focus position χF.

Further, the contrast signal is not only obtained as the output of the peak hold circuit 72 as in the embodiment, but also the maximum and minimum of the output W of the bandpass filter 68 are determined by w (M) and w (m
) as (W(M)W (m) ) / (W (M
) +w (m) ) may be used as the contrast signal.

Furthermore, it goes without saying that the number of regions may be four or more.

(Effects of the Invention) As described above, the present invention focuses on the fact that the in-focus position due to dust on the back side of the original image is largely shifted from the in-focus position due to the image on the front side of the original image, and divides the image sensor into multiple areas. A set of in-focus positions for each region excluding the in-focus positions on the back surface of the original image is obtained, and the final in-focus position of the projection lens is determined based on this set. Therefore, it is possible to determine the focus position excluding areas where there is dust, scratches, or dirt on the back side of the original image, and it is possible to always correctly focus on the front side of the original image.

[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 operation, and FIG. 4 is a diagram showing output waveforms. FIG. 5 is a diagram showing the change in contrast signal with respect to the lens position. DESCRIPTION OF SYMBOLS 10... Original image, 20... Projection lens, 56... Line sensor, ■... Output signal, C... Contrast signal, I, ~technique 4... Area, χF... Focusing position. Patent Applicant Fuji Photo Film Co., Ltd. Agent Patent Attorney Yama 1) Wen Yu' Figure 4 Figure 5

Claims (3)

[Claims] (1) In an autofocus 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, a contrast signal is provided for each of a plurality of regions of the image sensor. The projection lens position where each of these contrast signals is maximum is determined as the focal position for each area, and the projection lens position is determined using a set of focal positions that include the focal position of the largest number of areas and are close to each other. An autofocus method characterized by determining a focus position. (2) The autofocus method according to claim 1, wherein the arithmetic mean of the set is set as the focus position. (3) The autofocus method according to claim 1, wherein the center value of the set is set as the focus position.