JPH02276363A - Image reader - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image reading device that scans a transparent original such as a photographic film to read an image, and particularly relates to an automatic focus adjustment technique for this image reading device.

[Prior Art] Conventionally, this type of apparatus for reading transparent originals such as 35Il1m photographic film did not have an autofocus (AF) mechanism for automatically adjusting the focus.

However, reversal film (positive film) is generally stored one sheet at a time in a mount, but since the thickness of the mount is not constant, if you try to handle the film while it is mounted, it will not work in the optical axis direction of the film surface. Since the position of the lens varies within a range of several millimeters, manual focus adjustment is required each time an attempt is made to read an image without blur.

In addition, since both mounted and unmounted films tend to curve under normal conditions, it is difficult to maintain a constant position of the film surface.

For this reason, in the past, the film was generally pasted on the glass surface or sandwiched between two pieces of glass to ensure that the film surfaces were always aligned and to prevent the film from curving. It was.

[Problem to be solved by the invention] However, as an imaging means, CB (i-charge coupling device)
Conventional flatbed type film scanners using solid-state imaging devices such as the above have the following problems.

In other words, as mentioned above, when the film is sandwiched between glasses to position the film surface and prevent the film from curving, there is no need to take out the mounted film from the mount and attach it to the glass. There are disadvantages such as requiring laborious work, creating Newton's rings when the film is sandwiched between glass, and making it easier for dust to adhere.

Furthermore, since the thickness of the above-mentioned mount is not constant, if you try to handle the film while it is mounted, the position of the film surface in the optical axis direction will vary within a range of several millimeters, so devices without an autofocus mechanism will produce blurred images. was supposed to be read.

In addition, it is cumbersome and time-consuming for humans to manually adjust the focus for each mount, and it is difficult to achieve accurate focusing.

On the other hand, due to various aberrations such as field curvature, astigmatism, and chromatic aberration of the imaging lens, the focal position for each point on the top surface of the film varies, for example, R (red), G (green), B (
The focal position of the color-separated image of the three colors (blue) was shifted, and the optimal focal position could not be determined.

Therefore, it came to mind that the autofocus (automatic focus adjustment) technology used in cameras or microscopes could be used in the image reading device for this transparent manuscript, but various types of autofocus technology have been proposed. .

Among these, an autofocus method that is particularly effective for image reading devices for transparent originals is one in which a CCD sensor (solid-state image sensor) for image reading is also used as a sensor for detecting the focal point of autofocus. There is an autofocus method that detects the in-focus position based on the contrast amount of a human-powered image signal from the sensor. This method is used, for example, in N)I, Technical Research Vol. 17, 1
No., 11sP3364815, and Special Publication No. 42-14
It has been disclosed in Publication No. 096 and the like.

In addition, as a control method for controlling the position of the lens system when detecting the focal point position, for example, as disclosed in Japanese Patent Publication No. 58-58868, the contrast evaluation amount is always maximized. A device that controls the lens system using a servo circuit. For example, as disclosed in Japanese Patent Publication No. 60-39203, the lens system is moved once over the entire area, the contrast evaluation amount is calculated, and the contrast evaluation that is the maximum value is performed. The contrast evaluation amount is memorized, and the contrast evaluation amount is calculated again when the lens system moves backward, and when the contrast evaluation amount becomes equal to the maximum value of the contrast evaluation amount calculated and memorized during the previous forward movement, the lens system There are things that control the system to stop.

However, in all of these control methods, the movement of the lens system is controlled while constantly obtaining the contrast evaluation amount, so the calculation processing time is long and high-speed automatic focus adjustment (autofocus) is not possible. For devices such as film reading devices where the position of the copy object is limited to some extent, this results in unnecessary detection control.
Work efficiency was getting worse.

Furthermore, when a film is sandwiched between two pieces of glass, such as in a glass mount, the maximum value of the contrast evaluation amount may be at the in-focus position due to dirt or other dirt adhering to the surface of the glass. In many cases, the focus is on the glass surface.

Therefore, in order to prevent this problem, it is necessary to take the trouble of removing the film from the glass mount.
Work efficiency was poor.

It is an object of the present invention to solve the above-mentioned problems, and to provide an image sensor that can quickly and easily automatically focus an imaging lens on an original image reliably even when the film is housed in a glass mount. The purpose of the present invention is to provide a reading device.

[Means for Solving the Problems] In order to achieve the above object, a first aspect of the present invention includes an imaging lens that projects and forms an image of a document, and a photoelectric converter that converts the image formed by the imaging lens into an electrical signal. an image sensor to convert, an analog-to-digital conversion means to convert an output signal of the image sensor into a digital signal, a moving means capable of moving the imaging lens from the starting end to the ending end along the optical axis, and the moving means causes the imaging lens to start. Calculating means for calculating a contrast evaluation amount P according to a predetermined contrast evaluation calculation formula based on the output signal of the analog-to-digital conversion means during forward movement from one end to the other; and storing the contrast evaluation amount P calculated by the calculation means. and a storage means for detecting local maximum points of a set level or higher from among the contrast evaluation amount P stored in the storage means, and selecting one local maximum point from among the plurality of local maximum points according to the number of detected local maximum points. The present invention is provided with a detection means for detecting a focus position by changing the detection method of the selected focus position, and a control means for moving the imaging lens back through a moving means to the focus position detected by the detection means. It is characterized by

Furthermore, the second aspect of the present invention is characterized in that the detection means repeatedly detects the in-focus position by changing the setting level according to the number of local maximum points.

Further, in a third aspect of the present invention, in the case where there are three maximum points, the detection means detects the position of the central maximum point as the in-focus position when the maximum points are equally spaced from each other, and the maximum points are mutually spaced from each other. If the distances are not equal, the position of the local maximum point with the highest contrast and trust evaluation amount is detected as the in-focus position.

[Function] With the above configuration, the present invention allows the contrast evaluation amount P to be adjusted during the forward movement of moving the imaging lens from the initial end (starting end) to the final end.
is calculated by digital calculation and stored in the storage means. Then, when determining the in-focus position ΔXO from the data stored in the storage means, the maximum points of the data are determined, and the maximum points are calculated according to the number of the maximum points. The focus detection method has been changed to detect the in-focus point, so even for glass-mounted originals (samples), the image can be accurately displayed on the original screen without being affected by F9 due to dust on the glass surface. Can focus automatically.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the basic configuration of an embodiment of the present invention. In this figure, A is an imaging lens that projects and forms an image of a document.

B is an imaging element that photoelectrically converts the image formed by the imaging lens A into an electrical signal. C is an analog-to-digital conversion means for converting the output signal of the image sensor B into a digital signal. D is a moving means that can move the imaging lens A eight times along the optical axis from the starting end to the ending end. E is when the imaging lens A is moved from the starting end to the ending end by the moving means,
This calculation means calculates the contrast evaluation amount P based on the output signal of the analog-to-digital conversion means C using a predetermined contrast evaluation calculation formula.

F is a storage means for storing the contrast evaluation MP calculated by the calculation means E. G detects local maximum points that are higher than a set level from among the contrast evaluation amounts P stored in the storage means F, and selects one local maximum point from a plurality of local maximum points according to the number of detected local maximum points. This is a detection means that detects the focused point position by changing the method of detecting the focused point position. Reference numeral H denotes a control means for moving the imaging lens A back to the in-focus position after being detected by the detection means G via the moving means.

The detection means G changes the setting level according to the number of local maximum points and repeatedly detects the focal point position.

Further, in the case where there are three maximum points, the detection means G detects the position of the central maximum point as the in-focus position if the maximum points are equally spaced from each other, and detects the position of the central maximum point as the in-focus position when the maximum points are not equally spaced from each other. The position of the maximum point with a high evaluation amount is detected as the focal point position.

FIG. 2 shows a specific circuit configuration of an embodiment of the present invention.

In this figure, 3001 is a light source (lamp) for illuminating a transparent original, 3002 is a heat ray absorption filter that removes heat rays from the light rays from the light source 3001, and 3003 is a filter 30.
This is an illumination optical system that converts the illumination light that passes through 02 into a parallel light beam. 3004 is a sub-scanning drive table that moves the transparent original in the sub-scanning direction; 3005 is a rotating table that rotates the transparent original; 3006
3007 is a film holder that stores transparent originals, and 3
It is a transparent original such as 5+am photographic film. 300
8 is a movable mirror that switches the optical path of the light beam (original image) transmitted through the transparent original 3007, 3009 is a mirror that deflects the optical path of the original image, and 301O is an imaging lens that forms the original image that has passed through the mirror 3009.

3011 is a projection lens for projecting the original image reflected by the movable mirror 3008; 3012 is a mirror that deflects the optical path; 3013 is a mirror that deflects the same optical path; 3014
is a screen serving as a monitor on which the original image that has passed through the mirror 3013 is projected. 3015 is the screen 3014
3016 is the screen 3
014 is a touch panel that manually controls the trimming area.

3017 is a lamp holding member that supports the light source 3001. 3018.3019. ' 3020 is CC
D alignment mechanism; 3021 is a three-color separation prism that separates the transparent original image formed by the imaging lens 3010 into three colors of R, G, and B; 3022, 3023, and 3024 are each color separated by the prism 3021; This is a CCD line sensor that uses a CCD (charge coupled device) array that photoelectrically converts each document image, and this CCD line sensor has a corresponding CCD alignment mechanism 3018.3019.30
20 allows fine adjustment of the reading position.

3025 is CCD line sensor 3022.3023.3
An analog circuit that amplifies the analog output of 024 and performs A/D (analog-to-digital) conversion, 3026 is an adjustment signal generation source that generates standard No. 43 for adjustment to the analog circuit 3025, and 3027 is an analog circuit section. 302
3028 is a shading correction circuit that performs shading correction on the output signal of the dark correction circuit 3027; 3029 is the output of the shading correction circuit 3028; A pixel shift correction circuit 3030 corrects pixel shift in the main scanning direction with respect to the signal, and a pixel shift correction circuit 3030 outputs the R, G, and B signals that have passed through the pixel shift correction circuit 3029, for example, Y (yellow), M (magenta) depending on the output device. , C (cyan). Further, 3031 is a lookup table (LtlT) that performs LOG conversion and γ conversion of the signal.

3032 is a minimum value detection circuit that detects the minimum value of the output signal of the lookup table 3031, and 3033 is an under color removal circuit (υC1()) according to the detected value of the minimum value detection circuit 3032.
Look-up table (LIT) to obtain the control amount for
, 3034 is a masking circuit that performs masking processing on the output signal of the lookup table 3031;
035 is an OCR circuit (undercolor removal circuit) that performs undercolor removal processing on the output signal of the masking circuit 3034 based on the output value of the lookup table 3033. 3036
3037 is a density conversion circuit that converts the recording density of the output signal of the OCR circuit 3035 into a specified density, and 3037 is a scaling processing circuit that converts the output signal of the density conversion circuit 3036 to a specified scaling factor.

3038 is an interface circuit (1/F) that transmits signals between a printer or input/output terminal (not shown) and this device.
, 3θ39 is a controller that controls the entire device, and inside the controller 3039 there is a CPU (central processing unit) such as a microcomputer, and processing procedures as shown in FIGS. 3 and 9 are stored in program form. ROM (read-on memory), RAM (random access memory) used for data storage and work area, etc.

3040 is a peak detection circuit that detects the peak value of the output value manually input from the scaling processing circuit 3037 through the interface circuit 3038 and the controller 3039; 3041 is an operation unit that issues instructions to the controller 3039; 3042
is a display unit that displays the control status of the controller 3039 and the like.

3043 is a lens aperture control unit that controls the aperture of the imaging lens 301O, 3044 is a lens distance ring control unit that adjusts the focus of the imaging lens 301O, and 3045 is a mirror drive unit that drives the movable mirror 1008. 3046
3047 is a trimming frame control unit that controls the trimming frame display 3015 and a touch panel control unit that controls the touch panel 3016. 3048 is a rotary table rotation control unit that drives and controls the rotary table 3005, and 3049 is a sub-scanning ff.
i! ! a sub-scanning control unit that controls the scanning of the J1 unit 3004;
3050 is a light source (lamp) 3001 is a lamp light 1 control circuit that controls the amount of light; 3051 is a lamp holding member 301
7 is a lamp position driving source that adjusts the position of the light source 3001.

3052 is a timing generator that generates a timing signal (clock) based on the control of the controller 3039; 3053 is a bus that connects each of the above-mentioned control units and processing circuits with the controller 3039; 3054 is a data line for the output device; 3055 is an output Synchronization signal line for equipment,
and 3056 are communication lines.

Next, the operation of each part will be explained.

The light source 3001 is a light source such as a halogen lamp, and the light emitted from the light source 3001 is passed through a heat absorption filter 30.
02 and an illumination optical system 3003 to illuminate a transparent original such as a 35 mm photographic film placed on a film holder 3006. The image of the transparent original is captured by a movable mirror 3008
By switching the optical path, ■ passing through the projection lens 3011 and mirrors 3012 and 3013 onto the screen 3014, or ■ passing through the mirror 3009, the imaging lens 3010, and the three-color separation prism 3021 onto the CCD line sensor 30.
22 to 3024.

In the case of mode (■) mentioned above, the CD line sensors 3022 to 3024 are connected to the timing generator 305.
The output signals of each CCD line sensor are input to an analog circuit 3025. The CCO alignment mechanisms 3018 to 3020 are
This is for registering each of the CCD line sensors 3022 to 3024 with respect to the three-color separation prism 3021, and needs to be adjusted at least once. The analog circuit 3025 is composed of an amplifier and a ^/D converter, and converts the signal amplified by the amplifier into the ^/D converter in synchronization with the timing clock for A/D conversion output from the timing generator 3052. ^/D
Convert.

Next, RlG, B output from the analog circuit 3025
A dark processing circuit 3027 applies dark signal level correction to each digital signal, a shading correction circuit 3028 performs shading correction in the main scanning direction, and a pixel deviation correction circuit 3029 corrects pixel deviation in the main scanning direction. , for example, by shifting the write timing of a FIFO (first-in, first-out) buffer.

Next, in the color conversion circuit 3030, the color separation optical system 3021
R, G, etc., depending on the output device.

Convert B signal to Y, M, C color signals, Y.

1, convert to Q color signal. In the next lookup table 3031, the luminance linear signal is converted to LOG or arbitrary γ by referring to the table.

Reference numerals 3032 to 3037 constitute image processing circuits for outputting images in four colors of Y, M, C, and B (black), which are mainly used in printers such as color laser copying machines. Here, a minimum value detection circuit 3032, a masking circuit 3034, a lookup table 3033, and an OC
The combination of the R circuit 3035 performs printer masking and IIcR (undercolor removal).

Next, the density conversion circuit 3036 performs table conversion of each density signal, and the scaling processing circuit 3037 roughly performs scaling processing in the main scanning direction.
The M', C', and BK' signals are sent to the printer of the output device via the interface circuit 3038.

The interface circuit 3038 includes a data line 3054 and a synchronization signal line 3055 for the output device, for example, R52.
A control command communication line such as 32C is connected.
It is also possible to communicate with a general computer (for example, a personal computer) via a communication line 3056.

On the other hand, the lamp position driving source 3051 is the lamp 305 as a light source.
This is for adjusting the lamp position when converting 1, and the lamp 3001 is positioned manually or automatically in accordance with the manual key operation on the operation unit 3041. Lamp light amount control section 3050 and lens aperture control section 3043
adjusts the amount of received light of the image projected onto the CCO line sensors 3022 to 3024. In addition, the mirror drive unit 3045
controls the movable mirror 3008 to change the optical path for switching between guiding the image of the transparent original 3007 to the screen 3014 and to the CCO line sensors 3022 to 3024.

In the case of mode (2) in which an image of the transparent original 3007 is projected onto the screen 3014, a trimming frame display controller 3046 displays a trimming area in order to instruct trimming of the image displayed on the screen 3014. 3015, and a touch panel control unit 3047 controls a touch panel 3016 for inputting a trimming area.

Further, the lens distance ring control unit 3044 controls the imaging lens 3
Controlling the distance ring of 01O, the CCD line sensor 30
The images projected on 22 to 3024 and the screen 3014 are focused. The adjustment signal generation source 3026 generates a signal manually input as a standard signal when adjusting the analog circuit 3025.

Next, the overall control operation of this apparatus will be explained with reference to the flowchart in FIG.

Note that the control procedure in this flowchart is based on the controller 3.
039 is stored in the internal ROM.

Operation: When the power switch (not shown) is turned on, the controller 3039 initializes each part (step S1) and waits for a command input from an external device or from the operation unit 3041 via the interface circuit 3038. Become. In this state, when the film holder 3006 with the transparent original 3007 mounted thereon is set on the rotary table 3005, the light source 3001 illuminates the heat ray absorption filter 3006.
002, an illumination optical system 30 including a condenser lens, etc.
The image of the transparent original illuminated through the movable mirror 3
008 and projection lens 3011 and mirror 3012.3
013 and is projected onto the screen 3014.

Transparent originals 3007 have images in vertical and horizontal orientations, but when the image is rotated and projected, the image is transferred from an external device via the interface circuit 3038 or from the operation unit 3041 to the controller 3039. When the rotation of the controller 303 is instructed (step S2), the controller 303
9 sends a rotation control command to the rotary table rotation control unit 3048 via the bus 3053 to rotate the rotary table 3005 (step 53). At this time, since the film holder 3006 is fixed to the rotating table 3005, it rotates together with the rotating table 3005. In this way, the transmission thickness 1
When % 3007 is rotated, the image projected onto screen 3014 is also rotated.

Next, if you want to trim the image, use the operation section 3041.
or from an external device via the interface circuit 3038 (step S4), the controller 3039 sends a manual command of trimming information to the touch panel control unit 3047, and the touch panel control unit 3034 displays the trimming information on the touch panel. The trimming information entered manually from 3016 is imported into the controller 3039 via the bus 3053, and the controller 3039 sends trimming frame control information created based on the imported trimming information to the trimming frame display control unit 3046 via the bus 3053. Then, the trimming area is displayed (step S5).

Next, from the operation unit 3041 or the interface circuit 3
When the external device instructs the controller 3039 to start image reading via 038, image reading starts.
This is carried out according to the following procedure (step S6).

Optical path switching: First, the controller 3039 outputs a drive control signal to the mirror drive unit 3045 to move the movable mirror 3008, and an image with a transmission thickness f of +43007 is transmitted by the mirror 3009 and the imaging lens 3010 through the three-color prism: 1021. Switch the optical path so that each CCOCC line sensor 3022 to 3024 is guided (
Step 57).

Dark correction signal set: Next, dark correction circuit 3027
In order to set the dark correction information to
039, the lamp light amount control circuit 3050 is controlled to turn off the lamp, or the sub-scanning control unit 304
9 to move the sub-scanning drive stand 3004 to a light-shielding position where each CCD line sensor 3022 to 3024 is shielded from light (before step S8). Next, the dark correction circuit 3027 is controlled by the controller 3039, and the dark correction circuit 3027 is controlled based on the signal that is converted into a digital signal and outputted via the analog circuit 3025.
A dark correction signal is set up (after step S8).

8E (automatic exposure adjustment): Next, controller 3039
controls the lamp light amount control circuit 3050 to
001 is turned on, and the dark correction circuit 3027, shading correction circuit 3028, pixel blur correction circuit 3029, color conversion circuit 3030, lookup table 3031, masking circuit 3034, tlcR circuit 3035, density conversion circuit 3036, and scaling processing circuit 3037 are activated. All through (
In step S9), the controller 3039 is controlled via the interface circuit 3038 while performing sub-scanning at high speed.
Peak detection times &% for the raw data that is manually input:
1040 to detect peaks (step 510).

Then, the lamp light amount control circuit 3050 is controlled to change the brightness of the light source 3001, or the lens aperture control unit 3o43 is controlled so that the detected peak value approaches a certain level (step 511). By changing the aperture of the imaging lens 301O, the amount of light to the CCD line sensors 3022 to 3024 is adjusted (step 512).

AF (autofocus) - Next, dark correction circuit 30
The signal subjected to dark correction by 27 is input to the controller 3039 via the interface circuit 3038 with the subsequent processing circuit set to through mode, and the lens distance ring control unit 304 uses the information of the input signal.
4 to adjust the bin of the imaging lens: +ot6 (step Sl: 1).

Shading correction data set: Subsequently, each CCD line sensor 3022-3024 is 100
Step 514) of moving the sub-scanning drive base 3004 to the exposure position where % exposure is to be performed, the lamp light amount control circuit 3050 adjusts the lamp light amount to an appropriate brightness, and the dark correction circuit 30
Shading correction data is manually set in the shading correction circuit 3028 using the dark-corrected signal in Step 515.

Selection: Next, a pixel shift correction amount is set in the pixel shift correction circuit 3029 (step 516). In addition, the color conversion circuit 3
Select the type of color conversion for 030, select the type of lookup table for lookup tables 3031 and 3033, select the type of masking for masking circuit 3034, and select the presence or absence of ucn for UCR circuit 3035. Then, the type of density conversion is selected for the density conversion circuit 3036, and the type of scaling and sharpness is selected for the scaling processing circuit 3037 (step 517). Furthermore, the lamp light intensity is controlled to be optimal via the lamp light intensity control circuit 3050, and the sub-scanning speed and trimming information are sent to the sub-scanning control unit 3049 to move the transparent original 3007 to the sub-scanning start position and put it on standby. (Step 518).

Data output A: In an operation based on a read start command from the operation unit 3041 (step 519), a start command is issued to an output device (not shown) via the interface circuit 3038 (step 520), based on a synchronization signal from the output device. Sub-scanning is started (step 522), and the image is captured while being synchronized with the output device, and the processed image data is output via the interface circuit 3038 (step 523).

Data output B: In the reading operation based on the reading start command via the interface circuit 3038 (step 519
), reports the completion of preparation to the output device (not shown) via the interface circuit 3038 (step 521), starts sub-scanning based on the synchronization signal from the output device (step 522), captures images while being synchronized with the output device Then, the processed image data is output via the interface circuit 3038 (step 523).

FIG. 4 shows another circuit configuration of the embodiment of the present invention.

In this figure, 3059 is the pixel shift correction circuit 3 of FIG.
029 is a corresponding buffer memory, 3060 is the entire image sensor, 3061 is a CCD line sensor with an R color separation filter, and 3062 is a CCD line sensor with a G color separation filter.
CD line sensor 3o63 is a CCD line sensor with a B color separation filter. Also, 3064 is CC
CCO positioning mechanism for positioning D-y insensors 30fi1 to 3063, 3065 to 30678;
tccD This is a drive signal output from the timing generator 3052 to drive each of the line sensors 3061 to 3o63. The rest of the structure is the same as that of the previous embodiment shown in FIG.

The image sensor 3060 is a 3-line line sensor 3061~
3063, each line sensor 3061 to 3o
63 are independently driven by drive signals 3065 to 3067 output from the timing generator 3052. Further, each of the line sensors 3061 to 3o63 is capable of capturing R, G, and B color separated images using respective on-chip color filters.

The buffer memory 3059 stores each line sensor 3061 to 3.
This is a delay memory for correcting positional deviation in the sub-scanning direction in 063, and is configured using several FIFO memories, for example. The amount of delay for each color is set in advance by the controller 3039 according to the sub-scanning speed.

FIG. 5 shows the configuration of a control system for performing automatic focus adjustment in the embodiment of FIG. 4. In this figure, 3069 is a distance ring attached to the outer periphery of the imaging lens 301O, 3070 is a deceleration mechanism that meshes with the distance ring 3069, and 3071 is a motor that rotates the distance ring 3069 via the deceleration mechanism 3070. 3073 is an image processing section, which includes the dark correction circuit 3027 to the conversion processing circuit 3037 shown in FIG. In addition, Xp is the position of point P'' on the film 3007 in the optical axis direction, and Xq is the imaging position (optical axis direction) of the image (Qo) of point P''.
It is.

Furthermore, Q'' is the point P when the focal position of the imaging lens 301O is changed by driving the motor 3o71 via the distance ring control unit 3044 by the controller 3039 and moving the distance ring 3069 via the deceleration device 3070. This shows the imaging position in °.

Note that, except for the image sensor 3060, the configuration of automatic focus adjustment in the embodiment shown in FIG. 2 is also the same as that in FIG. 5.

FIG. 6 shows a specific example of the image reference area for automatic focus adjustment in the embodiment of the present invention. In this figure, 310
Q is an image area of the transparent original 3007, and 3101 is an image reference area for AF (automatic focus adjustment) that is referred to when performing automatic focus adjustment. 3100° is an image area when the orientation of the transparent original 3007 is rotated by 90°.

As shown in FIG. 7, when an image area 3100 of a subject document is trimmed and scanned by a trimming area 3120 surrounded by two points P1 and P2, the effective image is within the trimming area. It is most desirable to perform automatic focus m control (AF) within the trimming region 3120. By doing this, even if the transparent original 3007 such as a photographic film is tilted or warped with respect to the optical axis, it is possible to focus on the necessary image area with high accuracy.

Note that the 3-line sensor 3 as shown in FIGS. 4 and 5
061 to 3063 to find the focal position of each color, use both AF image reference areas 3101 (or 3
The CCD alignment mechanism 3064 moves the line sensors 3061 to 3063 in the sub-scanning direction so that the line sensors 101') coincide with the film surface of the image area 3100 of the document.

Next, an automatic focus detection mechanism according to an embodiment of the present invention using the contrast evaluation amount disclosed in US Pat. No. 3,364,815 will be described.

The contrast evaluation amount P described above is given by the following equation (1).

(However, X is the output level of the j-th pixel in the main scanning direction,
a and b are the numbers of the second pixel from the beginning and the last pixel in the AF image reference area 3101 in the main scanning direction.

FIG. 8 shows the amount of contrast evaluation (hereinafter referred to as the degree of focus) when the distance ring 3069 of the imaging lens 3101 is moved by the lens distance ring control unit 3044, thereby changing the lens aperture amount ΔX of the lens 3010 and changing the focal position. This figure shows an example of a change in the value of P (referred to as P). Here, the degree of focus P is calculated using the above equation (1). In this way, the degree of focus P obtained is maximum P. The lens extension position ΔXo is the in-focus position.

In the embodiment of the present invention, when determining the in-focus point P, the degree of focus P is determined by the microcomputer of the controller 3039 according to the control procedure shown in the flowchart of FIG.
The maximum value P of the degree of focus P. Shouting lens extension amount ΔX
The in-focus position is detected by determining o.

The degree of focus P used in the embodiments of the present invention is given by the following equation (2).

P=view -! -(Otsu-Ding'I 2(2)"kai aK (However, the island is averaged data, and K is a normalization constant.) In addition, the square value in the above formula (2) is an integer such as the cube. It may be a power.

Next, the operation of the control system shown in FIG. 5 will be explained with reference to the flowchart shown in FIG.

Note that the control procedure in this flowchart is based on the controller 3.
039 is stored in the internal ROM.

In step S31, lens control (2) is first performed.

This control is performed from the initial end (starting end) to the lens distance ring 3069.
is controlled by a constant amount Δ1a via the lens distance ring control unit 3044. Next, the process moves to step S32.

In step S32, data reading and averaging processing are performed. In order to obtain a better focus P, read the digital signal X, which is obtained by converting the output signals from the CCD line sensors 3061 to 3063 into D/D, several times.
The averaged data stone is calculated and stored in internal memory.

The process of step S32 is repeated until the averaging process is completed, and after the process is completed, the process moves to the next step S34.

In step S34, K is a normalization constant. Next, the process moves to step S35.

In step S35, the value of P resulting from the calculation is stored in the internal memory, and the processes from steps 531 to 534 described above are repeated until the imaging lens 3010 reaches the end position.

When the imaging lens 301O reaches the terminal position, the process moves to the next step 33B.

In steps 536 to 552, the focused point ΔXO is detected from the value of P, which is the calculation result obtained in the processing up to step S35, in the following manner.

First, in step 536, a local maximum value of the focus degree P that is equal to or higher than a set level is detected.

Next, in step S37, the number of local maximum points is determined.

Next, from step 538 onward, in-focus point detection is performed in accordance with the number of maximum points. First, if the number of local maximum points is 0, the process proceeds from step 538 to step S39, where the set level is lowered by a certain level, and step 540
After that, the process returns to step 536.

In step 540, when the set level reaches the lower limit level or less, an error is determined in the next step 541, and the error is displayed on the display section 3042, and the process ends.

If the number of maximum points is one, the process proceeds from step S42 to step 543, where it is determined that the sample is not a glass mount, and this maximum point is determined to be the in-focus position ΔXo.

If the number of local maximum points is two, the process proceeds from step S44 to step 545, where the set level is lowered by a certain level, and the process returns to step 536 via step 546.

In step 546, when the set level reaches the lower limit level or less, the process proceeds to the next step S47, where it is determined that the sample is not a glass mount, and the one of the two local maximum values is generally determined to be the in-focus point ΔXO.

If the number of local maximum points is three, the process proceeds from step 548 to step S49, where it is determined that the sample is sandwiched between glass or the like, and the central maximum value position is set as the in-focus point ΔXo.
It is determined that

If the number of maximum points is four or more, the process moves from step 548 to step 550, the setting level is increased by a certain level, and the process returns to step 536 via step S51. When the set level reaches the upper limit level or higher in step 551, in the next step S52, the position having the largest local maximum value is determined to be the in-focus position Δx0.

Step S43, 547 described above. S49. If the in-focus point Δx0 is determined in any step S52, the process proceeds to the next step S53, and lens control process (2) is performed.

In this lens control ■, the focal point position (lens aperture amount)
The lens distance ring 3069 is set to Δx0 by the lens distance m ring control unit 3.
044. Thereafter, the process returns to the main routine (not shown).

For example, in the process based on the flowchart shown in FIG. 9, the degree of focus P of a curve as shown in FIG.
If the relationship is the lens aperture amount Δ×, the number of maximum points is determined to be two in step S37, and the setting level of the threshold value is changed in step S345.

As a result, as shown in Fig. 1θ (B), when the set level is lowered, the maximum point is
The number is determined to be three, and in this case, it is determined in step S49 that the sample is sandwiched between glass or the like.

At this time, the maximum points at both ends are the contrast evaluation amount when the glass surface is in focus due to the influence of dust, scratches, etc. on the glass surface, and the maximum point in the center is the contrast evaluation amount when the film is in focus. It is. Therefore, step 549
, the central maximum point is determined to be the in-focus point Δ×o.

Another Embodiment FIG. 11 shows a control procedure of another embodiment of the present invention. 1st
In the control procedure shown in FIG. 1, the steps having the same step numbers as those in FIG. 9 have the same contents as the control processing explained in FIG. 9, but the explanation thereof will be omitted. Below, only the contents that are different from the previous implementation will be explained.

Steps 531 to S47 are the same as the control procedure shown in FIG.

If the number of local maximum points is three in the determination in step S37, a determination is made in step 549-1, and if the distances between the local maximum points are substantially equal distances, the process proceeds to step 549-1, where the The central maximum position is determined to be the in-focus position ΔXo. On the other hand, if the distances of the local maximum points are not substantially equidistant, step 549
Proceeding to step -3, it is determined that the sample is not sandwiched between glass or the like, and the position where the maximum value is the largest among the three maximum points is determined to be the in-focus position ΔXO.

Further, if the number of maximum points is four or more as determined in step 537, the set level is increased by a certain level in step 550, and the process returns to step 536 via step 551. When the set level reaches the upper limit level or higher, the process proceeds from step 551 to step 552-1.
A set of three substantially equally spaced maximum points including the maximum point that takes the largest local maximum value is selected, and if this set exists, the center maximum of the three sets is selected. The position of the point is determined to be the in-focus position ΔXo. On the other hand, if the above set does not exist, step 552-4
The position of the local maximum point that takes the largest local maximum value is determined to be the in-focus position ΔXo.

Above-mentioned step S43,547.549-2,549-
If the in-focus point ΔXo is determined at either 3,552-3°552-4, the process advances to the next step S53 to execute the lens control process (2), and then returns to the main routine.

For example, in the process based on the flowchart shown in FIG. 11, the degree of focus P of a curve as shown in FIG.
If the lens extension amount ΔX is in the relationship, the number of local maximum points is determined to be five in step S37, and the setting level is changed in step S5G.

As a result, as shown in FIG. 12(B), when the set level is raised, the number of local maximum points is determined to be four in step 5, and if the set level has reached the upper limit level at this time, step 552 -1, a set of three substantially equally spaced maxima, one of which contains the maxima with the largest maxima, is selected.

At this time, since there are three equally spaced sets, it is determined that the sample is sandwiched between glasses, and in step 552-3, the position of the maximum point at the center of this set is determined by the focal point position Δ×
It is determined as o. The selected set is indicated by an O mark in FIG. 12(B).

[Effects of the Invention] As explained above, according to the present invention, during the forward movement of moving the imaging lens from the initial end (starting end) to the final end, the contrast evaluation amount P is calculated by digital calculation and stored in the storage means, After that, when determining the in-focus point position Δx(, from the data stored in the storage means, the maximum point of the data is determined, and the method of detecting the in-focus point is changed according to the number of the maximum points. Since the focus is detected, even for glass-mounted originals (samples), the automatic focus can be accurately set on the original screen without being affected by dust on the glass surface. Colander.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of an embodiment of the present invention, FIG. 2 is a block diagram showing a specific circuit configuration of an embodiment of the present invention, and FIG. 3 is an overall diagram of the embodiment of FIG. 2. Flowchart showing the control procedure, FIG. 4 is a block diagram showing the circuit configuration of another embodiment of the present invention, FIG. 5 is a block diagram showing the main part configuration of the embodiment of the invention shown in FIG. 4, FIG. FIG. 7 is a plan view showing a specific example of the image reference area for automatic focus adjustment in the embodiment of the present invention. FIG. 7 is a plan view showing an example of the relationship between the trimming region and the reference region in the embodiment of the present invention. FIG. A diagram showing the relationship between the focus degree P and the lens aperture amount ΔX in the embodiment, FIG. 9 is a flowchart showing the control procedure of focus detection control in the embodiment of the present invention, and FIGS. 1O (A) and (B) is a diagram showing a specific example of the control operation according to the control procedure of FIG. 9 in terms of the relationship between the focus degree P and the lens extension amount ΔX, and FIG. 11 is a diagram showing the control procedure of the focused point detection control in another embodiment of the present invention. Flowchart shown in Figure 12 (8),
(B) is a diagram showing a specific example of the control operation according to the control procedure of FIG. 11, showing the relationship between the focusing degree P and the lens extension amount ΔX. 3041...Operation unit, 3042...Display unit, 3044...Lens range 1 ring control unit, 3049...
Sub-scanning control unit, 3060... Entire image sensor, 3061, 3062.3083... CCD line sensor, 3069... Lens distance Il! lt ring, 3071・
...Motor, 3073... Image processing unit, 3101... Image reference area for AF. 1... Light source, 3005... Turntable (stage), 3006... Film holder 3007... Transparent original (film), 301O...
Imaging lens, 3025...Analog circuit, 3039...Controller, Fig. 5, Fig. 6, Fig. 37 (X), Fig. 7, Δx6 17゛nos.

Claims (1)

[Scope of Claims] 1) An imaging lens that projects and forms an image of a document, an imaging device that photoelectrically converts the image formed by the imaging lens into an electrical signal, and an output signal of the imaging device that converts the output signal into a digital signal. analog-to-digital converting means for converting; a moving means capable of moving the imaging lens along the optical axis from a starting end to a terminal end; calculation means for calculating a contrast evaluation amount P using a predetermined contrast evaluation calculation formula based on the output signal of the conversion means; storage means for storing the contrast evaluation amount P calculated by the calculation means; and storage means for storing the contrast evaluation amount P calculated by the calculation means. Detecting a focal point position by detecting a maximum point of a set level or higher from among the contrast evaluation amount P, and selecting one maximum point from a plurality of maximum points according to the number of detected maximum points. In a different method, the present invention is characterized in that it includes a detection means for detecting a focal point position, and a control means for moving the imaging lens back through the moving means to the focal point position detected by the detection means. Image reading device. 2) The image reading device according to claim 1, wherein the detection means repeatedly detects the in-focus position by changing the setting level according to the number of the maximum points. 3) In the case where there are three maximum points, the detection means detects the position of the central maximum point as the in-focus position if the maximum points are equally spaced from each other, and if the maximum points are not equally spaced from each other, the detection means detects the position of the central maximum point as the focused position. 3. The image reading apparatus according to claim 1, wherein: is detected as the position of the maximum point having the highest contrast evaluation amount and the in-focus position.