JPH04369161A - Picture reading method - Google Patents

Abstract

PURPOSE:To improve the picture read processing speed and to shorten the entire read scanning time together with preliminary scanning by moving a scanner exposing a light beam extended in the main scanning direction into the subscanning direction almost orthogonal to the main scanning direction. CONSTITUTION:When a picture of an original G placed on an original platen 22 is read photoelectriccally continuously with a scanner 31 moving in the subscanning direction for each line in the main scanning direction, preliminary scanning is implemented by moving the scanner into one direction (a) in the subscanning direction at a highest speed Vrmax. Moreover, a valid picture area of an original G or part of it is detected from a picture read data in the preliminary scanning as required. Then the main scanning is implemented by moving the scanner in the other direction (b) at a speed Vr. In this case, the scanner 31 is moved at the highest speed Vrmax other than the main scanning. Thus, the entire sequence time is reduced.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides a method for pre-scanning an image carried by a document placed on a document table of an image reading device using a scanning element, and then using the scanning element for preliminary scanning (pre-scanning).
The present invention relates to an image reading method in which the document image is read by moving in the opposite direction to perform a main scan.

0002

2. Description of the Related Art Conventionally, image reading apparatuses for scanning and reading images of originals placed on original plates have been used in various image forming apparatuses such as printing plate-making apparatuses and copying apparatuses.

Such an image reading device uses a light source that extends in one dimension, such as a fluorescent lamp or an LED array light source, or a light source that is deflected in one dimension, such as a laser light source that is deflected by an optical deflector. The light is irradiated onto the document on the stand, the reflected light is reflected in a predetermined direction using multiple mirrors, and transmitted through a projection lens, and the CCD is placed at a predetermined position.
The image is formed on a solid-state imaging device such as , and photoelectrically converted into an electrical signal by this solid-state imaging device, thereby obtaining original image data as, for example, a density signal.

[0004] In an image forming apparatus such as the above-mentioned printing plate-making apparatus, the document image data obtained in this way is subjected to various processing in an image processing apparatus, and then transmitted to an image recording apparatus, where it is processed by a laser or the like. The emitted light beam is modulated, and the light beam modulated according to the image data is reflected and deflected in the main scanning direction by an optical deflector such as a resonant scanner or a galvanometer mirror. A recording material conveyed at a constant speed in a sub-scanning direction substantially orthogonal to the image plane is scanned and exposed two-dimensionally to perform image recording and obtain a reproduced image.

By the way, in image forming apparatuses such as copying machines and printing plate-making apparatuses, there is an image reading device in which a scanner for scanning an original image performs preliminary scanning (prescanning) on the forward path and main scanning (main scanning) on the backward path. There are some that apply In such an image reading device, even if the size of the document or the effective image size of the document is small compared to the size of the document table or the scanning area of the scanner, after preliminary scanning of the document and its effective image, Performing a main scan of the document on the document table or a valid image in the document, and performing the main scan by moving the scanner over the entire document table including the document or the entire scanning area at the main scanning speed in order to read the image; It has returned to its home position. For this reason, not only the original and its effective image area, but also non-original or non-image areas on the document table are scanned at a slow main scanning speed, which lengthens the cycle time and reduces productivity. There was a problem with that.

[0006]

SUMMARY OF THE INVENTION The main object of the present invention is to solve the above-mentioned problems of the prior art, and to scan an image of a document placed on a document table in the main scanning direction using a scanner that moves in the sub-scanning direction. In an image reading device that photoelectrically reads each line continuously, the image reading process is performed when preliminary scanning is performed on the forward pass and scanning of the document or the effective image area in the document is performed at a main scanning speed according to the magnification during the return pass. An object of the present invention is to provide an image reading method capable of improving speed and shortening the total reading scanning time including preliminary scanning.

In addition to the above objects, another object of the present invention is to read original image data by preliminary scanning of the original image by the scanner on the outward path, and to process this image data to improve parts such as sensors. Automatically detects the end and/or leading edge of the document or its effective image on the document table in the sub-scanning direction without reloading it, and automatically determines the main scanning range of the document or its effective image area on the return path. An object of the present invention is to provide a low-cost image reading method with good operability.

[0008]

Means for Solving the Problems In order to achieve the above object, a first aspect of the present invention is to move a scanning element that irradiates a light beam extending in a main scanning direction to a sub scanning direction substantially orthogonal to the main scanning direction. In an image reading method in which a document placed on a document table is two-dimensionally scanned by moving in a direction, an image of the document is photoelectrically read, the scanning element is moved to one side in a sub-scanning direction. Provided is an image reading method, characterized in that, after performing preliminary scanning, when main scanning of an effective image area is performed by moving to the other side, the scanning element is moved at the highest speed except for the main scanning. It is something to do.

Further, in a second aspect of the present invention, the scanning element that irradiates the light beam extending in the main scanning direction is moved in the sub-scanning direction that is substantially orthogonal to the main scanning direction. In an image reading method in which a placed original is two-dimensionally scanned and an image of the original is read photoelectrically, when performing preliminary scanning by moving the scanner at the maximum speed to one side in the sub-scanning direction, At a pre-scanning predetermined position, after reading image density data for one line in the main scanning direction of the scanning element at that position, this image density data is averaged in the main scanning direction to obtain the density average value of the line. Repeating the process of obtaining data or its rate of change and storing this result in a memory according to the preliminary scanning by the scanner from the preliminary scanning start point at one end of the document table to the preliminary scanning end point at the other end; A density average value distribution map or a change rate distribution map thereof for the entire sub-scanning range in the sub-scanning direction is created in the memory, a preliminary scan is completed, the scanner is stopped, and the data is stored in the memory. The edge of the document or document effective image is determined by searching the density average value distribution map or its change rate distribution map, and determining the continuity of the density average value near a predetermined reference density value or the continuity of the change rate near 0. After detecting the end of the document or document valid image, if the end of the document or the effective image of the document is different from the end point of the preliminary scan, move the scanner at maximum speed to the side opposite to the end of the preliminary scan until the end and stop once. After that, the scanning element is moved at a main scanning speed corresponding to a predetermined magnification to perform main scanning over the sub-scanning range from the end to the leading edge of the document or document effective image, and then When the scanning start points are different, the scanning element is accelerated from the main scanning speed to the maximum speed, and after moving the scanning element to the preliminary scanning starting point at this maximum speed, the scanning element is stopped. The present invention provides a method.

[0010] Here, it is preferable that the preliminary scanning is performed on the outward path and the main scanning is performed on the backward path. In addition, in order to detect edges such as the end and/or leading edge of the document or its effective image, predetermined threshold values are set to α and β, and the density average value in the main scanning direction of a certain line is set to Da, or its rate of change is set to fa. , and when Do' is the density Do of the document platen cover or the reference density of areas other than effective image areas such as margins and frames in the document, |
This is done by determining that when a predetermined number of consecutive lines satisfy Da-Do | It is something. Further, it is preferable that the image data of one main scanning line is thinned data.

[0011]

Effect of the Invention The image reading method according to the first aspect of the present invention includes:
In an image reading device that photoelectrically reads an image of a document placed on a document table successively line by line in the main scanning direction by a scanner moving in the sub-scanning direction, preliminary scanning is performed on the forward pass, and on the return pass, Image reading processing speed is improved by scanning only the main scanning range, such as the original or the effective image area in the original, at the main scanning speed according to the magnification, and moving the scanning element at the maximum speed outside the main scanning range. This is a method that can shorten the total reading scanning time, including the preliminary scanning.

Further, in the image reading method of the second aspect of the present invention, in the image reading apparatus that performs scanning reading using the above-mentioned scanning element, image data read by preliminary scanning at the maximum speed of the scanning element on the forward pass is used. By processing this, the end and/or leading edge of the main scanning range, such as the document on the document table or its effective image area, is automatically detected, the scanner is temporarily stopped after the preliminary scan is completed, and the scanner is stopped on the return path. The direction is changed, the scanning element is moved at the maximum speed until it reaches this main scanning range, and after once stopping, the scanning element is moved at a predetermined main scanning speed for the main scanning range, and after the main scanning is completed. The scanning sequence for reading the original image is carried out in which the scanner is accelerated as it is and returned to the base point at the maximum speed.

[0013] Therefore, the user does not have to manually input the range of the document or the range of its effective image using a digitizer or the like, and there is no need to add a large number of new sensors, so the system is easy to operate and inexpensive. It is possible to improve the processing speed (time reduction) of the entire image reading scan.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The image reading method according to the present invention will be described in detail with reference to preferred embodiments shown in the accompanying drawings. FIG. 1 is a schematic diagram of a printing plate-making device of an image reading device that implements the image reading method of the present invention.

As shown in the figure, the printing plate-making apparatus 10 includes an image reading device 12, an image processing device 14, and an image recording device 16. While scanning in the sub-scanning direction indicated by arrows a and b in the figure, each line is photoelectrically read in the main-scanning direction (direction perpendicular to the plane of the paper in the figure) substantially orthogonal to the sub-scanning directions a and b and converted into electrical signals. After that, the image processing device 14 generates a binarized halftone image signal R, which is exposed and recorded as a halftone gradation image on the photosensitive material F in the image recording device 16, and is reproduced by processing the photosensitive material. be.

The image reading device 12 includes an original platen 22 made of a transparent glass plate or the like on which the original G is placed, an original platen cover 24 for fixing the original G to the original platen 22, and an original platen 22.
Two long fluorescent lamps 26 and 26 extending in one dimension (main scanning direction) constitute a light source for illuminating the original G placed on the original table 22 from the lower surface side of the original table 22. 26,2
Directly below the casing 29 that covers the fluorescent lamps 26 and 26 and directly below the slit 28 is a slit 28 that transmits the reflected light L emitted by the document G and reflected by the document G as a slit light having a predetermined slit width and length. A light source unit 31 includes a first mirror 30 arranged to reflect the optical path L of the reflected light in the sub-scanning direction a, and a second mirror 32 and a third mirror 34 facing in the direction b opposite to the optical path L. a mirror unit 35; an imaging lens 36 that forms an image of the slit-shaped reflected light carrying the original image;
A CCD 38 disposed at the imaging position of the reflected light and photoelectrically converts the document image of one line in the main scanning direction as one block to convert it into an analog electrical signal as image density data Sa.
and has.

Here, the light source unit 31 constitutes the scanner of the present invention, and when the light source unit 31 scans the lower surface of the document table 22 in the sub-scanning direction a or b at a predetermined sub-scanning speed, the scanning C of the optical path L of the reflected light from the medium original G
The mirror unit 35 moves in the same sub-scanning direction at half the sub-scanning speed so that the optical path lengths up to the CD 38 are equal. In the apparatus shown in FIG. 1, the light source unit 31, which is a scanner, has a home position (base point) at a predetermined position on the left end side of the document table 22. Here, the light source unit 31 performs preliminary scanning (prescanning) when moving in the sub-scanning direction shown by arrow a from the base point (scanning start point) to the scanning end point on the right end side of the document table 22, that is, on the forward path. Then, the scanner (light source unit 31) reverses itself at the scanning end point, and during the return trip until it returns to the base point, performs main scanning (main scanning range) of the original or an effective image area in the original (hereinafter referred to as the main scanning range). scan).

Further, as shown in FIG. 2, the image reading device 12 includes a drive device 90 that drives the light source unit 31 and mirror unit 35, which are scanning elements, during pre-scanning and main scanning. The drive device 90 includes a drive motor 92, a deceleration means 93, a wire drive pulley 94,
Wires 95a and 95b, movable pulleys 96a and 96b attached to both ends of the mirror unit 35,
It has a plurality of idlers 97a and 97b. In the drive device 90 , the rotation of a drive motor 92 such as a pulse motor (stepping motor) or a servo motor is decelerated by a deceleration means 93 such as a belt transmission means and transmitted to a wire drive pulley 94 . A wire 95a indicated by a chain double-dashed line in FIG. 2 has one end connected to a wire 96a on the right side of the figure via a spring, and from here, an idler 97a,
Movable pulley 96a, idler 97 (right side), wire drive pulley 94, idler 97 (left side), light source unit 31
The fixed end 98a of the wire 95a is wound around the movable pulley 96a, and the other end of the wire 95a is fixed to the wire fixed end 99a. Similarly, the wire 95b indicated by the dashed line in FIG.
From the connection side of 5a, idler 97b (right side), movable pulley 96b, idler 97b, idler 97 (right side), wire drive pulley 94, idler 97 (left side), idler 9
7b (left side), fixed end 98b of light source unit 31, and fixed to wire fixed end 99b via movable pulley 96b. Here, the wires 95a and 95b are both wound around the wire drive pulley 94 at least once, and as the wire drive pulley 94 rotates, the wires 95a and 95b are wound or unwound to move the light source unit 31 at a predetermined moving speed, e.g. Moves at scanning speed and mirror unit 3 at the same time
5 at 1/2 the speed. Here, the moving speed of the light source unit 31 during pre-scanning and main scanning, that is, the scanning speed may be changed by changing the rotational speed of the motor 92 itself, or by changing the rotational speed by the deceleration means 93.

Here, the CCD 38 is a line sensor that photoelectrically converts a document image for one main scanning line and outputs it as an analog image data signal Sa for one main scanning line. can be used. By the way, the analog image data Sa for one line in the main scanning direction read by the CCD 38 is analog image data covering the entire length of the slit 28 in the main scanning direction, that is, the effective range in the main scanning direction of the document platen.
When the length of the document G in the main scanning direction is smaller than the length of the slit 28, image data other than the document image data, such as data on the back side of the document cover 24, is also included as image data.

Further, the light source for illuminating one line in the main scanning direction is not limited to one that illuminates one line in the main scanning direction at the same time, such as the long fluorescent lamp 26 shown in the figure, but may include a laser light source and a light deflector. Alternatively, a laser beam emitted from a laser light source may be deflected in the main scanning direction to sequentially illuminate the original G. Further, instead of fixing the original G on the original platen 22 and moving the light source in the sub-scanning direction, the original G may be conveyed in the sub-scanning direction while being placed on the original platen 22.

The image processing device 14 includes a clock generator 40 that generates a main scanning clock φx that determines the timing for reading one main scanning line of image data from the CCD 38, and an analog image read from the CCD 38 based on the main scanning clock φx. The image reading method of the present invention uses an A/D converter 42 that performs analog correction such as gain correction on the data signal Sa and then converts it into an image data signal S as a digital signal, and this image data signal S during pre-scanning. At the same time, this signal S is used in the main scan.
and an image processing section 44 which processes the image and finally outputs it to the image recording device 16 as a halftone image signal. here,
The image processing section 44 is the most characteristic part of the present invention, and the image processing section 44 receives the main scanning clock signal φx and the sub-scanning clock signal φy from the clock generator 40.
After performing corrections such as CCD shading correction and dark time correction on the image signal S based on the above, as described later, thinning processing is performed during pre-scanning, and various image processing, such as edge detection of the document, is performed. During the main scan, logarithmic conversion processing, gradation conversion processing, magnification conversion processing, smoothing processing, sharpening processing,
It is subjected to image processing such as halftone processing and outputted to the image recording device 16 as a binarized halftone image signal R.

The image recording device 16 processes the original image signal read by the image reading device 12 at a predetermined scanning speed according to the magnification by the image processing device 14, and converts the halftone dot image signal R obtained by using a laser beam into the image recording device 16. Convert it to an optical signal such as
an image exposure section 46 that guides and exposes light onto the photosensitive material F that is conveyed at a speed synchronized with the scanning speed and records a halftone gradation image; and an image exposure section 46 that records a halftone gradation image by developing and fixing the exposed photosensitive material; It consists of a photosensitive material processing section 48 that reproduces the original image as an image. Here, the photosensitive material processing section 48 does not necessarily have to be integrated, and the exposed photosensitive material F may be processed by another photosensitive material processing device.

FIG. 3 shows the configuration of the image processing section 44 shown in FIG. 1. In this case, the image processing section 44 first includes a correction processing section 50, a magnification conversion circuit 52, a conversion processing circuit 54, a halftone dot generation section, and a magnification conversion circuit 52 and a conversion processing circuit 54, to which image data is sequentially transmitted via an image bus. A line memory 58 connected to the CPU bus from the image bus between the CPU and the CPU exchanging information via the CPU bus.
60, ROM62, and RAM64, and the correction circuit section 5
0, magnification conversion circuit 52, conversion processing circuit 54, halftone dot generation section 56, CPU 60, ROM 62, and RAM 64
are connected to perform various image processing.

The correction circuit section 50 includes a preprocessing circuit and a CCD correction circuit. Here, the preprocessing circuit compensates for noise components associated with offset error fluctuations such as temperature drift and voltage fluctuations of analog elements such as line sensors, amplifiers, and A/D converters by using the mask image signal in the dark. For example, when the image signal level in the dark varies over a plurality of scanning lines, offset errors are compensated for each line to stabilize the signal. In addition, the CCD correction circuit uses a CCD which is a solid-state image sensor.
The fluctuation in the amount of received light due to the variation in each pixel of 38 is expressed as (
It performs shading correction to correct (including fluctuations in illumination light) and dark correction to correct base fluctuations for each pixel (which exist even when no light is incident). For example, if the document image density is the same, the image data (image signal) is the same. Such shading correction and dark correction are performed by A/
The processing may be performed on analog data before A/D conversion by the D converter 40. At this time, the CCD correction circuit is provided upstream of the signal transmission of the A/D converter 40. Also, CCD
The correction circuit may be placed after the logarithmic conversion circuit, which will be described later, and perform CCD correction after the logarithmic conversion.

The magnification conversion circuit 52 converts one line of image data in the main scanning direction read by the CCD 38 into an image signal corresponding to a pixel density in the main scanning direction according to an image forming magnification such as a predetermined enlargement magnification or reduction magnification. It is a circuit that converts
This circuit is capable of thinning out image data from one line of image data in the main scan at a predetermined thinning rate to make one line of image data into a required amount of image data. for example,
In the pre-scan, the magnification conversion circuit 52 thins out 7500 pixels of all input image data for one line to about 1/3.
The amount of data is approximately 250 pixels of 0.

The line memory 58 is used for detecting the main scanning range such as the document and its effective image area, which is carried out as necessary.
The magnification conversion circuit 5 is necessary for storing one line of image data in the effective range in the main scanning direction of the document platen read during pre-scanning for automatic density measurement, etc.
This is a memory for storing one line of image data thinned out by 2. Once stored, one line of image data is read out from this line memory 58 by the CPU 60 and subjected to various arithmetic operations for image processing.

The conversion processing circuit 54 includes a logarithmic conversion circuit for logarithmically converting the image signal and gradation characteristics (exposure-density characteristics).
It consists of a gradation conversion circuit, etc. that converts into an image signal corresponding to the image, and converts it into a signal for image recording.

The halftone dot generation section 56 includes a smoothing processing circuit 66, a sharpening processing circuit 68, and a halftone decomposition processing circuit 70, as shown in FIG. The smoothing processing circuit 66 averages the input image data and surrounding pixel data, performs unsharp processing on the input image data, reduces noise in the image data signal, and obtains corrected image data.

The sharpening processing circuit 68 emphasizes edges such as the outline of an image and performs sharpening processing. For example, it subtracts a constant times the smoothed image data from the original image data. It performs sharp masking to increase image sharpness and emphasize edges.

The halftone processing circuit 70 creates a halftone image signal from the image density signal, and this halftone image signal area-modulates the image density according to the required angle and number of lines. This halftone image signal is output to the image exposure section 46 of the image recording device 16.

The CPU 60 executes the correction processing circuit section 50 according to the control sequence stored in the ROM 62.
, magnification conversion circuit 52, conversion processing circuit 54, halftone dot generation section 5
4, such as the smoothing processing circuit 66, sharpening processing circuit 68, and shading processing circuit 70, and the control of the RAM 64 in advance.
Various data stored in the memory and data input by the user, such as effective image area data in the main scanning direction and various controls necessary for image processing, as well as one line of image data in the main scanning direction from the line memory 58 during pre-scanning. The data is read out to perform detection of the main scanning range, automatic density measurement, and measurement of other necessary image processing data. The CPU 60 also controls the movement of the light source unit 31 and the mirror unit 35, which are the scanners of the image reading device 12 during pre-scanning on the forward path, the movement pattern of the light source unit 31 and the mirror unit 35 on the return path, and the control of the image recording device 16. The reading speed of the original image is set according to the exposure speed and exposure magnification of the photosensitive material F in the image exposure section 46, that is, the main scanning speed synchronized with the exposure speed of the scanner (light source unit 31) in the return path. It also sets and controls speed patterns. Also, C
The PU 60 may control the entire operation of the printing plate making apparatus 10. The RAM 64 is a main memory that stores data necessary for control performed by various CPUs 60.

As described above, the image recording device 16 includes an image exposure section 46 and a photosensitive material processing section 48. As shown in FIG. 5, the image exposure section 46 emits a recording beam that is read by the image reading device 12, processed by the image processing device 14, and modulated according to the generated and transmitted halftone image signal R. a resonant scanner 74 that deflects the recording beam in one-dimensional direction; an fθ lens 76 that adjusts the focus of the deflected scanning beam on the photosensitive material F; An exposure drum 78 that conveys the exposed photosensitive material F while defining it at an exposure position, nip rollers 80 and 82 that press the photosensitive material F against the exposure drum 78 and convey it, and a diagram that cuts the exposed photosensitive material F into a predetermined length. It has a cutter that does not. Further, a synchronization signal detector for controlling exposure may be provided.

The recording beam emitted from the recording light source 72 modulated according to the halftone image information signal R is deflected in one dimension by a resonant scanner 74 and then passed through an fθ lens 7.
6, the photosensitive material F is pulled out from a magazine (not shown), and is conveyed in the sub-scanning direction by an exposure drum 78 and nip rollers 80, 82, and is exposed to light to record a halftone image two-dimensionally. At the same time, a synchronization signal detector (not shown) generates a synchronization signal to control exposure using the recording beam, thereby making it possible to perform accurate and good exposure. After the exposure is completed, the cut exposed photosensitive material F is sent to the photosensitive material processing section 48. In the photosensitive material processing section 48, the exposed photosensitive material F is subjected to wet processing such as development, fixing, bleaching, and water washing, and then dried.

In the printing plate making apparatus 10 described above, the sub-scanning conveyance speed of the photosensitive material F by the exposure drum 78 of the exposure section 46 of the image recording device 16 and the nip rollers 80, 82 is always controlled to a constant speed. That is, here, the exposure speed to the photosensitive material F is constant. Therefore, in the illustrated apparatus, the magnification when recording the original image read by the image reading device 12 on the photosensitive material F is changed by changing the moving speed of the scanning element in the image reading device 12. That is, when the exposure speed of the image recording device 16 is Vw, if the image reading speed in the main scan, and therefore the moving speed of the scanning element (main scanning speed) Vr, is made the same as the exposure speed Vw, it will be the same magnification, and it will be less than Vw. If it is set faster, it can be reduced, and if it is slower than Vw, it can be enlarged and recorded. For example, by changing the main scanning speed Vr of the scanning element from 6.25Vw to 0.25Vw, it is possible to change the magnification from 16% to 400%. At this time, it is sufficient to set the maximum speed of the scanning element to 6.25 Vw, and it is preferable to perform prescanning at this speed.

The printing plate-making apparatus 10 that implements the image reading method of the present invention is basically constructed as described above, and its operation and the image reading method of the present invention will be explained.

In the printing plate-making apparatus 10 shown in FIG. 1, a document G is placed at a predetermined position on a document table 22 and fixed by a document table cover 24. As shown in FIG. First, at the home position, the fluorescent lamps 26 and 26 disposed in the light source unit 31 are turned on and illuminate the document G from the lower surface of the document table 22. After this, the motor 92 shown in FIG. 2 starts rotating, and the light source unit 31 and mirror unit 35 are driven by the wire 95a driven by the wire drive pulley 94.
, 95b, the prescan speed and its first
It starts moving in the direction indicated by arrow a at a speed of /2, and after moving to the origin of the document table, pre-scanning of the document image is started. Here, in the present invention, the pre-scan is performed in the direction of arrow a at the maximum speed Vrmax as shown in FIG.

In pre-scanning, as shown in FIG. 1, the slit-shaped light emitted from the fluorescent lamps 26 and 26 and reflected on the document G is directed to a predetermined position by the first mirror 30 that moves integrally with the light source unit 31. The light is then reflected in a predetermined direction by the second mirror 32 and third mirror 34 of the mirror unit 35, which move in the same direction as the light source unit 31 at 1/2 the speed, and travels along the optical path L. The slit-shaped light extending in the main scanning direction, which has traveled along the optical path L, is imaged on the CCD 38 by the imaging lens 36, and the CCD sensor 38 photoelectrically converts the slit light in the main scanning direction into one line worth of light. The analog image data signal Sa is sent to the image processing device 14.

In the image processing device 14, the analog image data signal Sa is A/D converted by the A/D converter 42, and is sent to the image processing section 4 as a digital image data signal S.
Sent to 4. In the image processing unit 44, this image data signal S is subjected to various corrections in a correction processing circuit unit 50, and after being thinned out according to a predetermined thinning rate in a magnification conversion circuit 52, the image data signal S is thinned out according to a predetermined thinning rate of a predetermined amount of data in one line in the main scanning direction. Image data is stored in line memory 58. After this CPU6
0 uses the image data stored in the line memory 58 to perform various image processing, for example, calculation and processing of all data required during main scanning, such as image density and detection of the edge of the document, which will be described later. .

As shown in FIG. 6, if the leading and trailing edges of the document G are provided to the RAM 64 or the like by a digitizer (not shown), the scanner (light source unit 3)
When 1) is near the end of the document, the scanner 31 starts slowing down (deceleration) from a predetermined position corresponding to the stop position described later, decelerates at a predetermined deceleration rate, and scans the document corresponding to the image formation magnification. It stops at a predetermined position determined according to the scan speed. In this way, the prescan ends.

By the way, in the apparatus to which the present invention is applied, the reading of the image of the document G by the main scan of the image reading device 12 and the writing of the image onto the photosensitive material of the image recording device 16 are performed synchronously. Therefore, in order to obtain a high quality image with accurate dimensions, color reproduction, etc. and no unevenness, in the illustrated example, the image recording device 16 is first started to be driven. Thereafter, after a predetermined period of time has elapsed, the scanner 31 of the image reading device 12 reaches the reading start position of the document G, for example, the end of the document in the illustrated example, reaches a predetermined main scan speed Vr, and the main scan is started. Thereafter, the main scan of the document G in the direction of arrow b is performed by the scanner 31 at the main scan speed Vr.

In the main scan, the image reading device 12 scans the main scan 1 in the same manner as in the pre-scan described above.
The image data for the line is read, and the image processing device 14
The image is processed by , stored in the line memory 58 , read out again, subjected to gradation conversion etc. by the conversion processing circuit 54 , subjected to halftone processing by the halftone dot generation circuit 56 , and then converted into a binarized halftone image. Image recording device 1 as signal R
6 is output. The image recording device 16 forms an image on the photosensitive material F based on this halftone image signal R, and reproduces and records the image.

The main scanning movement by the scanner 31 in the direction of the arrow b continues at the main scanning speed Vr, and when the scanner 31 reaches the leading edge of the document G and the main scanning ends, the scanner 31 continues as it is. Slow up, Vrma
Accelerated to x (maximum speed). Thereafter, the scanning element 31 continues to move in the direction of arrow b at the maximum speed Vrmax, passes through the original platen origin, decelerates, returns to the home position, and stops. Such slowing up and slowing down (acceleration/deceleration) of the scanning element 31 may be performed by directly controlling the rotation of the motor 92 of the drive device 90, or by using the deceleration means 93. Timing control and speed control such as slowing up, slowing down, stopping, and starting drive of the motor 92 are not particularly limited, but in the case of a pulse motor or the like, a counter or the like may be used to control the motor 92.

In this way, the image reading sequence of the first aspect of the present invention shown in FIG. can be performed, so the total sequence time can be shortened.

Here, the example shown in FIG. 6 is an example in which the original G, which is smaller in size than the original table 22, is placed at the end of the original table 22, and the leading edge of the document is placed inside the original table 22. but,
FIG. 7 shows an example in which a small-sized document G is placed at the tip of the document table 22. In this example, since the end of the document G is in the middle of the document table 22, the scanner 31 is placed at the end of the document table 22. Rather than scanning up to the end, pre-scanning is performed up to the vicinity of the end of the document G, and the document G is stopped at a predetermined position in the vicinity. From here, the main scan is reversed from the end of the document G in the direction of arrow b at a main scanning speed corresponding to the image formation magnification, and the document image is read to the leading edge of the document G (ie, the starting point of the document table). When the scanner 31 reaches the starting point of the document table, it slows up and moves to the home position at the maximum speed Vrmax, and then slows down and stops at the home position.

In the first aspect of the present invention, the document table 2
The end or the end and the leading edge of the document G placed on the document G 2 are input by a digitizer or the like and stored in advance in the RAM 64 or the like, and the movement of the scanner 31 is controlled accordingly.
Controlled by U60. On the other hand, the second aspect of the present invention
In this embodiment, the end or end and leading edge of the document G is detected by pre-scanning, and the scanning element 31 is moved at the highest speed except during main scanning.

The image reading sequence of the second aspect of the present invention shown in FIG. 8 detects the leading edge and trailing edge of the document G by pre-scanning. When pre-scanning is started as described above, the image reading device 12 reads the document image, and the image processing device 14 reads the document image in the same way as in the first aspect.
Processed by After the image density data for one main scanning line is stored in the line memory 58, the CPU 60 shown in FIG. The average density value Da of the line is calculated by averaging the image data in the effective range in the main scanning direction of the document table. After this, the CPU
60 stores the corresponding sub-scanning position and density average value Da of the line in a line memory such as the RAM 64, and plots it on a density average value distribution diagram in the sub-scanning direction. Thereafter, the next line of image data is taken into the line memory 58 in the same manner, and the CPU 60 similarly completes the above-mentioned density average value distribution map.

The above-mentioned routine is repeated over almost the entire sub-scanning range of the document table 22 from the prescan start position (start point of the document table) of the scanner (light source unit) 31 under the document table 22 to the prescan end position (end of the document table). T,C
The PU 60 completes the density average value distribution map as shown in FIG.

When the pre-scanning is completed, the scanner 31 slows down and stops at a predetermined position at the end of the document table 22, and the CPU 60 searches for the density average value distribution diagram shown in FIG. 10 from the opposite side. In the case of FIG. 10, the starting part of the search is not the document area, so it is measured in advance and stored in the RAM 64.
It is approximately equal to the density Do of the original platen cover 24 stored in the memory. Therefore, if the allowable error range is Do±α, |Da−Do| is initially smaller than α. Therefore, CPU6
0 means that it is not detected as a document. After a predetermined line of non-document lines continues, the point where |Da-Do| is equal to or greater than α is determined to be the end of the document. After this, the search is continued and the density average value Da is almost the same as the original platen cover D.
Only when a predetermined line of lines equal to o, that is, |Da-Do|<α, continues, |Da-Do|<
The line α is determined to be the leading edge of the original, and the original
Detects the end and tip of and ends.

After the end and leading edge of the document G are detected, the data obtained by pre-scanning is processed, and various data necessary for the main scan are obtained, the document G is placed at a predetermined position near the end of the document table 22. The stopped scanner 31 is shown in FIG.
As shown in , it starts moving in the direction of arrow b, accelerates and moves at the maximum speed Vrmax, and when it comes near the end of the document G, it decelerates and is determined according to the image forming magnification and the end position of the document G. Stop in position. Thereafter, in synchronization with the image recording device 16, the scanner of the image reading device 12 starts moving again, accelerates, and reaches a predetermined main scanning speed V at the end of the document.
reaches r. From this point on, the scanner 31 moves in the direction of the arrow b and performs the main scan of the original G from the end to the leading edge of the original G in synchronization with the image recording device 16. Expose the image, play it back and record it. When the scanner 31 reaches the leading edge of the document and the main scan is completed, the scanner 31 slows down again to reach the maximum speed Vrmax, and at the maximum speed Vrmax it continues to move toward arrow b.
It moves in the direction, passes the original platen starting point, decelerates at a predetermined position, and stops at the home position. In this way, the image reading sequence of the second aspect of the present invention is performed.

Further, in the above example, the density average value distribution map was created, but the present invention is not limited to this, and the CPU 60
The rate of change fa of the average density value is determined using the average density value Da for several lines obtained by , and by completing a distribution map of this rate of change and searching it, the absolute value of this rate of change | The end and leading edge of the document may be detected using fa| and a predetermined minute threshold value β (within a permissible error range).

In the above example, the end and leading edge of the document are detected by searching after the prescan is completed.
During pre-scanning, the density average value Da or its rate of change fa
Every time we calculate |Da-Do| and α or |fa| and β
The edge of the document may also be detected by comparing with .

In the above example, the edge of the document, for example, the end, the leading edge, or both, is detected in the prescan, but in any embodiment of the present invention, the density measurement of the document image is automatically performed in the prescan. You can go to This density measurement is performed using the main scan 1 stored in the line memory.
This can be done by creating a cumulative density histogram of line image density data for the document area and determining the density of highlight areas, shadow areas, etc. A method for determining the density of highlight and shadow parts from a cumulative density histogram is described in Japanese Patent Laid-Open No. 63-61 by the present applicant.
The method disclosed in No. 579 can be used.

[0053]

As described in detail above, according to the present invention, preliminary scanning (prescanning) is performed in the forward pass, and in the return pass, the document or the effective image area in the document is scanned at a speed corresponding to the image formation magnification. When performing a scan (main scan), other than the above-mentioned main scan, moving scans are performed at the maximum speed, so the overall reading time including preliminary scanning is shortened, the image reading processing time is shortened, and the image reading processing speed is increased. , efficiency can be improved.

According to the second aspect of the present invention, in addition to the above-mentioned effects, the document area on the document table or the document can be scanned at low cost and with high precision during pre-scanning without newly installing parts such as sensors. Since the effective image area can be automatically detected and the main scanning range on the return trip can be automatically set, it is possible to improve the operability of image reading.

[0055] Therefore, an image forming apparatus such as a copying apparatus or a printing plate-making apparatus to which the method of the present invention is applied is extremely easy to operate for the user.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of a printing plate-making apparatus that implements an image reading method according to the present invention.

2 is a schematic top view of an embodiment of an image reading device of the printing plate-making apparatus shown in FIG. 1. FIG.

3 is a block diagram of an embodiment of an image processing device of the printing plate-making apparatus shown in FIG. 1. FIG.

4 is a block diagram of an embodiment of a halftone dot generation section of the image processing apparatus shown in FIG. 2. FIG.

5 is a perspective view of an embodiment of the image recording device of the printing plate-making apparatus shown in FIG. 1. FIG.

FIG. 6 is an example of a movement scanning speed diagram of a scanning element for explaining the image reading method of the present invention.

FIG. 7 is another example of a movement scanning speed diagram of a scanner for explaining the image reading method of the present invention.

FIG. 8 is another example of a movement scanning speed diagram of a scanner for explaining the image reading method of the present invention.

FIG. 9 is an example of a density distribution diagram in the main scanning direction obtained by the method of the present invention.

FIG. 10 is an example of a density average value distribution diagram in the sub-scanning direction obtained by the method of the present invention.

[Explanation of symbols]

10 Printing plate-making device 12 Image reading device 14 Image processing device 16
Image recording device 22 Original table
24 Original table cover 26 Fluorescent light
28 slits 30, 32, 34
Mirror 31 Light source unit (scanner) 35 Mirror unit 36 Imaging lens 38 CCD 44
Image processing section 50 Correction processing section
52 Magnification conversion circuit 54 Conversion processing circuit
56 Halftone dot generation section 58 Line memory
60 CPU62 ROM
64 RAM 66 Smoothing processing circuit 68 Sharpening processing circuit 70 Shading processing circuit 72 Recording light source 74 Resonant scanner 76 fθ lens 78 Exposure drum 80, 82 Nip roller 90 Drive device 92 Motor 93 Deceleration means 94
Wire drive pulley 95a, 95b wire
96a, 96b Movable pulley 97, 97a, 97b Idler 98a, 98b Fixed end 99a, 99b
wire fixed end

Claims (2)

[Claims] 1. Two-dimensional scanning of an original placed on a document table by moving a scanner that irradiates a light beam extending in the main scanning direction in a sub-scanning direction substantially perpendicular to the main scanning direction. In the image reading method of photoelectrically reading the image of the original document, the scanning element is moved to one side in the sub-scanning direction to perform preliminary scanning, and then moved to the other side to scan the effective image area of the original. An image reading method characterized in that when performing scanning, the scanning element is moved at a maximum speed except for the main scanning. 2. Two-dimensional scanning of an original placed on a document table by moving a scanner that irradiates a light beam extending in the main scanning direction in a sub-scanning direction substantially perpendicular to the main scanning direction. In the image reading method of photoelectrically reading the image of the original document, when performing preliminary scanning by moving the scanning element to one side in the sub-scanning direction at the maximum speed, at a predetermined position of the preliminary scanning, After reading image density data for one line in the main scanning direction of the scanning element at the position, averaging this image density data in the main scanning direction to obtain density average value data or a rate of change thereof for the line; Storing this result in the memory is repeated according to the preliminary scanning by the scanner from the preliminary scanning start point at one end of the document table to the preliminary scanning end point at the other end, and the results are stored in the memory in the sub-scanning direction. Create a density average value distribution map or its rate of change distribution map for the entire sub-scanning range, complete preliminary scanning, stop the scanner, and create a density average value distribution map or its rate of change distribution map stored in the memory. After searching the distribution map and detecting the edge of the document or document effective image based on the continuity of the density average value near a predetermined reference density value or the continuity of the rate of change near 0, the document or document effective image is detected. When the end of the valid document image differs from the end point of the preliminary scan, move the scanner at the maximum speed to the side opposite to the preliminary scan until the end, stop once, and then scan the document or document valid image. After carrying out main scanning by moving the scanner at a main scanning speed corresponding to a predetermined magnification over the sub-scanning range from the end to the tip, if the tip and the preliminary scanning start point are different, An image reading method comprising accelerating the main scanning speed to the maximum speed, moving the scanning element to the preliminary scanning start point at this maximum speed, and then stopping the scanning element.