JPH0221374A - Picture reader - Google Patents

Abstract

PURPOSE:To use the illumination light with efficiency by multiplying the Fourier transform value by the reciprocal of the photodetecting frequency characteristic decided by the form of a photosensitive part for CCD picture elements of a CCD linear image sensor or the approximate function of said frequency characteristics and applying the adverse Fourier transform of the obtained product to acquire the picture read data. CONSTITUTION:When the read data equivalent to one page are stored in a picture memory 48, a Fourier transform part 50 applies the Fourier transform to the read data on a line set in the secondary scan direction (y direction) into G(w). Then a multiplier 52 multiplies the reciprocal 1/H(w) of the response frequency characteristics of a system by the G(w) to obtain F(w). The 1/H(w) is decided by the form of a photosensitive part for CCD picture elements of a CCD linear image sensor 22 and the scan frequency N of the secondary scan direction. At the same time, an appropriate function can also serve as the 1/H(w). Then an adverse Fourier transformer 54 receives the F(w) for all frequencies and performs the adverse Fourier transform to send the transformed F(w) to a picture memory 56. Thus the illumination light is used with high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image reading device that reads images using a linear COD image sensor.

(Prior Art) In an image reading device that reads an image of a document, a CCD linear image sensor, which is a photoelectric conversion element, is used. The photosensitive area of one pixel of the current CCD linear image sensor is, for example, 5 μ! due to high-density reading. ×
It is as small as 7 μm (see FIG. 10. In this figure, the shaded area indicates the photosensitive area of each pixel. The size of one pixel is the same in both length and width, 7 μm.). In order to obtain images with high resolution, the photosensitive area must be made small. However, when the photosensitive area becomes smaller, the photosensitive area correspondingly decreases, resulting in an insufficient amount of light.

In order to read the image, it is necessary to illuminate the document. Light sources such as halogen lamps and fluorescent lamps are used for lighting.

Light reflected from the original by the illumination is detected by a CCD linear image sensor and converted into an electrical signal. Then, a digitized binary signal is obtained by A/D conversion.

(Problems to be solved by the invention) As explained above, the CCD linear image sensor
It receives only the reflected light of about 7μ shoulder width.

However, when using a halogen lamp to illuminate the manuscript,
Due to the positional accuracy of the filament of the halogen lamp and the manufacturing accuracy of the reflecting mirror, the width can only be narrowed to about 2 to 3ax at most, and condensed illumination with a width of about μ1 is difficult. On the other hand, even when using a fluorescent lamp, the illumination is based on light emitted from the fluorescent material on the tube wall, so condensed illumination is not possible.

Therefore, the illumination efficiency of both halogen lamps and fluorescent lamps is very poor, and it is necessary to provide strong illumination with large wattage lamps.

An object of the present invention is to provide an image reading device that can efficiently utilize illumination light.

(Means for Solving the Problems) An image reading device according to the present invention illuminates a document, projects an image of the document onto a CCD linear image sensor means, and a CCD linear image sensor.
An image reading device that reads an image by mechanically scanning an original in a sub-scanning direction perpendicular to the main-scanning direction in which CCD pixels of a linear image sensor are arranged, which has a photosensitive section that is longer in the sub-scanning direction than in the main-scanning direction. CCD linear image sensor means consisting of CCD pixels, A/D conversion means for digitizing the electrical signals detected by each CCD pixel of the CCD linear image sensor means, and a document digitized by the A/D conversion means! An image storage means for storing image data for a page, and image data for one line in the sub-scanning direction are read out from the image storage means and subjected to Fourier transformation, and the light reception is determined by the shape of the photosensitive part of the CCD pixel of the CCD linear image sensor. image quality compensation calculation means for compensating for image quality deterioration of image data by multiplying the Fourier transform value by the frequency characteristic of It is characterized by:

(Function) Generally, as shown in Figure 2 (a), in a certain system, [(y)
Suppose we input the input and get the output g(y). As an example, suppose that an output h(y) is produced by manually generating a pulse with no width (a point ray of light in terms of image), as shown in FIG. 2(b). This h(y) indicates the characteristics of the system.

The frequency characteristics of these r(y), g(y), and h(y) are f(y).

The Fourier transforms of g(y) and h(y) are respectively F (w
), G (v).

If H(w), it is expressed as follows.

Using this frequency characteristic, the output G (w) becomes the input F
The product of (w) and the system characteristic H(w) is expressed as an arithmetic operation.

G(w)=F(w)・H(w) (2
) Inverse Fourier transform, which transforms based on frequency characteristics, also holds true at the same time.

A general explanation of the above r, g, and h is given, for example, in Hiroshi Kubota, "Applied Optics" (Iwanami Zensen, 1970), page 211.

FIG. 3 shows an example of the shape of a pixel formed by the COD linear eye sensor 22. The shaded area is the photosensitive area 24 of each pixel.
, 24. ...is shown. The length b of the photosensitive section 24 in the y direction is made larger than the pitch a in the X direction (for example, b=
l 4 μrn, a=7 μx, b/a=2).

Note that the width c (=5μ shoulder) of the photosensitive portion 24 is shorter than the pitch a in order to separate pixels.

By elongating the shape of the photosensitive section 24 in the sub-scanning direction,
The amount of light received increases.

However, the contrast and resolution in the sub-scanning direction are reduced,
Image quality deteriorates. Therefore, the following arithmetic processing is performed.

First, the response characteristics of the COD linear image sensor 22 will be explained. Photosensitive section 24 of the COD pixel that constitutes this sensor
The characteristic of the light intensity I should originally be read as a point, but due to the influence of the mechanical movement of the optical system and the shape of the photosensitive section 24, it takes on the shape shown in FIG. 4. That is, if we take the coordinate axes at the center for analysis, then 1(y)=Oy≦-+3/2 (4)=1.
b/2≧y≧−b/2 =o y≧b/2 where b is the length of the photosensitive portion 24 in the y direction.

To be precise, one pixel in the CCD is mechanically scanned even while receiving light. However, the time that one pixel operates and scans is about 01 microseconds, and the mechanical scanning speed for sub-scanning is usually about 10011/second, so this 0.1 microsecond 0.01 μl between
Only a certain extent is scanned. This length is the element size 14μ
Since it is sufficiently small compared to l, it is ignored here.

In the theory of general system response described above, I (y) corresponds to h(y). Therefore, by Fourier transformation of r (y), a function H(w) representing the frequency characteristics of the system is obtained. That is, +I(w)=sin7rw/πw (
5) Here, w=b-N.

Here, b is the actual length in holo units, and N is the spatial frequency expressed in units of (hon/II). FIG. 5 shows the frequency characteristics of the function H(v). Naturally, the contrast in areas where the frequency is high, that is, in fine areas, is reduced.

The function H(w) will be specifically explained by applying the actual spatial frequency N. FIG. 6 shows the case where the length b of the photosensitive section in the sub-scanning direction is 14 μl and 7 μl! The frequency characteristics of f((N) in the case of When b = 7μ, the reading density is 143 lines/l.By the way, the reading density of a fine type image reading device is usually 400 dots per inch.If this is expressed in terms of spatial frequency N, it is 8 lines/R. The number of pixels of the COD linear image sensor is 5000E!A and 7μ!
In terms of pitch, the photosensitive size of the COD linear eye sensor is 35 mm. A3 size 297mm to this C
When reduced and projected onto the OD linear image sensor, the spatial frequency of 8 lines/j11 becomes 68 lines/sI. If the reciprocal (1/H(v)) becomes infinite, an appropriate maximum value may be used.

Since curve A is twice the size of curve B, its value is cos(0,
022N) times. Therefore, the reciprocal l
By multiplying curve A by /cos(0,022N), curve B is obtained. Despite increasing the size of the photosensitive area, the characteristics have returned to the original.

In the present invention, the function H(w
) is used to calculate the input value f(y) from the output g(y) of the optical characteristics.
seek. This restores the frequency characteristics that were degraded by enlarging the photosensitive area of the COD. At this time,
Use the following formula.

G(v)X(1/H(w))=F(w)・H(w)・(
+/H(w))=F(w)(6
) That is, by Fourier transform of the output value g(y), G
Find (w) (formula (1b)), then multiply by the reciprocal of H(w) to find F (w) (formula (6)), then perform the inverse Fourier transform of F (w) (( 3a) formula), the image force f(y) is obtained.

Specifically, the processing procedure shown in FIG. 7 is used.

First, all images of a document are sequentially scanned by an optical system (step S1), and two-dimensional information of one page's worth of images is stored in an image memory (step S2).

Next, X is specified (step S3), read data g(y) on one line in the sub-scanning direction is read out from the image memory (step S4), and G(v) is obtained by Fourier transformation (step S5).

Next, the reciprocal (+/
H(w)) is multiplied by G(w) to obtain F(w) (step S6).

Next, the image data r
(y) is obtained and stored in the image memory (step S7).
.

Next, if it is determined that it is not the final value of X (step S8)
, returns to step S3, changes X sequentially, and performs the same process for the lines in the sub-scanning direction.

When all X processing is completed, r(y) is output from the image memory as an image reading signal (step S9).

Thereafter, processing such as binarization is performed on this image reading signal, and the signal is output to an external printer or the like.

Even if the shape of the CCD pixel is not a rectangle but a parallelogram to avoid a moiré pattern, the same calculation process can be performed if the frequency of the photosensitive section determined by the shape of the CCD pixel is determined.

By performing the process of multiplying by this reciprocal, it is possible to further improve the characteristics of the signal read by the COD with the original small photosensitive area size.

It goes without saying that to improve the characteristics, it is effective to perform an operation that approximately increases the high frequency value, without multiplying it by its reciprocal (1/H(w)) exactly.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 8 shows a schematic arrangement of a mirror scanning type optical system which is an example of an image reading device. The light emitted from the halogen lamp 2 illuminates the original 10 placed on the original glass 8 via the reflecting mirror 4.6. The image of the manuscript is a mirror! 2.1
4 and 16, passes through a lens 18, passes through a filter 20, and forms an image on a CCD linear image sensor 22. Halogen lamp 2, reflector 4.6 and mirror 1
2 moves together to scan the original 10, and at the same time mirrors 14 and 16 also move at half the speed to keep the optical path length up to the lens 9 constant. CCD linear image sensor 2
2 has the shape shown in FIG.

FIG. 9 shows a method of reading the entire image by redrawing the configuration of FIG. 8 as a model. In the sub-scanning direction, optical systems 2 to 6.
12 to 16 move to scan the original 10.

The CCD linear image sensor 22 outputs signals of each pixel in the order perpendicular to the sub-scanning direction (referred to as the main-scanning direction). The entire image of the document 10 is read in both main scanning and sub-scanning. Hereinafter, the main scanning direction will be referred to as the X direction, and the sub-scanning direction will be referred to as the y direction.

Note that mechanical sub-scanning methods include a method of moving the document itself while illuminating the document in the main scanning direction as shown in FIG. 9, and a method of projecting the entire screen of the document using a lens. There is a method of moving the COD linear image sensor.

FIG. 1 is a block diagram of a circuit for detecting the density of a document.

The clock generation circuit 40 provides a necessary sample and hold signal to the CCD linear image sensor 22, and is also connected to a CPU 42 that controls document reading and is used as a clock signal. CCD linear image sensor 22
converts an optical signal into an electrical signal. The A/D converter 44 converts the analog output of the CCD linear image sensor 22 into a digital signal. The shading circuit 46 is for correcting the unevenness of light amount in the main scanning direction of this digital signal and the variation between bits (pixels) of the CCD linear image sensor 22, and its timing is given by a shading signal from the CPU 42. The output of the shading circuit 46 is input to an image memory 48. Image memory 48 is a RAM that stores all read data regarding document 10.

When one page of read data is stored in the image memory 48, the Fourier transform unit 50 first converts the data in the sub-scanning direction (y direction).
The read data of line I (corresponding to g(y) in the above general system response) is expressed as G (
Fourier transform to w). Next, the multiplier 52 multiplies G (w) by the reciprocal 1/H (w) of the frequency characteristic of the system response using equation (6) to obtain F (v). This 1/H(W
) is given by the shape of the photosensitive portion 12 of the CCD pixel of the CCD linear image sensor 22 and the scanning frequency N in the sub-scanning direction (see equation (5)), but an appropriate approximation function may be used. . Next, the inverse Fourier transformer 54 receives F(w) for all frequencies, performs inverse Fourier transform using equation (3a), and sends it to the image memory 56. The above calculation process is repeated at each position y in the sub-scanning direction. In this way, one page's worth of arithmetic-processed image read data is stored in the image memory 56. In the above description, two image memories 48 and 56 are used for convenience of explanation, but in reality, only one image memory can be used for calculation processing. Note that the CPU 42 determines the binary or dither attribute for each predetermined area based on the information written in the image memory 56, and writes it in the attribute RAM 58.

Next, binarization processing is performed in the same manner as before, and the result is output to the outside. That is, the above correction calculation read data is sequentially sent from the image memory 56 to the comparison circuit 60.

The pattern generation circuit 62 generates a threshold value at the time of dither selection, and the threshold value is generated in a matrix of (a+Xn). The selector 64 switches the threshold between binary and dither based on the information in the attribute RAM 5B during data transfer, and outputs the threshold to the comparison circuit 60. The comparison circuit 60 compares the corrected read data with the threshold value sent from the selector 64, and outputs the result in one bit to the output circuit 6.
Output to 6. The output circuit 66 outputs a 1-bit image signal and a synchronization signal to an external device (such as a printer) when a valid image signal (synchronization signal) is sent from the CPU 42.

Note that the CPU 42 inputs a motor signal, a lamp signal, a fixed position signal, a command signal, etc., and controls the operation of the image reading device.

(Effects of the Invention) Illumination light can be used efficiently by increasing the size of the photosensitive portion of the CCD linear image sensor in the sub-scanning direction. This allows the use of lower wattage lamps, reducing costs.

On the other hand, the deterioration in image quality caused by increasing the size of the photosensitive area can be compensated for by arithmetic processing, so that there is no deterioration in image contrast or resolution.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a circuit system of an image reading device. FIGS. 2(a) and 2(b) are diagrams showing the response of the system, respectively. FIG. 3 is a diagram of the photosensitive section of the CCD linear image sensor. FIG. 4 is a graph of the CCD pixel response. 5 and 6 are graphs of the frequency characteristics of the response of the system, respectively. FIG. 7 is a diagram showing the flow of arithmetic processing. FIG. 8 is a diagram of the optical system of the image reading device. FIG. 9 is a diagram showing scanning of the entire image. FIG. 10 is a diagram of a photosensitive section of an example of a conventional CCD linear image sensor. 22...CCD linear image sensor, 42.CPU
, 48... Image memory, 50... Fourier transformer, 52... Multiplier, 54... Fourier inverse transformer, 56... Image memory. Patent Applicant Minolta Camera Co., Ltd. Agent Patent Attorney Aoyama Ao Two idiots Figure 5 vC6 Figure INI 3゜4゜5゜ (book/mm) Figure 7 Notification - Rate

Claims (1)

[Claims] (1) The original is illuminated, the image of the original is projected onto the CCD linear image sensor means, and the original is mechanically scanned in the sub-scanning direction perpendicular to the main scanning direction in which the CCD pixels of the CCD linear image sensor are arranged. In an image reading device that reads images using
CCD linear image sensor means consisting of pixels; A/D conversion means for digitizing electrical signals detected by each CCD pixel of the CCD linear image sensor means; and one page of the original digitized by the A/D conversion means. An image storage means for storing image data of 1 line in the sub-scanning direction is read out from the image storage means and subjected to Fourier transformation to determine the frequency of light reception determined by the shape of the photosensitive part of the CCD pixel of the CCD linear image sensor. Image quality compensation calculation means for compensating for image quality deterioration of image data by multiplying the Fourier transform value by the reciprocal of the characteristic or its approximate function and performing inverse Fourier transform of the obtained product to obtain image reading data. An image reading device characterized by: