JPH05227428A - Picture reader - Google Patents

Abstract

PURPOSE:To execute more appropriate shading correction without reducing reducing the number of gradation in an output picture. CONSTITUTION:A light quantity distribution curve on a line passing a maximum light quantity point and a light quantity distribution curve with a smaller curvature out of the light quantity distribution curves on lines B and C are approximated by secondary curves. All values on the secondary curves are geometrically magnified so that a peak value on the secondary curves obtained by approximation becomes a prescribed value. The values of corresponding points on the two secondary curves obtained by geometric magnification are averaged and shading correction data in the direction of main scan is calculated. Shading correction in the direction of main scan is executed based on shading correction data in the direction of main scan for detected light quantity. The respective values of the secondary curves are geometrically magnified so that the peak value on the secondary curves passing through the respective intermediate values of light quantity on the corrected lines A, B and C and shading correction data in the direction of auxiliary scan is calculated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device.

[0002]

2. Description of the Related Art An image reading apparatus illuminates an image, for example, a microfilm with an illumination lamp, guides transmitted light from the microfilm to a screen with a projection lens and a mirror, and projects the image on the screen. The image information on the microfilm is read by an image sensor.

Further, since shading exists in both the main scanning direction and the sub-scanning direction on the projection image plane due to the light distribution characteristics of the illumination lamp, the transmission characteristics of the projection lens, etc., shading correction in both directions is performed. Is being done. Here, the main scanning direction is the arrangement direction of the image sensor chips with respect to the projection image plane, and the sub-scanning direction is the direction in which the image sensor moves for scanning.

FIG. 16 shows an example of a conventional shading correction circuit. This is an example in which the shading correction is performed according to the position of the pixel of the image data read by the image sensor 301.

First, the switching circuit 319 is loaded into the memory 317.
The image sensor 301 scans the projection image formation surface in a state where there is no image information of the subject on the projection image formation surface, and the illuminance data of all pixels on the projection image formation surface is stored in the memory 317 as shading correction data. ..

Then, the switching circuit 319 is switched to the surface correction circuit 318 side. With respect to the image data from the image sensor 301, the main scanning direction counter 308 and the sub scanning direction counter 309 manage the main scanning position and the sub scanning position on the projection image plane. Main scanning direction counter 30
8 and the value of the sub-scanning direction counter 309, the shading correction data corresponding to all the pixels of the projection image plane is output from the memory 317, and based on the shading correction data from the memory 317, the surface correction circuit 318
Shading correction is performed on the image data from the image sensor 301. The output of the surface correction circuit 318 is output to the image processing circuit 310, and the processed image data is output by the output circuit 3.
It is output from 11.

FIG. 17 shows another example of the conventional image reading apparatus. This is an example in which shading correction is performed based on the product of shading correction data in both scanning directions in accordance with the pixel position of the image data read by the image sensor 301.

First, the switching circuit 312 is loaded into the memory 302.
The image sensor 301 scans the projection image forming surface in a state where there is no image information of the subject on the projection image forming surface, and the illuminance data for one line in the main scanning direction is corrected by the main scanning shading correction of the projection image forming surface. Memory 302 as data
Remember. Then, the switching circuit 312 is switched to the main scanning direction correction circuit 303 side and the switching circuit 313 is switched to the memory 304 side, and the projection image formation surface is detected by the image sensor 301 in a state where there is no image information of the subject on the projection image formation surface. Scanning is performed in the sub-scanning direction, and the illuminance data for one line in the sub-scanning direction is stored in the memory 304 as sub-scanning shading correction data for the projection image plane.

When the main and sub-scanning shading correction data of the projection image plane are stored in the memories 302 and 304, respectively, only the switching circuit 313 is operated in the sub-scanning direction correction circuit 30.
Switch to side 5.

With respect to the image data from the image sensor 301, the main scanning direction counter 308 and the sub scanning direction counter 309 manage the main scanning position and the sub scanning position on the projection image plane. First, the main scanning direction counter 308
Depending on the value of, the shading correction data corresponding to the position of the projection image forming surface in the main scanning direction is output from the memory 302, and based on the shading correction data from the memory 302, the main scanning direction correction circuit 303 outputs the shading correction data from the image sensor 301. Shading correction in the main scanning direction is performed on the image data. The output from the main scanning direction correction circuit 303 is output to the sub scanning direction correction circuit 305.

Then, based on the value of the sub-scanning direction counter 309, shading correction data corresponding to the position of the projection image plane in the sub-scanning direction is output from the memory 304, and based on the shading correction data from the memory 304, the sub-scanning direction. By the correction circuit 305, the image sensor 301
The shading correction in the sub-scanning direction is performed on the image data from.

The output of the sub-scanning direction correction circuit 305 is output to the image processing circuit 310, and the processed image data is output from the output circuit 311.

[0013]

However, in the above-mentioned conventional example, when dust or the like exists on the optical path, the influence of the dust appears on the projection image forming plane and the light amount distribution fluctuates, so that the shading correction is not accurate. As a method of solving such a problem, a method of removing using shading correction data by using pixel data around a target pixel, for example, a method of removing using a low-pass filter is known. However, there are cases where it is not possible to completely eliminate the effects of dust, etc., because the effects of dust etc. are various.

Further, since the light quantity on the projection image forming plane is taken in directly or through a low-pass filter to perform shading correction, the peak value of the shading correction data depends on the illuminance on the projection image forming plane by the irradiation lamp, and the shading correction data is obtained. It is difficult to set the peak value to the upper limit value that the image sensor 301 can output, because the peak value cannot be made larger than the fetched value.

Generally, since shading correction is performed based on the following equation (1),

[0016]

## EQU00001 ## Data after correction = (data before correction / correction data) .times. ( ^2.sup.n- 1) (1) where each data is n bits.

When the shading correction is performed with the shading correction data having a peak value of less than (2 ⁿ -1), the number of gradations of the input image data that can be read by all the pixels corresponding to the projection image plane is lowered, and the output image is reduced. The number of gray scales will also decrease.

Further, in the conventional examples described in other examples, the obtained shading correction data does not have a sufficient correlation with the light amount distribution characteristic of the projection coupling surface, so that the shading correction is performed based on the shading correction data. However, the shading was not always the minimum.

An object of the present invention is to solve the above problems and provide an image reading apparatus capable of performing more appropriate shading correction without reducing the number of gradations of an output image. ..

[0020]

In order to achieve such an object, the present invention provides a light quantity detecting means for detecting the quantity of light on the projection image plane by sub-scanning and main scanning the projection image plane. In an image reading apparatus having surface shading correction means for performing surface shading correction based on the light quantity distribution detected by the light quantity detection means, the surface shading correction means is detected by the light quantity detection means in a line in the main scanning direction. The first on the first line passing through the maximum light intensity point
A light amount distribution curve and a second light amount distribution curve having a smaller curvature of the light amount distribution curves on the second and third lines which are parallel to the first line and along the front end and the rear end of the projection image formation surface. Approximating means for approximating each of the quadratic curves, and multiplying all the values on the two quadratic curves by equal ratio so that the peak values on the quadratic curves obtained by approximating by the approximating means become predetermined values. Main scanning correction data calculation for calculating shading correction data in the main scanning direction by averaging the values of corresponding points on two quadratic curves obtained by equal multiplication by the ratio multiplying means Means, shading correction means for performing shading correction in the main scanning direction on the light amount detected by the light amount detection means based on shading correction data in the main scanning direction calculated by the main scanning correction data calculation means, and the shading correction means. The shading in the main scanning direction is corrected by over loading correction means first, second, third
A quadratic curve determining means for determining a quadratic curve passing through an intermediate value obtained from the maximum value and the minimum value of the respective light amounts on the line, and a peak value of the quadratic curve determined by the quadratic curve determining means And a sub-scanning data calculation unit that calculates shading correction data in the sub-scanning direction by multiplying each value by a geometrical ratio so as to obtain a predetermined value.

Further, the present invention is based on a light amount detecting means for detecting the light amount of the projection image forming surface by sub-scanning and main scanning the projection image forming surface, and a light amount distribution detected by the light amount detecting means. In an image reading apparatus having surface shading correction means for performing surface shading correction, the surface shading correction means approximates a quadratic curve line by line in the main scanning direction with respect to the light quantity distribution detected by the light quantity detection means. Approximating means for approximating a quadratic curve line by line in the sub-scanning direction, and a geometric ratio multiplying means for equalizing all the approximate values so that the peak value of the values obtained by the approximation by the approximating means becomes a predetermined value. It is characterized by having and.

[0022]

According to the present invention, the surface shading correction means includes the first light quantity distribution curve on the first line passing through the maximum light quantity point detected by the light quantity detecting means among the lines in the main scanning direction and the first line. A second light quantity distribution curve having a smaller curvature of the light quantity distribution curves on the second and third lines which are parallel and along the front end and the rear end of the projection imaging plane is approximated to a quadratic curve by approximation means, respectively. All the values on the two quadratic curves are equal-ratio scaled by an equal-ratio multiplier and equalized by a geometrical-ratio multiplier so that the peak value on the quadratic curve approximated by the approximating means becomes a predetermined value. The values of corresponding points on the two quadratic curves obtained by multiplication are averaged by the main scanning correction data calculating means to calculate shading correction data in the main scanning direction, and are calculated by the main scanning correction data calculating means. Main scanning direction The shading correction unit performs shading correction in the main scanning direction on the light amount detected by the light amount detection unit based on the shading correction data, and the shading correction unit corrects shading in the main scanning direction. A quadratic curve passing through an intermediate value obtained from the maximum value and the minimum value of the respective light amounts on the three lines is determined by the quadratic curve determining means,
The shading correction data in the sub-scanning direction is calculated by multiplying each value by the sub-scanning data calculating means so that the peak value of the quadratic curve determined by the quadratic curve determining means becomes a predetermined value.

Further, according to the present invention, the surface shading correction means approximates the light quantity distribution detected by the light quantity detection means to the quadratic curve by the approximation means line by line in the main scanning direction and at the same time in the sub-scanning direction. For each line, a quadratic curve is approximated by the approximating means, and all the approximated values are scaled by the geometric scaling means so that the peak value of the values obtained by the approximating means becomes a predetermined value.

[0024]

Embodiments of the present invention will now be described in detail with reference to the drawings.

First Embodiment FIG. 1 shows a first embodiment of the present invention. This is an example of a microfilm reading system, the appearance of which is shown in FIG.

The microfilm reading system of this embodiment comprises a reader for reading a microfilm, a keyboard 39 for operating the reader, and a printer 11 for forming an image based on image information from the reader.

FIG. 3 shows the configuration of the reader shown in FIG.

In FIG. 3, reference numeral 32 denotes a carrier, which holds the microfilm. An illumination lamp 30 irradiates the microfilm held by the carrier 32.

A projection lens 33 can change the projection magnification. The projection lens 33 is an interchangeable lens (with different projection magnification) or a zoom lens. Reference numeral 34 is a prism for rotating an image placed vertically or horizontally. The prism 34 can be rotated every 45 degrees, and by rotating it every 45 degrees, the image can be rotated by 90 degrees, and the direction according to the image information can be selected. 37 is a screen, the size of which can be projected vertically or horizontally. The image information on the microfilm is written vertically or horizontally, and it is extremely rare that the information is written obliquely. Since the carrier 32 is rotatable, the prism 34 should be configured to rotate every 45 degrees. Is enough.

An optical system is constituted by the projection lens 33, the prism 34, the first mirror 35, and the second mirror 36, and the transmitted light of the microfilm is transmitted to the screen 3 by this optical system.
7, the image is enlarged and projected on the screen 37.

An image sensor 1 includes an amplification amplifier and an A / D converter, and scans a projection image plane 38 formed on the second mirror 36 which is moved by operating a keyboard 39 to read image information. Is. Output of the image sensor 1 is started by a start signal synchronized with the main scanning synchronization signal from the printer 11, and the image signal is sent out in synchronization with the drive signal. Reference numeral 21 denotes an image processing board on which an image from the image sensor 1 is processed.

FIG. 1 shows the configuration of a shading correction circuit on the image processing board 21 shown in FIG. In FIG. 1, 1 shows the same part as FIG. 2, and 11 shows the same part as FIG.
A main scanning memory 2 is for storing shading correction data in the main scanning direction. A main scanning direction correction unit 3 performs shading correction in the main scanning direction. A main scanning selection unit 12 sends the image signal from the image sensor 1 to the main scanning memory 2 in the shading data fetching mode, and to the main scanning direction correction unit 3 in the case of actually performing shading correction. To
The destination is selected. 8 is a main scanning counter,
This is for detecting the position of the image information from the image sensor 1 in the main scanning direction. The count value of the main scanning counter 8 is cleared by the start signal, and the count operation is performed by the drive signal.

Reference numeral 4 is a sub-scanning memory for storing shading correction data in the sub-scanning direction. 5
Is a sub-scanning direction correction unit that performs shading correction in the sub-scanning direction. A sub-scanning selection unit 13 selects a destination so that the sub-scanning data is sent to the sub-scanning memory 4 in the shading data acquisition mode, and to the sub-scanning direction correction unit 5 when the shading correction is actually performed. .. A sub-scanning counter 9 detects a position in the sub-scanning direction. The sub-scanning counter 9 is the image sensor 1
Is cleared by a signal from a home position sensor (not shown) that detects the home position of the device, and a signal that drives a stepping motor (not shown) that moves the image sensor 1 in the sub-scanning direction is synchronized with the start signal. Performs count operation. Reference numeral 14 denotes a counter selection unit for switching the signal for switching the address of the sub-scanning memory 4 to either the output of the main scanning counter 8 or the output of the sub-scanning counter 9.

An image processing unit 10 is a sub-scanning direction correction unit 5.
Various kinds of image processing are performed on the output from. Reference numeral 16 is a switch for taking in shading correction data.

As shown in FIG. 4, a control / data processing unit 15 has a CPU 151, a ROM 152, and a RAM 153, and a data bus and an address bus (including control signals for read / write, etc.) are used for the main scanning memory 2. , The sub-scanning memory 4, the main-scanning selection unit 12, the sub-scanning selection unit 13, and the counter selection unit 14.

The CPU 151 fetches the shading data by the signal from the switch 16 and controls the main scanning memory 2, the sub scanning memory 4, the main scanning selecting section 12, the sub scanning selecting section 13 and the counter selecting section 14. To do. The ROM 152 stores a shading correction data processing program. RAM153 is a CPU
151 for shading correction data processing work.

Next, the operation for obtaining the shading correction data will be described.

Here, it is assumed that the image signal and the shading correction data are n [bit] digital signals.

After setting the projection lens 33, the prism 34, etc. in the print state, the microfilm on the carrier 32 is retracted out of the optical path. At this time, it is desirable to exclude dust and the like in the optical path as much as possible. In this state, the switch 16 for taking in the shading correction data is operated. The lighting voltage of the illumination lamp 30 has a peak value of (2 ⁿ −1) [DEC] until the characteristic of the light amount distribution of the projection image forming surface 38 can be understood until the shading correction data is captured. ] Stabilize within a range not exceeding.

First, the operation for obtaining the main scanning correction data will be described.

On the projection image plane 38, in order to find the position where the light amount in the sub-scanning direction shows a peak, the control / data processing unit 15 uses the data of (2 ⁿ -1) [DEC] for the main scanning. It is written in the memory 2 so that shading correction in the main scanning direction cannot be performed. Further, the sub-scanning selection unit 13 is switched so that the data from the image sensor 1 is output to the sub-scanning memory 4, and the sub-scanning memory 4 operates according to the output of the sub-scanning counter 9. ..

In this state, the iso-light amount line of the projection image plane 38 is a concentric ellipse centered on the coordinates (x, y) = (α, β) as shown in FIG. The long axis corresponds to the sub scanning direction, and the short axis corresponds to the main scanning direction.
The central coordinates (α, β) of the light amount distribution and the size of the light amount distribution curve (hereinafter referred to as a shading curve) on a certain line are set by changing the projection magnification of the projection lens 33 or rotating the prism 34 by 45 degrees. In this case, although it may change, it is still a concentric ellipse whose major axis and minor axis coincide with the main scanning direction or the sub scanning direction. The shading curve is the weakest on the major axis or the minor axis, and becomes steeper as it goes away from the major axis and the minor axis.

Then, the projection image plane 38 is scanned by the image sensor 1. An arbitrary line in the sub-scanning direction on the projection image plane 38, for example, a line passing through the center of the projection image plane 38 is defined as a line D (see FIG. 5), and the data of the light amount distribution on the line D is used for the sub scan. Capture in memory 4. Then, control the shading curve consisting of the light intensity distribution data.
The data processing unit 15 approximates a quadratic curve to obtain the y coordinate (y = β) on the line D corresponding to the peak light amount, and stores it in the external storage device. As described above, the light amount distribution on the projection image plane 38 is a concentric ellipse whose major axis and minor axis coincide with the main scanning direction or the sub scanning direction, so that the y coordinates of the peak positions of all the lines in the sub scanning direction are equal. .. The shading curve corresponding to the line in the main scanning direction that passes y = β (hereinafter referred to as line A) is the gentlest.

Next, the main scanning selection unit 12 is switched,
Data from the image sensor 1 is sent to the main scanning memory 2, the projection image plane 38 is scanned by the image sensor 1, and the scanning start end (hereinafter referred to as line B) of the projection image plane 38, line A , And the data of the light amount distribution for one line at the end end (hereinafter, referred to as line C) are loaded into the main scanning memory 2. Here, the main scanning memory 2 is a RAM whose upper 2 bits are switched by the control / data processing unit 15, and the address area is switched according to the position of the line for fetching data.
Each area switched by the control / data processing unit 15 has a sufficient capacity to store one line of data of the image sensor 1.

FIG. 7 shows an example of the light amount distributions on the obtained lines A, B and C. As can be seen from FIG. 7, the shading curve of line A is the gentlest, and the shading curve of either line B or line C is the steepest.

When the data acquisition in each line is completed, the main scanning selection unit 12 is switched so that the data is output to the main scanning direction correction unit 3. Also,
Controls the data captured in the main scanning memory 2
The data processing unit 15 processes each line as follows.

(1) The shading curve corresponding to the lines A, B and C is approximated by a quadratic curve. Here, the second-order approximated lines A, B, and C shown in FIG.
Define as in (4).

[0048]

## EQU00002 ## Line A: z _A = A _A1 x ² + B _A1 x + C _A1 = A _A2 (x-α) ² + γ _A (2) Line B: z _B = A _B1 x ² + B _B1 x + C _B1 = A _B2 (X-α) ² + γ _B (3) Line C: z _C = A _C1 x ² + B _C1 x + C _C1 = A _C2 (x-α) ² + γ _C (4) (2) Obtained by quadratic curve approximation The obtained light amount distribution data is multiplied by an equal ratio so that the peak value becomes (2 ⁿ −1) [DEC], and each value on the quadratic curve obtained is stored in the original memory 2 for main scanning. Write in the area. The quadratic approximation formula of the curve obtained by multiplying the geometric ratio is defined as the following formulas (5) to (7).

[0049]

## EQU00003 ## Line A: z _{A (P = limit)} = A _A3 (x−α) ² + (2 ⁿ −1) (5) Line B: z _{B (P = limit)} = A _B3 (x− α) ² + (2 ⁿ -1) (6) Line C: z _{C (P = limit)} = A _C3 (x-α) ² + (2 ⁿ -1) (7) (3) Line B and In order to determine which of the lines C has a steeper shading curve, the light amount distribution data of the lines B and C corresponding to the same bit of the image sensor 1 (stored in the main scanning memory 2).
Are compared by the control / data processing unit 15, and the line having the smaller value is determined as the line having a sharp shading curve. That is, the absolute value of A _B3 in equation (6) and A in equation (7)
The absolute values of _C3 are compared, and the one with the larger absolute value is used as the sharp shading curve. The selected line is set as the line BC (see FIG. 8), and the selected line BC
_{Let the} quadratic term coefficient of A _BC3 .

Then, in order to obtain the main scanning correction data, the quadratic term coefficient A _A3 of the line A and the quadratic term coefficient A of the line BC are obtained.
_The main scanning correction data is defined as follows using _BC3 .

[0051]

Equation 4] main scanning correction data: the _{z H = H SH (x-} α) 2 + (2 n -1) ... (8) where the second order term coefficient H _SH in the main scanning direction corrected data

[0052]

[Formula 5] H _SH = (A _A3 + A _BC3 ) / 2 (9)

(4) After obtaining the main scanning correction data, the average value of the data corresponding to the same bit of the image sensor 1 is obtained for the line A and the line BC (see FIG. 9). Is written as main scanning shading correction data in an area of the main scanning memory 2 that is selected when actual correction is performed.

Next, main scanning shading correction is performed on the light amount distribution of the projection image plane 38 based on the obtained main scanning correction data, and each line for which the main scanning direction shading correction has been performed and the initials of its coefficient are indicated by "H". To do.

The shading curves of the lines A, B and C after shading correction in the main scanning direction are

[0056]

[Formula 6] Line A: Hz _A = HA _A1 x ² + HB _A1 x + HC _A1 = HA _A2 (x-α) ² + Hγ _A (10) Line B: Hz _B = HA _B1 x ² + HB _B1 x + HC _B1 = HA _B2 (X-α) ² + Hγ _B (11) Line C: Hz _C = HA _C1 x ² + HB _C1 x + HC _C1 = HA _C2 (x-α) ² + Hγ _C (12) The peak value is (2). The shading curves of the lines A, B, and C, which are all scaled so as to be ⁿ −1) [DEC], are

[0057]

Equation 7] Line _{A: Hz A (P = limit} ) = HA A3 (x-α) 2 + (2 n -1) ... (13) Line _{B: Hz B (P = limit} ) = HA B3 (x- α) ² + (2 ⁿ −1) (14) Line C: Hz _{C (P = limit)} = HA _C3 (x−α) ² + (2 ⁿ −1) (15)

If the quadratic term coefficient of line BC (P = limit) is HA _BC3 , the quadratic term coefficient of line A (P = limit) HA ₃ is:

[0059]

[Formula 8] HA ₃ = -HA _BC3 (16). This is the maximum value MAX when the above-mentioned processes (1) and (2) are applied to the shading curve of the line A when the main scanning shading correction is performed.
Represents that the difference between the minimum value MIN and the minimum value MIN is equal to the difference between the maximum value MAX and the minimum value MIN when the shading curve of the line BC is subjected to the processes (1) and (2) (FIG. 10). reference).

Next, the operation for obtaining the sub-scanning correction data will be described.

After obtaining the main-scanning correction data, the sub-scanning selection section 13 is switched so that the data is output to the sub-scanning memory 4 while maintaining the setting of the optical system. It operates according to the output of the main scanning counter 8. At this time, the address of the sub-scanning memory 4 has its upper 2 bits controlled by the control / data processing unit 15 and the other bits controlled by the main scanning counter 8.

In this state, the projection image plane 38 is scanned again by the image sensor 1. The light amount distribution data of the projection image plane 38 is subjected to shading correction in the main scanning direction by the main scanning direction correction unit 3 based on the main scanning correction data stored in the main scanning memory 2, and the main scanning direction shading is performed. The corrected light amount distribution data on the lines A, B, and C is stored in the sub-scanning memory 4. At this time, the control / data processing unit 15 switches the address area of the sub-scanning memory 4 in accordance with the position of the line. Each area selected by the control / data processing unit 15 in the sub-scanning memory 4 has a sufficient storage capacity for both main scanning line data and sub-scanning one line data. Be present.

After the main scanning direction shading-corrected light amount distribution data on the lines A, B, and C has been taken into the sub-scanning memory 4, the output of the main scanning direction correction unit 3 is changed to the sub-scanning direction correction unit. The sub-scanning selection unit 13 is switched so as to be sent to No. 5. Next, sub-scanning memory 4
The control / data processing unit 15 processes the light amount distribution data taken in by each line as follows.

A quadratic curve is approximated to the light amount distribution data on the lines A, B, and C that have undergone shading correction in the main scanning direction, and each value on the quadratic curve obtained is sub-scanned by the memory 4 for sub-scanning.
The original area is overwritten (see FIG. 11).

(5) The maximum value MA of these light amount distribution data
Intermediate value M for each line A, B, C from X and minimum value MIN
Ask for an ID.

(6) Intermediate value MI for line B and line C with the intermediate value MID for line A as a peak
A quadratic curve passing through D is obtained (see FIG. 12). The obtained quadratic curve is defined by the following equation.

[0067]

Z _V = A _V1 x ² + B _V1 x + C _V1 = A _V2 (y-β) ² + δ (17) (7) The peak value is (2 ⁿ -1) for the obtained quadratic curve.
The whole is multiplied by the same ratio so as to become [DEC], and the obtained quadratic curve is used as the sub-scanning correction data (see FIG. 13).

[0068]

Sub-scanning correction data: z _v = A _v3 (y-β) ² + (2 ⁿ -1) (18) Then, this data is selected when actually correcting in the sub-scanning memory 4. The data is written in the area to be written, and the creation of shading correction data in both scanning directions is completed.

When the shading correction in the sub-scanning direction is performed by the sub-scanning correction data, the line A and the line B are
The intermediate value MID of C becomes equal. As described above, between the quadratic term coefficients when the shading curves after the main scanning correction of the line A and the line BC are quadratic-approximated,

[0070]

Since there is a relation of HA ₃ = −HA _BC3 (19), when the shading correction is performed using the above-described shading correction data in both scanning directions, the maximum value MAX and the minimum value MAX of both lines are obtained. The MINs are almost equal to each other (see FIG. 14).

Next, the shading correction operation will be described.

The image information G (x, y) read by the image sensor 1 is synchronized with the timing at which it is output to the main scanning direction correction section 3, and the main scanning correction data H of 8 bits is read from the main scanning memory 2. (X) is sent to the main scanning direction correction unit 3. However, x is the value of the main scanning counter 8 and y is the value of the sub-scanning counter 9.

Then, the main scanning direction correction unit 3 performs main scanning correction on the image information G (x, y) and the main scanning correction data H (x) according to the following equation (20).

[0074]

AH (x, y) = G (x, y) / H (x) × (2 ⁿ −1) (20) The output AH (x, y) from the main scanning direction correction unit 3 is a sub When input to the scanning direction correction unit 5, the sub-scanning correction data V (y) is synchronized with the sub-scanning direction correction unit 5 from the sub-scanning memory 4.
And the sub-scanning correction is performed based on the following equation (21).

[0075]

AHV (x, y) = AH (x, y) / V (y) × (2 ⁿ −1) (21) Equation (20) is obtained by substituting Equation (20) into Equation (21). 22)
Accordingly, the output of the image sensor 1 is subjected to shading correction in the main scanning direction and the sub scanning direction.

[0076]

AHV (x, y) = (G (x, y) / H (x) × (2 ⁿ −1))) / V (y) × (2 ⁿ −1) (22) Sub-scan The output AHV (x, y) of the direction correction unit 5 is sent to the image processing unit 10 to be subjected to various image processing, and the printer 1
It is output to 1.

In this embodiment, since the shading correction is carried out by the main scanning correction data and the sub scanning direction correction data obtained by the above-mentioned method, the projection image plane 38 is formed.
The shading at is almost minimal. Further, since both shading correction data are quadratic curves in contact with (2 ⁿ −1) [DEC], as can be seen from the formula (22), the number of gradations is reduced in the central portion of the projection image plane 38 due to the shading correction. It is possible to reduce the reduction in the number of gradations due to the shading correction even in the entire image.

Second Embodiment In this embodiment, the RAM 153 stores the y-coordinate (y = β) on the line D corresponding to the peak light amount, and the lines A,
The shading curves of B and C are quadratic-approximated, and the peak value is (2 ⁿ −1) for the obtained light amount distribution data.
The maximum value M of the light intensity distribution data is stored by storing the quadratic term coefficient of a quadratic curve obtained by multiplying the whole by the same ratio so as to be [DEC].
The intermediate value MIN for the lines A, B and C obtained from AX and the minimum value MIN is stored. Also, line A
A quadratic curve passing through the intermediate value MID for the line B and the line C with the intermediate value MID for the peak as the peak is obtained, and the peak value is (2 ⁿ −1) [DE
C], and the quadratic coefficient of the obtained quadratic curve is stored.

Therefore, the main scanning memory 2 only needs to have a capacity for storing data for one main scanning line, and the sub scanning memory 4 has data for one main scanning line.
Alternatively, it suffices to have a capacity capable of storing one of the data for one sub-scanning line having a large data amount.

In this embodiment, since this is done, the operational effects are essentially the same as those of the first embodiment.

In this embodiment, the shading curves of the lines A, B and C are approximated by a quadratic curve, and the obtained light amount distribution data has a peak value of (2 ⁿ -1) [DEC].
The quadratic term coefficient of the quadratic curve obtained by multiplying the whole by equal ratio is stored in the RAM 153. However, the quadratic curve is determined when the coordinates of three independent points are determined.
M153 has three independent values on the quadratic curve, for example,
The values at both ends and the center may be stored.

Third Embodiment FIG. 15 shows a third embodiment of the present invention.

15, the same parts as those in FIG. 1 are designated by the same reference numerals. Reference numeral 17 denotes a surface correction memory which has a capacity capable of recording the values of all the pixels of the projection image forming surface 38 and operates according to the values of the main scanning counter 8 and the sub scanning counter 9. Reference numeral 18 denotes a surface shading portion, which is the image sensor 1
The image shading correction is performed based on the shading correction from the surface correction memory 17. Reference numeral 19 denotes a selection unit, which converts the image data from the image sensor 1 into the surface correction memory 17 or the surface shading unit 18.
One of the two is switched.

Next, the operation will be described.

The selection unit 19 is switched to switch the image sensor 1
The output from is output to the surface correction memory 17. The projection image plane 38 is scanned by the image sensor 1 and the light amount distribution data is loaded into the plane correction memory 17,
When the capturing is completed, the selection unit 19 is switched so that the data is sent to the surface shading unit 18.
Then, control the data in the surface correction memory 17
The data processing unit 15 processes as follows.

The quadratic curve approximation is performed for each data of one line of the main scanning, and the result of the quadratic curve approximation is sequentially overwritten in the surface correction memory 17. Next, the data in the surface correction memory 17 is subjected to quadratic curve approximation for each line in the sub-scanning direction, and the results of the quadratic curve approximation are sequentially applied to the surface correction memory 1.
Overwrite to 7.

A peak value is obtained from the data in the surface correction memory 17, and all the correction data are multiplied by the same ratio so that the peak value becomes 255 [H]. The shading correction data obtained in this way takes a continuous and uniform value in the main scanning direction and the sub-scanning direction, respectively, and becomes close to the light amount distribution without the influence of dust in the optical path. It is possible to minimize the decrease in the number of gradations due to shading correction.

[0088]

As described above, according to the present invention,
With the above configuration, it is possible to minimize the decrease in the number of gradations due to shading correction.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an appearance of a microfilm reading system.

FIG. 3 is a cross-sectional view showing the structure of the reader shown in FIG.

FIG. 4 is a block diagram showing a configuration of a control / data processing unit 15 shown in FIG.

5 is a diagram showing an example of a light amount distribution on a projection image plane 38. FIG.

FIG. 6 is a diagram showing isolight lines on a projection image plane 38.

FIG. 7 is a diagram showing an example of shading curves corresponding to lines A, B, and C.

FIG. 8 is an explanatory diagram illustrating a method of obtaining a line BC.

FIG. 9 is a diagram showing an example of main scanning correction data.

FIG. 10 is a diagram showing an example of shading curves corresponding to lines A and BC after main scanning shading correction.

FIG. 11 is a diagram showing an example of lines A, B, and C after shading correction in the main scanning direction.

FIG. 12 is a diagram showing an example of a quadratic curve passing through an intermediate value MID.

FIG. 13 is a diagram showing an example of sub-scanning correction data.

FIG. 14 is a diagram showing an example of a light amount distribution curve corresponding to lines A, B, and C after shading correction.

FIG. 15 is a block diagram showing a third embodiment of the present invention.

FIG. 16 is a block diagram showing a configuration of an example of a conventional image reading apparatus.

FIG. 17 is a block diagram showing the configuration of another example of the conventional image reading apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 image sensor 2 main scanning memory 3 main scanning direction correction unit 4 sub scanning memory 5 sub scanning direction correction unit 8 main scanning counter 9 sub scanning counter 10 image processing unit 11 printer 12 main scanning selection unit 13 sub scanning selection Part 14 counter selection part 15 control / data processing part 16 switch

Claims (2)

[Claims] 1. A light amount detecting means for detecting the light amount on the projection image forming surface by sub-scanning and main scanning the projection image forming surface, and surface shading correction based on the light amount distribution detected by the light amount detecting means. In an image reading apparatus having a surface shading correction unit, the surface shading correction unit includes a first light amount distribution curve on a first line of a line in the main scanning direction that passes through a maximum light amount point detected by the light amount detection unit, The second light quantity distribution curve having the smaller curvature of the light quantity distribution curves on the second and third lines parallel to the first line and along the front end and the rear end of the projection image plane is 2 respectively.
Approximating means for approximating a quadratic curve, and a geometrical multiplication that equalizes all the values on the quadratic curves so that the peak value on the quadratic curve obtained by approximation by the approximating means becomes a predetermined value. Means and a main scanning correction data calculating means for calculating shading correction data in the main scanning direction by averaging values of corresponding points on two quadratic curves obtained by the geometric multiplication by the geometric ratio multiplying means. A shading correction unit that performs shading correction in the main scanning direction with respect to the light amount detected by the light amount detection unit based on the shading correction data in the main scanning direction calculated by the main scanning correction data calculation unit; Secondary that passes through the intermediate value obtained from the maximum value and the minimum value of the respective light amounts on the first, second, and third lines whose shading in the main scanning direction has been corrected Secondary curve determining means for determining a curve, and shading correction data in the sub-scanning direction by multiplying each value so that the peak value of the secondary curve determined by the secondary curve determining means becomes a predetermined value. An image reading apparatus comprising: a sub-scanning data calculating unit that calculates 2. A light amount detecting means for detecting a light amount on the projection image forming surface by sub-scanning and main scanning the projection image forming surface, and surface shading correction based on the light amount distribution detected by the light amount detecting means. In the image reading apparatus having the surface shading correction unit, the surface shading correction unit approximates a quadratic curve line by line in the main scanning direction with respect to the light amount distribution detected by the light amount detection unit,
Approximating means for performing quadratic curve approximation line by line in the sub-scanning direction, and a geometric ratio multiplying means for equalizing all approximate values so that the peak value of the values obtained by the approximation by the approximating means becomes a predetermined value. An image reading apparatus comprising: