JPH03211962A - Digital picture reader - Google Patents

Abstract

PURPOSE:To obtain picture data, which detection sensitivity is exactly corrected, even when generating the dispersion of illuminance corresponding to the distribution of a reflection factor on the surface of an original by providing plural illuminance detecting means to detect the illuminance at respective scanning positions and compensating the density of the picture data based on the result of the detection. CONSTITUTION:An exposing means 21 is provided to expose the surface of the original to be arranged at a prescribed picture read position and a picture read means 5 is provided while being faced to the picture read position so that plural read cells can be arranged in one line along a prescribed axis at least. Plural illuminance detecting means 6A are provided at the mutually various positions in the axial direction of the picture read means 5, and a picture correcting means is provided to correct information to be outputted by the picture read means 5 based on the illuminance detected by the respective plural illuminance detecting means 6A. Thus, the distributing state of the illuminance in the axial direction is detected and the output data (density) of the picture read means is compensated so as to cancel the dispersion of the illuminance. Then, the dispersion of the detection sensitivity is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to digital image reading devices, and particularly to compensation for variations in reading sensitivity depending on differences in reading positions.

[Prior Art] Generally, in a digital image reading device, the surface of the document is exposed to light using a light source such as a fluorescent lamp, and the light reflected from the document is converted into CO2.
Light is received by an image sensor such as D, and the density distribution corresponding to the light reflectance of the document surface at each pixel position, that is, the document image, is read as a one-dimensional or two-dimensional pixel data array. When using a -dimensional image sensor, a two-dimensional image is obtained by further combining it with a mechanical scanning mechanism and sequentially reading one-dimensional images of each line while moving the reading position in the sub-scanning direction.

However, in this type of device, the amount of light emitted by the light source, the detection sensitivity of each of the many detection cells incorporated in the image sensor, and variations in the light transmission characteristics of the optical system (lenses, mirrors, etc.) depending on the position, etc., affect the reading of the device. This appears as variations in sensitivity. In particular, variations in the sensitivity of each cell of the image sensor have a large negative effect on the quality of the read image. Therefore, in this type of apparatus, sensitivity compensation called shading correction has been conventionally performed.

- For casual shading correction, a reference density plate with uniform light reflectance over the entire surface is placed near the scanner's home position, and the reflected light from the reference density plate is imaged immediately before starting to read the image. The sensor reads the image, sets a correction coefficient for each pixel position based on the result, and reads the image and outputs the read data while correcting the density according to the set correction coefficient.

[Problems to be Solved by the Invention] Even when performing conventional shading correction, it is possible to accurately compensate for variations in detection sensitivity specific to the device. However, even though this type of shading correction is performed, variations in detection sensitivity may occur depending on the reading position.

This variation in detection sensitivity is caused by the density distribution of the original. In other words, the light reflected from the document surface is irradiated onto the surrounding area, and a portion of that light is reflected from the surface and interior of the light source, mirrors, etc., and reaches the document surface again, and this secondary reflected light is reflected from the document surface. Since it affects the illuminance, variations occur in the illuminance distribution depending on the magnitude of the light reflectance on the document surface, that is, the distribution of the density of the image, and this appears as a variation in detection sensitivity depending on the reading position. Since this variation does not appear when reading a reference density plate with uniform light reflectance over the entire surface, it is impossible to remove it using conventional shading correction.

Note that this kind of variation in illuminance distribution appears particularly when a fluorescent lamp (aperture type) is used as a light source for illumination.

Therefore, it is an object of the present invention to realize accurate image reading by compensating for variations in illuminance distribution caused by differences in light reflectance on the surface of a document.

[Means for Solving Problem i1] In order to solve the above problem, the present invention provides an exposure means for exposing the surface of a document placed at a predetermined image reading position; placed opposite to the image reading position. an image reading means in which a plurality of reading cells are arranged in at least one row along a predetermined axis; the image reading means is arranged at mutually different positions in the axial direction; a plurality of illuminance detection means; and an image correction means for correcting information output by the image reading means based on the illuminance detected by each of the plurality of illuminance detection means;
will be established.

[Operation] According to the present invention, since the plurality of illuminance detection means are arranged at mutually different positions in the direction of the reading axis of the image reading means, it is possible to detect the distribution state of illuminance in the axial direction.

Therefore, if variations occur in the illuminance distribution due to differences in the reflectance of the document surface, this can be detected and the output data (density) of the image reading means can be compensated to offset the variations in illuminance. Variations in sensitivity can be eliminated. Of course, if it is combined with conventional shading correction, it is possible to compensate for variations in detection sensitivity inherent in the device.

Other objects and features of the present invention will become clear from the following description of embodiments with reference to the drawings.

[Embodiment] FIG. 2 shows the main parts of the mechanism of one type of image scanner that implements the present invention. This will be explained with reference to FIG. Contact glass 1 is transparent, and an original is placed on it with the image surface facing down. An optical scanning system 2 is provided below the contact glass l. Optical scanning system 2
The exposure lamp 21. Opposing reflector plate 22. 1st mirror 2
3. Second mirror 24. Third mirror 25. It is equipped with a shading correction plate 2G and a lens 27, which exposes the original and guides reflected light from the original to the reading surface of the image sensor IMS of the reading unit 5. Image sensor IMS is
It is a -dimensional CCD image sensor and includes a large number of reading cells arranged in a line in a direction perpendicular to one drawing.

In order to read a two-dimensional image, the optical scanning system 2 is mechanically driven and scanned in the lateral direction of the drawing by an electric motor (not shown). Exposure lamp 21. The opposing reflector 22 and the first mirror 23 are mounted on the first carriage, and the second mirror 24 and the third mirror 25 are mounted on the second carriage. It is scan driven at twice the speed of the carriage.

The home position of the optical scanning system 2 is a state in which the reading position is at the right end of the contact glass l, and the optical scanning system 2 starts scanning from this home position toward the left, and when it reaches a predetermined reading end position, it starts scanning again. Return to home position. A reference density plate 4 is arranged at the right end of the contact glass 1 (slightly to the left of the home position of the optical scanning system 2). The reference density plate 4 is a thin plate elongated in the direction perpendicular to the drawing, and one surface of the plate is uniformly colored with white at a predetermined density. This reference density plate 4 is used as a standard for compensating for variations in image reading sensitivity due to characteristics specific to this device, for example, variations in sensitivity between reading cells of the image sensor IMS, and is used as a reference before starting image reading. image sensor IMS via optical scanning system 2
is read.

In this example, the exposure lamp 21 is composed of a cylindrical fluorescent lamp, and the longitudinal direction of the fluorescent lamp is oriented perpendicular to the plane of the drawing. FIG. 3 shows an enlarged view of the vicinity of the exposure lamp 21, and FIG. 4 shows the state seen from below in FIG.

Referring to FIGS. 3 and 4, in this example, three sets of optical sensors 6A.

6B and 6C are arranged with their detection surfaces facing the exposure lamp 21. Immediately before the detection surface of each optical sensor,
Each has a slit-shaped pinhole (7A a
) are arranged on light shielding plates 7A, 7B and 7C. The reason for providing these light shielding plates is that each optical sensor detects only light in a relatively narrow area, thereby increasing the resolution of illuminance distribution detection. Three sets of optical sensors 6A.

6B and 6C are arranged so that the distances from the exposure lamp 21 are equal to each other. In addition, the illuminance reading positions of the three sets of optical sensors are set at three locations, as shown in Figure 5, at the center of the effective image reading range (of the image sensor) and at both ends of the range in the width direction. .

FIG. 1 shows a circuit for compensating the image detection sensitivity of this device. This will be explained with reference to FIG. Optical sensor SA, SB
and SC each incorporate optical sensors 6A, 6B, and 6C shown in FIG. 4, and detect the amount of light from the exposure lamp 21 at each position. Each light amount sensor is configured as shown in FIG. 6, and includes photodiodes PD (6A, 6B, s
The signal output from (corresponding to
is converted into digital illuminance data.

Note that the resistance value of the variable resistor VR connected to the operational amplifier OP is adjusted in advance so that the detection sensitivities of the three sets of light amount sensors SA, SB, and SC are the same.

Illuminance data D2, Da output from each light amount sensor.

D4 and preset fixed value data D1 and D5 are simultaneously input to the data selector 31. Data selector 3
1 sets four of the five sets of input values D1 to D5 to Da,
Db, DC, and Dd are input to each address input terminal of ROM (read-only memory: hereinafter the same) 32, 33, 34, and 35, respectively. Which input value the data selector 31 outputs as each output data is determined by the value X output by the counter 37. Also,
The value X output by the counter 37 is simultaneously applied to the remaining address input terminals of the ROMs 32-35.

The counter 37 is configured to start counting pixel clock pulses CLK in synchronization with the scanning line synchronization signal L5ync, and the value X outputted by this counter 37 is the scanning pixel position (X coordinate) in the main scanning direction at that time. It corresponds to R
The data output by each of OM32 to OM35 is sent to adder 36.
and is input to the ROM 38 as illuminance data. Simply put, the illuminance data output by the adder 36 is the illuminance data at the current position (X) obtained by interpolation calculation based on the input data D a = D d.

On the other hand, the image data (pixel density) detected by the image sensor IMS is applied to the remaining address input terminals of the ROM 38. The ROM 38 stores in advance pixel density values corrected according to the illuminance data in different memory addresses for all combinations of each illuminance value and each pixel density value, and stores image data and illuminance data in advance. By giving it as an address value, the data stored at that address is output as a calculation result, that is, as a corrected density value.

Variations in detection sensitivity based on characteristics unique to this device, such as variations in sensitivity between reading cells of the image sensor IMS, are corrected by the ROM 40 in the next stage. In this correction, the result of reading the density of the reference density plate 4 mentioned above is used. The density of the reference density plate is determined by the image sensor IMS.
The signal is read by the ROM 38 and applied to a data input terminal of a RAM (read/write memory) 39. In this case, the system control unit 41 sets the RAM 39 to a writing state, so that each memory address of the RAM 39 stores density value data obtained by reading each position on the reference density plate 4.

At the timing of reading the original image, the system control unit 41 sets the RAM 39 to a reading state. Therefore, the RAM 39 reads the calibration density value of the reference density plate 4 stored at the memory address corresponding to the current scanning position (x).
Apply to one address terminal of OM40. At the same time, the image data output from the ROM 38 is applied to the remaining address input terminals of the ROM 40.

The ROM 40 performs calculations to compensate for variations (differences between each data stored in the RAM 39) in the detection sensitivity (reference density value) in the main scanning direction detected when reading the density of the reference density plate 4. The results are stored in advance in different memory addresses for each combination of all the image density values and all the reference density values, and by applying the image density values and the reference density values to the address terminals at the same time, The result of the calculation, that is, the image density value at each position with sensitivity variations compensated for, is immediately output as output data.

Next, a supplementary explanation will be provided regarding the principle of density compensation processing in the circuit shown in FIG.

In the image scanner shown in Fig. 2, the image sensor I
The correlation between the image density value S (x) detected by the MS and the reflectance T (X) of the document surface is expressed by the following equation (1) (%) (1) AI (x): of the optical scanning system. Mirror reflectance A2 (X)
: Lens characteristics of the optical scanning system B(x) : Lens characteristics correction coefficient (shading correction plate eC(x) : Sensitivity L1 (X, t,, T) of each cell of the image sensor : Illuminance L2 (x, t, T): Light incident from outside the optical path (flare) In equation (1), the device can be configured so that the term L2 (x, t, r) becomes zero, so From now on, we will ignore it.Also, A1(x)
.

A2 (X), B(X), and C(x) do not change over time and are characteristics unique to the device, so by multiplying each position by a specific constant, variations in sensitivity can be eliminated. can be compensated as such. This compensation is processed by the ROM 40 in FIG. 1 based on the reference density value obtained from the reference density plate 4 in this embodiment.

Here, if the reflectance of the reference density plate is Tref (constant) and the reference density obtained by reading it is 5ref(x), then the image density value S' (X) after compensation is given by the following equation (2). It is expressed by the formula.

S'(x)=S(x)/5ref(X)=11
(x, t, T)T(x)/Lref(x, to, To)
-Tref - (2) However, tO: Time when reading the reference density plate TO = Density of the part where reflected light enters the fluorescent lamp (reference density plate,
mHere, if we set T'(x)=T(x)/Tref,
The following formula holds true 6 S'(x)=T'(x)・Ll (x, t, T)/Lr
ef(x, to, To)T'(x)=S'(x)・L
ref(x, to, To)/L1 (x, t, T)...
・(3) In other words, T'(x) obtained by calculating equation (3)
is used as the compensation value D (X), then A of equation (1)
1 (X), A2 (X), B (X) and C (X)
It is possible to compensate for variations in sensitivity caused by

The above equation (3) can be transformed as follows.

D(x)=T'(x)=(S(x)/5ref(x))(Lref(x, t
o, To)/Lt (x, t, T)) = (S (x
)/L 1 (x, t, T))/ (S ref(x)
/Lref(x, to, To)...(4) Here, E
By setting (x)=S (x)/Lt (x, j, T), equation (4) can be transformed as follows.

D(x)=E(x)/Eref(x)・
...(5) Also, the illuminance L 1' (
x+C+T), the following equation holds true.

Ll' (x, t, T) = A - L 1 (x, t
, T) ... (6) However, A: constant Therefore, equation (4) can be transformed as follows.

D'(X)''(S(x)/Lt,,' (x, t,
, ding))/(Sref(x)/Lref' (x, to
, To)=E'(x)/E'ref(x
)” (S (x)/A −Lt (x, t, T))
/(Sref(x)/A-Lref(x, t, o, To
)=(S (x)/L1 (x mountain))/(Sref
(x)/Lref(x, to, To)=D(x)
...(7) Therefore, the compensation value D (x) is the illuminance L 1 ' detected at an arbitrary position.
The same can be applied to (x, t, T), and the illuminance detected by an illuminance sensor placed at an arbitrary position can be used to compensate for the image density value S (X). . However, there is a limit to the number of sensors that can actually be arranged, and it is not possible to arrange a sensor for detecting the illuminance at each pixel position X. Therefore, the illuminance data at each position X is interpolated based on the illuminance at several actually detected positions.

The illuminance L'x at one point Px corresponding to an arbitrary position X within the effective image range as shown in FIG.

It can be determined by the following interpolation calculation based on the illuminance data of surrounding specific points Pa, Pb, Pc, and PD.

L'x=(L'a-h(+y+Δx)+L'b-h(Δ
x)+L'c-h(σ-ΔX)+L'd-h(2σ-Δ
X))/(h(σ+Δx)+h (Δx)+h(a−Δ
X)+h(2σ-ΔX))
...(8) However, L'a: Illuminance t at point Pa, 'b: Illuminance at point pb L'c: Illuminance at point Pc L'd: Illuminance h at point Pd (): Interpolation of each point Coefficient Here, H (Δx) = h (Δx) / h (σ + Δx) + h (Δx)
+h(cy-Δx) +h(2a-ΔX)H(cr+
Δx)=h(σ+Δx)/h(cr+Δx)+h(Δx
)+h(cr-Δx)+h(2σ-ΔX) H(a-Δx)=h(σ-Δx)/h(cr+Δx)+
h(Δx) 10h(cr-Δx)+h(2σ-ΔX) H(2σ-Δx)=h(2cr-ΔX)/11((F+
Δx) 10h(Δx)+h(cr-Δx)+h(2σ-Δ
X)...If we set (9), equation (8) can be transformed as follows.

L'x=L'a-H(σ+Δx)+L'tyH(Δx)
+L'c-H(cr-Δx)+L'd-H(2σ-ΔX
)...(10) In other words, by using equation (10), any point Px can be determined based on the illuminance of the four points Pa, Pb, Pc, and Pd surrounding the Px point.
The illuminance can be found.

In the apparatus shown in FIG. 1, four of the illuminance D2 + Da s Da actually detected by the three light sensors and predetermined fixed values D1 and D5 are calculated as Pa, Pb, and Pb, respectively.
Illuminance Da corresponding to points Pc and Pd.

They are selected by the selector 31 as Db, Dc, and Dd. In other words, when the scanning position X is located between the light amount sensors SB and SC, D2 to D5 are selectively used, and when the scanning position Selectively use these four. Note that the fixed value D
1 and D5, values are experimentally determined and used so that the value determined by interpolation is close to the actual illuminance when the scanning position X is near the end.

ROMs 32, 33, 34 and 35 in FIG. 1 are L'a-H (cr+Δx) and L'b of equation (10), respectively
-H(ΔX), L'c-H(a-ΔxL and L'd
−H(2σ−Δs) is calculated as input illuminance (D
a-Dd) and the current scanning position X, and apply them to the input terminals of the adder 36, respectively. The adder 36 adds the four input values,
The result is output as illuminance data, that is, L'x in equation (10).

Note that in the device of the embodiment, three optical sensors 6A
, 6B, and 6G are arranged so that the distances from the exposure lamp are equal to each other, the intervals between them are set at equal intervals, and the detection sensitivities are also adjusted to be equal to each other.

The ROM 38 stores the input image data S (S) based on the illuminance (L'x) of the current position obtained by interpolation.
is compensated for, and the image data whose illuminance has been compensated is applied to the ROM 40.

On the other hand, the RAM 39 stores the illuminance correction result E of the data S ref(x) when reading the reference density of the reference density plate 4.
' ref (x) is written, and this data is read out corresponding to the scanning address X when reading the original image9.
It is applied to the address terminal of the ROM 40.

The ROM 40 stores the image data E' (x) whose illuminance has been compensated by the ROM 38 and the base 4! Concentration data E'ref (
x) and 'E'(x)/E're
The result of calculating f(x) is output as D(s).

[Effect] As described above, according to the present invention, a plurality of illuminance detection means (6
A, 6B, 6C) to detect the illuminance at each scanning position,
The density of the image data is compensated based on the result, so
Even when variations in illuminance occur depending on the distribution of reflectance on the document surface, image data whose detection sensitivity is accurately corrected can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a main part of a density compensation circuit of an image scanner implementing the present invention. 2 is a front view showing the image reading mechanism section of the apparatus shown in FIG. 1. FIG. Fig. 3 is a partially enlarged front view showing a part of Fig. 2, Fig. 4 is a bottom view showing the sensor layout seen from below in Fig. 3, and Fig. 5 is an image reading area and illuminance distribution. FIG. FIG. 6 is an electrical circuit diagram showing the configuration of one light amount sensor. FIG. 7 is a plan view showing the positional relationship between an arbitrary point and a point used for interpolation of illuminance at that point. 1: Contact glass 2: Optical scanning system 21: 11! Light lamp (exposure means) 22: Opposed reflecting plate 23, 24, 25: Mirror 26: Shading correction plate 27: Lens 4: Reference density plate 5: Reading units 6A, 6B, sc: Optical sensor (illuminance detection means) 7A,
7B, 7C: Light shielding plate 31: Data selectors 32 to 35, 40: ROM 36: Adder 37: Counter 38: ROM (image correction means) 3 9: RAM 41 System control unit SA, SB, SC: Light amount sensor

Claims (2)

[Claims] (1) Exposure means for exposing the surface of a document placed at a predetermined image reading position; an image in which a plurality of reading cells are arranged in at least one line along a predetermined axis, and is placed opposite to the image reading position; reading means; a plurality of illuminance detecting means disposed at mutually different positions in the axial direction of the image reading means; and information output by the image reading means based on the illuminance detected by each of the plurality of illuminance detecting means. A digital image reading device comprising: an image correction means for correcting; (2) The digital image reading device according to claim 1, wherein the illuminance detection means includes a light-shielding plate in which a small window is opened between the detection surface and the detection target.