JP2003032452A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove the influence upon an image caused by a shading correction defect in real time which occurs when dust or the like is sticking on a reference density board for shading correction. SOLUTION: In the device for applying a shading correction to data reading an original on the basis of data that read the reference density board having a uniform density while using a line sensor having a photoelectric transducer. The shading correction is applied to data that read the reference density board at a position displaced from a position to perform reading for the shading correction in a sub-scanning direction, an abnormal pixel is detected from the result. A coefficient for shading correction corresponding to that pixel is corrected by being changed to a value so that the shading correction result can become a specified value.

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 In a digital image reading apparatus such as an image scanner, shading correction is generally performed in order to correct the optical transmission characteristics of a reading optical system and the variation in sensitivity between pixels of a CCD sensor.

Shading correction is performed on the basis of data obtained by reading a density reference plate (usually a white plate) having a uniform density at least in the main scanning direction.

An example of the shading correction formula is shown below. Dout (n) = K × Din (n) / Dwb (n) (1) where Din (n): read data (shaded correction data) Dwb (n): density reference plate read data K Target density setting coefficient Dout (n): Calculated K / Dwb (n) ... (2) in the data expression (1) after shading correction is called a shading correction coefficient.

If dust or the like adheres to the reading position of the density reference plate and there is a location having a density unique to the surrounding density (hereinafter referred to as a singular point), shading correction is performed with a density reference different from other locations. Will be done. For example, considering a case where a document of uniform density is read and shading correction is performed, originally, the data after shading correction must have a uniform value within a range that is allowed as an error, but if there is a singular point, it is peculiar. Only the locations corresponding to the points have different densities after shading correction from the other locations. Normally, while reading one original, the shading correction is performed with the same density reference plate read data, so that the position corresponding to the singular point appears as a line in the sub-scanning direction.

In order to solve such a problem, several methods have been conventionally proposed.

In Japanese Patent No. 2736536, the density reference plate is read before image reading to create a shading correction coefficient, and the density reference plate is read at another position displaced in the sub-scanning direction to perform shading correction. The singular point of the density reference plate is detected at the position where the density reference plate is read from. If singularity is found,
A shading correction coefficient is created by searching for a position where the singular point is not recognized due to further displacement in the sub-scanning direction. If there is no location where no singularity is found, the shading correction coefficient is created at the location with the least singularity.

Further, in Japanese Laid-Open Patent Publication No. 11-112800, the density reference plate is read, and when the output difference from adjacent data is a predetermined value or more, it is determined to be a singular point, and the data of the singular point is determined. Is replaced with the value of the adjacent data to perform shading correction based on the data from which the singularity is removed.

[0009]

However, with respect to the above proposals, Since a place without a singular point is searched every time before reading an image, it may take a long time to read the image. 2. If there is no place where no singularity exists, the effect of the singularity appears in the image. 3. If correction is performed using the data of adjacent pixels, it becomes impossible to correct the sensitivity between pixels of the CCD sensor. There are problems such as.

An object of the present invention is to solve the above problems and detect the singular point of the density reference plate and eliminate its influence.

[0011]

[Means and Actions for Solving the Problems] The above problems can be solved by providing the following configuration.

(1) Reading means using a line sensor having a plurality of photoelectric conversion elements arranged one-dimensionally in the main scanning direction A uniform density is provided and a length covering the entire main scanning direction is provided. And a reference density plate having a predetermined width in the sub-scanning direction, a shading correction coefficient generating means for generating a shading correction coefficient based on the data read by the reading means, the shading correction coefficient generated by the shading correction coefficient generating means. Coefficient storage means to store the data read by the reading means of the original image is corrected by the shading correction coefficient Shading correction means Image data storage means for storing the data corrected by the shading correction means Shading correction coefficient at the time of reading the original image Read the reference concentration plate for First reading position (in the scanning direction) Data having the second reading position displaced in the sub-scanning direction within the range of the reference density plate from the first reading position, and reading the reference density plate at the first reading position A shading correction coefficient is generated based on the shading correction coefficient, and the shading correction coefficient is stored in the coefficient storage means. The shading correction coefficient is stored in the second reading position and the shading correction coefficient is stored. Then, a correction coefficient is calculated so that the data value after shading correction of the pixel judged to be abnormal by the judgment means for detecting the abnormality by comparing with the judgment reference becomes a predetermined reference value, and the shading correction coefficient corresponding to the corresponding pixel is obtained. The value multiplied by the correction coefficient is stored as a shading correction coefficient, and the data of the data read from the original is read using the corrected shading correction coefficient. Image reading apparatus and performing over loading correction.

(2) The image reading device according to (1), wherein the predetermined reference value is a value theoretically obtained when shading correction is performed on the same read data.

(3) The image reading apparatus described in (1) or (2) above, wherein the criterion is one value obtained by adding a predetermined value to a predetermined reference value.

(4) The image reading apparatus according to (1) or (2), wherein the criterion is one value obtained by multiplying a predetermined reference value by a predetermined rate.

(5) The above-mentioned (1), (3), characterized in that the judging means judges that the data value after the shading correction of interest exceeds the judgment standard or is abnormal if the data value exceeds the judgment standard. ) Or (4), the image reading device.

(6) The criterion is constituted by a first value obtained by adding a predetermined value to a predetermined reference value and a second value obtained by subtracting the predetermined value. The image reading device described in (1) or (2).

(7) The criterion is characterized by being composed of a first value obtained by increasing a predetermined reference value in accordance with a predetermined increase / decrease rate and a second value obtained by decreasing it. The image reading device according to (1) or (2) above.

(8) The above-mentioned (6) is characterized in that the judging means judges that the shading-corrected data value of interest is abnormal if the data value is outside the range indicated by the two judgment criteria. Alternatively, the image reading device described in (7).

By doing so, the influence of the singularity can be removed without lengthening the time required to prepare the shading correction coefficient, so that it is possible to read with stable image quality while maintaining the original reading time. Becomes

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a main block diagram of a reading device of the present invention.

The apparatus of this embodiment plays a role of positioning when placing the original 7 on the same surface as the original 7 is placed on the edge of the original glass 2 on which the original 7 is placed. The concentration reference plate 1 which also serves is attached.

The lamp 3 illuminates the density reference plate 1 and the original 7, and the reflected light is condensed by the lens 5 via the reading system 4 including the lamp 3 and is read by the CCD sensor 6 to obtain image data. Become.

The reading system 4 is moved in the horizontal direction (left and right) in FIG. 1 by a drive unit (not shown) controlled by a control unit including a CPU (not shown).

FIG. 2 is a block diagram of the shading correction function.

Input image data D (n) obtained by converting the information read by the CCD sensor 6 into a usable state as digital data is input to the selector 8. Selector 8
Switches and outputs the input data to "A" or "B" by the SEL signal. A divider 9 is connected to the output of "A" that is selected when the SEL signal is set to High, and the target concentration coefficient K that is set separately is Dwb output from "A".
The operation of dividing by (n), that is, the calculation of the above equation (2) is performed. The value ShC (n) calculated by the divider 9 is stored in the shading correction storage unit 10.

On the other hand, the output of "B" selected when the SEL signal is set to Low is Din (n) and the multiplier 11
Entered in. The shading correction storage unit 10 is connected to the other input of the multiplier 11, and Din
ShC (n) is input according to (n). here,
The data Dout after shading correction is performed by multiplying two inputs, Din (n) × ShC (n) ... (3)
It is stored in the image data storage unit 12 as (n). The data stored in the image data storage unit 12 is further processed by a data processing system (not shown) located downstream.

The reading of a document on which ordinary shading correction has been performed will be described with reference to FIGS.

First, the reading system 4 is moved below the reference density plate 1 (s1), the lamp is turned on (s2), the SEL signal is set to High (s3), and then the position of the reading system 4 is fixed. Reading is performed (s4). At this time, if there is no singular point element in the density reference plate 1 as shown in FIG. 3A, the data as shown in FIG. 3B can be read, and the shading correction coefficient ShC (n) is generated based on this data. . Next, the SEL signal is set to Low (s5), and the image of the original 7 having a uniform density is read while moving the reading system 4 (s6). An image of arbitrary one-line data at that time is shown in FIG. The data of FIG.
When shading correction is performed with the shading correction coefficient based on the data in (b), image data of uniform density is obtained as shown in FIG. 3 (d).

When the reading of the original 7 is completed, the lamp is turned off (s7) and the processing is completed.

FIG. 4 shows how shading correction is performed when the singularity element exists on the density reference plate 1.

As shown in FIG. 4A, if dust and the like are attached to the reference position, which is the position for reading for shading correction, and there is a singular point, it becomes a singular point as shown in FIG. 4B. The data of the corresponding pixel becomes α lower than the originally expected value. If the position of this pixel is M and the originally expected value is Du (M), the shading correction coefficient ShC
(M) is a value obtained by multiplying the originally expected value by Du (M) / α ... (4). By the way, Du (M) / α> 1
Is. Figure 4 after shading correction for originals with uniform density
As shown in (d), the value of the data of the pixel corresponding to the singular point becomes β higher than that of the surroundings.

FIGS. 5 and 6 show the case where the density reference plate 1 itself is read for this shading correction.

Similarly to FIG. 3, a density reference plate 1 without singularity elements
The case of FIG. 5 will be described. FIG. 5B which is data obtained by reading the reference position when the shading correction is performed on the read data of the reference position which is displaced from the reference position which is the reading position for shading correction in the sub-scanning direction, and FIG. The data shown in FIG. 5 (c) is theoretically the same, and since Din (n) = Dwb (n) is established in the above equation (1), the data after shading correction is All theoretically have the target concentration setting coefficient K. Utilizing this is the most important point of the present invention.

FIG. 6 shows that the singularity element exists on the density reference plate 1.
The most important points of the present invention will be described with reference to FIG.

Similar to FIG. 4, FIG. 6 has a singular point such as dust at the reference position, and the read data value is shown in FIG.
It is assumed that α is the same as in (b) (FIG. 6 (b)).

When the shading correction is performed on the reference position data with the shading correction coefficient created based on the read data as shown in FIG. 6B, the result becomes as shown in FIG. 6D. As described above, since the shading correction is performed between the read data on the density reference plate 1, the expected value after the shading correction is the target density setting coefficient K. However, where there is a singular point at the reference position, the value becomes high as in FIG. It can be said that this value γ is γ = K × Du (M) / α (5).

Therefore, as shown in FIG. 8, the reading is performed at the reference position to generate the shading correction coefficient ShC (n) (s10 to s13). Subsequently, the reading system is moved to the reference position, the SEL signal is set to Low (s15), and the read data at the reference position of the standard density plate 1 is shading-corrected (s16). After the shading correction stored in the image data storage unit, it is compared with Jdg = K + Tg (6) (s17). Tg is a predetermined value. A method of obtaining Jdg by multiplying K by a predetermined ratio is also effective.

Data Dout after shading correction
When (n) is larger than Jdg = K + Tg, that is, in FIG.
In the case of γ shown in (d), the shading correction coefficient ShC (n) at the position corresponding to the pixel is replaced with ShC (n) × K / Dout (n) ... (7) (s18) ). This operation is performed for all pixels (s19).

Thus, the original is read while performing shading correction using the corrected shading correction coefficient ShC (n) (s20, s21). What is corrected is Du (n): The reading value α of the reference position of the density reference plate 1 that should be obtained originally: The value M obtained by reading the singular point M: The pixel position Din (n) where the singular point exists: The density reference plate When shown as a read value of the reference position of 1, ShC (M) = K / α (8) When the shading correction is performed on the data of the reference position with this shading correction coefficient, Dout (M) = Din (M) × ShC (M) ··· (9) Substituting equation (8) into this Dout (M) = Din (M) × K / α ··· (10) Equation (7) to correct this pixel When applied, ShC (M) × K / Dout (M) = ShC (M) × K / (Din (M) × K / α) = K / α × K / Din (M) / K × α = K / Din (M) ··· (11) where K = K × Din (n) / Du (n) .. (12) is substituted into the equation (11) = K.times.Din (M) / Du (M) / Din (M) = K / Du (M) .... (13) It can be seen that the shading correction coefficient should be obtained. Normal shading correction can be performed by using this result as a new shading correction coefficient.

[0041]

As described above, according to the present invention, since the singular point can be found and the shading correction coefficient at the singular point position can be corrected by a simple and reliable method, the shading correction coefficient can be prepared. Since the influence of the singularity can be removed without increasing the time required, it is possible to read with stable image quality while maintaining the document reading time.

[Brief description of drawings]

FIG. 1 is a diagram showing a main configuration of an embodiment.

FIG. 2 is a block diagram of a shading correction circuit function in the embodiment.

FIG. 3 is a diagram of an example of shading correction of a uniform-density original according to the embodiment.

FIG. 4 is a diagram of an example of shading correction of a uniform-density original including a singular point in the embodiment.

FIG. 5 is a diagram of an example of shading correction between the density reference plates in the embodiment.

FIG. 6 is a diagram of an example of shading correction between density reference plates including singular points in the embodiment.

FIG. 7 is a flowchart of image reading with normal shading correction.

FIG. 8 is a flowchart of image reading with shading correction according to the present invention.

[Explanation of symbols]

1 Concentration reference plate 2 Platen glass 3 lamps 4 reading system 5 lenses 6 CCD sensor 7 manuscript 8 selector 9 divider 10 Shading correction storage unit 11 multiplier 12 Image data storage

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5B047 AA01 BA02 BB02 BC14 CB04                       DA04                 5C072 AA01 BA08 BA17 CA02 FB12                       LA15 RA16 UA02                 5C077 LL04 MM27 MP01 PP06 PP10                       PP47 PP48 PQ12 PQ20 PQ24                       SS01 TT06

Claims (8)

[Claims] 1. A reading means using a line sensor having a plurality of photoelectric conversion elements arranged one-dimensionally in the main scanning direction, having a uniform density, and having a length covering the whole area in the main scanning direction. Reference density plate having a predetermined width in the sub-scanning direction Shading correction coefficient generating means for generating a shading correction coefficient based on data read by the reading means. Shading correction coefficient generated by the shading correction coefficient generating means is stored. Coefficient storage means for correcting data read by the reading means with the shading correction coefficient shading correction means for storing data corrected by the shading correction means image data storage means for generating shading correction coefficients for reading the original image Read the reference density plate for The first reading position is provided with a second reading position displaced in the sub-scanning direction within the range of the reference density plate from the first reading position, and data read from the reference density plate at the first reading position A shading correction coefficient is generated based on the shading correction coefficient stored in the coefficient storage means, and data obtained by reading the reference density plate at the second reading position is subjected to shading correction using the stored shading correction coefficient, and for each pixel. The shading correction coefficient is calculated so that the data value after shading correction of the pixel judged to be abnormal by the judging means for detecting abnormality by comparing with the judgment standard becomes the predetermined reference value, and corrected to the shading correction coefficient corresponding to the corresponding pixel. The value multiplied by the coefficient is stored as the shading correction coefficient, and the shading correction coefficient after correction is used to form the shade of the data read from the document. Image reading apparatus and performs Ingu correction. 2. The image reading apparatus according to claim 1, wherein the predetermined reference value is a value theoretically obtained when shading correction is performed on the same read data. 3. The image reading apparatus according to claim 1, wherein the determination standard is one value obtained by adding a predetermined value to a predetermined standard value. 4. The image reading apparatus according to claim 1, wherein the determination standard is one value obtained by multiplying a predetermined standard value by a predetermined rate. 5. The determination means determines that there is an abnormality when the data value after the target shading correction exceeds the determination standard or is equal to or larger than the determination value. The image reading device according to claim 4. 6. The judgment criterion is composed of a first value obtained by adding a predetermined value to a predetermined reference value and a second value obtained by subtracting the predetermined value. The image reading apparatus according to claim 1 or claim 3. 7. The judgment criterion comprises a first value obtained by increasing a predetermined reference value according to a predetermined increase / decrease rate and a second value obtained by decreasing the predetermined reference value. The image reading device according to claim 1 or 2. 8. The method according to claim 6, wherein the determination means determines that the data value after the target shading correction is abnormal if the data value is out of the range indicated by the two values of the determination standard. Item 7. The image reading device according to item 7.