JP2000270216A - Original reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply obtain optimal picture data at the time of reading an original by providing an adjusting means for adjusting the characteristic of shading correction to be executed by a shading correction means corresponding to the picture of the reading original. SOLUTION: A picture inputting part 10 line-scans a reference sheet or an original surface to obtain its image data. An A/D converter 14 converts an analog picture signal to a digital picture signal. A shading correction means 15 executes shading correction by holding a white level and a black level. In order to obtain read picture data of a desired gradation characteristic, an adjusting means 16 calculates adjusting coefficients respectively concerning the white level, the black level of shading correction and the picture signal, controls one or plurality of a shutter lamp 11, an image pickup element 12, an amplifier 13 and the A/D converter 14 in a picture inputting part 10 and corrects the black/white levels and the level of the read picture signal to generate the adjusting value of each.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading apparatus having a shading correction function, and more particularly, to providing a means for adjusting a shading correction characteristic so that appropriate image data can be obtained in accordance with gradation characteristics of a document image. And a document reading apparatus configured to obtain the document.

[0002]

2. Description of the Related Art Generally, in a document reading apparatus capable of reading a halftone image such as a photograph, an automatic scanning is performed for the light condensing characteristics of a lens, the unevenness of illumination of a fluorescent lamp, a change in the amount of light emission with time, or a change in ground color of a document. The shading correction is performed so that the image can always be read at an appropriate gradation by following the image.

FIG. 9 shows an example of a shading waveform.
Shows a white level waveform I _w and the black level waveform I _b during line scanning, and an image signal waveform I _r by CCD. In general, at both ends of the line scanning, the light amount from an illumination light source such as a fluorescent lamp is insufficient compared with the central portion, so that a level drop occurs. In particular, shading correction is necessary.

FIG. 10 shows an example of a conventional shading correction circuit. 10, reference numeral 1 denotes a CCD of an image sensor, 2 denotes an amplifier that amplifies an analog image signal output from the CCD 1, 3 denotes an A / D converter that converts an analog image signal into a digital image signal, and 4 denotes a reference sheet or a document. A black-and-white follower circuit for creating a white level value and a black level value for shading correction at the time of reading; 5, a white level memory for storing the created white level value; 6, a black level memory for storing the created black level value; Reference numerals 7 and 8 denote D / A converters for converting the digital signal format white level value and black level value read from the white level memory 5 and the black level memory 6 into an analog signal format.

[0005] When reading the document, CCD 1 is in synchronism with that line scans the original surface, read out the white level value I _w and the black level value I _b of each one line from the white level memory 5 and the black level memory 6 The signals are converted into analog signals by the D / A converters 7 and 8 and applied to the reference voltage terminals ref1 and ref2 of the A / D converter 3, respectively. On the other hand, amplifier 2
Is input to a signal input terminal in of the A / D converter 3. Thus, the A / D converter 3 sets the dynamic range between the white level value (I _w ) and the black level value (I _b ) as the input analog image signal (I _r ).
To a digital image signal. Black and white follower circuit 4
Creates a new white level value (I _w ) and a new black level value (I _b ) based on the digital image signal and the currently stored values of the white level memory 5 and the black level memory 6 following the reading of the original. Update the contents of the memory.

Such a conventional shading correction circuit operates so as to automatically perform correction in response to a change in the light amount of an illumination light source or a change in the ground color of a document. Could not be corrected.

[0007]

In a conventional document reading apparatus, it is not possible to correct the gradation characteristics of a read image when reading a document. Had to be corrected. However, correction processing performed later is complicated, and correction is often difficult.

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to easily obtain optimum image data when reading a document.

[0009]

SUMMARY OF THE INVENTION According to the present invention, the characteristics of shading correction performed at the time of reading a document can be adjusted according to the gradation distribution of the document image so that image data of the optimum gradation can be obtained. Is what you do.

The document reading apparatus according to the present invention is configured as follows. (1) In a document reading apparatus provided with a shading correction unit that performs shading correction on an image signal output from an image sensor, the characteristics of the shading correction performed by the shading correction unit are optimally adjusted according to the image of the read document. An adjusting means is provided. (2) In the above item (1), the adjustment means adjusts the characteristics of shading correction by controlling the gain of an amplifier having a variable gain provided on the output side of the image sensor. (3) In the above item (1), the adjustment means adjusts the characteristics of shading correction by controlling the driving frequency of the image sensor. (4) In the above item (1), the adjustment means adjusts the characteristics of the shading correction by controlling the exposure time of the image sensor. (5) In the above item (1), the adjustment means adjusts the characteristics of shading correction by controlling a reference voltage of an A / D converter provided on the output side of the image sensor. (6) In the above item (1), the adjusting means includes means for acquiring image data of a desired read document, means for calculating a maximum value and a minimum value in the acquired image data, and a calculated maximum value. Means for instructing respective correction values for the minimum value and the maximum value, and a necessary shading correction value is calculated based on the calculated maximum value and minimum value and the specified maximum value and minimum value. And means for performing the operation. (7) In the above item (1), the adjusting means instructs means for acquiring image data of a desired read document, means for calculating a histogram for the acquired image data, and a correction value for the calculated histogram. And a means for calculating a necessary shading correction adjustment value based on the calculated histogram and the specified histogram correction value. (8) In the above item (6) or (7), the adjusting means sets α as an adjustment coefficient of an image signal at the time of reading a document, and sets β and γ as white levels in shading correction white storage and black storage, respectively. The black level adjustment coefficient, W
_highlight and W _shadow are the maximum and minimum values of the white level, B _highlight and B _shadow are the maximum and minimum values of the black level, and V _highlight and V _shadow are the maximum and minimum values of the original read data. Then, when storing the black and white level for shading correction and when reading the original, each adjustment value of the black and white level and the original read data is calculated using the adjustment coefficient of the following equation. α = (1-V _shadow ) ・ B _shadow・ R _highlight − (1-V _shadow )
_highlight ) ・ B _highlight・ R _shadow β = (1-V
_shadow ) ・ B _shadow・ W _highlight・ V _highlight − (1
−V _highlight ) ・ B _highlight・ W _shadow・ V _shadow γ = W _highlight・ B _highlight・ R _shadow −W _shadow
• V _shadow / R _highlight (9) In the above item (7), the adjustment means sets the adjustment value when storing the black level for shading correction to a fixed value, and sets each data when storing the white level and when reading the original. Is calculated. (10) In the above item (7), the adjustment means may calculate the adjustment value for the read data at the time of reading the original document, with each adjustment value when storing the black level and the white level for shading correction as a constant value. It is characterized by. (11) In the above item (6) or (7), the adjusting means may be a means for acquiring image data of a desired read original provided by the adjusting means, and the adjusting means may arbitrarily select one or more lines or all lines on the read original. Image data can be obtained, and the maximum value,
It is characterized in that the calculation of the minimum value or the calculation of the histogram is performed. (12) In the above (1) to (11), the adjustment means has a configuration for performing adjustment for each readable color.

FIG. 1 shows the basic configuration of the present invention.

In FIG. 1, reference numeral 10 denotes an image input unit, which scans a reference sheet or a document surface with a line to acquire image data.

A shutter / lamp 11 illuminates the original surface. By controlling the opening and closing time of the shutter and the lighting time of the lamp, the exposure time can be changed.

Reference numeral 12 denotes an image pickup device such as a CCD. By controlling the driving frequency, the output level of the analog image signal can be changed.

Reference numeral 13 denotes an amplifier for amplifying an analog image signal output from the image sensor. By controlling the amplification rate, the level of the analog image signal can be changed.

An A / D converter 14 converts an analog image signal into a digital image signal. By controlling the reference voltage for A / D conversion, the conversion ratio (scale) can be changed.

15 holds a white level and a black level,
Shading correction means for performing shading correction of an image signal.

Numeral 16 denotes an adjusting means which calculates adjustment coefficients for the white and black levels of shading correction and the image signal in order to obtain read image data having desired gradation characteristics. One or more of the elements 11 to 14 are controlled to correct the white and black levels and the level of the read image signal to generate respective adjustment values.

Referring to FIG. 2, the operation of the adjusting means 16 of FIG. 1 will be described.

FIG. 2A shows a shading waveform similar to the conventional one before the adjustment by the adjusting means 16.
I _w white level waveform, I _b is a black level waveform, I _r denotes an image signal waveform. The adjusting means 16 calculates each of these waveforms.
I _w, I _b, respectively calculate the level of I _r, based on the desired gradation characteristics to be set for the scanned image, the adjustment factor to optimize the tone characteristic of the read image data alpha, beta, and γ White level, black level, read image data adjustment value G _w ,
G _b, seeking G _r, converts waveform O _w as shown in the FIG. 2 _(b), O b, the O _r. Shading correction is performed based on the waveform of FIG. The output image data O as a result of the correction is represented by the following general formula (1).

[0021]

(Equation 1)

From this equation, it is understood that if the values of the adjustment values G _w , G _b , and G _r are properly determined, image data O having desired gradation characteristics can be obtained.

The equation (1) is expressed by the following equation (2) by performing the following coefficient conversion.

G _r · I _r → R, G _b · I _b → B, G _w · I _w → W

[0025]

(Equation 2)

[0026]

3A to 3D show four embodiments of the basic structure of the present invention shown in FIG.

FIG. 3A shows a second embodiment of the present invention.
The adjusting means 16 controls the amplifier 13 based on the calculated adjustment value.
To correct the level of the analog image signal output from the image sensor 12. Thus, the gradation characteristics of the read image are corrected simultaneously with the shading correction.

FIG. 3B shows a third embodiment of the present invention.
The adjusting unit 16 changes the driving frequency of the image sensor 12 based on the adjustment value, thereby controlling the gain of the image sensor and correcting the level of the output analog image signal.

FIG. 3C shows a fourth embodiment of the present invention.
The adjusting unit 16 changes the exposure time of the image sensor by controlling the shutter opening / closing of the shutter / lamp 11 or the lighting of the lamp, and corrects the level of the analog image signal output from the image sensor 12.

FIG. 3D shows an embodiment of the present invention.
The adjusting unit 16 changes the A / D conversion scale by controlling the reference voltage of the A / D converter 14 based on the adjustment value, and corrects the level of the output digital image signal.

FIG. 4 is an overall flowchart showing the processing function of the adjusting means 16. Each block shown by S1 to S15 in the drawing is a processing function of an element realized by software.

S1 to S12 constitute the main flow. First, pre-scanning is performed, an adjustment value is calculated based on the obtained image data, the reading condition is changed (corrected) using the adjustment value, and the main reading is executed.

In S1, a pre-reading condition is set, and a pre-reading operation is executed in S2 according to the condition. The image data obtained by the pre-reading is held in S3. For the stored image data, the maximum value and the minimum value are detected in S4, and a histogram is generated in S5.

In step S6, a change setting is performed on the detected maximum value, minimum value, or generated histogram so that the image is read with desired gradation characteristics. In S7, an adjustment value for the necessary shading correction is calculated based on the gradation level range for performing image reading set in S6, and held in S8.

In S9, conditions such as shading correction characteristics in the main reading are set, and in S10, the set conditions are changed according to the adjustment values held in S8. Thereafter, if the start of the main reading operation is instructed in S11, the main reading operation is executed in S12.

The adjustment value held in S8 is held in S13 as a previous adjustment value in preparation for the next original reading. Then, when the next original is read, S
It can be used instead of performing the pre-reading of 1 to S7 to obtain the adjustment value. In that case, it is set as the previous adjustment value in S14, and held and used as the current adjustment value in S8.
Similarly, an arbitrary desired adjustment value can be set in S15, and the set adjustment value is held as a current adjustment value in S8 and is made usable.

FIG. 5 shows an example of the adjustment value calculation processing in S6 of the flow of FIG. (A) of FIG.
7 is a shading waveform before adjustment according to the present invention. FIG. 5B is a waveform of the output image data O when the shading correction is directly performed by the conventional method based on the shading waveform of FIG. This figure 5
In (b) of the output image data O, the gradation level changes between the maximum value O _highlight and the minimum value O _shadow .
This change range is concentrated in the middle part of the dynamic range of the output level, and the contrast of the image is not so high. In order to increase the contrast of the image, as shown by V _highlight and V _shadow in FIG. 5D, it is necessary to increase the maximum value, lower the minimum value, and expand the entire image up and down. This gradation correction process is performed by the process shown in FIG.
Is multiplied by appropriate adjustment coefficients α, β, and γ to convert the image signal waveform R, the white level waveform W, and the black level waveform B into a shading waveform as shown in FIG. Is achieved. In the case of the illustrated example, FIG.
By lowering the white level waveform W in (a) and narrowing the dynamic range between the white level waveform W and the black level waveform B, the image contrast is relatively increased.

FIG. 6 shows an example of the desired level range setting process in S7 of FIG. FIG. 6A shows a case where the maximum / minimum value adjustment is performed based on the gradation frequency distribution, and FIG. 6B shows a case where the adjustment is performed using the histogram.

The upper graph in FIG. 6A shows the S in FIG.
4 is a frequency distribution graph of the gradation values of the original image created by the maximum / minimum value detection processing in FIG.
By setting so as to expand between the _highlight and the minimum value O _shadow , the gradation distribution of the read image is deformed and adjusted as shown in the lower graph.

The upper graph of FIG. 6B shows the graph of S in FIG.
5 of the gradation value generated in the histogram generation processing.
A histogram where the true maximum and minimum are
_highlightAnd O_shadowIndicated by Histog here
Set virtual maximum and minimum values at any two points on the ram
You. These virtual maximum and minimum values are on the horizontal axis (gradation value).
And V _highlightAnd V_shadowOr the vertical axis
(Cumulative frequency)^' _{highli ght}And V^' _shadowSpecify with
You may. According to the specified value,
Thus, the histogram is adjusted for deformation.

Next, the algorithm of the adjustment processing shown in FIGS. 5 and 6 will be described. In the case of the shading waveform correction in FIG. 5, the level of the output image signal is obtained from the following equation (3).

[0042]

(Equation 3)

Here, α: adjustment coefficient at the time of reading (α ≠ 0) β: adjustment coefficient at the time of white storage (β ≠ 0) γ: adjustment coefficient at the time of black storage (γ ≠ 0) Denominator on the right side of Equation 3 And the numerator are divided by γ to obtain the following equation 4.

[0044]

(Equation 4)

Here, the variable substitution α ′ = α / γ, β ′ = β /
Expression 5 is obtained by performing γ.

[0046]

(Equation 5)

The maximum value and the minimum value (O _highlight , O _shadow ) of the gradation detected from the read image data shown in FIGS. 6A and 6B or the histogram thereof are shown in FIG.
From the shading waveform of (a), the following Expression 6 is obtained.

[0048]

(Equation 6)

The maximum / minimum value (V _highlight ,
V _shadow ) and equations 5 and 6, the following equation 7 is obtained.

[0050]

(Equation 7)

The adjustment coefficients α ′ and β ′ in Equation 7 are expressed by the following Equation 8.
Can be obtained by

[0052]

(Equation 8)

From the equations (5) and (8), the adjustment values G _r ′, G _w ′
Is as shown in the following Expression 9.

[0054]

(Equation 9)

Assuming that the respective adjustment values at the time of reading an image and at the time of storing a black and white level are G _r ′, G _w ′, and G _b ′, they are expressed by the following equation (10).

[0056]

(Equation 10)

From Equations 4 and 5, the adjustment coefficients α, β, and γ are as shown in the following Equation 11.

[0058]

[Equation 11]

FIG. 7 shows an outline of an embodiment of the adjustment value calculating process. First, the maximum value and the minimum value and their coordinates are detected from the image data obtained by the pre-reading. If the user considers that the detected values of the maximum value and the minimum value need to be changed, a desired value is set. From the detected values of the maximum value and the minimum value and the desired value, adjustment coefficients α, β, and γ required for each of the white level, the black level of the shading correction, and the read image data are calculated.

The adjustment coefficients α, β, and γ are multiplied by the white level, the black level, and the read image data read from the white storage memory, the black storage memory, and the read memory, respectively. As the respective adjustment values, a white storage adjustment value, a black storage adjustment value, and a read adjustment value are generated. The generated white storage adjustment value G _w , black storage adjustment value G _b , and read adjustment value _Gr are held in adjustment value holding means (a predetermined memory area). Incidentally, black stored adjustment value G _b or even white storage adjustment value G _w, is a constant value, that is not to be changed with respect to the line scan flat value, it is possible to assume a.

FIG. 8 is a flowchart of a reading condition changing process based on the adjustment value, which is performed for the main reading following the pre-reading. S21 to S29 are each step of the process.

First, when the main reading is started, storage of the white level used for shading correction in the main reading is started in S21.

[0063] In S22, with reference to the adjustment value holding means, read if white storage adjustment value G _w, is stored as the new value of the white level at S23.

[0064] S24, S25, in S26, a black level changes stored for black stored adjustment value G _b in the same manner.

Next, the main reading process is started in S27, and in S28
The readout adjustment value _Gr is read out by referring to the adjustment value holding means at step S29, and at S29, the white level previously changed and stored is _Gw ,
Performs shading correction using the black level G _b, and ends by outputting the read data of the correction results.

[0066]

According to the present invention, the gradation correction of the read image at the time of reading the original is realized relatively easily and at low cost by utilizing the shading correction function provided in the ordinary original reading apparatus. And the quality of the read image can be improved.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of the present invention.

FIG. 2 is an explanatory diagram of an operation of an adjusting means in the present invention.

FIG. 3 is a basic configuration diagram of an embodiment of the present invention.

FIG. 4 is an overall flowchart of an adjusting unit.

FIG. 5 is an explanatory diagram of an example of an adjustment value calculation process.

FIG. 6 is an explanatory diagram of an example of a desired level range setting process.

FIG. 7 is an explanatory diagram of an adjustment value calculation process.

FIG. 8 is a flowchart of changing a reading condition based on an adjustment value.

FIG. 9 is an explanatory diagram of an example of a shading waveform.

FIG. 10 is a configuration diagram of an example of a conventional shading correction circuit.

[Explanation of symbols]

 10: Image input unit 11: Shutter / lamp 12: Image sensor 13: Amplifier 14: A / D converter 15: Shading correction unit 16: Adjustment unit

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 5B047 AA01 AB02 DA01 DA04 DA06 DB06 DC02 DC04 5C072 AA01 BA08 UA02 UA05 UA06 UA17 5C077 LL04 MM03 MP01 MP08 PP06 PP10 PP43 PP44 PP45 PQ08 PQ12 PQ19 RR01 RR11 RR12

Claims (12)

[Claims] 1. A document reading apparatus comprising a shading correction unit for performing shading correction on an image signal output from an image pickup device, wherein a characteristic of the shading correction performed by the shading correction unit is optimally adjusted to an image of a read document. An original reading device comprising an adjusting means for adjusting. 2. An original according to claim 1, wherein said adjusting means adjusts a shading correction characteristic by controlling an amplification factor of an amplifier having a variable amplification factor provided on an output side of the image sensor. Reader. 3. The document reading apparatus according to claim 1, wherein the adjustment unit adjusts the characteristics of shading correction by controlling a driving frequency of the image sensor. 4. An original reading apparatus according to claim 1, wherein said adjusting means adjusts characteristics of shading correction by controlling an exposure time of an image sensor. 5. An original according to claim 1, wherein said adjusting means adjusts a shading correction characteristic by controlling a reference voltage of an A / D converter provided on an output side of the image sensor. Reader. 6. The image processing apparatus according to claim 1, wherein the adjusting unit obtains image data of a desired read original, calculates a maximum value and a minimum value of the obtained image data, and calculates the calculated maximum value. Means for instructing the respective correction values for the values and the minimum values, and the necessary shading correction values based on the calculated maximum and minimum values and the specified maximum and minimum correction values. A document reading device comprising: means for calculating. 7. The image processing apparatus according to claim 1, wherein the adjusting unit obtains image data of a desired read original, calculates a histogram of the obtained image data, and designates a correction value of the calculated histogram. And a means for calculating a necessary shading correction adjustment value based on the calculated histogram and the specified histogram correction value. 8. The image processing apparatus according to claim 6, wherein α is an adjustment coefficient for an image signal at the time of reading the original, and β and γ are white levels at the time of white storage and black storage of shading correction, respectively. W _highlight and W _shadow are the maximum and minimum values of the white level, B _highlight and B _shadow are the maximum and minimum values of the black level, and V _highlight and V _shadow are the manuscripts. When the maximum value and the minimum value of the read data are used, when adjusting the black and white level for shading correction and when reading the original, each adjustment value of the black and white level and the original read data is calculated using the adjustment coefficient of the following equation. A document reading apparatus characterized by the above-mentioned. α = (1-V _shadow ) ・ B _shadow・ R _highlight − (1-V _shadow )
_highlight ) ・ B _highlight・ R _shadow β = (1-V
_shadow ) ・ B _shadow・ W _highlight・ V _highlight − (1
−V _highlight ) ・ B _highlight・ W _shadow・ V _shadow γ = W _highlight・ B _highlight・ R _shadow −W _shadow
・ V _shadow・ R _highlight 9. An image forming apparatus according to claim 7, wherein said adjusting means calculates an adjustment value for each data at the time of storing the white level and at the time of reading the document, with the adjustment value when storing the black level for shading correction as a constant value. A document reading device. 10. The adjusting device according to claim 7, wherein
An original reading apparatus, wherein each adjustment value for storing a black level and a white level for shading correction is a fixed value, and an adjustment value for read data at the time of reading an original is calculated. 11. The reading device according to claim 6, wherein said adjusting means is provided with means for acquiring image data of a desired reading original, and the adjusting means comprises an arbitrary one line, a plurality of lines, or all lines on the reading original. A document reading apparatus that can obtain the maximum value and the minimum value or calculate the histogram in the image data of the obtained line. 12. The method according to claim 1, wherein
The document reading apparatus according to claim 1, wherein the adjusting means adjusts shading correction for each readable color.