JP3641365B2 - Image reading device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus capable of reading a document at a high speed even when unadjusted illumination is used.
[0002]
[Prior art]
As a conventional image reading apparatus, a “gradation image reading apparatus” described in JP-A-6-253149 has been reported.
This is a histogram of image data obtained at the time of pre-scanning, or a sensor for detecting the brightness of the light irradiated on the document, and the amount of accumulated light by controlling the amount of light or controlling the light accumulation time. The image data is obtained during the main scan.
[0003]
Also, an “image reading apparatus” described in Japanese Patent Laid-Open No. 8-279910 has been reported. This creates a histogram of the image data obtained during pre-scanning, adjusts the light intensity and gain based on the maximum and minimum values, and performs gradation conversion based on the gradation characteristics and histogram during pre-scanning. A table (γ conversion table) is determined to obtain image data at the time of the main scan.
[0004]
Furthermore, “Color image reading method, color image reading apparatus and color image reading system” described in Japanese Patent Laid-Open No. 9-307774 has been reported.
This determines the γ conversion table and the amount of light based on the image data after γ correction obtained at the prescan, and obtains the image data at the main scan.
[0005]
Thus, in the conventional image reading apparatus, both to control the amount of light, it had the advantage of being able to obtain a very high image data of gradation.
[0006]
[Problems to be solved by the invention]
However, those described in JP-A-8-279910 and JP-A-9-307774 control only the light amount and the γ conversion table and do not contribute to the improvement of the reading speed.
Japanese Patent Laid-Open No. 6-253149 also controls the light accumulation time, so that the document reading speed can be improved when there is a sufficient amount of light from the light source.
[0007]
However, when the amount of light is insufficient, the document reading speed cannot be improved. In general, the reflection type image reading apparatus that is widely used uses a xenon lamp, a fluorescent lamp, a cold cathode tube, an LED, or the like as a light source, and the reading speed is not determined by the frequency characteristics of the image sensor. It is determined in relation to sensor sensitivity. In this case, since the amount of illumination light is insufficient, the speed is set so as to compensate for the shortage of illumination light amount, and the sensor is often operated at a speed of a fraction of the upper limit of the light accumulation time of the sensor.
[0008]
Further, in the conventional image reading apparatus, when the light amount becomes insufficient, noise becomes conspicuous in a solid image in a dark part. Particularly, in the CCD sensor and the MOS sensor, the gradation characteristic deteriorates if there is no light accumulation amount above a certain level. For example, in a MOS sensor, the degree to which the γ characteristic is convex downward increases. Therefore, in order to increase the light accumulation amount (light volume time × light amount), it is necessary to slow down the reading speed in order to increase the illumination light amount or to increase the light accumulation time.
[0009]
The present invention has been made in view of the above, and an object of the present invention is to provide an image reading apparatus capable of reading a document at high speed even using the above-described non-adjusted illumination.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention described in claim 1 illuminates an unadjusted light on the document surface and accumulates the light reflected by the document surface for each light accumulation time for each line. photoelectric conversion means for converting into an electric signal in the main scanning direction, moving means Before moving at the moving speed specified in the sub-scanning direction the illuminating means and the photoelectric conversion means to the document surface, by the photoelectric conversion means amplifying means for amplifying in the converted specified gain an electrical signal, an a / D converting means for converting the electrical signal amplified by the amplifying means into digital data, and operating means for specifying a document reading speed, the An image reading apparatus comprising : adjusting a moving speed of the moving means, a light accumulation time of the photoelectric converting means , and a gain of the amplifying means according to a reading speed designated by the operating means ; light For less than a value corresponding to the predetermined value of the density, and summarized in that a control means for controlling to output the processed value corresponding to the predetermined value.
[0011]
According to a second aspect of the present invention, in order to solve the above problem, the control means adjusts the offset of the amplification means and optimizes the output with respect to the dynamic range of the A / D conversion means. The gist of this is to control so that
[0012]
According to a third aspect of the present invention, in order to solve the above problem, a histogram generating means for generating a histogram representing the degree of appearance of the read density based on the image data at the time of pre-scanning, and a histogram generated by the histogram generating means And a control unit for controlling the reading speed of the document to be variable based on the optical density of the high density region in the histogram obtained at the time of pre-scanning. To do.
[0013]
According to a fourth aspect of the present invention, in order to solve the above-mentioned problem, the control means is configured such that the high density area of the document does not appear in the histogram obtained at the time of pre-scanning, or the high density area is only a character / line image. Is determined, an offset value that should limit the optical density of the document is determined and set in the amplification means, and the reading speed of the document is controlled to be variable.
[0014]
According to a fifth aspect of the present invention, in order to solve the above-mentioned problem, the control means is configured such that the high density area of the document does not appear in the histogram obtained at the time of pre-scanning, or the high density area is only a character / line image. Is determined, the offset and gain of the amplifying means are adjusted based on the maximum and minimum values in the histogram, the dynamic range at the time of A / D conversion is expanded, and the document reading speed is made variable. The gist of the control is as follows.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram showing a configuration of an image reading apparatus 1 according to the first embodiment of the present invention.
As shown in FIG. 1, the document 3, the light source unit 5, the image sensor 7, the travel control unit 9, the amplifier 11, the A / D converter 13, the shading correction unit 15, and the γ conversion unit 17 The operation unit 19 and the scanner control unit 21 are configured.
[0016]
The document 3 is placed on a document table made of a transparent glass plate prior to reading, and the document surface on which images, characters, and the like are drawn is directed to the light source unit 5 and the image sensor 7 side.
The light source unit 5 uses unregulated light from a xenon lamp, a fluorescent lamp, a cold cathode tube, an LED, or the like. The image sensor 7 is composed of a charge accumulation type line sensor such as a CCD, and one line of a light image reflected from the original 3 is irradiated with light from the light source and is photoelectrically converted for each light accumulation time. The electric charge is accumulated and is sequentially output to the amplifier 11 as an electric signal for each line.
[0017]
The travel control unit 9 travels the image sensor 7 and the light source unit 5 along the document surface of the document 3 at a designated moving speed for each line and performs sub-scanning. The amplifier 11 is composed of, for example, an operational amplifier circuit, and amplifies the electrical signal output from the image sensor 7 according to a designated gain. When the electrical signal output from the amplifier 11 is in the range above the designated reference voltage, the A / D converter 13 A / D converts this into digital data and quantizes it.
[0018]
The shading correction unit 15 stores correction value data for one line in advance, subtracts the correction value data from the A / D converted digital data, and corrects the sensitivity variation for each photoelectric element of the image sensor 7.
The γ conversion unit 17 γ-converts digital data using the values of the γ conversion table stored in advance in the scanner control unit 21 and outputs image data.
[0019]
The scanner control unit 21 is composed of a microcomputer having a CPU, ROM, RAM, etc., a timing circuit, a reference voltage output circuit, and the like. In order to reduce the optical density of the read original and variably set the reading speed, In accordance with the control program stored in the ROM, the sub-scanning speed is set in the travel control unit 9 according to the scanning speed designated by the user through the operation unit 19, and the photoelectric conversion of the image sensor 7 is controlled for each line period. The amplification gain of the amplifier 11 is set, and further, the entire apparatus is controlled by setting a reference voltage in the A / D converter 13.
[0020]
Next, the relationship between the optical density and the reading speed employed in the image reading apparatus 1 according to the present embodiment shown in FIG. 1 will be described. First, a reflection type image reading apparatus that is generally used is configured to be able to read a document having an optical density OD of 1.8 to 2.0.
[0021]
In the case where the original 3 is an image having no dark image area and a character / line image only in black and a lighter color image, it is assumed that the optical density OD is equal to or smaller than a certain value. There is no problem if the read image is converted into data even if a value equal to or greater than the value is set as a gradation processing target, that is, the certain value is set to the minimum value after (gradation) processing . Alternatively, if the dark image area may be collapsed, the noise becomes inconspicuous if a certain value of the optical density OD is similarly set to the minimum value after the (gradation) processing . In the following, setting the minimum value after processing (gradation) as described above to perform data conversion will be referred to as “reducing the optical density OD” or “restricting the optical density OD”.
[0022]
Therefore, after cutting out image data with an optical density OD = 1.0 (reflectance r = 0.1), good image data is obtained even with an optical density OD = 2.0 (reflectance r = 0.01). In such a case, the same image data can be obtained in the portion where the optical density OD = 1.0 even if photoelectric conversion is performed at a speed of 10 times, so that the image sensor 7, the light source unit 5, and the travel control unit 9 are operated at high speed. For example, the document can be read at a speed of 10 times.
[0023]
Further, for an original from which good image data can be obtained in an optical density range of OD = 1.8 (r = 0.016) to 2.0, it also depends on the S / N ratio during normal operation. It is appropriate to set a reading speed of about double speed when the optical density is OD = 1.5 (r = 0.03), and about 4 times speed when the optical density is OD = 1.0.
[0024]
Next, the operation of the image reading apparatus 1 shown in FIG. 1 will be described with reference to FIG. First, the operation unit 19 is provided with a speed range from standard to about 4 × speed as a speed range designated by the user, and the designated value is m. When the scanner control unit 21 receives the specified value m from the operation unit 19, the scanner control unit 21 sets and specifies the gain m in the amplifier 11 in order to change the photoelectric conversion gain to the specified value m.
[0025]
Then, as shown in FIG. 2, the scanner control unit 21 reads the γ conversion table based on the saturation light amount obtained when the gain m is set in the amplifier 11 from the internal ROM and sets it in the internal RAM of the γ conversion unit 17. To do. Specifically, the resolution of the reflectance r of the γ conversion table at the time of standard reading set in the γ conversion unit 17 is set to m times, and a γ conversion table is generated using a part thereof. Alternatively, a γ conversion table with a resolution of m times is generated from the reflectance r of the γ conversion table at the time of standard reading based on the interpolation method. However, since there is a limit on the optical density OD corresponding to the resolution of m times, as shown in FIG. 2, the reflectance r or less corresponding to this limit is set to the minimum value.
[0026]
Then, the scanner control unit 21 sets the light accumulation time corresponding to the line cycle of the image sensor 7 to 1 / m of the standard time, and sequentially outputs to the image sensor 7 with respect to the internal timing circuit. . Further, since the drive clock of the image sensor 7 only needs to have a period for the number of pixels of one line shorter than the period of one line, the clock frequency is switched so that the clock frequency can be set according to the setting range of the designated value m. A circuit may be prepared in this timing circuit.
Further, the scanner control unit 21 sets a moving speed so that the traveling control unit 9 travels at a speed that is m times that at the time of standard reading.
[0027]
As described above, the scanner control unit 21 sets each unit of the image reading apparatus 1 in accordance with the designated value m designated by the user using the operation unit 19 as described above. Is irradiated from the light source unit 5, the image sensor 7 performs main scanning on the light reflected by the document surface every light storage time T / m designated for each line and photoelectrically converts it into an electrical signal. The amplifier 11 amplifies the electrical signal photoelectrically converted by the image sensor 7 according to the designated gain m. Then, the A / D converter 13 converts the electric signal amplified by the amplifier 11 into digital data within a dynamic range equal to or higher than a designated reference voltage. Then, the shading correction unit 15 stores correction value data for one line in advance and subtracts the correction value data from the A / D converted digital data to correct the sensitivity variation for each photoelectric element of the image sensor 7. To do. Then, the γ conversion unit 17 γ-converts the digital data using the value of the γ conversion table stored in advance in the scanner control unit 21 and outputs image data. Further, the travel control unit 9 travels the image sensor 7 and the light source unit 5 along the document surface of the document 3 at a moving speed designated for each line and sequentially performs sub-scanning, and only one document 3 is scanned. Read.
[0028]
Therefore, the optical density OD of the document 3 read by the image sensor 7 can be narrowed down and the gain at the time of photoelectric conversion can be adjusted to make the reading speed variable. As a result, the original can be read with the optical density OD limited according to the reading speed designated by the user, and high-speed reading with less noise can be performed.
[0029]
(Second Embodiment)
FIG. 3 is a diagram showing the configuration of the image reading apparatus 21 according to the second embodiment of the present invention. 3 that are the same as those shown in FIG. 1 are assigned the same reference numerals, and descriptions thereof are omitted.
[0030]
In the first embodiment, since the optical density OD is limited, a dynamic range capable of A / D conversion is wasted below the reflectance r corresponding to the optical density OD.
Therefore, in the second embodiment, the scanner control unit 39 controls the offset and gain of the amplifier 33 and extends the dynamic range in which A / D conversion by the A / D converter 35 is possible from the reflectance r to the upper limit. The A / D conversion is performed on the electric signal input from the amplifier 33.
[0031]
The offset of the amplifier 33 may be set so as to decrease to a voltage equivalent to the output value ofs in consideration of the reflectance r corresponding to the limit of the optical density OD at the time of standard reading. Further, the gain g of the amplifier 33 is set so that the maximum output value of the A / D converter 35 is k.
g = mx (k / (k-ofs))
Then, as shown in FIG. 4, the white level W is in the vicinity of the maximum value k. In the scanner control unit 39, the amplifier 33 controls the offset and gain voltages.
In the scanner control unit 39, the white reference data W of the shading correction designated to the shading correction unit 37 is based on the white correction data W and the offset ofs at the time of full range reading.
w = (W-ofs) × g
Generate as
[0032]
In this way, in addition to the first embodiment, the dynamic range during substantial A / D conversion is expanded to improve the gradation resolution during A / D conversion. Yon) It is possible to suppress the occurrence of pseudo contours in the area. As a result, the dynamic range at the time of A / D conversion corresponding to the restriction of the optical density OD can be expanded, and high-speed reading can be performed in a state where the generation of noise with improved gradation is small.
[0033]
(Third embodiment)
FIG. 5 is a diagram showing a configuration of an image reading apparatus 31 according to the third embodiment of the present invention. Of the components shown in FIG. 5, the same components as those shown in FIG.
In the first and second embodiments, the user needs to designate the speed by the operation unit 19, but in the third embodiment, the optical data is obtained by using the histogram of the image data obtained at the time of pre-scanning. By determining the value to be set for the density OD and performing speed control, designation of the speed by the user is omitted.
[0034]
The scanner control unit 39 first generates a histogram of the reading density of the document 3 based on the image data obtained at the time of pre-scanning and stores it in the histogram storage unit 53.
Here, the high density region is discriminated in the histogram stored in the histogram storage unit 53, and as described above, the optical density is OD = 1.8 (r = 0.016) to 2.0. Reading speed, optical density OD = 1.5 (r = 0.03), double reading speed, optical density OD = 1.0 (reflectance r = 0.1), 4 times reading speed. Is appropriate.
On the other hand, as shown in FIG. 6, when there is no high density region, the optical density OD may be limited by the minimum value ofs.
[0035]
In the histogram stored in the histogram storage unit 53, as shown in FIG. 7, when there is no high density area different from the character / line image (A), the character / line image part (A) is excluded. The optical density OD may be limited by the minimum value ofs of the region. Specifically, as shown in FIG. 7, it is determined that there is no gradation image in a region (B) where the frequency of a certain density ofs or less is x or less, and the obtained offset minimum value ofs is used as an offset for the amplifier 33. Should be set.
[0036]
In this way, in addition to the second embodiment, the offset to be limited of the optical density OD can be determined and automatically set in the amplifier based on the histogram of the image data obtained at the time of pre-scanning. Specification of the speed can be omitted, and high-speed reading can be performed in a state in which the generation of noise is small.
[0037]
(Fourth embodiment)
The configuration of the image reading apparatus according to the fourth embodiment of the present invention is the same as that of the image reading apparatus according to the third embodiment shown in FIG.
In the second and third embodiments, as shown in FIG. 8, the dynamic range (c) of A / D conversion on the white side is not expanded, but in the fourth embodiment, it is obtained at the time of pre-scanning. Since the maximum value of the optical density OD can be detected by using the histogram of the obtained image data, the scanner control unit 39 offsets the amplifier 33 so that the maximum value of the optical density OD is within the dynamic range of A / D conversion. And the gain may be adjusted.
[0038]
The reading speed ratio m with the standard reading corresponds to the reflectance r (0.016 to 0.01) of the target optical density OD (about 1.8 to 2.0) and the optical density OD at the time of standard reading. It is the ratio of reflectance.
The offset of the amplifier 33 may be set so as to decrease to a voltage equivalent to the output value ofs in consideration of the reflectance r corresponding to the limit of the optical density OD at the time of standard reading.
As for the gain g of the amplifier 33, if the maximum value that can be output by the A / D converter 35 is k and the detected maximum value is j,
g = mx (k / (j-ofs))
Should be set to be.
[0039]
If the offset and gain of the amplifier 33 are adjusted so that the dynamic range of the A / D converter 35 falls within a certain range, a problem may occur in shading correction depending on the offset adjustment amount. Based on the data and black correction data, adjusted black correction data and white correction data are generated.
[0040]
When the white reference data at full range reading is W, the black reference data is B, the white reference data at the main scan is w, and the black reference data is b, the relationship is as shown in FIG.
w = (W-ofs) × g
b = (B-ofs) × g
As described above, white reference data and black reference data at the time of the main scan can be obtained.
However, if the number of bits of the A / D converter 35 is n,
b <0, w> 2n
Therefore, it is necessary to increase the number of data bits of the shading correction unit 37 and the γ conversion unit 17 by 1 or 2 bits during the process from the shading correction to the end of the γ conversion. is there.
[0041]
As described above, in addition to the third embodiment, the maximum value of the optical density OD is set as the limit value based on the histogram of the image data obtained at the time of pre-scanning, and based on the maximum value and the minimum value. Since the dynamic range of A / D conversion is expanded, it is possible to improve the gradation by omitting designation by the user, and high-speed reading can be performed with little noise.
[0042]
【The invention's effect】
As described above, according to the first aspect of the present invention, the optical density OD of the original read by the image sensor can be reduced, and the gain at the time of photoelectric conversion can be adjusted to make the reading speed variable. . As a result, the original can be read with the optical density OD limited according to the reading speed designated by the user, and high-speed reading with less noise can be performed.
[0043]
According to the image reading apparatus of the second aspect, since the dynamic range at the time of substantial A / D conversion is expanded and the gradation resolution at the time of A / D conversion is improved, continuous gradation change (gradation) It is possible to suppress the occurrence of a pseudo contour with respect to the region. As a result, the dynamic range at the time of A / D conversion corresponding to the restriction of the optical density OD can be expanded, and high-speed reading can be performed in a state where the generation of noise with improved gradation is small.
[0044]
According to the image reading apparatus according to claim 3, the reading speed of the original is controlled by making the reading speed of the document variable based on the optical density of the high density area in the histogram obtained at the time of pre-scanning. Can be omitted, and high-speed reading can be performed.
[0045]
According to the image reading device of the fourth aspect, the offset to be limited of the optical density OD can be determined and automatically set in the amplifier based on the histogram of the image data obtained at the time of pre-scanning. Specification of the speed can be omitted, and high-speed reading can be performed in a state in which the generation of noise is small.
[0046]
According to the image reading device of claim 5, based on the histogram of the image data obtained at the time of pre-scanning, the maximum value of the optical density OD is set as the limit value, and based on the maximum value and the minimum value, Since the dynamic range of the A / D conversion is expanded, it is possible to improve the gradation by omitting designation by the user, and high-speed reading can be performed in a state where there is little noise generation.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an image reading apparatus 1 according to a first embodiment of the present invention.
FIG. 2 is a diagram for explaining the operation of the image reading apparatus 1;
FIG. 3 is a diagram showing a configuration of an image reading apparatus 21 according to a second embodiment of the present invention.
4 is a diagram illustrating an offset and a gain set in an amplifier 33. FIG.
FIG. 5 is a diagram showing a configuration of an image reading apparatus 31 according to a third embodiment of the present invention.
FIG. 6 is a diagram showing a histogram of the reading density of the document 3 generated based on image data obtained at the time of pre-scanning.
FIG. 7 is a diagram illustrating that a character / line image (A) is included as a histogram of the reading density of the document 3 generated based on image data obtained at the time of pre-scanning.
8 is a diagram illustrating an offset and a gain set in an amplifier 33. FIG.
[Explanation of symbols]
1, 21, 31 Image reading apparatus 3 Document 5 Light source unit 7 Image sensor 9 Travel control unit 11 Amplifier 13 A / D converter 15 Shading correction unit 17 γ conversion unit 19 Operation unit 21 Scanner control unit 33 Amplifier 35 A / D conversion 37 Shading correction unit 39 Scanner control unit 53 Histogram storage unit

Claims (5)

Illumination means for irradiating unadjusted light on the document surface;
Photoelectric conversion means for accumulating the light reflected by the document surface for each light accumulating time for each line and converting it into an electric signal in the main scanning direction;
Moving means Before moving at the moving speed specified in the sub-scanning direction the illuminating means and the photoelectric conversion means to the document surface,
Amplifying means for amplifying the electrical signal converted by the photoelectric conversion means with a specified gain;
A / D conversion means for converting the electric signal amplified by the amplification means into digital data;
An operation means for specifying a document reading speed;
An image reading apparatus comprising:
In accordance with the designated reading speed by the operation means, the moving speed of the moving means, the light accumulating time of the photoelectric conversion means, to adjust the gain of the amplifying means, the output of the amplifying means of the optical density of the document An image reading apparatus comprising: a control unit configured to control to output a processing value corresponding to the predetermined value when the value is less than a value corresponding to the predetermined value . 2. The image reading apparatus according to claim 1, wherein the control unit adjusts the offset of the amplification unit and controls the output to optimize the dynamic range of the A / D conversion unit . Histogram generation means for generating a histogram representing the degree of appearance of reading density based on image data at the time of pre-scanning;
Histogram storage means for storing the histogram generated by the histogram generation means,
The control means includes
2. The image reading apparatus according to claim 1, wherein the reading speed of the document is controlled to be variable based on the optical density of the high density area in the histogram obtained at the time of pre-scanning. The control means includes
If the high-density area of the document does not appear in the histogram obtained during pre-scanning, or if the high-density area is determined to be only a character / line image, the offset value that should limit the optical density of the document is determined. 4. The image reading apparatus according to claim 3, wherein the image reading apparatus is set to the amplifying unit and is controlled so that the reading speed of the original is variable. The control means includes
If the high density area of the document does not appear in the histogram obtained during prescan, or if it is determined that the high density area is only a character / line image, based on the maximum and minimum values in this histogram, 4. The image reading apparatus according to claim 3, wherein an offset and a gain of the amplifying unit are adjusted, a dynamic range at the time of A / D conversion is extended, and a document reading speed is controlled to be variable.

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