JP3547964B2 - Image reading device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image reading apparatus used for a facsimile apparatus or the like and for reading a document image.
[0002]
[Prior art]
This type of apparatus performs various kinds of signal processing on an image signal obtained by an image sensor such as a contact image sensor to generate image data in a predetermined form. One of the above-mentioned signal processes is a gamma correction process for correcting a gradation characteristic.
[0003]
In general, the gamma correction process is performed by preparing a gamma correction parameter corresponding to the characteristics of the image sensor in advance and performing gamma conversion on an image signal output from the image sensor based on the gamma correction parameter.
[0004]
Here, it is necessary to prepare a gamma correction parameter for each gradation value (for example, 256) in the image signal. Further, when a plurality of reading modes are provided, different gamma correction parameters are required for each reading mode even for the same gradation value.
[0005]
Thus, gamma correction parameter groups consisting of the same number of gamma correction parameters as the number of tones in the image signal must be prepared for the number of read mode types, and the total number of gamma correction parameters becomes very large. Therefore, the data amount of the gamma correction parameter becomes extremely large, and there is a problem that a large memory is required to store the data.
[0006]
Therefore, various devices have been devised to reduce the amount of data prepared in advance, and one of them is disclosed in Japanese Patent Application Laid-Open No. 2-230873.
[0007]
In Japanese Unexamined Patent Publication No. Hei. 2-230873, individual values are written in a ROM for a portion where the gamma correction characteristic indicates non-linearity, and a calculation is performed for a portion where the gamma correction characteristic indicates linearity. Is disclosed.
[0008]
Therefore, according to JP-A-2-230873, it is sufficient to prepare only a part where the gamma correction characteristic indicates non-linearity, that is, only a part of all the correction values. The amount of data prepared in advance is reduced.
[0009]
[Problems to be solved by the invention]
By the way, according to the technology disclosed in JP-A-2-230873, it is possible to cope only with a single gamma correction characteristic. Any device can be applied as long as the gamma correction characteristic of the device can be considered.
[0010]
However, the facsimile machine has various modes such as high definition, fine, and standard, and the reading density can be set in several steps in each of these modes. The power gamma correction characteristics differ. Therefore, it is difficult to apply the technology disclosed in Japanese Patent Application Laid-Open No. 2-230873 to a device having such conditions.
[0011]
An image processing LSI (LC82103) manufactured by Mitsubishi Electric Corporation is known as a gamma correction circuit applicable to a case where a plurality of reading modes are provided.
[0012]
Prior to executing the gamma correction processing, this image processing LSI performs 00 (H), 10 (H), 20 (H),..., F0 of 256 gradations from 00 (H) to FF (H). When gamma correction parameters for 17 (H) and FF (H) are given, gamma correction parameters for all 256 gradations are generated by linear interpolation processing based on these values, and thereafter, based on the generated gamma correction parameters. It has a function of executing gamma conversion processing.
[0013]
Therefore, if this image processing LSI is used, gamma correction processing based on various gamma correction characteristics can be performed by changing a given gamma correction parameter, and the gamma correction parameter prepared in advance for one gamma correction characteristic is 17 Individuals are fine.
[0014]
However, in the case of the image processing LSI described above, since 256 gamma correction parameters are generated from 17 discrete gamma correction parameters by linear interpolation processing, original gamma correction parameters may be reproduced depending on gamma correction characteristics. In some cases, the gamma correction process cannot be performed accurately.
[0015]
The present invention has been made in view of such circumstances, and a purpose thereof is to generate all gamma correction parameters from arbitrary discrete gamma correction parameters and use them for gamma correction processing. By using the method, it is possible to support a plurality of gamma correction characteristics, and use a more appropriate gamma correction parameter without significantly reducing the effect of reducing the amount of data prepared in advance. An object of the present invention is to provide an image reading apparatus capable of performing an accurate gamma correction process and generating appropriate image data.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an image signal generated by an image sensor in accordance with a reflected light image from a document, with each of predetermined gradation values existing at predetermined intervals within a predetermined gradation range. Gamma conversion is performed by a gamma conversion unit using a gamma correction parameter related to the image signal to obtain a gamma-corrected image signal. The gamma correction parameter differs according to a specified reading mode among a plurality of reading modes. in the image reading apparatus using the group, for each of the gamma correction parameter groups corresponding to the reading density settable Oite number stage to each of the plurality of reading modes, the discrete part of the gamma correction parameters included Discrete value storage means such as, for example, a discrete value storage unit for storing discrete tone values as discrete values; For gamma correction parameter groups corresponding to the reading density of a predetermined reading mode of the gamma correction parameter groups corresponding to the reading density settable Oite number stages each mode, the plurality comprising a boundary the discrete gradation values And a gamma correction parameter group to be used by the gamma conversion means for storing, as detailed values, gamma correction parameters related to all the gradation values included in a predetermined part of the predetermined gradation section. For example, a use parameter storage means such as a use parameter memory, and a discrete value corresponding to a designated read mode are read from the discrete value storage means, and the predetermined value is interpolated based on the discrete value. Generates all gamma correction parameters for each of a predetermined number of tone values existing at predetermined intervals within the tonal range, The write to the use parameter storage unit, for example the use parameter generating means comprising a usage parameter generation control means and the linear interpolation section, details value corresponding to the read density of the read mode is the specified in the detail value storage means stores And a detailed value writing means for writing the detailed value in place of the gamma correction parameter related to the same gradation value among the gamma correction parameters written to the used parameter storage means by the used parameter generating means if the specified value has been set. .
[0017]
By adopting such means, the gamma correction parameter to be used by the gamma conversion means is generated by an interpolation process based on the discrete value corresponding to the specified reading mode among the discrete values stored in the discrete value storage means. . Further, for a predetermined reading mode of a part of the plurality of reading modes, a part of the generated gamma correction parameter is changed to the detailed value stored in the detailed value storage unit.
[0018]
Therefore, all gamma correction parameters for a certain reading mode are required based on some gamma correction parameters of all the gamma correction parameters for one reading mode stored in the discrete value storage unit and the detailed value storage unit. Therefore, it is not necessary to prepare all the gamma correction parameters in advance. Then, for a gradation section in which an appropriate value cannot be generated by the interpolation processing, the gamma correction parameter generated by the interpolation processing is replaced with a value prepared in advance as a detailed value, so that an appropriate gamma correction parameter group is can get.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an image reading apparatus according to an embodiment of the present invention will be described with reference to the drawings.
[0020]
FIG. 1 is a functional block diagram illustrating a main configuration of the image reading apparatus according to the present embodiment.
[0021]
As shown in this figure, the image reading apparatus of the present embodiment has an image sensor 1, a gamma correction unit 2, an image processing unit 3, a correction parameter memory 4, and a reading control unit 5.
[0022]
The image sensor 1 uses, for example, a well-known sensor such as a contact image sensor. The image sensor 1 converts a reflected light image from an original when illuminating the original into an electric signal, and furthermore, converts the gradation of the image in pixel units. , And is output as an image signal represented by a gradation value obtained by dividing a gradation range from “white” to “black” into a predetermined number (here, 256) at equal intervals.
[0023]
The gamma correction unit 2 performs gamma correction processing on an image signal output from the image sensor 1 and includes a linear interpolation unit 21, a use parameter memory 22, and a gamma conversion unit 23. As the gamma correction unit 2, for example, an image processing LSI (LC82103) manufactured by Mitsubishi Electric Corporation or the like can be used.
[0024]
The linear interpolation unit 21 generates 256 gamma correction parameters by linear interpolation processing based on the 17 gamma correction parameters provided from the reading control unit 5. Then, the linear interpolation unit 21 writes the generated 256 gamma correction parameters into the use parameter memory 22. The use parameter memory 22 stores the 256 gamma correction parameters written by the linear interpolation unit 21 as use parameters for the gamma conversion unit 23 to use. The gamma conversion unit 23 performs gamma conversion processing on the image signal output from the image sensor 1 using the gamma correction parameter stored in the use parameter memory 22, and outputs the processed image signal to the image processing unit 3. Give to
[0025]
The image processing unit 3 arbitrarily performs known image processing such as pseudo halftone binary data processing on the image signal that has been gamma-corrected by the gamma correction unit 2 to generate image data in a predetermined form. I do.
[0026]
The candidate parameter memory 4 stores data relating to gamma correction characteristics corresponding to each of a plurality of reading modes of the image reading apparatus. The candidate parameter memory 4 stores the discrete value storage unit 4a and the detailed value storage unit 4b. Have. The discrete value storage unit 4a stores, for each of the gamma correction characteristics corresponding to each of the plurality of reading modes, 00 (H), 10 (H), and 00 (H) of 256 gradations from 00 (H) to FF (H). 20 (H)..., F0 (H), FF (H), only the gamma correction parameters relating to the 17 parameters, that is, the gamma correction parameters discretely present in each gamma correction characteristic (hereinafter referred to as discrete values) are written. ing. The detailed value storage unit 4b stores gamma correction parameters (hereinafter referred to as “details”) for each of 15 gradations from 01 (H) to 0F (H) regarding gamma correction characteristics corresponding to some of the plurality of reading modes. Value) is written.
[0027]
For example, a facsimile apparatus generally has a high-definition halftone mode, a fine halftone mode, a standard halftone mode, and the like, and in each of these modes, the reading density can be set in several steps.
[0028]
FIG. 2 is a diagram showing an example of a gamma correction characteristic in a high definition halftone mode in a facsimile apparatus. In this figure, the horizontal axis indicates the tone value of the image signal, the vertical axis indicates the gamma correction parameter value to be used for the gamma conversion process of the tone value, and each curve has a different read density. 9 shows gamma correction characteristics under the circumstances. Note that the reading density changes in the order of D3, D2, D1, N, L1, L2, and L3. Then, based on such characteristics, data as shown in FIG. 3 is generated in advance and written to the discrete value storage unit 4a.
[0029]
Also, as can be seen from FIG. 2, the reading densities of N, L1, L2, and L3 in the section from 00 (H) to 10 (H) are obtained by linear interpolation based on actual characteristics and discrete values. Will be different. Therefore, only for these read densities, as shown in FIG. 4, gamma correction parameter values for each gradation value of 01 (H) to 0F (H) are written to the detailed value storage unit 4b.
[0030]
The reading control section 5 has, for example, a microcomputer as a main control circuit, and realizes an operation as an image reading apparatus by controlling each part of the present image reading apparatus. The reading control unit 5 includes a use parameter generation control unit 5a and a detailed value writing unit 5b in addition to a well-known control unit for realizing a well-known general operation in the image reading apparatus. It is realized by.
[0031]
Here, the usage parameter generation control unit 5a causes the linear interpolation unit 21 to generate 256 gamma correction parameters according to the reading mode. The detailed value writing means 5b overwrites a part of the gamma correction parameter written in the use parameter memory 22 with the detailed value stored in the detailed value storage unit 4b.
[0032]
Next, the operation of the image reading apparatus configured as described above will be described.
[0033]
When reading is instructed from outside (for example, from a control unit of a facsimile apparatus to which the present image reading apparatus is applied), the reading control unit 5 performs the use as shown in FIG. Execute the parameter setting process.
[0034]
In the use parameter setting process, the reading control unit 5 first determines the designated reading mode based on the reading mode designation data given from the outside (step ST1). Then, a discrete value corresponding to the designated reading mode is read out from the discrete value storage section 4a of the candidate parameter memory 4a, and given to the linear interpolation section 21 (step ST2).
[0035]
In response, the linear interpolation unit 21 generates the remaining 239 gamma correction parameters by linear interpolation based on the given discrete values, and prepares all 256 gamma correction parameters. Then, the linear interpolation unit 21 writes the 256 gamma correction parameters into the use parameter memory 22.
[0036]
Therefore, after giving the discrete value to the linear interpolation unit 21 in step ST2, the reading control unit 5 waits for the completion of the writing of the gamma correction parameter into the use parameter memory 22 by the linear interpolation unit 21 (step ST3). . When the writing of the gamma correction parameter is completed, the reading control unit 5 determines whether or not the detailed value relating to the designated reading mode is stored in the detailed value storage unit 4b (step ST4). If so, the detailed values are overwritten on the gamma correction parameters written in the use parameter memory 22 corresponding to the 15 gradations from 01 (H) to 0F (H) (step ST5). Thereafter, the use parameter setting process ends. If the detailed value related to the designated reading mode is not stored in the detailed value storage unit 4b, the reading control unit 5 ends the use parameter setting process without performing the process of step ST5.
[0037]
After the above-described use parameter setting processing is completed, an actual reading operation is performed by, for example, a well-known procedure. At the time of this reading operation, the image signal output from the image sensor 1 is subjected to gamma conversion by the gamma conversion unit 23 using the gamma correction parameter written in the usage parameter memory 22 by the above-described usage parameter setting process. By performing the gamma correction, gamma correction based on the gamma correction characteristic according to the designated reading mode is performed.
[0038]
As described above, according to the present embodiment, basically, the remaining 239 gamma correction parameters are generated when necessary by linear interpolation processing based on 17 discrete values, so that all 256 gamma correction parameters are generated. However, for each gamma correction parameter in a part of the gamma correction characteristic corresponding to a part of the reading mode, each value is separately prepared as a detailed value, and the gamma correction generated by linear interpolation is prepared. They are used instead of parameters.
[0039]
As a result, even if a complicated characteristic that cannot be dealt with by the linear interpolation process is included in a part of the gamma correction characteristic, the gamma correction characteristic is prompted to the actual gamma correction characteristic for the part. Correction parameters can be used. Therefore, appropriate gamma correction processing can be performed using more appropriate gamma correction parameters.
[0040]
In addition, since the gamma correction parameters prepared as detailed values are only the gamma correction parameters for some sections of the gamma correction characteristics corresponding to some reading modes, the amount of information prepared in advance is discrete. The value does not increase so much as compared with the case where only the value is prepared, and is extremely small as compared with the case where all the gamma correction parameters are prepared.
[0041]
Note that the present invention is not limited to the above embodiment. For example, in the above embodiment, the discrete values are used as the gamma correction parameters for 17 of 00 (H), 10 (H), 20 (H),..., F0 (H), and FF (H). Is possible.
[0042]
Further, in the above embodiment, the detailed value is set as the gamma correction parameter for each of the 15 gradations from 01 (H) to 0F (H), but the gamma correction parameter for the other gradation sections may be set as the detailed value. It is possible.
[0043]
In addition, various modifications can be made without departing from the spirit of the present invention.
[0044]
【The invention's effect】
According to the present invention, an image signal generated by an image sensor according to a reflected light image from a document is converted to a gamma correction parameter for each of predetermined gradation values existing at predetermined intervals within a predetermined gradation range. An image reading apparatus that obtains an image signal subjected to gamma correction by performing gamma conversion by a gamma conversion unit using different gamma correction parameter groups according to a designated reading mode among a plurality of reading modes in, for each of the gamma correction parameter groups corresponding to the reading density settable Oite number stage to each of the plurality of reading modes and related to discrete tone value of discrete part of the gamma correction parameters included a discrete value storing means for storing an object as a discrete value, settable by Oite number stage to each of the plurality of reading modes For gamma correction parameter groups corresponding to the reading density of a predetermined reading mode of the gamma correction parameter groups corresponding to the concentration taken, a predetermined portion of the plurality of gray level section comprising the discrete tone value as a border A detailed value storage means for storing gamma correction parameters relating to all included gradation values as detailed values, a use parameter storage means for storing a gamma correction parameter group to be used by the gamma conversion means, A discrete value corresponding to the read mode being read is read out from the discrete value storage means, and interpolation processing based on the discrete value is performed to obtain a predetermined number of tone values existing at given intervals within the given tone range. Use parameter generation means for generating all of the gamma correction parameters and writing the same in the use parameter storage means; If more information value corresponding to the read density of the read mode the specified in憶means is stored the detailed values, of the gamma correction parameters written in the usage parameter memory means by the use parameter generating means And a detailed value writing means for writing in place of the one relating to the same gradation value. Therefore, a method of generating all gamma correction parameters from arbitrary discrete gamma correction parameters and using them for gamma correction processing By using this, it is possible to cope with a plurality of gamma correction characteristics, and without reducing the effect of reducing the amount of data prepared in advance, an accurate gamma correction parameter using a more appropriate gamma correction parameter can be used. An image reading device that can generate appropriate image data by performing gamma correction processing.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a main configuration of an image reading apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram showing an example of a gamma correction characteristic in a high definition halftone mode in a facsimile apparatus.
FIG. 3 is a diagram schematically illustrating an example of a storage state of a gamma correction parameter in a discrete value storage unit 4a.
FIG. 4 is a diagram schematically illustrating an example of a storage state of a gamma correction parameter in a detailed value storage unit 4b.
FIG. 5 is a flowchart showing a processing procedure of a reading control unit 5 relating to use parameter setting processing.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image sensor 2 ... Gamma correction part 21 ... Linear interpolation part 22 ... Used parameter memory 23 ... Gamma conversion part 3 ... Image processing part 4 ... Correction parameter memory 4a ... Sparse value storage part 4b ... Detailed value storage part 5 ... Reading control Unit 5a: Usage parameter generation control unit 5b: Detailed value writing unit

Claims (1)

The image signal generated by the image sensor according to the reflected light image from the document is converted into a gamma by a gamma conversion unit using a gamma correction parameter for each of predetermined gradation values existing at predetermined intervals within a predetermined gradation range. An image reading apparatus that obtains an image signal subjected to gamma correction by performing conversion, and uses a different gamma correction parameter group according to a designated reading mode among a plurality of reading modes,
For each gamma correction parameter groups corresponding to the reading density settable Oite number stage to each of the plurality of reading modes, those related to the discrete gradation values of discrete part of the gamma correction parameters included Discrete value storage means for storing as a discrete value,
For gamma correction parameter groups corresponding to the reading density of a predetermined reading mode of the gamma correction parameter groups corresponding to the reading density settable Oite number stage to each of the plurality of reading modes, the discrete tone value Detailed value storage means for storing, as detailed values, gamma correction parameters related to all the gradation values included in a predetermined part of the plurality of gradation sections as boundaries,
Use parameter storage means for storing a gamma correction parameter group to be used by the gamma conversion means,
A discrete value corresponding to the designated reading mode is read from the discrete value storage means, and interpolation processing based on the discrete value is used to execute each of a predetermined number of gradation values existing at predetermined intervals within the predetermined gradation range. Generation parameter generation means for generating all of the gamma correction parameters related to, and writing it to the usage parameter storage means,
If a detailed value corresponding to the read density of the designated reading mode is stored in the detailed value storage means, the detailed value is used for the gamma correction written in the use parameter storage means by the use parameter generation means. An image reading apparatus comprising: a detailed value writing unit that writes in place of a parameter relating to the same gradation value among parameters.

Images