Facsimile and static presentation processing – Natural color facsimile – Color correction
Reexamination Certificate
1997-06-04
2001-01-30
Mehta, Bhavesh (Department: 2721)
Facsimile and static presentation processing
Natural color facsimile
Color correction
C358S521000
Reexamination Certificate
active
06181444
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image reading apparatus which is capable of performing &ggr;-correction and background gray level correction in a facsimile machine or a photocopying machine for example. The present invention also relates to an information storing medium which is used for controlling such an image reading apparatus.
2. Description of the Related Art
Typically, an image reading apparatus, such as an image scanner of a facsimile machine, comprises an image reader for reading images of an image carrying paper for output of corresponding analog image signals, an A/D converter for converting the analog image signals into multi-bit digital image data, a &ggr;-correction unit for performing &ggr;-correction of the digital image data. Further, the image reading apparatus also includes means for correcting the background gray level of the image signals at the time of converting the analog image signals into the digital image data. Such background gray level correction is necessary because the dynamic range of the non-background image signals relative to the background image signals reduces to result in poor resolution if the background is relatively dark.
For background gray level correction, a conventional image reading apparatus incorporates a peak hold circuit for holding the peak level of analog image signals from an image reader, and the peak level held by the peak hold circuit is utilized as a high level reference value for an A/D converter. Thus, when the voltage of the analog image signals becomes equal to the peak value, the digital output of the A/D converter becomes equal to the high level reference value which is the highest value of the converter.
Another image reading apparatus is also known which incorporates an automatic gain control circuit including an amplifier for amplifying analog image signals to such a degree that the peak level of the analog image signals is elevated to coincide with the high level reference value of an A/D converter.
However, either of the image reading apparatuses described above requires hardware addition of the peak hold circuit or the automatic gain control circuit, consequently resulting in a cost increase.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention is to provide an image reading apparatus which is capable of performing background gray level correction without hardware addition.
Another object of the present invention is to provide an information storing medium which can be advantageously used for such an image reading apparatus.
According to one aspect of the present invention, there is provided an image reading apparatus comprising: reading means for reading images for output of corresponding analog image signals; an A/D converter for converting the analog image signals into multi-bit digital image data; &ggr;-correction means for performing &ggr;-correction of the digital image data; background gray level detection means for detecting a background gray level of the analog image signals on the basis of the digital image data; and coefficient modifying means for modifying a standard set of &ggr;-correction coefficient data into a modified set of &ggr;-correction coefficient data on the basis of the detected background gray level.
With the image reading apparatus described above, the background gray level detection means and the coefficient modifying means can be incorporated in a central processing unit of the image reading apparatus. Thus, the background gray level correction can be realized only by software addition, thereby obviating the need for hardware addition of a peak hold circuit or an automatic gain control circuit for example. Further, since the background gray level correction can be performed together with the &ggr;-correction, the time required for performing the background gray level correction can be minimized.
Preferably, the image reading apparatus may further comprise storing means for storing a standard &ggr;-correction look-up table, so that the coefficient modifying means modifies the standard &ggr;-correction look-up table into a modified &ggr;-correction look-up table on the basis of the detected background gray level for supplying to the &ggr;-correction means. Further, the storing means may also store a coefficient modifying program used for modifying the standard &ggr;-correction look-up table into the modified &ggr;-correction look-up table. The storing means may advantageously comprise a ROM.
Preferably, the image reading apparatus may further comprise a shading compensation circuit between the reading means and the A/D converter for performing shading compensation of the analog image signals. In this case, the background gray level detection means may be in the form of a peak level detection circuit for detecting a peak level of the digital image data which is used for determining the background gray level of the analog image signals. Further, storing means such as a ROM may be provided for storing a peak level detection program.
According to a preferred embodiment, the &ggr;-correction means, the background gray level detection means and the coefficient modifying means are incorporated in a central processing unit of the image reading apparatus.
According to another aspect of the present invention, there is provided an image reading apparatus comprising: reading means for reading images for output of corresponding analog image signals; an A/D converter for converting the analog image signals into multi-bit digital image data; and means for performing &ggr;-correction of the digital image data together with background gray level correction of the digital image data.
Further, the means for performing the &ggr;-correction and the background gray level correction comprises: background gray level detection means for detecting a background gray level of the analog image signals on the basis of the digital image data; coefficient modifying means for modifying a standard &ggr;-correction look-up table into a modified &ggr;-correction look-up table on the basis of the detected background gray level; and &ggr;-correction means for performing &ggr;-correction of the digital image data on the basis of the modified &ggr;-correction look-up table.
According to a further aspect of the present invention, there is provided an information storing medium used for controlling an image reading apparatus which comprises reading means for reading images for output of corresponding analog image signals, an A/D converter for converting the analog image signals into multi-bit digital image data, and &ggr;-correction means for performing &ggr;-correction of the digital image data, the medium storing: a background gray level detection program for detecting a background gray level of the analog image signals on the basis of the digital image data; and a coefficient modifying program for modifying a standard set of &ggr;-correction coefficient data into a modified set of &ggr;-correction coefficient data on the basis of the detected background gray level.
Preferably, the standard set of &ggr;-correction coefficient data may be in the form of a standard &ggr;-correction look-up table. In this case, the coefficient modifying program is used for modifying the standard &ggr;-correction look-up table into a modified &ggr;-correction look-up table as the modified set of &ggr;-correction coefficient data.
Preferably, the background gray level detection program may be in the form of a peak level detection program for detecting a peak level of the digital image data which is used for determining the background gray level of the analog image signals.
Typically, the information storing medium may be in the form of a ROM.
Other objects, features and advantages of the present invention will be apparent from the detailed description of the embodiment given below with reference to the accompanying drawings.
REFERENCES:
patent: 4535351 (1985-08-01), Van Roessel
patent: 4608595 (1986-08-01), Nakayama et al.
patent: 4709274 (1987-11-01), Taniok
Brother Kogyo Kabushiki Kaisha
Mehta Bhavesh
Oliff & Berridg,e PLC
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