JPH01264072A - Image scanner - Google Patents

Abstract

PURPOSE:To correct a digital signal surely and accurately and to eliminate the dispersion in an output signal by obtaining a mean value of remaining values except, e.g., a maximum value or a minimum value among digital picture signals and varying a reference voltage given to an AD converter in response to the mean value. CONSTITUTION:The mean value of remaining digital signals except the maximum value and the minimum value among plural digital signals representing the contrast of a reference color plane 3 is used as a reference voltage of the AD converter 6, the picture information of an original or the like is converted into a digital signal to correct the dispersion in the output signal. Thus, no error is caused to the outputted digital signal such as a flaw or dirt on the reference color face difference from only one reading of the reference color face in a conventional method. Thus, the reading of the original or the like by the line sensor 1 is endured and the read data is printed out with a proper density and wasteful reading is avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an image scanner that reads image information of a document or the like, converts it into a digital signal, and outputs the digital signal.

<Prior Art> Conventionally, this type of image scanner consists of a light emitting element that emits light toward the document surface and a light receiving element that receives the light reflected from the document surface and converts the density of the document into an analog image signal. It is equipped with a line sensor that moves in the lateral direction of the document, and an AD converter that converts the output signal from the line sensor into a digital signal. Since the analog image signal from the line sensor varies bit by bit, a reference color surface is provided on the reference surface of the platen glass on which the document is placed approximately parallel to the line sensor, and the above-mentioned values obtained for this reference color surface are The reference voltage input to the AD converter is changed in accordance with the output signal of the AD converter to correct the digital output signal and eliminate variations.

<Problems to be Solved by the Invention> However, the above-mentioned conventional image scanners cannot generate digital image signals by using digital output signals obtained by reading only once a reference color plane provided on a reference plane of a platen glass. Since this is corrected, there is a drawback that if this reference color surface becomes scratched or dirty, it will directly affect the digital output signal. As a result, the document read by the image scanner cannot be printed out at an appropriate density, making the scanner operation completely useless.

Therefore, an object of the present invention is to reliably and accurately correct a digital signal read out by an image scanner and outputted via an AD converter using a reference color plane, thereby eliminating variations in the output signal. To provide an image scanner.

Means for Solving the Problems To achieve the above objects, the image scanner of the present invention includes a line sensor that reads image information of a document placed on a reference surface, and an analog signal output from the line sensor. an AD converter that performs AD conversion, a reference color plane provided on the reference plane, and a base Q voltage that reads this reference color plane multiple times and inputs it to the AD converter when reading the original based on the average value thereof. It includes an output correction means for changing the output.

Function> The line sensor reads the shading of a reference color surface provided on a reference surface such as a platen glass multiple times in parallel to the line sensor and outputs it as an analog image signal to the AD converter, and the AD converter The image signal is converted into a digital signal and inputted to the output correction means. The output correction means calculates the average value of the remaining values after removing the maximum value and minimum value from the digital image signal, and changes the reference voltage input to the AD converter according to this average value, To eliminate variations in output signals by reliably and accurately correcting digital signals representing the shading of a document output from an AD converter.

<Example> Hereinafter, the present invention will be explained in detail with reference to illustrated embodiments.

FIG. 1 is a perspective view showing the general appearance of the image scanner of the present invention, in which the line sensor l has a built-in light-emitting element and a light-receiving element (not shown), and is mounted on a platen glass 2 on which a document is placed with its surface facing down. The document is read while moving along the lower surface in the direction indicated by arrow A, and the shading of the document is output as an analog image signal. A reference color surface 3 is provided on the lower surface of the platen glass 2 in parallel with the line sensor 1.

FIG. 2 shows a schematic block diagram of the above-mentioned image scanner. In the same figure, 5 is a CPU which controls each block and also serves as an output correction means to be described later, and 6 is a CPU which controls analog signals output from the above-mentioned line sensor 1. An AD converter 7 converts into a digital signal, and a first memory 8 stores each digital signal obtained by reading the reference color plane 3 a plurality of times output from the AD converter 6.
A second memory 9 stores an average value calculated by the CPU 5 from the remaining digital signals after removing the maximum and minimum values of each of the digital signals stored in the first memory 7;
is a DA converter that outputs a reference voltage corresponding to the average value stored in the second memory 8 to the AD converter 6,
The AD converter 6 compares the analog signal manually input from the line sensor 1 with the reference voltage and outputs a corresponding digital signal.

The operation of the image scanner having the above configuration will be described next.

Before reading a document, the line sensor 1 reads a reference color surface 3 provided on a reference surface 2a of a platen glass 2 a plurality of times, converts each signal into a digital signal, and stores the signal in a first memory 7. Then, the CPU 5, which is the output correction means,
The average value is calculated from the remaining digital signals after removing the maximum and minimum values of each of the digital signals stored in the memory 7, and this average value is stored in the second memory 8.
The A converter 9 outputs a reference voltage corresponding to the average value stored in the second memory 8 to the AD converter 6. Thereafter, the line sensor l reads the original placed on the north surface of the platen glass 2 while moving in the direction of the arrow A, and outputs the density of the original as an analog image signal to the AD converter 6.
The D converter 6 converts the image signal into a digital signal and outputs the digital signal. At that time, the AD converter 6
An analog signal representing the shading of the document inputted from the converter is compared with the reference voltage, and a digital signal having a magnitude corresponding to the comparison result is output.

In this way, in this embodiment, the average value of the remaining digital signals excluding the maximum and minimum values among the plurality of digital signals representing the shading of the reference color plane 3 is used as the reference voltage of the AD converter 6, and the original Since the image information such as images is converted into a digital signal and variations in the output signal are corrected, the output digital signal is changed from scratches on the reference color surface and No errors occur due to dirt. Therefore, the line sensor 1 can reliably read a document or the like, and the read data can be printed out at an appropriate density, and wasteful reading operations can be eliminated.

Furthermore, it goes without saying that the present invention is not limited to the above embodiments.

<Effects of the Invention> As is clear from the above description, the image scanner of the present invention uses the reference voltage of an AD converter that AD converts an analog signal output from a line sensor that reads a document placed on a reference surface. is changed by an output correction means based on the average value of digital signals obtained by reading a reference color plane provided on the reference plane a plurality of times, thereby correcting the digital signal of the image information to be output. This eliminates errors in the output signal due to scratches or dirt on the reference surface, unlike when the reference color surface is read only once.
Document reading, printing, etc. can be performed reliably and appropriately.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an overview of the image scanner of the present invention, and FIG. 2 is a schematic block diagram of the image scanner. 1... Line sensor, 2... Platen glass, 3...
...Reference color plane, 5...CPU, 6...AD converter,
7...First memory, 8...Second memory, 9...D
A converter.

Claims (1)

[Claims] (1) A line sensor that reads image information such as a document placed on a reference surface, an AD converter that converts analog signals output from the line sensor from analog to digital, and a reference color surface provided on the reference surface; An image scanner comprising an output correction means for reading this reference color plane a plurality of times and changing a reference voltage input to the AD converter when reading the original based on the average value.