JPH06189132A - Image reader - Google Patents

Abstract

PURPOSE:To obtain an image reader capable of performing the optimum A/D conversion by performing the adjustment of light quantity of a light source, that of amplification factor of an amplifier means, and that of reference of an A/D converter. CONSTITUTION:This reader is provided with a linear image sensor which reads reflected light from an original illuminated with an illumination system as an electrical signal, the light source 7 which illuminates the original, a variable gain AMP 50 which amplifies the electrical signal, and the A/D converter 51 which performs the A/D conversion of an amplified electrical signal. The light quantity, the amplification factor of the AMP, and the reference of the A/D converter can be adjusted by detecting the mean value of plural images continuing in a main scanning direction behind the A/D converter 51 is detected within the number of picture elements decided in advance. and feeding back it from a D/A converter 52.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device provided in a digital copying machine, a facsimile or the like, and more particularly to a CCD.
The present invention relates to an image reading device using a line sensor.

[0002]

2. Description of the Related Art Conventionally, in a signal processing circuit of a CCD line sensor, a sample hold circuit detects a peak of a signal output of a light shield section output from the CCD, and the signal output is used to output the CCD in a dark state. Offset adjustment,
The amplified electric signal is subjected to peak detection by a sample hold circuit and converted as a conversion reference of the A / D converter. An image reading apparatus of this type is disclosed in, for example, Japanese Patent Laid-Open No. 62-
It is disclosed in Japanese Patent No. 76964.

[0003]

By the way, the conventional CC
In the signal processing circuit of the D-line sensor, the signal output of the light shield section output from the CCD is peak-detected by the sample hold circuit as described above, and the signal output is used to adjust the dark output offset of the CCD. Peak detection of the amplified electric signal with a sample and hold circuit,
Conversion was performed as the conversion reference voltage of the A / D converter.

Therefore, when the peak of the electric signal is detected by the sample-hold circuit, a leakage current is generated due to the characteristics of the capacitor used in the sample-hold circuit, and the peak detection voltage gradually decreases with the passage of time. Occurs, the CCD output offset adjustment failure during darkness, A
A conversion error occurs due to a change in the conversion reference voltage of the / D converter.

Further, since the peak of the electric signal of the sample hold circuit is detected before the A / D converter, a conversion error occurs between the reference voltage of the A / D converter and the input signal in the case of no adjustment. Also, in order to prevent an error, A /
It was necessary to make adjustments while watching the output of the D converter, which was troublesome.

An object of the present invention is to provide an image reading apparatus capable of optimal AD conversion by adjusting the light amount of a light source, adjusting the amplification factor of an amplifying means, and adjusting the reference of an A / D converter. .

[0007]

In order to achieve the above object, the present invention provides a linear image sensor for reading the reflected light from a document illuminated by an illumination system as an electric signal, and an illumination means for illuminating the document. In an image reading apparatus having an amplifying means for amplifying the electric signal and an A / D converting means for A / D converting the amplified electric signal, the image reading device is continuous in the main scanning direction after the A / D converting means. The plurality of images are configured as a first means for detecting an average value within a predetermined number of pixels in a specific section.

In order to achieve the above-mentioned object, the present invention is configured as a second means in the first means, in which the specific section is made variable according to a mode.

[0009]

In the first means, by detecting the average value of the image data, it is possible to reduce noise carried on the image data, and it is possible to eliminate setting mistakes due to noise.

In the second means, the specific section is made variable according to the reading mode, so that the average value of the image data is detected separately for the black dummy part, the image data part, the effective image range part and the like. It is possible to feed back the image data of the specific section efficiently.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view showing an example of an image reading apparatus using the present invention, and this image reading apparatus is of a type capable of reading a reflective original.

The image reading apparatus is a traveling body (scanner) 3 for reading an image while traveling along the guide rod 8 by a driving source and a driving system (not shown) when reading a reflection original.
The contact glass 2, the frame 1, the printed circuit board 21 for analog signal processing, and the printed circuit board 22 for digital signal processing.
A light source 7 for illuminating a reflection original, a converging light transmission body 4, and a photoelectric conversion element 6 are held in the traveling body 3. Reference numeral 5 is a color correction filter for correcting the color sensitivity balance of the photoelectric conversion element 6. Further, although not shown in the figure, a board for driving the photoelectric conversion element 6 and a printed board having an amplifier circuit for amplifying the output of the photoelectric conversion element are carried in the traveling body 3, and the traveling body 3 and the above-mentioned signal are carried. The processing substrates 21 and 22 are electrically connected via a cable 23.

FIG. 2 is a control block diagram of the image reading apparatus. The scanner unit is a scanner control unit 3 centered on the CPU.
4, a mechanical drive unit 35 for a motor or a cooling fan that drives the traveling body 3, a fluorescent lamp and a lamp lighting circuit 3 for a reflection original.
6 and a sensor portion 37 for detecting the home position and detecting the temperature of the fluorescent lamp tube wall.

On the other hand, as the image signal system, the CCD 38,
It is composed of an analog processing section 39, a shading correction circuit 40, and a digital processing section 41. The reflected original image is illuminated by the light source 7 and passes through the converging light transmitter 4 to the CCD 3
The image signal is converted into an image signal in 8, the analog signal is processed in the analog processing unit 39, and then A / D converted to a digital signal.

In the shading correction circuit 40, the light source 7
The data obtained by reading the reference original document is stored in the memory as the shading correction data in order to correct the variation in the light intensity distribution of the CCD 38 and the sensitivity of each pixel of the CCD 38, and when the actual original document is read, the data is read from the memory and the correction is performed. .

The digital processing section 41 performs image processing such as scaling processing, γ conversion, color conversion and the like, and outputs it as a scanner image output signal to a printer section or the like. A timing signal is given from the scanner control unit 34 to each unit of these image signal systems to operate.

Next, the configuration of the shading correction circuit 40 will be described for each operation mode with reference to FIG. (1) Pixel data processing mode From the signal from the CCD 38 and the contents of the black level and the white level in the mode for performing the shading correction, Vo = {(pixel data)-(black level)} * 255 / {(white level)-(black Level)} to obtain a shading-corrected value.

(2) Black level processing mode In a mode for generating a black level at the time of reading a document, first, all the contents of the black memory (M0) are set to "0", and the black level signal from the CCD 38 is read 16 times and averaged. Generate a black level.

(3) White level processing mode In the mode for generating a white level at the time of reading an original, the contents of the lower 4 bits of the white memory (M1) and the black memory (M0) are all set to "0" and the white from the CCD is set. 16 level signal
Read twice and average to produce a white level.

(4) Data through mode In this mode, the input CCD output signal is output as it is.

Next, the shading correction operation will be described with reference to the flowchart of FIG. Before performing the shading correction, the light source 7 is turned off and the'black level processing mode 'is activated to generate the black reference level at the time of reading the original (S1), and then the light source 7 is turned on to drive the drive (not shown). While the traveling body 3 for reading an image is traveling along the guide rod 8 by turning on the power source and the drive system, the white level processing mode is activated on the white reference plate to generate a white reference level (S2). . Finally, the'pixel data processing mode 'is activated to read the original, and the shading-corrected image data can be obtained (S
3).

Next, the detecting means of the image signal detecting circuit which is characteristic of the present invention will be described with reference to FIGS. Figure 5
FIG. 5A is an explanatory diagram showing each signal, and FIG. 5B is FIG. 5A.
FIG. 5C is an explanatory diagram showing an enlarged part A of FIG. 5, and FIG. 5C is an explanatory diagram showing a formula for calculating an average value. As shown in FIG. 3, the image signal detection circuit is included in the shading correction circuit. LSYNC in FIG. 5A indicates an effective area in the main scanning direction of the scanner. Image signal detection circuit is external terminal TP
While the signal input from is at'L ',
As shown in (b), 8 consecutive pixels are added and averaged independently, the average value is compared with the maximum value up to the previous time, and the maximum value of the average values is stored in the register (see FIG. 5C). In the above process, TP is
The process is performed until H'is reached, and the value of the register at that time becomes the maximum value in the section. In this example, 8
Although the average value is taken in pixels, it may be 4 pixels, 16 pixels, or any other value.

Further, although the TP signal is shown within one line period, it may have a period of a plurality of lines, and in that case, the maximum value of the average values within the lines can be detected. Although the method of detecting the maximum value has been described in the present embodiment, the minimum value can be obtained in the same manner. The selection of the maximum value or the minimum value is determined by setting in the register of the image signal detection circuit from the CPU in the scanner control unit 34.

Next, the field back means based on the MAX value or the MIN value obtained by the image signal detection circuit will be described with reference to FIG. Note that FIG. 6 substantially corresponds to the analog processing section.

The analog processing section has an amplification means (variable gain AMP) 50 for amplifying the photoelectric conversion signal from the CCD,
Amplifies the amplified signal by a predetermined reference plus (hereinafter Vrp) and minus (hereinafter Vrm)
An AD converter 51 for D conversion, an amplification factor (hereinafter DA) and a negative input (hereinafter D) of the amplification means 50.
A), Vrp (hereinafter DA) and Vrm (hereinafter DA10 [circle number]) of the AD converter 51, a DA converter 52 for adjusting the light amount (hereinafter DA), and the like. The DA converter 52 is a CP in the scanner control unit 34.
The output can be set independently for each DA converter 52 by setting the register by U53, and CP can be set based on the data obtained by the image signal detection circuit.
U sets each DA converter 52 again.

Next, a method of setting each DA converter 52 will be described for each claim.

(A) DA, DA, DA, DA in advance
, DA10 [circle number] is set to an initial value, the light source 7 is turned off, and DA is adjusted so that the MIN value of the image signal of the black dummy portion of the CCD 38 becomes a certain value. As a result, the offset adjustment of the CCD 38 is completed.

After setting the DA, the MIN value of the image signal when the light source 7 is off is adjusted to a certain value by adjusting DA10 [circle number]. As a result, Vr of the AD converter 51
You can set m and decide the black level.

(B) DA and DA10 [circle numbers] are determined by the above (A), and after setting other DAs to initial values, the light source 7 is turned on and the MAX value of the image signal on the white reference plate is present. Adjust DA so that it becomes the value. This makes A
The Vrp of the D converter 51 can be optimized. With the above, the white level can be set.

Next, when the DA value is not set to a certain value by the DA when the DA is set in the above (B), (C) DA, DA10 [circle number] is determined by the above (A), and other DAs are initially set. After setting the value, the exposure amount is adjusted by DA, the light source 7 is turned on, and the MAX value of the image signal on the white reference plate is set to a certain value. As a result, feedback such as variation with time of the light source 7 is performed.
In other words, Vr of each AD converter 51 depends on the MAX value.
The signal output is adjusted by feeding back to p.
If the X value is lower than a predetermined value, the light amount is increased, and conversely, if the X value is high, the light amount is decreased.

(D) Variable gain AMP50 by DA
Is adjusted so that the MAX becomes a certain value.

According to the above-described embodiment, the linear image sensor for reading the reflected light from the document illuminated by the illumination system as an electric signal, the light source 7 for illuminating the document, and the electric signal thereof. In the image reading apparatus having the variable gain AMP50 for amplifying the signal and the AD converter 51 for A / D converting the amplified electric signal,
After the AD converter 51, the average value of a plurality of images continuous in the main scanning direction is detected within a predetermined number of pixels. Therefore, by detecting the average value of the image data, the noise that gets on the image data is detected. Can be reduced, and setting mistakes due to noise can be eliminated.

Further, according to the above-mentioned embodiment, there is provided means for detecting only the MAX value from the average values detected in the specific section, or, alternatively, from the average values detected in the specific section. Since a means for detecting only the MIN value is provided,
By detecting only the MAX value (MIN value) from the average value, it is possible to reduce the memory capacity compared to storing the data of all the average values.

Further, according to the above-described embodiment, since the detection of the MAX value and the MIN value can be switched according to the mode, it is possible to reduce the number of detection circuits.

Further, according to the above-described embodiment, since the specific section is made variable according to the reading mode, the average value of the image data is detected separately for the black dummy part, the image data part, the effective image range part and the like. It is possible to feed back the image data of the specific section efficiently.

[0036]

According to the first aspect of the invention, by detecting the average value of the image data, it is possible to reduce the noise carried on the image data, and it is possible to eliminate the setting error due to the noise. .

According to the second aspect of the invention, the specific section is made variable according to the reading mode, so that the average value of the image data is divided into the black dummy portion, the image data portion, the effective image range portion and the like. It becomes possible to detect, and it is possible to efficiently feed back the image data of the specific section.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of an image reading apparatus using the present invention.

FIG. 2 is a control block diagram of the image reading apparatus.

FIG. 3 is an explanatory diagram showing a configuration of a shading correction circuit.

FIG. 4 is a flowchart showing an operation of shading correction.

FIG. 5 is an explanatory diagram showing detection by an image signal detection circuit.

FIG. 6 is an explanatory diagram showing a field back means based on a MAX value or a MIN value.

[Explanation of symbols]

 7 light source 34 scanner control unit 38 CCD 50 variable gain AMP 51 AD converter 52 DA converter 53 CPU

Claims (2)

[Claims] 1. A linear image sensor for reading, as an electric signal, reflected light from a document illuminated by an illumination system, an illumination means for illuminating the document, an amplification means for amplifying the electrical signal, and an amplified electricity. In an image reading apparatus having A / D conversion means for A / D converting a signal, after the A / D conversion means, a plurality of images continuous in the main scanning direction are averaged within a predetermined number of pixels in a specific section. An image reading device characterized by detecting a value. 2. The image reading device according to claim 1, wherein the specific section is variable according to a mode.