JP3262609B2 - Image reading device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus provided in a digital copying machine, a facsimile, etc.
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 signal output of a light shield portion output from a CCD is detected by a sample-and-hold circuit, and a peak output of the CCD is detected using the signal output. Offset adjustment,
The peak of the amplified electric signal is detected by a sample-and-hold circuit, and conversion is performed as a conversion reference of an A / D converter. This type of image reading apparatus is disclosed in, for example,
No. 76964.

[0003]

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

For this reason, when the peak of an electric signal is detected by the sample-and-hold circuit, a leakage current occurs due to the characteristics of the capacitor used in the sample-and-hold circuit, and the peak detection voltage gradually decreases over time. Occurs, the output offset of the CCD is poorly adjusted in the dark, A
A conversion error occurs due to a change in the conversion reference voltage of the / D converter.

In addition, since the peak of the electric signal of the sample and 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. In order to prevent an error from occurring, A /
It is necessary to adjust while looking at the output of the D converter, which is troublesome.

An object of the present invention is to provide an illumination unit, an amplification unit,
Control each means of the A / D conversion means efficiently and automatically
It is an object of the present invention to provide an image reading apparatus that can perform the following.

[0007]

To SUMMARY OF THE INVENTION To achieve the above object, the present invention comprises an illuminating means for illuminating an original, reflected light from the illuminated original, a linear image sensor for reading an electric signal, the electric Amplification means for amplifying the air signal;
In the image reading apparatus having an A / D converting means for A / D conversion of the electric signal amplified by the amplifying means, the main run
Multiple image data in a specific section that is continuous in the
Maximum or minimum average value averaged within the number of pixels
Detecting means for detecting the value, and using the maximum value or the minimum value.
Controlling the illumination means, the amplification means or the A / D conversion means.
The first means is provided with an adjusting means for adjusting the control value .

In order to achieve the above object, according to the present invention, in the first means, detection of a maximum value and a minimum value is switched.
Control means for inputting a control signal to the adjusting means.
This is configured as a second means.

[0009]

According to the above-mentioned means, a feature continuous in the main scanning direction is provided.
A plurality of image data in a fixed section are averaged within a predetermined number of pixels.
Finds the maximum or minimum value of the average
Feedback using the maximum or minimum value
The control values of each of the lighting means, the amplification means, and the A / D conversion means
Adjustment means that each means can be efficiently and automatically
Can be controlled.

[0010]

[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. This image reading apparatus is of a type capable of reading a reflection original.

The image reading apparatus is a traveling body (scanner) 3 that reads an image while traveling along a guide rod 8 by a driving source and a driving system (not shown) when reading a reflection original.
, A contact glass 2, a frame 1, a printed circuit board 21 for analog signal processing, and a printed circuit board 22 for digital signal processing.
A light source 7 for illuminating a reflection original, a convergent light transmitter 4, and a photoelectric conversion element 6 are held in the traveling body 3. Reference numeral 5 denotes a color correction filter for correcting the color sensitivity balance of the photoelectric conversion element 6. Although not shown in the drawing, a board for driving the photoelectric conversion element 6 and a printed circuit board having an amplification circuit for amplifying the output of the photoelectric conversion element are carried in the traveling body 3. The processing substrates 21 and 22 are electrically connected via the 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 driving unit 35 of a motor or a cooling fan for driving the traveling body 3, and a fluorescent lamp and a lamp lighting circuit 3 for a reflection original.
6 and a sensor section 37 for detecting the home position and for detecting the fluorescent lamp tube wall temperature.

On the other hand, as an image signal system, a CCD 38,
It comprises 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 is transmitted through the converging light transmitting body 4 to the CCD 3.
The digital signal is converted into an image signal by an analog processing section 8 and processed by an analog processing section 39. The analog signal is converted into a digital signal by performing A / D conversion.

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

The digital processing section 41 performs image processing such as scaling processing, γ conversion, and color conversion, and outputs a scanner image output signal to a printer section or the like. Each unit of the image signal system is operated by receiving a timing signal from the scanner control unit 34.

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

(2) Black level processing mode In this mode, the contents of the black memory (M0) are first set to "0", and the black level signal from the CCD 38 is read 16 times and averaged. To generate a black level.

(3) White level processing mode In this mode, a white level is generated at the time of reading a document. First, the contents of the lower 4 bits of the white memory (M1) and the black memory (M0) are all set to "0" and white from the CCD is read. Level signal 16
Read once and average to generate white level.

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

Next, the operation of the shading correction will be described with reference to the flowchart of FIG. Before the shading correction is performed, the light source 7 is turned off, the 'black level processing mode' is started, a black reference level for reading a document is generated (S1), and then the light source 7 is turned on and a drive (not shown) is performed. The white level processing mode is activated on the white reference plate while the traveling body 3 that reads an image along the guide rod 8 is turned on by turning on the source and the drive system to generate a white reference level (S2). . Finally, the 'pixel data processing mode' is activated to read the original, and to obtain image data subjected to shading correction (S
3).

Next, the detecting means of the image signal detecting circuit showing the features of the present invention will be described with reference to FIGS. FIG.
5A is an explanatory diagram showing each signal, and FIG. 5B is a diagram showing FIG.
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. The image signal detection circuit is connected to the external terminal TP
5 while the signal input from the terminal is 'L'.
As shown in (b), eight consecutive pixels are added and averaged independently, compared with the maximum value up to the previous time, and the maximum value of the average value is stored in a register (see FIG. 5C). In the above process, TP
The processing is performed until H ′ is reached, and the value of the register at that time becomes the maximum value in that section. In the present embodiment, the continuous 8
The average value is taken for each pixel, but may be 4 pixels, 16 pixels, or any other value.

Although the present TP signal is shown within one line cycle, it may be a cycle of a plurality of lines, in which case the maximum value of the average value between the lines can be detected. In this embodiment, the method of detecting the maximum value has been described, but the minimum value can be obtained in the same manner. The selection between the maximum value and the minimum value is determined by setting the CPU in the scanner control unit 34 to the register of the image signal detection circuit.

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

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

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

(A) DA, DA, DA, DA
, DA10 [circled numbers] are set to initial values, the light source 7 is turned off, and adjustment is performed so that the MIN value of the image signal of the black dummy portion of the CCD 38 becomes a certain value by adjusting DA. As a result, the offset of the CCD 38 can be adjusted.

After the DA is set, the MIN value of the image signal when the light source 7 is turned off is adjusted to a certain value by adjusting DA10 [circled number]. Thereby, Vr of the AD converter 51
m can be set and the black level is determined.

(B) DA, DA10 [circled numbers] are determined by the above (A), and after setting other DAs to the initial values, the light source 7 is turned on, and there is a MAX value of the image signal on the white reference plate. Adjust DA to a value. This gives A
Vrp of the D converter 51 can be optimized. Thus, the white level can be set.

Next, when the MAX value does not enter a certain value due to DA when DA is set in (B) (C) DA and DA10 [circled numbers] are determined by (A), and the 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. In this way, feedback such as the time variation of the light source 7 is provided.
That is, the Vr of each AD converter 51 is determined by the MAX value.
p is fed back to adjust the signal output, and MA
If the X value is lower than a predetermined value, the light amount is increased, and if it is higher, the light amount is reduced.

(D) Variable gain AMP50 by DA
Is adjusted so that the MAX value 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 An image reading device having a variable gain AMP 50 for amplifying the signal and an AD converter 51 for A / D converting the amplified electric signal,
After the A / D converter 51, the average value of a plurality of continuous images in the main scanning direction is detected within a predetermined number of pixels. Can be reduced, and setting errors due to noise can be eliminated.

According to the above-described embodiment, means for detecting only the MAX value from the average values detected in the specific section is provided, or the average value detected in the specific section is selected 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 as compared with storing the data of the entire average value.

Further, according to the above embodiment, the detection of the MAX value and the detection of the MIN value can be switched according to the mode, so that the number of detection circuits can be reduced.

Further, according to the embodiment, since the specific section can be changed according to the reading mode, the average value of the image data is detected separately for the black dummy section, the image data section, the effective image range section and the like. This makes it possible to efficiently feed back image data of a specific section.

[0036]

As described above, according to the image reading apparatus of the present invention, the specific area within the specific section continuous in the main scanning direction is provided.
Of multiple image data within a predetermined number of pixels
The maximum or minimum value of the average value is detected, and the detected maximum value
Or lighting means with feedback using the minimum value,
Adjusting the control value of each means of the amplification means and the A / D conversion means
So that each of the above means can be controlled efficiently and automatically
can do.

[0037]

[Brief description of the 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 illustrating a configuration of a shading correction circuit.

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

FIG. 5 is an explanatory diagram illustrating 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

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-101180 (JP, A) JP-A-62-182983 (JP, A) JP-A-4-17462 (JP, A) JP-A-1- 256871 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H04N 1/40-1/409

Claims (2)

(57) [Claims] [1 claim] illuminating means for illuminating an original, reflected light from the illuminated original, a linear image sensor for reading an electrical signal, amplifying means for amplifying the electrical signal,
In an image reading apparatus having A / D conversion means for A / D converting the electric signal amplified by the amplification means , a plurality of image data in a specific section continuous in the main scanning direction is stored.
The maximum value of the average value averaged within a certain number of pixels or
Detecting means for detecting the minimum value, and the maximum value or the minimum value
Illuminating means, amplifying means or A / D converting means using
An image reading apparatus provided with an adjusting means for adjusting the control value of the image reading apparatus. 2. Control for switching between detection of a maximum value and a minimum value.
That control means for inputting a signal to the adjustment means is provided.
The image reading device according to claim 1, wherein: