JP2822674B2 - 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 for converting an image into an electric signal in a facsimile or a copying machine.

[0002]

2. Description of the Related Art FIG. 9 shows, for example, Japanese Patent Application Laid-Open No. 63-316567.
FIG. 1 is a perspective view showing a conventional image reading apparatus disclosed in Japanese Patent Application Laid-Open Publication No. H10-207, in which 23 is a document, 21 is a light source, 22 is a rod lens array, 1 is a line image sensor, and 24 is a sub-scanning direction adjacent to the document. Reference plate. The sub-scan normally takes about several seconds. If the light amount of the light source 21 changes during that time, the output signal of the line image sensor 1 changes, and a uniform image cannot be obtained. Therefore, the conventional image reading apparatus is provided with an automatic gain control circuit (hereinafter, an AGC circuit). FIG. 10 is a diagram showing an AGC circuit in a conventional image reading apparatus, wherein 2 is an amplifier, 3 is an analog / digital converter (hereinafter, A / D converter), 4 is a sample-hold circuit, and 25 is an amplifier.

Next, the operation will be described. In FIG. 9, images of the original 23 and the reference plate 24 illuminated by the light source 21 are formed on the line image sensor 1 by the rod lens array 22. In FIG. 10, an image signal output from the line image sensor 1 is amplified by an amplifier 2 and input to V _IN of an A / D converter 3. The image signal of the reference plate 24 is transmitted to the line image sensor 1 and the amplifier 2
S / which is output only when the reference plate 24 is read after passing
The sample and hold circuit 4 performs sample and hold by the H pulse. After the output is amplified by the amplifier 25, it is input to V _REF of the A / D converter 3 and used as a reference voltage.

FIG. 11 shows a signal waveform at an arbitrary time in FIG. In FIG. 11, S3 is an image signal input to V _IN of the A / D converter 3, S / H pulses are pulses for sampling and holding only the image signal at the position of the reference plate, and V _REF1 is an A / D converter 3 Are shown respectively. Further, as shown in FIG. 11, the level of the image signal S3 near the both ends is lower than that at the center of one line due to the shading effect of the light source 21 as shown in FIG. Therefore, as shown in FIG.
The reference voltage V _REF input to the converter 3 becomes a voltage slightly higher than the image signal at the center of one line at an appropriate magnification (for example, Ai times (Ai ≧ 1)) by the amplifier 25 by the output of the sample hold circuit 4. So that the image signal for one line falls within the A / D conversion range. Here, the _{reason why} the reference voltage V _REF is set to a voltage slightly higher than the central image signal is that if the reference voltage V _REF is set to a voltage much higher than the image signal, the A / D conversion is performed. This is because an error with respect to the subsequent image signal increases, and a uniform image cannot be obtained.

With the above configuration, even when the light amount of the light source 21 changes uniformly during the sub-scanning and the level of the image signal S3 changes, the reference voltage V _REF1 input to the A / D converter 3 is changed. Changes at the same ratio as the image signal and is always set to the optimum value for the image signal, so that the A / D conversion is performed with high accuracy and a uniform image is obtained.

[0006]

Since the conventional image reading apparatus is configured as described above, as shown in FIG. 12, the light quantity does not change uniformly in each pixel, and only the end of the light quantity 21 is changed. When the voltage extremely decreases, the output of the reference plate 24 sampled and held decreases, and the reference voltage V _REF2 also decreases.
As a result, we are beyond the central hatched portion of the output reference voltage V _REF2 of Eshingo S4, the output after A / D conversion is saturated,
There is a problem that the gain adjustment of the image signal is not performed normally.

In Japanese Patent Application Laid-Open No. 64-89667, A /
Shading correction means after D conversion
Japanese Patent Application Laid-Open No. 177656 discloses means for detecting the light amount of the light source before the A / D conversion in the main scanning direction and the sub-scanning direction, but the A / D conversion means is provided in the same manner as in JP-A-63-316567. If you do, similar problems are inherent.

The present invention has been made in order to solve the above-mentioned problems. Even when the output at the end of the light source 21 is remarkably reduced, all the image signal outputs do not exceed the reference voltage. It is an object of the present invention to provide an AGC circuit capable of preventing an output after A / D conversion from being saturated and performing gain adjustment with high accuracy.

[0009]

An image reading apparatus according to the present invention comprises a document and a sub-scanning direction provided near the document.
A light source that irradiates light to the reference plate , an image sensor that converts light signals from the original and the reference plate into electric signals, and an A / A that converts electric signals from the image sensor into digital signals.
A D-converter, a sample-and-hold circuit for holding an electric signal from an image sensor based on an optical signal from a reference plate,
Amplifying means for amplifying the output of the sample and hold circuit and setting it as a reference voltage for the A / D converter; and detecting means for detecting the maximum light amount and the light amount at a position corresponding to the reference plate in the main scanning direction of the light source. And control means for calculating a ratio between the maximum light amount detected by the detection means and the light amount at the position corresponding to the reference plate, and setting the gain of the amplification means based on the calculated ratio.

[0010]

The image reading apparatus according to the present invention detects the maximum light amount among the light amounts in the main scanning direction and the light amount at a position corresponding to the reference plate in the sub-scanning direction, and performs A / D based on the detected light amount ratio. Since the gain of the amplifier is set so as to obtain the optimum reference voltage of the converter, the output after A / D conversion does not become saturated.

[0011]

[Embodiment 1] An embodiment of the present invention will be described below with reference to the drawings. FIG.
1, 1 is a line image sensor, 2 is an amplifier for amplifying an image signal from the line image sensor 1, and 3 is an A / A
D converter and 4 are sample and hold circuits, each of which is shown in FIG.
0 performs the same function as that of the conventional image reading apparatus having the same reference numeral. 5 is a switch for switching between the output of the sample and hold circuit 4 and the constant voltage power supply 6, and 7 is a switch 5
, A reference signal for the A / D converter 3, and a variable gain amplifier 9 for storing an image signal for one line, 8 a variable gain amplifier based on the data of the line buffer 9. This is a CPU that determines the gain of.

FIG. 6 is a perspective view of an image reading apparatus according to the present invention, which includes a line image sensor 1, a light source 21, a rod lens array 22, a document 23, and a reference plate 24 in the sub-scanning direction.
Perform the same functions as those of the conventional device having the same reference numerals. Reference numeral 25 denotes a reference plate attached in the main scanning direction.

Next, the operation will be described. In FIG. 1, before reading a document, a switch 5
Are set to the constant voltage power supply 6 side, and a predetermined constant voltage is input to the variable gain amplifier 7, and the gain of the variable gain amplifier 7 at this time is adjusted by the A / D converter 3.
Is set to be a sufficiently high voltage.
This reference voltage is shown as fixed V _{REF in} FIG. 6, the image signal of the reference plate 25 in the main scanning direction read by the line image sensor 1 passes through the amplifier 2 in FIG. 1, and is converted into a digital signal by the A / D converter 3. At this time, as shown in FIG. 7, since the reference voltage is set to a sufficiently high voltage with respect to the image signal S1 input to V _IN of the A / D converter 3, the output of the A / D converter 3 becomes low. It does not saturate. Then, the output of the A / D converter 3 is stored in the line buffer 9. The CPU 8 reads out the image signals stored in the line buffer 9 in order, and
As shown in the figure, the sub scanning in the main scanning direction (horizontal axis) of the light source
The light amount distribution of the light source 21 can be detected by extracting the light amount V _MIN and the maximum light amount V _MAX at the position corresponding to the reference plate 24 in the inspection direction , that is, the position corresponding to the light source end. CPU8 calculates the ratio of the V _MAX and V _MIN, slightly larger than this ratio as the new gain value of the variable gain amplifier 7

A′i = V _MAX / V _MIN + α (A′i> 1, α is a predetermined constant) is set, and an instruction is given to the variable gain amplifier 7. Where α
Is a predetermined constant for setting the reference voltage to a value slightly higher than V _MAX of the image signal.

When reading of the reference plate 24 and the original 23 in the sub-scanning direction is started after reading of the reference plate 25 in the main scanning direction is completed, the contact point of the switch 5 in FIG. 4 output side. Then, the image signal read from the reference plate 24 in the sub-scanning direction is sampled and held by the sample and hold circuit 4, and is input to the variable amplifier 7 via the switch 5. This signal is amplified by the gain A′i newly set by the variable gain amplifier 7, input to V _REF of the A / D converter 3, and used as a reference voltage.

An image signal obtained by reading the reference plate 24 and the original 23 in the sub-scanning direction is input to V _IN of the A / D converter 3 as in the prior art, A / D converted, and converted in the next step. Signal processing is performed. At this time, the image signals of the reference plate 24 and the document 23 in the sub-scanning direction are also stored in the line buffer 9, but the CPU 8 does not read these signals and the gain of the variable gain amplifier is held at A'i. .

FIG. 8 shows a state in which the amount of light at the end of the light source 21 becomes extremely short. In the case of the conventional AGC circuit, the voltage at the center of the output waveform S2 exceeds the reference voltage as shown by the hatched portion due to the decrease in the reference voltage V _REF , and the output after A / D conversion is saturated. According to the present invention, S
2, the gain value of the variable gain amplifier 7 can be obtained to obtain the optimum reference voltage _V'REF, and the output after A / D conversion can be prevented from being saturated.

In this embodiment, the CPU 8 takes in the values of V _MAX and V _MIN stored in the line buffer 9 and calculates the ratio, but this function can also be performed using a divider.

Embodiment 2 FIG. FIG. 2 is a block diagram of an AGC circuit showing another embodiment of the present invention. In this embodiment, a latch circuit 10 and a peak detector 11 are provided in place of the line buffer 9 of the above embodiment, and a reference plate 25 in the main scanning direction is provided. At the time of reading, the light amount at a position corresponding to the reference plate 24 in the sub-scanning direction among the light amounts in the main scanning direction of the light source 21 is detected by the latch circuit 10 by the S / H pulse, and the maximum light amount of the light source 21 is detected by the peak detector 11. The CPU 8 takes in these two values and instructs the variable gain amplifier 7 with a predetermined gain.

Embodiment 3 FIG. FIG. 3 is a block diagram of an AGC circuit showing another embodiment of the present invention. In this embodiment, an analog memory 12 such as a CCD analog shift register is provided in place of the line buffer 9 in the first embodiment. A / of plate 25
The analog output before the D conversion is stored, and the CPU 8 determines the reference amount of the light amount of the light source 21 in the main scanning direction in the sub scanning direction.
The light amount at the position corresponding to the plate 24 and the maximum light amount of the light source 21 are detected, and a predetermined gain is instructed to the variable gain amplifier 7. In this embodiment, since the gain is determined from the analog output of the reference plate 25 before A / D conversion, the switch 5 and the constant voltage power supply 6 in the first and second embodiments are unnecessary.

Embodiment 4 FIG. FIG. 4 is a block diagram of an AGC circuit showing another embodiment of the present invention. Among the light amounts of the light source 21 in the main scanning direction, the light amount at a position corresponding to the reference plate 24 in the sub-scanning direction is determined by the sample hold circuit 4. CPU 8 takes in the light source 21
Is detected by the peak detector 11, and the CPU 8 takes in the value to instruct the variable gain amplifier 7 of a predetermined gain. In this embodiment, since the operation in the second embodiment is performed with an analog signal before A / D conversion,
The latch circuit 10 in the second embodiment is unnecessary, and the switch 5 and the constant voltage power supply 6 are unnecessary as in the third embodiment.

Embodiment 5 FIG. 5 is a block diagram of an AGC circuit showing another embodiment of the present invention. A photosensor 13 is provided at an end of a light source 21 and a photosensor 14 is provided at a center of the light source 21. And the output is directly compared to the sub- light amount in the main scanning direction.
The CPU 8 assumes the light amount at the position corresponding to the reference plate 24 in the scanning direction and the maximum light amount, and instructs the variable gain amplifier 7 to have a predetermined gain by taking in the values. In this embodiment, the light from the light source 21 is
And 14 receive light directly, so that Embodiments 1 to 4
, The reference plate 25 in the main scanning direction is unnecessary.
As in the third and fourth embodiments, the switch 5 and the constant voltage power supply 6 are unnecessary.

[0023]

As it is evident from the foregoing description, the maximum amount of light and the sub-scanning direction of the light amount in the main scanning direction of the light source according to the present invention
The light amount at the position corresponding to the reference plate is detected, and the gain of the amplifier for generating the reference voltage of the A / D converter can be set based on the ratio of the detected light amount. Even when the output is significantly reduced, gain adjustment can be performed with high precision, and an image reading apparatus with higher image quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an AGC circuit according to Embodiment 1 of the present invention.

FIG. 2 is a block diagram showing an AGC circuit according to Embodiment 2 of the present invention.

FIG. 3 is a block diagram showing an AGC circuit according to Embodiment 3 of the present invention.

FIG. 4 is a block diagram showing an AGC circuit according to Embodiment 4 of the present invention.

FIG. 5 is a block diagram showing an AGC circuit according to Embodiment 5 of the present invention.

FIG. 6 is a schematic perspective view of an image reading apparatus according to Embodiments 1 to 4 of the present invention.

FIG. 7 is a signal waveform diagram of each part of the AGC circuit according to the present invention.

FIG. 8 is a diagram showing the effect of the present invention.

FIG. 9 is a schematic perspective view of a conventional image reading apparatus.

FIG. 10 is a block diagram showing a conventional AGC circuit.

FIG. 11 is a signal waveform diagram of each part of a conventional AGC circuit.

FIG. 12 is a signal waveform diagram of each part of the conventional AGC circuit when the light amount at the end of the light source is significantly reduced.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Line image sensor 3 A / D converter 4 Sample hold circuit 7 Variable gain amplifier 21 Light source 23 Document 24 Reference plate

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 1/401

Claims (1)

(57) [Claims] 1. A manuscript and a sub-run installed near the manuscript
A light source for irradiating the reference plate in the scanning direction with light, an image sensor for converting light signals from the original and the reference plate into electric signals, and an analog / digital conversion for converting electric signals from the image sensor into digital signals A sample-and-hold circuit for holding an electric signal from the image sensor based on an optical signal from the reference plate, and amplifying means for amplifying an output of the sample-and-hold circuit and setting it as a reference voltage of the analog / digital converter. Detecting means for detecting the maximum light quantity of the light source in the main scanning direction and the light quantity at a position corresponding to the reference plate; and the maximum light quantity detected by the detection means and the position corresponding to the reference plate. Control means for calculating a ratio with respect to the light amount of the light, and setting the gain of the amplifying means based on the calculated ratio. Apparatus.