JPH02130077A - Original reader - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a picture generated due to the dirt of a pressure plate without dropping the performance of an automatic shading correction by constituting a peak holding circuit of the circuit with a fast response speed for correcting a shading and the circuit with a late response speed for quantizing. CONSTITUTION:A peak holding circuit has two types of a high speed response type and a low speed response type. A high speed response type peak holding circuit (2) 18A can respond to the signal of 1 bit and a low speed response type peak holding circuit (2) 18B responds to only the signal of several bits. Consequently, at the time of reading the data for correcting shading, even when the signal having the high level by only one bit exists, the signla is corrected, at the time of reading the data for correcting a shading, even when the signal having the high level by only one bit exists, this can be ignored. Thus, the deterioration of the picture generated due to the dirt of a pressure plate can be prevented without dropping the performance of an automatic shading correction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a document reading device used in a facsimile machine, etc., and in particular, it is possible to reduce image deterioration caused by dirt on a pressure plate without reducing the performance of automatic shading correction.
The present invention relates to a document reading device that enables prevention.

[Conventional technology]

FIG. 2 shows a specific configuration diagram of a conventional document reading device used in a facsimile machine or the like. In the figure, 11 is a document that is read while being conveyed from right to left in the figure, and 12 is f
Reference numeral 13 indicates a light source for illuminating the fX manuscript, 13 indicates a press plate for suppressing the original, 14 indicates a mirror, 15 indicates a lens, and 16 indicates a light receiving element. Third
The figure shows a block diagram of the document reading device. In the figure, 16 is the above-mentioned light receiving element, 17 is a variable gain amplifier, and 18
is a peak hold circuit, 19 is an A/D conversion circuit, 20
indicates a memory element.

In this document reading device, shading correction was performed in the following procedure.

That is, when reading the shading correction data, the Jf'X draft suppression pressure plate I3 is read to obtain the base fQi value, but the gain of the variable gain amplifier 17 is set to 1, and the image signal is sent to the peak hold circuit 18. The image information is input to the A/D conversion circuit 19, and the image information is quantized using the peak value from the peak hold circuit 18 as a reference voltage.

This data is stored in the memory element 20.

Further, when reading a document, the data inputted to the storage element 20 is inputted to the variable gain amplifier 17, and the gain is controlled depending on the magnitude of the data and converted into a flat image signal. Next, peak hold circuit 18. The signal is input to the A/D conversion circuit 19 and quantized with reference to the peak value.

At this time, in order to accurately perform shading correction, the peak hold circuit 18 has a response speed that can follow the image signal of 1 bit (see FIG. 4).

Note that related techniques of this type include, for example, the technique disclosed in Japanese Unexamined Patent Publication No. 55-53777.

[Problem to be solved by the invention]

By the way, there are times when the pressure plate, which serves as a reference surface for shading correction, is dirty. In this case, since the signal level becomes low, the gain of the variable gain amplifier becomes large to correct the signal level. However, while the document is being read, the dirt on the pressure plate is hidden. Then, the signal level becomes high and the gain remains high, so only one bit becomes a very high level. The peak hold circuit is this L
Since both bit signals are tracked, the peak value becomes a very large value. Since quantization is performed with reference to this peak value, there is a problem in that the image becomes entirely black. FIG. 5 shows the waveform when reading the pressure plate in case 2, and FIG. 6 shows the original waveform at this time.

The present invention has been made in view of the above circumstances, and its purpose is to solve the above-mentioned problems in the conventional technology, reduce image deterioration caused by dirt on the pressure plate, and reduce the performance of automatic shading correction. An object of the present invention is to provide a document reading device that can prevent the above problems without causing problems.

[Means to solve the problem]

The above object of the present invention is to provide a light receiving element that reads reflected light from a document, a peak hold circuit that detects the peak of a signal from the light receiving element, and a peak hold circuit that detects the peak of a signal from the light receiving element, and converts the signal from the light receiving element into a signal from the peak hold circuit. In the document reading device, the peak hold circuit includes a shape ink correction circuit that performs correction based on the shape ink correction circuit, and a quantization circuit that quantizes the shading corrected signal based on the signal from the peak hold circuit. A document reading device comprising a fast one for quantization and a slow response speed for quantization, means for determining the quality of an image read by the light receiving element in the document reading device; A document reading device characterized in that it has a means for notifying an operator of the result of determination by the determination device, or in the document reading device, a difference between consecutive pixel signals read by the light receiving element is set to a predetermined value. and as a result of the comparison by the comparison means, if the difference between consecutive pixel signals read by the light receiving element is larger than a predetermined value, the value of the rear pixel is compared with the value of the front pixel. This is achieved by a document taking device characterized in that it has a correction means that performs the following steps.

[Function] In the original reading device according to the first aspect of the present invention, the peak hold circuit is composed of a fast response speed circuit for shading correction and a slow response speed circuit for quantization, so that the peak hold circuit can perform shading correction. When reading data for a document, even if there is a signal with a level of 41G, only 1 bit is corrected, and when reading a document, 1 bit is
This makes it possible to ignore even high-level signals.

In addition, in the document reading device according to the second aspect of the present invention, C captures the read signals into the CPU, and when some of the read signals have a value of 1, for example, 50% or less of the peak value,
By determining this as a value corresponding to dirt, stopping reading when an abnormality is detected, and issuing an alarm or display to notify the operator of an abnormality in the reading system.
It is possible to prevent reading errors from occurring.

Furthermore, in the document reading device according to the third aspect of the present invention, the difference between the successive pixel signals read by the light receiving element is compared with a predetermined value, and as a result of the comparison, the difference between the successive pixel signals read by the light receiving element is If the difference is larger than a predetermined value, by setting the value of the rear pixel to the value of the front pixel, dirt, scratches, etc. can be canceled and reading errors can be prevented from occurring. Can be done.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a block diagram of a document reading device showing a first embodiment of the present invention. The feature of this example is that it has two types of peak hold circuits: a high-speed response type and a low-speed response type. The high-speed response peak hold circuit (IH8A) mentioned above can respond to a 1-bit signal, and the low-speed response peak hold circuit (2) 18B
responds to only a few bits of signals.

In the operation of the document reading device shown in this embodiment, when reading data for shading correction, the peak value from the high-speed response peak hold circuit is used as a reference value for the A/D conversion circuit, and when reading the document,
Uses the peak value from the slow response peak hold circuit.

As a result, when reading data for shading correction, even if there is a signal with a high level of 1bil:,
This can be corrected, and when reading the original,
Even if there is a signal whose level is only 1 bit higher, it can be ignored. As a result, the problem of the entire image becoming black does not occur, only 1 bit becomes whitish, and the deterioration of the image as a whole is extremely small.

In the embodiment described above, as shown in FIG. It is used by switching between response type and slow response type. FIG. 7 shows a specific example of the circuit configuration for the peak hole 1 capable of switching between high-speed response and low-speed response.

The circuit shown in FIG. 7 has two holding capacitors, one of which can be connected and disconnected by a switch. Therefore, when reading shading correction data, the number of capacitors is multiplied by nine, the time constant is reduced, and the response characteristics are made faster.
When reading a document, it is possible to slow down the response characteristics by connecting the capacitor and increasing the time constant, and it can be used in place of two peak hold circuits.

Figure 8 also shows a specific configuration example of a peak hold circuit that can switch between high-speed response and low-speed response. By using this, the response time can be slowed down, and by short-circuiting the switching element, the response time can be made faster.

For reference, FIG. 9 shows a specific configuration example of a conventional peak hold circuit.

According to the above embodiment, when reading data for shading correction, even if there is a signal with a high level by 1 bit, this can be corrected, and when reading a document, even if there is a signal with a high level by 1 bit, this can be corrected. Even though
You can ignore this.

This situation is shown in Figure 1O. The effects of the present invention can be understood by comparing FIG. 10 with FIGS. 4 to 6.

Next, as a second embodiment of the present invention, a device that determines the quality of the read image and notifies the operator of the result will be described.

As mentioned above, if a part of the pressure plate 13 is dirty,
The read signal becomes as shown in FIG. 5, and when the original is read, the read signal becomes as shown in FIG. 6. In the above-mentioned embodiment, when reading data for shading correction, even if there is a signal with a high level of 1 bit, it can be corrected, and when reading a document, 1 bit can be corrected.
Even if there is a signal with a level as high as it, it is ignored, but in this embodiment, this is done as follows.

That is, the signal shown in FIG.
% or less, it is determined that the dirt has a value corresponding to the above-mentioned stain. In this case, reading is stopped when an abnormality is detected, and an alarm or display is provided to notify the operator of the abnormality in the reading system. An example of the configuration is shown in FIG.

According to this embodiment, by notifying the operator that there is a possibility that an abnormality may occur in reading, the operator is prompted to clean the reading section, thereby preventing the occurrence of reading errors. Can be done.

The A/D converted signal (W) is compared with a predetermined reference value.
is greater than or equal to a predetermined reference value (X, ), that is, if W≧X, the above W is directly stored in the storage device 2o, and W<
If it is X, it is also effective to store X in the storage device 20.

According to this embodiment, when the pressure plate 13 is dirty, auto shading failure can be prevented.

In the above embodiment, the correction at the time of dirt detection was set to W=X, but
W=X+1. W=X+2, etc. may be used, or these calculations may be performed by an operator.

Next, an example will be described in which if the value obtained through a differential circuit that compares the read signal values of the city pixel and the current pixel is larger than a predetermined value, the current pixel is determined to be a scratched or dirty pixel. do.

FIG. 12 shows a block diagram of the document reading apparatus of this embodiment, and FIG. 13 shows a block diagram of its shading correction circuit.

In FIG. 13, d2 is image information that has passed through the A/D converter, d is image information after shading correction processing, 21 is a differential circuit, and 22 is a threshold value that can be set externally (
Thresh value) storage section, 23 is a comparator, and 23 is a comparator.

24 indicates a selection circuit. In the following explanation,
The current pixel is the 1st pixel, the previous pixel is the i-1th pixel,
The next pixel is the 1+1th pixel.

In this embodiment, the contents of the i-1 pixel port are held in the shading correction circuit, and the difference 1 obtained by passing through the difference circuit 21 that compares this with the current pixel of the 1st pixel. , Th in the Thresh value storage section 22
The comparator 23 compares it with the resh value.

As a result of the comparison, if the T hresh value is larger, the signal S to the selection circuit 24 is set so that the content of the first pixel becomes active, and if the 'I' hresh value is smaller, the signal S is set to be activated. S is set so that the content of the j-1th pixel becomes active.

For example, consider a case where the pressure plate has two scratches and stains. The read signal in this case is as shown in Figure 14,
At this point A, as shown in FIG. Since the difference Δn between the contents of the first pixel is larger than Thresh (IffT), the content n of the first pixel is corrected with the content n-1 of the previous i-1 pixel, and as a result, the shading correction signal is The result is as shown in FIG.

'rhresh value'
) in Fig. 15.

r hresh value T for proper shading waveform
It is possible to change the boundary value with . This shows that, for example, even if the shading waveform fluctuates due to a change in the amount of light due to deterioration of the light source lamp in the image reading device, it can be coped with using only the Thrashhresh value r.

An example of the configuration of another shading correction circuit is shown in FIG.
show. The difference from the circuit shown in FIG. 13 is that the comparators 2;
A is configured to compare the contents of the current 5-pixel aperture with the T thresh value.

In this method, when the T hresh value is smaller, the (B No. S to the selection circuits 2 and 1 is set so that the content of the i-th picture
If the value is smaller, the "-" signal S is set so that the content of the j-1th pixel becomes active. In FIG. 18, when the content n of the first pixel is smaller than the rhresh value n1, the content of the first pixel is corrected as the content of the previous i-1 pixel r)-1, and the resulting shading is The correction signal becomes as shown in FIG.

In the case of this configuration example, since the differential circuit can be omitted, there is an advantage that the device configuration can be simplified and a corresponding effect can be obtained.

The above embodiments are shown as examples of the present invention, and the present invention should not be limited thereto.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to realize a document reading device that can prevent image deterioration caused by dirt on the pressure plate without deteriorating the performance of automatic shading correction. It is something.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram of a document reading device showing a first embodiment of the present invention, FIG. 2 is a specific configuration diagram of a conventional document reading device, and FIG. 3 is a block configuration diagram of the same document reading device. FIG. 4 is a diagram showing the response characteristics of the peak hold circuit, FIGS. 5 and 6 are response characteristic diagrams for explaining the problems, and FIGS. 7 and 8 are specific diagrams of the peak hold circuit of the embodiment. 9 is a diagram showing a specific configuration example of a conventional peak hold circuit, FIG. 10 is a diagram showing the response characteristics of the peak hold circuit of the embodiment, and FIG. 11 is a diagram showing the response characteristic of the peak hold circuit of the second embodiment. FIG. 12 is a block diagram of the document reading device of the third embodiment, FIG. 13 is a block diagram of its shading correction circuit, FIG. 14 is a diagram showing read signals, and FIG.
The figure is a partially enlarged view of FIG. 14, FIG. 16 is a diagram showing the signal after shading correction of the signal in FIG. 15, FIG. 17 is a diagram showing a configuration example of another shading correction circuit, and FIG. FIG. 3 is a diagram showing response characteristics. 11: original, 13: original pressing plate, 16: light receiving element,
17: Variable gain amplifier, 18.18A, 18B: Peak hold circuit, 19: A/D conversion circuit, 20: Memory element, 21 Difference circuit, 22: Threshhre
sh value 3.23A: Comparator, 24: Selection circuit. Figure Φ Figure Figure Φ Figure Figure Figure PU Figure H-1t i+i Figure PU Figure 1+1 Figure -t i 1+t

Claims (3)

[Claims] (1) A light receiving element that reads reflected light from a document, a peak hold circuit that detects the peak of the signal from the light receiving element, and shading that corrects the signal from the light receiving element based on the signal from the peak hold circuit. In a document reading device having a correction circuit and a quantization circuit that quantizes a signal subjected to shading correction based on a signal from the peak hold circuit, the peak hold circuit is configured to have a fast response speed for shading correction and a quantum What is claimed is: 1. A document reading device characterized by comprising a device with a slow response speed for processing. (2) A light receiving element that reads reflected light from a document, a peak hold circuit that detects the peak of the signal from the light receiving element, and shading that corrects the signal from the light receiving element based on the signal from the peak hold circuit. In an original reading device having a correction circuit and a quantization circuit that quantizes a shading-corrected signal based on a signal from the peak hold circuit, means for determining whether an image read by the light receiving element is good or bad, and the determining means 1. A document reading device comprising means for notifying an operator of the determination result. (3) A light receiving element that reads reflected light from a document, a peak hold circuit that detects the peak of the signal from the light receiving element, and shading that corrects the signal from the light receiving element based on the signal from the peak hold circuit. In an original reading device having a correction circuit and a quantization circuit that quantizes the shading-corrected signal based on the signal from the peak hold circuit, the difference between consecutive pixel signals read by the light receiving element is determined in advance. means for comparing the values, and as a result of the comparison by the comparing means, if the difference between consecutive pixel signals read by the light receiving element is larger than a predetermined value, the value of the rear pixel is replaced with the value of the front pixel. What is claimed is: 1. A document reading device comprising: a correction means.