JP3859102B2 - Image reader - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus used for a facsimile, a scanner, a digital copying machine, and the like, and more particularly to an image reading apparatus that performs image processing based on a peak level (document background level) of a read image signal.
[0002]
[Prior art]
As a conventional device of this type, for example, devices disclosed in JP-A-7-170401 and JP-A-8-317201 are known.
The former apparatus reads an image of a reference white member prior to reading a document image and enables an image signal output from the image sensor to be compatible with the peak tracking speed and the dynamic range of quantization. Correction data for correcting shading distortion due to the optical system is collected for each pixel and stored in the line buffer. When reading a document image, the shading distortion due to the optical system of the image signal output from the image sensor is corrected. The correction unit based on the correction data, the selector selects one of the image signals before and after correction of the shading distortion, the peak detection unit detects the peak level of the selected image signal, The AD conversion unit follows the peak level detected by the peak detection unit for the image signal after shading distortion correction. It is obtained so as to quantized. In this apparatus, the peak tracking speed and the dynamic range of quantization are made compatible, but no consideration is given to preventing an excessive increase in peak level due to disturbance.
[0003]
In addition, the latter device uses a read image signal in order to achieve both noise resistance and peak level tracking when the read image signal is quantized based on the peak level of the input read signal. As the peak level holding means, a first peak hold unit with a fast tracking speed and a second peak hold unit with a low tracking speed are provided, and binary / halftone is determined from the holding values of these two types of peak hold units. The optimum peak level is given to the reference generator as a reference maximum value for quantization according to the reading mode or the like. Although this apparatus performs good image processing, this method has a problem that the circuit scale increases because it has two types of peak detection units having different tracking speeds.
[0004]
[Problems to be solved by the invention]
That is, the conventional image reading apparatus has the following problems.
(1) Since the tracking speed of the image signal peak level is a predetermined fixed value or switching between fixed values, image quality may be deteriorated due to an abnormal document or disturbance noise.
(2) Since the tracking speed of the image signal peak level is switched between a fixed value and a fixed value when rising and falling, image quality may be deteriorated due to an abnormal document or disturbance noise. .
[0005]
(3) Since there is no correlation between the rising and falling operations of the peak level, it takes time to return to a steady state when the peak level is excessively increased due to an abnormal document, disturbance noise, or the like, resulting in degradation of image quality.
(4) Since a fixed peak level tracking speed is set regardless of the peak level value of the image signal, it is difficult to ensure both image quality during normal operation and prevention of image quality degradation during abnormal operation.
SUMMARY OF THE INVENTION An object of the present invention is to provide an image reading apparatus that solves the above-mentioned problems in the prior art and can perform finer image processing than the conventional one based on the peak level of the read image signal. is there.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, the peak detection means 5 for detecting and keeping track of the peak level of the read image signal, and the read image signal is processed based on the peak level held by the peak detection means 5. The image reading apparatus having the image processing means 4 is characterized in that the tracking speed of the peak level can be changed.
Further, the present invention is characterized in that the follow-up speed can be arbitrarily changed during document reading, and the follow-up speed can be individually changed when the peak level rises and falls.
[0007]
Further, the present invention is characterized in that the peak level lowering control is performed only during the simple binarization process, and the tracking speed when the peak level increases is faster than the tracking speed when the peak level is lowered.
Furthermore, in the present invention, the follow-up speed when the peak level is lowered is set to be high in a predetermined area at the front end of the document, and the follow-up speed when the peak level is lowered is controlled in conjunction with the follow-up speed when the peak level is raised. Features.
Furthermore, the present invention is characterized in that the follow-up speed is changed according to the value of the image signal peak level, and the relationship between the image signal peak level and the peak level follow-up speed is non-linear.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing a basic configuration of an image reading apparatus according to an embodiment of the present invention. In FIG. 1, 1 is an image sensor that converts a reflected light signal from a document illuminated by a light source (not shown) (also not shown in the figure) into an analog electrical signal, and 2 is from the image sensor 1. An operational amplifier (op-amp) that amplifies the analog signal at a predetermined amplification factor, 3 is an A / D converter that converts the analog signal amplified by the operational amplifier 2 into a digital signal with a predetermined resolution, and 4 is an A / D converter. An image processing unit 5 for performing various image processing based on the digital signal from the device 3, 5 is a peak level tracking control unit for detecting and tracking the peak level of the analog signal amplified by the operational amplifier 2, and 6 is a peak level tracking control. The reference generation unit 7 generates a reference voltage of the A / D converter 3 based on the peak level of the image signal detected and held by the unit 5. Shows a system control unit that controls the operation sequentially.
[0009]
As described above, in the conventional image reading apparatus that processes the image signal based on the background level of the document, if the document tip is warped or scratched when the document is read, the illumination light from the light source is regularly reflected. Thus, an excessive amount of light enters the image sensor. As a result, the output level of the image sensor suddenly rises, and the peak level follows this, resulting in an excessive rise.
If the image signal is binarized or multi-valued with the peak level as a reference, the apparent signal level is lowered due to an excessive rise in the peak level, and an image abnormality such as background contamination occurs.
In view of this, in the image reading apparatus according to the present embodiment, the image signal peak level rising / lowering tracking speed can be arbitrarily controlled individually, thereby preventing image quality deterioration.
[0010]
That is, in the first embodiment, the peak level follow-up speed set by the fixed or fixed value switching in the conventional apparatus can be changed during the document reading. Hereinafter, this operation will be described with reference to the flowchart shown in FIG.
After initialization (step 11), an ascending follow-up speed initial value Vr0 and a descending follow-up speed initial value Vf0 are set (step 12). When reading is started, the original is read at the upward follow-up speed and the downward follow-up speed set above (steps 13 to 15), and if it is necessary to change the speed, the follow-up speed is changed (steps 16 and 17). ).
As a result, the original reading state can be fed back to the peak level, and deterioration of the image quality can be prevented in advance.
[0011]
The flowchart shown in FIG. 3 further details this operation. The main points will be described below with reference to FIG.
Steps 11 to 15 are the same as the previous operation shown in FIG. In this operation, when the speed needs to be changed, the ascending speed and the descending speed can be changed separately (steps 21 to 24).
Of the change in the peak level tracking speed, the descending control may be performed only during the simple binarization process. This is because the peak level lowering control is performed to follow the peak level when the background density changes (bright → dark) from the middle of the document. Processing), it is always possible to reproduce the original background as a white background.
[0012]
As a special case of the above-described operation shown in FIG. 3, it can be considered that the follow-up speed at the time of ascent is set higher (Vf1 <Vr1) than the follow-up speed at the time of descent in step 24 in the flowchart. By setting the tracking speed in this way, it is possible to quickly track even a region where the document density is sharply lowered. In addition, the background detection capability at the front end of the document can be enhanced.
On the other hand, for areas where the document density is sharply increased, for example, partial black areas, it is necessary to reproduce this as a full black image without using the background. It is preferable to set it to a sufficiently slow setting.
[0013]
FIG. 4 shows still another operation example. In this example, normally, the follow-up speed when the peak level is gradually lowered is high in a predetermined area at the front end of the document. That is, after the initialization (step 11), the ascending follow-up speed initial value Vr0, the descending follow-up speed initial value Vf0, and the document tip descending follow-up speed Vf2 are set (step 31).
When reading is started, the original is read at the rising follow-up speed and the document tip descending follow-up speed set above (steps 13, 32, and 15), and after the document tip passes, the descending follow-up speed is changed to Vf0. (Steps 33 and 34). If it is necessary to change the speed, the follow-up speed is changed as in the previous operation example (steps 21 to 24).
In this operation, as described above, the tracking speed when the peak level rises is set to be higher than that when the peak level falls, so it takes a considerable time to converge to the true peak level once it rises once. it can. That is, since the A / D conversion of the image signal is generated by the reference based on the peak level, the image signal is A / D converted at a low level, that is, in a high density state while the peak level is excessively high. As a result, the processed image is accompanied by image quality deterioration such as background stains.
[0014]
In facsimile machines, etc., when reading a document, the diffuse reflection component of the illumination light from the light source is guided to the image sensor and imaged to produce a signal. May enter the image sensor. Since the regular reflection light has a larger amount of light than the irregular reflection light, the output level of the image sensor is also increased, and the peak level is excessively increased.
In the conventional image reading apparatus, the follow-up speed when the peak level is lowered is always constant and low, so that there is a problem that it is easily affected by such a transient disturbance. Since the descending follow-up speed in the region is increased, even when the peak level rises due to a disturbance, it can be quickly lowered to the true peak level.
Since the above-mentioned mechanism has various conditions depending on the mechanism design, it is desirable to tune the document leading edge predetermined region, the descent follow-up speed, and the like for each product.
[0015]
FIG. 5 shows still another operation example. In this example, the follow-up speed when the peak level is lowered is changed in conjunction with the follow-up speed when the peak level is raised. That is, when the peak level rises quickly, an excessive rise due to disturbance can be considered. Therefore, in a certain period thereafter, deterioration of the image quality can be prevented by setting the drop rate to a high speed.
The operation will be described below with reference to FIG.
First, a threshold value for determining the peak level increase speed is set (step 41). When reading of the document is started (step 13), the system control unit 7 monitors the peak level increasing speed Vr based on the value held by the peak level tracking control unit. When Vr is larger than the predetermined level, it is determined that the peak level may be excessively increased, and the peak level decreasing speed is set to a high speed (steps 42 and 43). If Vr is equal to or lower than a predetermined level, it is determined that the document is normally read, and the lowering speed is set to a low speed (steps 42 and 44).
In the example shown above, there are two types of descending speeds, high speed and low speed, but more precise control can be performed by increasing the judgment level / speed type.
[0016]
FIG. 6 shows still another operation example. In this example, an object is to prevent the peak level from excessively rising and image quality deterioration by variably controlling the tracking speed of the peak level according to the value of the peak level.
Hereinafter, the operation will be described with reference to FIG.
First, a threshold value (TH2) for peak level determination is set (step 51). When reading of the document is started (step 13), the system control unit 7 monitors the peak level. If the peak level exceeds the threshold, the rising speed is set to a low speed and the falling speed is set to a high speed (steps 52 and 53). On the contrary, if the peak level does not exceed the threshold value, the rising speed is set to a high speed and the falling speed is set to a low speed (steps 42 and 44).
[0017]
According to the above-described embodiment, as the peak level increases, the peak level increase tracking speed is decreased to improve the response until the true peak level is detected, and the image signal level temporarily changes due to disturbance. In the case of excessive increase, the peak level excessive increase can be reduced by decreasing the responsiveness.
Further, according to the above embodiment, by increasing the peak level lowering tracking speed as the peak level becomes higher, even if the peak level is excessively increased, the return time to the true peak level can be shortened. Degradation of image quality can be prevented.
Further, as the peak level is lowered, the descending follow-up speed is also lowered, so that there is no problem in all black area reproducibility in the middle of the document.
[0018]
In each of the above embodiments, it is desirable that the relationship between the peak level and the tracking speed is nonlinear in each of the image reading devices. The descending speed of the peak level is slower as the image signal peak level is lower, and the speed is increased as the peak level is increased. What is important here is a region where the peak level is low.
That is, as shown in FIG. 7A, regarding the descending speed of the peak level, it is determined that the true peak level is supplemented in the region where the peak level of the image signal is higher than the predetermined level (TH2). By increasing the descending speed, it is possible to shorten the return time to the steady state when the peak level rises excessively due to some disturbance.
[0019]
On the other hand, regarding the rising speed of the peak level, as shown in FIG. 7B, the peak level is maintained even if noise or the like is mixed in the image signal by performing low speed control in a region where the peak level is large with TH2 as a boundary. The image signal can be prevented from deteriorating without following this. In the region where the peak level is low, it can be determined that the true peak level has not yet been supplemented, the rising speed can be increased, and the time required to supplement the true peak level can be shortened.
It should be noted that each of the above embodiments shows an example of the present invention, and it goes without saying that the present invention should not be limited thereto.
[0020]
【The invention's effect】
As described above in detail, according to the present invention, there is a remarkable effect that it is possible to realize an image reading apparatus capable of performing finer image processing than the prior art based on the peak level of the read image signal. Is.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a basic configuration of an image reading apparatus according to an embodiment of the present invention.
FIG. 2 is a flowchart showing an operation of the image reading apparatus according to the embodiment.
FIG. 3 is a flowchart showing an operation of the image reading apparatus according to the embodiment.
FIG. 4 is a flowchart showing an operation of the image reading apparatus according to the embodiment.
FIG. 5 is a flowchart showing an operation of the image reading apparatus according to the embodiment.
FIG. 6 is a flowchart showing an operation of the image reading apparatus according to the embodiment.
FIG. 7 is a graph showing a relationship between a peak level and a follow-up speed control characteristic.
[Explanation of symbols]
1 Image Sensor 2 Operational Amplifier (Op Amp)
3 A / D converter 4 Image processing unit 5 Peak level tracking control unit 6 Reference generation unit 7 System control unit

Claims (7)

In an image reading apparatus having a peak detection means for detecting and keeping track of a peak level of a read image signal, and an image processing means for processing a read image signal based on the peak level held by the peak detection means,
The higher the peak level of the read image signal, the lower the tracking speed when the peak level rises in the peak detection means to increase the tracking speed when the peak level falls,
When the peak level of the read image signal exceeds a predetermined level, the speed at which the tracking speed when the peak level rises at the peak detecting means ( down speed ) is lowered until the peak level exceeds the predetermined level. image reading apparatus, characterized in that the higher speed with the rise rate up to more than the level at which said predetermined speed to increase more follow-up speed of the peak level lowered by slow (ascending speed) relative to the speed .   The image reading apparatus according to claim 1, wherein the tracking speed of the peak level can be changed during document reading.   The image reading apparatus according to claim 1, wherein the control of the tracking speed when the peak level is lowered is performed only during the simple binarization process.   4. The image reading apparatus according to claim 1, wherein the tracking speed when the peak level is increased is higher than the tracking speed when the peak level is lowered.   5. The image reading apparatus according to claim 1, wherein the follow-up speed when the peak level is lowered is high in a predetermined area at the front end of the document.   6. The image reading apparatus according to claim 1, wherein the follow-up speed when the peak level is lowered is variably controlled in conjunction with the follow-up speed when the peak level is raised. When the peak level exceeds a predetermined level, the tracking speed when the peak level rises is slower than the tracking speed when it falls.
The tracking speed when the peak level rises is higher than the tracking speed when the peak level falls if the peak level does not exceed a predetermined level. An image reading apparatus according to claim 1.

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