JPH0452028B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resolution correction device for correcting an image signal read by a facsimile device or the like using a solid-state image sensor.

In general, in reading devices such as facsimile machines, when the spatial frequency of the reflected light from the light irradiated on the document that enters the photoelectric conversion element increases, various causes of optical system problems such as chromatic aberration and comatic aberration of the optical lens occur. As a result, the amplitude of the image signal is attenuated, causing deterioration of the so-called MTF (modulation transfer function), making it impossible to reproduce thin lines, thin white areas, thin black and white stripes, etc. in the original, resulting in a decrease in resolution.

Conventionally, in order to solve the above-mentioned problems, in facsimile machines that use a solid-state scanning method, a delay circuit is used to detect and compare multiple consecutive signals. A method is used to detect this and forcibly format it.

However, a delay circuit, a driving means for the delay circuit, a means for detecting thin lines or thin white areas in a document, that is, a signal that is different from the preceding and succeeding signals in the signal, a means for forcibly shaping the signal, etc. need,
This has the disadvantage that the circuit configuration becomes extremely complicated and, in addition, it becomes expensive.

The present invention has been made in view of this point, and it is an object of the present invention to provide a resolution correction device that has a simple circuit configuration, improves resolution, and is inexpensive.

The present invention focuses reflected light emitted from a light source and irradiated onto the document surface using a lens, photoelectrically converts the light using a solid-state image sensor, amplifies the image signal, and then attenuates unnecessary harmonics. The signal is passed through a resolution correction circuit that corrects the amplitude, and in the sample hold circuit, the trailing end of the signal corresponding to the pixel is read out as a rectangular wave in synchronization with the image signal creation timing of the photoelectric converter. The aim is to achieve the objectives of

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a resolution correction device according to an embodiment of the present invention.

The reflected light of the light irradiated from the light source 1 to the original 2 is
The light is focused by the lens 3 and formed into an image on the light receiving window of the CCD image sensor 4. The CCD image sensor 4 converts the received light into an electrical signal and outputs it to the preamplifier 5. The preamplifier 5 amplifies the input signal and outputs it to the resolution correction circuit 6. The resolution correction circuit 6 includes a light source 1 and a lens 3, as described later.
It has a function of correcting MTF deterioration, that is, signal amplitude attenuation, which occurs due to various causes in the optical system composed of the CCD image sensor 4. The sample hold circuit 7 converts the analog signal input from the resolution correction circuit 6 into a rectangular wave and outputs the rectangular wave. The drive circuit 8 is a circuit that drives the CCD image sensor 4 and the sample hold circuit 7.

FIG. 2 shows an embodiment of the resolution correction circuit 6. In FIG. The resolution correction circuit 6 has a function of removing unnecessary high frequency components from the signal in order to prevent the occurrence of so-called overshoot and undershoot, in which the amplitude is suddenly emphasized at the rise and fall of the signal. It has an integrating circuit 11 consisting of a resistor 9 and a capacitor 10, and an operational amplifier 12, resistors 13 and 14, and a capacitor 15 are connected as shown in FIG. 2 in order to amplify the attenuated amplitude when the frequency exceeds a certain level. A peaking circuit 16 is provided. Note that 17 is an input terminal to which the output of the preamplifier 5 is input, 18 is an output terminal, and the output of the resolution correction circuit 6 is input to the sample and hold circuit 7.

FIG. 3 shows the signal waveform of the main part of the above embodiment, where A is the signal after being photoelectrically converted and amplified in the preamplifier 5, and A is the signal after being photoelectrically converted and amplified in the preamplifier 5.
is the input signal to B is a signal waveform at the time of passing through the integrating circuit in the resolution correction circuit 6 and before being input to the peaking circuit, and C is an output signal from the resolution correction circuit 6. D is a timing signal output from the drive circuit to read a signal from the sample and hold circuit, and E is an output signal from the sample and hold circuit 7.

Further, FIG. 4 shows the original 2, and the interval between the stripes is the same as the width of the light receiving window of the CCD image sensor. Further, FIG. 5 shows the relationship between the frequency and amplitude of the signal A, FIG. 6 shows the characteristics of the peaking circuit, that is, the relationship between the input signal frequency and the amplification degree, and FIG. 7 shows the signal passed through the peaking circuit. This shows the relationship between the frequency and amplitude of C.

The operation of the above embodiment will be explained below.

Light irradiated from a light source 1 onto a document 2 is focused by a lens 3 and formed into an image on a light receiving window of a CCD image sensor 4, and is input into a preamplifier 5 after being photoelectrically converted. The output of the preamplifier 5, that is, the signal after being amplified, is as shown in the original as shown in FIG.
When reading black and white stripes with a width corresponding to the width of the light-receiving window of the CCD image sensor 4, the frequency becomes the highest image frequency l, as shown in FIG. The waveform is as shown in signal A in the figure. Signal A is input to the input terminal 17 of the resolution correction circuit 6, and when it passes through the integration circuit 11 provided to prevent overshoot and undershoot caused by the peaking circuit 16, the signal B is generated with unnecessary harmonic components attenuated. The waveform is shown in .
In signal B, the rear end of the signal corresponding to one pixel represents information of the original image signal. Furthermore, signal B is
A signal C is obtained as the output of the resolution correction circuit 6 by passing through a peaking circuit 16 that amplifies the signal only when the input signal has a high frequency above a certain value. The peaking circuit 16 in the resolution correction circuit 6 amplifies only the part where the amplitude is attenuated when a signal with a frequency higher than m in FIG. 6, that is, the frequency at which the amplitude of the input signal starts attenuating, is input. - Correct it and output a signal C with a constant amplitude as shown in FIG. The output signal C of the resolution correction circuit 6 is input to the sample hold circuit 7, and the output signal C is inputted to the sample hold circuit 7, and the output signal C is input to the sample hold circuit 7, and the signal E is outputted according to the rising timing of the sampling signal D output from the drive circuit 8.
Output. The sampling timing is
It is synchronized with the drive timing of the CCD image sensor 4, and is set to be sampled at the rear end of the signal corresponding to one pixel with the largest amplitude. Accurate information can be obtained by reading at the above-mentioned timing when the amplitude result rate is low and the original image signal information appears, and by reading at timing.

Note that, as shown in FIG. 6, it is preferable that the amplification degree of the resolution correction circuit 6 is sufficiently attenuated in order to remove unnecessary harmonic components when the frequency of the input signal is equal to or higher than the maximum image frequency l. Needless to say, this objective can be achieved by stacking the integration circuits placed in front of the peaking circuit in multiple stages to increase the order.

As is clear from the above description, the present invention focuses light emitted from a light source and irradiated onto the document surface using a lens, photoelectrically converts it using a solid-state image sensor, amplifies it, and then attenuates unnecessary high frequencies. The signal passes through a resolution correction circuit that corrects the amplitude, and in a sample hold circuit, the signal is read out as a rectangular wave at or near the rear end of the signal corresponding to the pixel in synchronization with the image signal output timing of the photoelectric converter. ,
It is possible to improve the resolution with a simple circuit configuration, and it is also low-cost.In addition, in the resolution correction circuit, high frequencies higher than the highest image frequency are attenuated by an integrating circuit, which causes distortion and fluctuation of the image signal. Therefore, it has the effect of not impairing the reproducibility of intermediate tones.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of a resolution correction device according to an embodiment of the present invention, Fig. 2 is a circuit diagram of the resolution correction circuit, Fig. 3 is a signal waveform diagram of the main parts in the device, and Fig. 4 is The manuscript, Figures 5 and 7 are diagrams of the relationship between the frequency and amplitude of the signal in the device, and Figure 6 is a diagram of the relationship between the frequency and amplification of the input signal of the main part of the resolution correction circuit in the device. It is. 4...CCD image sensor 4, 6...Resolution correction circuit, 7...Sample hold circuit, 8...
...drive circuit, 12... operational amplifier.

Claims (1)

[Claims] 1. A photoelectric converter consisting of a solid-state image sensor, an amplifier that amplifies the digital signal output from this photoelectric converter, an integrating circuit that attenuates unnecessary high frequencies of the signal input from this amplifier, and a signal input from this integrating circuit. a peaking circuit that amplifies the attenuated amplitude of the signal; a sample-and-hold circuit that holds the analog signal input from the peaking circuit for a certain period of time and reads out the signal at or near the rear end of the signal to the pixel; and this sample-and-hold circuit and the photoelectric A resolution correction device having a drive circuit that drives a converter in synchronization with the converter.