JPH0125472B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an image reading device that reads an original image using an image sensor such as a CCD, converts it into a binary signal, and outputs the binary signal.

Prior Art When trying to reproduce an image read by the image reading device using a digital output device such as a laser printer, if the number of pixels or pixel density of the image reading device and the digital output device do not match, the read image may not match. It is not possible to reproduce the same image.

However, conventional image reading devices can only output at a fixed pixel density. On the other hand, the pixel densities of digital output devices vary, and the combination of the two lacks versatility.

Furthermore, image reading devices having reduction/enlargement functions have been proposed. According to the device described in Japanese Patent Application Laid-Open No. 57-48154, the pixel density is converted, that is, changed, by temporarily storing a binary signal input from an image sensor, etc., and sampling it again at a different pitch. I'm doing twice as much. However, in the device described in this publication, after an image is read by an image sensor or the like and the binarized digital signal is stored, processing is performed to change the pixel density again, resulting in a very complex signal. processing is required.

Purpose The present invention has been made in view of the above points, and can output a binary signal of an original image at any pixel density with a simple configuration, and can be used with an output device of any pixel density. It is an object of the present invention to provide an image reading device which can be combined with a conventional image reading device and which can also reduce and enlarge an image.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a frequency band for removing high-frequency noise from the image sensor output in an image reading device that reads a document image with an image sensor, converts it into a binary signal, and outputs it. a variable low-pass filter; a comparator that compares the image sensor output inputted through the low-pass filter with a reference voltage and converts it into a binary value; and a clock pulse output means whose frequency can be changed; and a control means for changing the frequency of the clock pulse and changing the frequency band of the low-pass filter in conjunction with the change in the frequency of the clock pulse.
The pixel density of the binary signal output from the latch can be changed by changing the frequency of the clock pulse.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

Image sensor 1 that reads the original in Figure 1
is driven by a drive clock CD from a drive circuit (not shown), and its output a is driven by the drive clock CD from a drive circuit (not shown).
It is sampled by a sample hold circuit 2 using CD as a sampling pulse, and the output b of the sample hold circuit 2 is input to a low pass filter 3. Note that an image sensor having a built-in sample and hold circuit may be used.

The low-pass filter 3 is for removing high-frequency noise, and here a variable frequency band filter is used due to the relationship with the D latch, which will be described later.

The output c of the low pass filter 3 is the comparator 4
The binary signal d is compared with the reference voltage V _c by
and is input to the D terminal of the D latch 5.
The D latch 5 latches the D terminal input in accordance with the clock pulse CK from the pulse generator 6 and outputs an output signal OUT from the Q terminal.

Pulse generator 6 and low pass filter 3
is also connected to the control circuit 7, and is configured to be able to control the frequency _CK of the clock pulse CK and the cut-off frequency _CF of the low-pass filter in a correlated manner.

2 by changing the frequency _CK of the clock pulse CK.
The pixel density of the digitized signal is changed, and the cutoff frequency _CF of the low-pass filter 3 is set so that harmful high-frequency noise can be removed from the clock pulse frequency _CK when the D latch 5 changes the pixel density. The amplification must be set so as not to become too low, and both frequencies are controlled so as to maintain this relationship.

The operation of the above-mentioned circuit will be explained based on FIG.

The output a of the image sensor 1 is sampled by a sample hold circuit 2 at the frequency of the drive clock CD. The signal b that has passed through the sample and hold circuit 2 has a reset noise N as shown in FIG.
Contains.

These high frequency components such as reset noise are removed by a low-pass filter 3 and smoothed into a signal c, and then compared with a reference voltage _Vc by a comparator 4 to become a binary signal d.

Since this binary signal d is a signal corresponding to the pixel density of the reading device, if this signal is output as is to a printer with a different pixel density, only a distorted image will be obtained.

To correct this, the binary signal d is input to the D terminal of the D latch 5 and latched in response to the clock pulse CK input to the CK terminal. In this case, if the pixel density on the printer side is 2/3 times the pixel density on the reading device side, then the clock pulse CK with a clock frequency _CK1 that is 2/3 times the driving clock frequency _CD of the image sensor 1 is used. Enter ₁ .

D latch 5 determines the state of the D terminal input at the rising edge of clock pulse _CK1 input to the CK terminal.
The binary signal d is an output signal suitable for printers with different pixel densities.
It is converted to OUT ₁ and output from the Q terminal.

In addition, the cutoff frequency of low pass filter 3
_CF is also changed according to changes in the frequency _CK of the clock pulse CK, giving a good image with less noise.

For example, if the pixel density on the printer side is equal to or 1/4 times the pixel density on the reading device side,
CK ₂ ( _CK2 = _CD ) and CK ₃ ( _CK3
= 1/4 _CD ). The output signals for each case will be OUT ₂ and OUT ₃ respectively.

On the other hand, in the above explanation, it was mentioned that a copy image equal to the read image is reproduced when used in combination with printers with different pixel densities, but if the pixel density of the printer is constant, the clock pulse CK By changing the frequency of the image, it is possible to enlarge or reduce the copy image.

For example, if the pixel density on the printer side and the reading device side are equal, the clock pulse as described above
If the binary signal d is latched by CK ₁ , CK ₂ and CK ₃ and the output signals OUT ₁ , OUT ₂ and OUT ₃ are outputted to the printer, the output signals are 2/3 times, 1 times and 1/4 respectively. A copy of the image can be obtained.

From the above, the relationship between the drive clock frequency _CD of the image sensor 1 and the clock pulse frequency _CK given to the D latch 5 can be summarized as follows: ・_CD > _CK ... pixel density becomes coarse (coarse conversion) ・_CD = _CK ... change None/ _CD < _CK ...The pixel density becomes denser (fine conversion), and if you want to obtain a copy image that is the same as the original image on an output device with a different pixel density than the reading device, for an output device with a low pixel density, Coarse conversion may be performed, and fine conversion may be performed for output devices with a high pixel density. Further, if the pixel density of the output device is kept constant and a coarsely converted binary signal is input, a reduced image can be obtained, and if a finely converted binary signal is inputted, an enlarged image can be obtained. Incidentally, the magnification in the sub-scanning direction is also converted at the same time as this magnification conversion in the main scanning direction, but since this can be done by a known method, a description thereof will be omitted.

Effects As is clear from the above description, the image reading device of the present invention has a simple configuration and can be combined with an output device of any pixel density, and can also reduce or enlarge a copied image.

In addition, since the image sensor output is passed through a low-pass filter with a variable frequency band, and the cutoff frequency of the filter is changed in relation to the clock pulse frequency of the D latch, high-frequency noise can be removed regardless of changes in pixel density. A duplicate image can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG.
The figure is a diagram showing waveforms at each stage of the circuit diagram. 1... Image sensor, 2... Sample hold circuit, 3... Low pass filter, 4... Comparator,
5...D latch, 6...Pulse generator, 7...Control circuit, _CD ...Drive clock frequency, _CK ...Clock pulse frequency, _CF ...Cutoff frequency.

Claims (1)

[Scope of Claims] 1. An image reading device that reads an original image with an image sensor, converts it into a binary signal, and outputs it, comprising: a low-pass filter with a variable frequency band for removing high-frequency noise from the image sensor output; a comparator that compares the image sensor output input via a filter with a reference voltage and converts it into a binary value; a clock pulse output means whose frequency can be changed; a D latch that outputs the output of the comparator in accordance with the clock pulse; and the clock pulse. and control means for changing the frequency band of the low-pass filter in conjunction with changing the frequency of the clock pulse, and controlling the pixel density of the binary signal output from the D latch by changing the frequency of the clock pulse. An image reading device characterized by being changeable.