JPS635484A - Picture reader - Google Patents

Abstract

PURPOSE:To obtain a picture having good contrast changing a reference value for reading a black and white target, perfoming an efficient A/D conversion and moving the reference value of black/white according to the state of an original document. CONSTITUTION:There are provided two types of switching circuits 20, 21 for switching the reference value at the time of reading the black and white target, an A/D converting circuit 22 of 6 bits, for instance, a circuit 23 for switching the output, a memory 24 for storing a white level, a memory 25 for storing a black level, ROMs 26, 27 for moving the black and white levels respectively and storing a value for converting the reading level of the original document, D/A converting circuits 28, 29 and a control circuit 30 for switching the conversion values of the ROMs 26, 27 according to the instruction from a terminal J. The switching circuits 20, 21 are controlled by the control circuit 30, the range of the reference value of the A/D converting circuit 22 is made small at the time of reading the black and white target, the reference value obtained from the black and white target is converted by the conversion values of the ROMs 26, 27 according to an external instruction and the reference value suitable for the density of the original document is fed to the A/D converting circuit 22. According to such constitution, the capacities of the circuit 22 or the memories 24, 25 can be made a small and the picture having good quality can be obtained.

Description

[Detailed Description of the Invention] [Summary] In an image reading device, the density level of the entire reproduced image can be arbitrarily specified in accordance with the density of a photograph read by a photoelectric conversion element, and dark parts are made white as a whole. This makes it possible to improve the contrast and increase the resolution of the target part, and to reduce the capacity of the A/D conversion circuit and memory by supplying two types of reference potentials when reading white and black targets. made it possible.

[Industrial application field]

The present invention relates to an image reading device that converts an image containing gray levels, such as a photograph, into a multi-tone digital signal, and particularly relates to an image reading device that can create an image with good contrast with a small amount of hardware.

An image containing gray levels such as a photograph is converted into a multi-tone digital signal, converted into a binary signal by a halftone conversion circuit, and outputted to a laser printer to be printed. A manuscript is printed in small quantities using a copying machine.

By the way, in order to express a photo as halftone dots, 64 or more gradations are required at a level with many changes in density, but since the photos themselves can be either lighter or darker overall,
25 at the stage of converting into a digital signal for the image reading device.
656 gradations are required.

Therefore, the hardware of the image reading device becomes larger, but
By setting the white standard and black standard according to the density of the photo,
Since the amount of signals to be processed is small, it is desirable to have an image reading device that can set the standard according to the density of the photograph, reduce the amount of hardware, and arbitrarily set the density of the entire reproduced image. ing.

[Conventional technology]

FIG. 4 is a diagram illustrating an example of the configuration of an image reading device.

A photograph of an original is placed on a glass 1, which is illuminated by a fluorescent lamp 2, and the reflected light enters a photoelectric conversion element 3 such as a CCD through a reflecting mirror and a lens as shown by the dotted line. The video circuit 4 converts the electrical signal converted by the CCD 3 into, for example, an 8-bit digital signal and sends it to the control circuit 5.

A motor 6 drives this video circuit 4, etc. to move it in the direction of arrow G or H to read the photograph.First, the black and white levels that will be the reference values when reading this photograph are determined. An operation is performed to read the target 8 and the white target throat 9.

The power supply/morph drive circuit 7 supplies power to the control circuit 5 and the video circuit 4, and also drives the motor 6 to perform the above operations under the control of the control circuit 5.

FIG. 5 is a block diagram of a circuit showing an example of a conventional image reading device.

Control circuit 5 (Fig. 4) connects terminals C and E to switching circuit 10.
and 1) respectively, send the reference value and ground level input from the terminal to the A/D conversion circuit 12, and
/D conversion circuit 12 connects white target 9 and black target 8
is used as the reference value to determine the reading level.

The control circuit 5 moves the video circuit 4 to the position of the white target throat 9, sends a switching signal from the terminal F to the switching circuit 13, and changes the state of the A/D conversion circuit 12 when the white target input from the terminal B is read. The output is stored in memory 14.

Next, the control circuit 5 moves the video circuit 4 to the position of the black target 8, sends a switching signal from the terminal F to the switching circuit 13, and outputs the A/D when the black target input from the terminal B is read.
The output of the conversion circuit 12 is stored in the memory 15.

Next, the control circuit 5 switches the switching circuits 1o and 1), converts the white level stored in the memory 14 into an analog value by the D/A conversion circuit 16, and sends it to the A/D conversion circuit 12 as an upper reference. , the black level stored in the memory 15 is D/A
The conversion circuit 17 converts it into an analog value and sends it to the A/D conversion circuit 12 as a lower-order reference.

Next, the control circuit 5 reads the photo input from the terminal B
The output of the CD is input to an A/D conversion circuit 12, and a video signal converted into a digital value is sent out from terminal A based on the upper reference and lower reference provided from the memories 14 and 15.

[Problem that the invention seeks to solve]

The A/D conversion circuit 12 is an 8-bit one, and the memory 1
4.15 is 2x if the CCD is 2 bits
An 8-bit image is required, making the image reading device expensive. Also, some photos have no white parts and are completely black, while others are completely whitish.By changing the standard level of black or white, the contrast can be strengthened. There is a problem in that there is no means to freely set the contrast.

In view of these problems, the present invention provides means for performing efficient A/D conversion by changing the reference values for reading the white and ring targets, and for moving the white/black reference values depending on the condition of the document. By providing this information, an image with good contrast can be obtained.

[Means for solving problems]

FIG. 1 is a schematic diagram of a circuit showing an embodiment of the present invention.

20. 21 is a switching circuit that can switch between two types of reference values when reading white and ring targets; 22 is, for example, a 6-bit A/D conversion circuit; 23 is a switching circuit that switches the output of the A/D conversion circuit 22; 24 is a memory for storing the white level;
5 is a memory for storing the black level.

A ROM 26 stores values for moving the white level stored in the memory 24 and converting the reading level of the original, and 27 stores a value for moving the black level stored in the memory 25 and converting the reading level of the original. ROM, 28.29 is D/
A conversion circuit 30 is RO based on the instruction input from terminal J.
This is a control circuit that switches the conversion value of M26.27.

Regulation? 'S1) When the circuit 30 controls the switching circuit 20.21 to read the white and ring targets, the circuit 30 switches the A/D conversion circuit 22.
By reducing the range of the reference value of A/D and converting the reference values obtained from the white and ring targets using the conversion value of ROM26.27 according to an external instruction, the appropriate reference value corresponding to the original density can be set to A/A. The configuration is such that the signal is sent to the D conversion circuit 22.

[Effect]

With the above configuration, the control circuit 22 can reduce the capacity of the A/D conversion circuit 22 and the memories 24 and 25, as well as the ROM 26.

With the conversion value of 27, an image with good contrast can be obtained.

〔Example〕

FIG. 2 is a diagram for explaining the operation of FIG. 1, and FIG. 3 is a diagram for explaining density specification.

In FIG. 1, the control circuit 30 sends switching signals to the switching circuits 20 and 21, and the reference potential shown at Vl in FIG. is sent to the A/D conversion circuit 22, and using this reference potential, the signal input from terminal B that reads the white target is converted into A/D converter circuit 22.
It is converted by the D conversion circuit 22 and stored in the memory 24 via the switching circuit 23. The video output at this time has the waveform shown in FIG.

Next, the control circuit 30 switches the switching circuits 20 and 21, sends the reference potential shown in 3 in FIG. 2 from the terminal and the ground level to the A/D conversion circuit 22, and uses this reference potential The signal read from the ring target entering from terminal B is
The signal is converted by the /D conversion circuit 22 and stored in the memory 25 via the switching circuit 23. The video output at this time has the waveform shown in FIG.

Using these reference potentials V, , V, and the ground level, the A/D conversion circuit 22 converts, for example, 6-bit A
/D conversion circuit is sufficient, and the memories 24 and 25 may have a capacity of 2×6 bits.

A concentration designation, for example, in %, is input from the operator to the control circuit 30 from the terminal J. That is, depending on whether the photograph is entirely black as shown in FIG. 3(a) or whitish as shown in FIG. 3(b), the operator may
Input an instruction to move the reference potential given to as shown by the dotted line.

Figure 3 (In the case of al, the white level occurs less frequently and the black level occurs more frequently. Therefore, in order to output an overall whitish image, the white level in the memory 24 is set to R.
The OM 26 is converted with a preset conversion value and sent to the D/A conversion circuit 28, and the black level of the memory 25 is converted to the ROM.
For example, an instruction is inputted to the control circuit 30 to convert the data with a preset conversion value to the D/A conversion circuit 27 and send it to the D/A conversion circuit 29, for example, 80%.

Therefore, the D/A conversion circuit 28 sends a white reference output corresponding to the waveform shown in FIG. Therefore, an image with good contrast and improved resolution in areas with a high black level can be obtained.

In the case of Figure 3(b), the black level occurs less frequently and the white level occurs more frequently.Therefore, in order to output a blackish image, contrary to the above, the black standard is increased by 10% toward the white side. An instruction to do this is input to the control circuit 30.

Therefore, the D/A conversion circuit 29 sends a black reference output corresponding to the waveform shown in FIG. Therefore, an image with the density desired by the operator can be obtained.

〔Effect of the invention〕

As described above, the present invention can reduce the capacity of the A/D converter circuit and memory, and can obtain an image having the density distribution desired by the operator.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a circuit showing an embodiment of the present invention, FIG. 2 is a diagram explaining the operation of FIG. 1, FIG. 3 is a diagram explaining density specification, and FIG. 4 is a diagram of an image reading device. FIG. 5 is a block diagram of a circuit showing an example of a conventional image reading device. In the figure, 1 is glass, 2 is a fluorescent light, 3 is a photoelectric conversion element, 4 is a video circuit, 5.30 is a control circuit, 6 is a motor, 7 is a power supply/motor drive circuit, 8 is a black target, and 9 is a White target, 10.1)
, 13, 20.21.23 is a switching circuit, 12.22 is A
/D conversion circuit, 14, 15.24.25 is memory,

Claims (2)

[Claims] (1) A that converts the output of the photoelectric conversion element into a digital value
a /D conversion circuit (22), a switching circuit (20, 21) that supplies two types of reference values for the A/D conversion circuit (22), and a switching circuit (20, 21) that supplies two types of reference values for the A/D conversion circuit (22); Storage means (24, 25) for separately storing the output of the A/D conversion circuit (22) in white and black, and the storage means (
ROMs (26, 27) that convert the outputs of 24, 25) using preset conversion values, and the ROMs (26, 27).
and D/A conversion circuits (28, 29) that convert the outputs of the ROMs (26, 27) into analog values, respectively. ), the A/D conversion circuit (2
2) converts the reference value used when converting the output of the photoelectric conversion element into a digital value by the ROM (26, 27) and supplies it to the A/D conversion circuit (22).
An image reading device that arbitrarily changes the density of the entire reproduced image based on a video signal sent by the image reading device. (2) The A/D conversion circuit (22) and the storage means (24,
25) The image reading device according to claim 1, wherein the capacity of the switching circuit (20, 21) is determined in accordance with two types of reference values supplied by the switching circuit (20, 21).