JPS60248075A - Picture reader - Google Patents

Abstract

PURPOSE:To improve the density level correction of an original by detecting maximum white/black density in forward operation in the movement toward sub scanning and controlling variably the offset and gain of a variable amplifier in the forward operation. CONSTITUTION:An original table 14 is moved in the direction 17 by a sub scanning motor 16. In this case the original table 14 is moved in a high speed and the maximum white density and the maximum black density of an original 13 are stored. In order to read an ordinary signal, the motor 16 moves the table 14 in the direction 18. In this case, the density level correction of an input signal is executed by the maximum white/black densities so as to control the density level range of an input original up to the maximum quantized power of an A/D conveter.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image reading apparatus that corrects the density level of an image signal read by scanning a continuous tone original such as a photograph. Example configuration and its problems In general, an image signal having density information photoelectrically converted by a national scanning device such as a COD is once converted into a digital value by an A/D converter, and then converted into a multi-valued signal. Various image signal processes are performed in this state.

Conventionally, in gradation facsimile machines for the purpose of electronically transmitting photographs and the like, gradation density level correction has not been particularly applied to the density level of a document.

FIG. 1 illustrates the main part configuration of a conventional image reading section using an A/D converter in an image reading device such as a gradation facsimile machine. In Figure 1, 1 is a photoelectric conversion circuit that reads a document and outputs the read information as an analog signal, and 2 is a ^/D conversion circuit that converts the analog output signal sent from the photoelectric conversion circuit 1 into a digital signal. 3 and 4 are resistor dividers that respectively apply upper and lower reference voltages to the A/D converter 2.

In the above configuration, the output from the photoelectric conversion unit 1 that has read the original is applied to the input terminal vio of the A/D converter 2, and the range defined by the upper and lower reference voltages vRA and vRB is divided into ≦266, for example. Output terminal 0UTo-OUT as an 8-bit digital image signal by determining whether the voltage matches the output voltage.
7, and is sent via an image signal processing section (not shown) and a modem to a transmission line, for example, to a recipient's receiving facsimile machine (2) to a computer device.

Now, the resistor divider 3 determines the conversion range of the A/D converter 2.
, 4, this corresponds to the whitest part (maximum white density) and the blackest part (maximum black density), respectively, assuming the type of document that the reference voltages vRA and vRB are expected to read. The method of use was such that it was adjusted in advance and fixed to be equal to the output voltage of the photoelectric conversion circuit section 1.

In the conventional configuration as described above, when the density level of the input original varies widely depending on the type of the original, such as a dark photo original or a light photo original, the maximum white density as described above,
A large number of reference voltages vRA and vRB corresponding to the maximum black density are prepared, and the operator sets the reference voltage vRA each time according to the density level of the input document.

The operation was inconvenient because the vRB settings had to be redone. Furthermore, in the conventional method, when converting into a highly accurate multilevel digital image signal, the linearity of the conversion level deteriorates, and there is a problem in image quality in terms of density gradation.

OBJECTS OF THE INVENTION In view of the above drawbacks, the present invention provides an image reading apparatus that is suitable for reading continuous tone originals such as photographs and is capable of correcting density levels.

Structure of the Invention The present invention includes a variable amplifier that amplifies a photoelectrically converted input image signal, and an A/D that converts an analog output signal output from the variable amplifier into a digital image signal according to the signal level.
a converter, a level detecting means for detecting a maximum value and a minimum value level of the image signal from a black reference of the digital image signal, and controlling the gain of the variable amplifier according to the value detected by the level detecting means. control means, which detects the maximum value and minimum level of the image signal when controlling the forward sub-scanning movement of the scanning means; By configuring the control means to control the variable amplifier during conversion reading,
This aims to achieve the above objectives.

Description of examples An embodiment of the present invention will be described below.

FIG. 2 is a perspective view showing an embodiment of the mechanical section of the image reading device according to the present invention. In Figure 2, 1o is COD
11 is a lens, 12 is an illumination light source,
13 is a document for reading, 14 is a document table, 15 is a feed screw in the sub-scanning direction, and 16 is a sub-scanning motor.

In order to correct the density level of an input original in the present invention, first, the maximum white density and the maximum point density of the density level of the original are detected. For this purpose, the one-document table 14 is moved in the moving direction 17 by the sub-scanning motor 16. This is an outward movement of the original table 14, but at this time, the original table 14 is moved at high speed, and the maximum white density of the original 13 is
The maximum black density is stored. Next, in order to perform normal image signal reading, the original table 14 is moved in the moving direction 18 by the sub-scanning motor 16. This is the manuscript table 14
This will be a return trip. At this time, the density level of the input image signal is corrected using the maximum white density and maximum black density described above, so that even if the density level of the input original, such as a high-density photographic original or a thin photographic original, changes greatly, It is possible to correct the density level of the original so that the A/D converter operates up to the highest quantization voltage.

FIG. 3 is a block diagram of an image reading apparatus according to an embodiment of the present invention which detects the maximum white density and maximum black density described above and corrects the density level when reading an image.

In FIG. 3, 20F'f, a solid-state scanning element such as COD, 21 a variable amplifier for amplifying the analog signal of the solid-state scanning element 20, and 22 converting the analog signal of the variable amplifier 21 into a digital signal. 23 is a maximum white density detector that detects the maximum white density from the output of the A/D converter 22; 24 is a maximum black density detector that detects the maximum black density from the output of the A/D converter 22; 26 is a maximum white density detector 23,
An arithmetic circuit that performs a calculation described later from the output of the maximum black density detector 24, 26.29 is a latch circuit, and 28.30 is a D/A.
It is a converter. Note that 31 is a sampling pulse signal for A/D conversion, 32 is a trigger signal for the latch circuit, and 33
34 is a gain control signal, 34 is an offset control signal, 35 is an input image signal, 36 is an output image signal, and 3A is a digital image signal.

Also, 38 and 39 are switches, each of which is a variable amplifier 21.
Gain control signal 3 from D/A converter 28.30 for
3. and for switching the offset signal 34,
Switches 38 and 39 are open when the document table is moving forward when maximum black density and maximum white density are detected, and are closed during normal image reading, and the variable amplification is controlled by the control signals 33 and 34 described above. The amplification rate of the device 21 can be changed.

The operation of the above embodiment will be explained in detail below.

First, when detecting the maximum white density and maximum black density of the original,
Switches 38 and 39 are opened to input the analog output image signal 36 obtained by the variable amplifier 21 to the A/D converter 22 and convert it into a digital signal. This converted digital image signal output 37 is also sent to a maximum white density detector 23 and a maximum black density detector 24 to detect the maximum white density of the image signal at the time of image reading.

The digital image signal output 37 is stored as the maximum black density. This detection is done sequentially over the entire area of the document being read. FIG. 4 shows an example of an input image signal. Point A shown in the figure is the maximum white density, and point B is the maximum black density, that is, the maximum white density is the minimum value of the input original density level, and the maximum black density represents the maximum value of the original density level. The detection of the maximum and minimum values is performed in synchronization with the sampling link pulse signal 31 to the A/D converter 22, and the maximum and minimum values are stored while being successively compared with the digital image signal 37.

The arithmetic circuit 23 receives input of the maximum value B and the minimum value A and performs a predetermined arithmetic operation to control the variable amplifier 21. The output of this arithmetic operation is sent to the latch circuit 26. On the other hand, the maximum black density is sent to the latch circuit 29.

The above operation is performed during the outward movement of the document table 14 shown in FIG. The operation of the device 28°3o is performed. Therefore, during the return movement of the document table for normal document reading, the switches 38 and 39 act to close, so that the maximum black density is adjusted by the offset control signal 34 from the output of the D/A converter 30. The offset of the variable amplifier 21 is controlled to match the minimum value (VR, ) of the reference voltage of the A/D converter 22, while the gain control signal 33 from the D/A converter 28 controls the offset of the variable amplifier 21. Control the amplification rate of 21. Therefore, even if the voltage level range of the input image signal 36 changes depending on the density level of the original, when inputting it to the A/D converter, the level range is always constant up to the input voltage range of the A/D converter. Since it is possible to correct up to 100%, the linearity of image quality associated with multi-value A/D conversion can be reproduced well.

During image reading, the gain of the variable amplifier is kept constant, so even if noise occurs, image reproduction will not be adversely affected.

Note that the level detection of the output signal in this embodiment is not limited to the detection of the maximum value and the minimum value, but may be, for example, the detection of the average value. Further, the circuit shown in FIG. 3 can be easily realized using a microcomputer, and the above-mentioned processing can be automatically controlled without depending on the operation of an operator as in the conventional case.

Further, in the embodiment, the gain control of the variable amplifier 21 is performed by the D/A converter 28, but it is controlled by the digital signal.
The amplification rate may be varied by providing a circuit or the like for selecting the feedback resistance of the variable amplifier 21.

Effects of the Invention As described above, according to the present invention, the maximum white density and the maximum black density of the document are detected by the forward movement during movement in the sub-scanning direction, and the variable amplifier is controlled by these calculation results in the backward movement. By making the offset and gain variable control, the density level range of the input document can always be controlled up to the maximum quantization voltage of the A/D converter, which simplifies the circuit configuration for image reading and at the same time increases the A remarkable effect of density level correction can be achieved.

, 4. Brief description of the drawings FIG. 1 is a block diagram of main parts of a conventional image reading apparatus, FIG. 2 is a perspective view of main parts showing an embodiment of the mechanical part of an image reading apparatus according to the present invention, FIG. 3 is a block diagram of an image reading device according to an embodiment of the present invention, and FIG. 4 is a waveform diagram of an image signal.

2o... Solid state scanning element, 21... Variable gain amplifier, 22... A/D converter, 23...
...Maximum white density detector, 24...Maximum black density detector, 25...Arithmetic circuit, 26.29...
... Latch circuit, 28.30 ... D/A converter, 38.39 ... Selector switch.

Name of agent: Patent attorney Toshio Nakao and 1 other person
Figure 1. .

Figure 2 Figure 4

Claims (1)

[Claims] a variable amplifier that amplifies a photoelectrically converted input image signal; an A/D converter that converts an analog output signal output from the variable amplifier into a digital image signal according to a signal level; A level detection means for detecting a maximum value and a minimum value level of the image signal from a black reference of the image signal, and a control means for controlling the gain of the variable amplifier according to the value detected by the level detection means. , detecting the maximum value and minimum value level of the image signal when controlling the forward sub-scanning movement of the scanning means, and performing photoelectric conversion reading of the image signal during the sub-scanning movement control of the backward movement of the scanning means. , an image reading device for controlling the variable intensifier by the control means;