JPH01248762A - Picture input device - Google Patents

Abstract

PURPOSE:To vary freely the contrast in real time while applying picture input expressing the graduation accurately by using an analog signal being the result of D/A-converting a data being the read reference of each picture element of a line sensor as an A/D conversion reference voltage. CONSTITUTION:When the output signal of a line sensor 16 is A/D-converted by an A/D converter 220, the analog value of a data being the read reference of each picture element of the line sensor 16 is given from a D/A converter 24 as the conversion reference voltage. Thus, the specific characteristic of the read optical system is corrected as to all picture elements and the picture data whose intermediate gradation is expressed accurately is obtained. When the reference voltage of the D/A converter 24 is varied into a desired value by an adjustment bias circuit 28 for contrast adjustment, the conversion reference voltage of the A/D converter 20 is changed in proportion thereto and the contrast is changed in the same ratio over the picture of one line. Thus, the picture data expressing accurately the gradation is generated to all picture elements and the contrast of the picture is varied in real time.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image input device that inputs an image with gradation, and more specifically, an image input device that allows the gradation expression of the input image to be changed at any time. Regarding equipment.

[Prior Art] An image input device is a device that reads image information such as characters, figures, photographs, etc. as is and inputs it into a computer, etc., and is built into a facsimile machine, a copier, etc., or is used as a stand-alone image scanner in a personal computer. connected to.

FIG. 10 shows a schematic configuration of a conventional image input device. This image input device 100 uses a manuscript paper 10 to be read.
2, horizontally elongated fluorescent tubes 104 along the main scanning direction are arranged opposite to each other, and out of the light emitted from the fluorescent tubes 10.4 toward the reading line, the light rays are reflected by the reading line and transmitted through the converging lens 106. is imaged on the light-receiving surface of a line sensor 108 made of a CCD (solid-state image sensor). The line sensor 108 converts image information on the reading line into electric charge and outputs an analog reading signal. This analog signal is A/D converted by an A/D converter 110 and sent to a subsequent signal processing circuit 112 as digital data.

[Problems to be Solved by the Invention] By the way, when the image on the manuscript paper 102 has a gradation, the gradation is expressed as the level of the analog output of the line sensor 108, and in turn, the level of the digital output of the A/D converter 108. It is expressed as an output value. Therefore, when an image is assembled based on the digital data in a reproduction or recording system, the image on the original paper 102 is reproduced.

However, the characteristics of playback/recording devices such as CRTs and printers,
There are cases where it is desired to change the contrast of the input image at any time depending on various conditions or the user's preference.

As a means to realize this request, the line sensor 108
A method of changing the gain of the output analog signal,
The first method that can be considered is to change the value of digital data after /D conversion.

The former method has disadvantages in that increasing accuracy requires a complex and expensive amplifier circuit, and it is susceptible to noise and environmental changes.

On the other hand, the latter method involves arithmetic processing, and if it were to be able to change the contrast in real time, it would require a large-scale logic circuit.

Furthermore, the image data input by this type of image input device must faithfully represent the gradation of the image on the document 102. However, the distribution of the amount of light actually received by the line sensor 104 is such that the amount of light received is greatest at the center and gradually decreases toward both ends, as shown by the dashed line in FIG. Therefore, the A/D converter converts the amount of light received by the line sensor 104 into A/D.
If a constant conversion standard is set in the D converter 108 while ignoring the light amount distribution, image data that does not accurately represent intermediate gradations will be generated.

Conventionally, in order to flatten the light receiving characteristics of the line sensor 104, a reflector with a special shape (not shown) has been used to solve this problem, or an automatic gain control circuit (not shown) has been used. However, when using a reflector, it is not possible to deal with variations in the individual pixels of the line sensor 104,
When an automatic gain control circuit (not shown) is used, the circuit configuration is complicated and there are many adjustment points, making it unsuitable for general users.

The present invention has been made in view of these problems, and it is possible to freely change the contrast in real time while inputting an image that enables reliable gradation expression, and also to freely change the brightness. An object of the present invention is to provide an image input device with a simple configuration.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an image input device that reads and inputs an image having gradation one line at a time using a line sensor. an A/D converter that performs D conversion; a line memory means that stores data serving as a reading reference for each pixel of the line sensor and reads out the reading reference data in synchronization with the output operation of the line sensor; Convert the read reference data to an analog voltage, and convert the analog voltage to A.
The configuration includes a D/A converter that supplies a conversion reference voltage to the D/D converter; and a DC bias circuit for contrast adjustment that selects the reference voltage of the D/A converter to a desired value.

In addition, in order to freely change the brightness, the present invention provides a DC bias for brightness adjustment that adds a desired value of DC voltage to the read output of the line sensor and uses it as an input signal to the A/D converter. The configuration is such that a circuit is provided.

Furthermore, the present invention provides a circuit for detecting a black level for defining the lowest level of the input voltage range of the A/D converter from the read output of the line sensor as a DC bias circuit for bright adjustment. The black level DC voltage obtained from the level detection circuit is added to the readout output of the line sensor and is used as an input signal to the A/D converter.

[In the action main A/D converter, the output signal of the line sensor is
During conversion, the analog value of the data that serves as the reading reference for each pixel of the line sensor is given as the conversion reference voltage by the D/A converter, so the inherent characteristics of the reading optical system are corrected for all pixels, and the intermediate Image data with accurate gradations can be obtained.

When the reference voltage of the D/A converter is changed to a desired value by the adjustment bias circuit for contrast adjustment, the conversion reference voltage of the A/D converter is changed in proportion to the contrast adjustment, and the image for one line is changed. Hunto Trust changes at the same rate over time.

Furthermore, when the DC output voltage of the bias circuit for brightness adjustment is changed, the absolute value of the input voltage of the A/D converter increases or decreases by that amount, thereby increasing or decreasing the brightness of the image.

Then, by adding the black level DC voltage to the bright adjustment DC bias circuit using the black level detection circuit, the increase or decrease within the input voltage range of the A/D converter is made proportional to the ratio of the bias amount. This makes it possible to make changes.

[Embodiment] The present invention will be described in detail below with reference to FIGS. 1 to 9.

Support! FIG. 1 shows the overall configuration of an image input device according to a first embodiment.

In this figure, a document 1 illuminated by a fluorescent tube 10
The light reflected from the image for one line on 2 forms an image on the light receiving surface of the line sensor 16 made of COD via the condenser lens 14, and the line sensor 16 generates an analog image representing the gradation of the image for one line. A signal Sa is output. This analog signal Sa is supplied to the analog signal input terminal VIN of the A/D converter 20 via the amplifier 18.

As shown in FIG. 3, this A/D converter 20 is of a fully parallel type or a flash type, and includes n (for example, 16) comparators 20a and a decoding circuit 20b, each having a stepwise different comparison standard. Consisting of Any comparator 20a,
The input analog signals are compared in magnitude almost simultaneously based on individual comparison standards. In response to the comparison result, the decoding circuit 20b calculates the log number of pinots corresponding to the number n of comparators 20a.
2n digital signals are generated. The comparison standard of each comparator 20a is given by a divided voltage value by resistors R, 2R, 2R, . . . 2R, R connected in series to the conversion reference input terminal V REF.

The line memory 22 stores one line of data that serves as a reading reference for each pixel of the line sensor 16. Preferably, as this reading reference data, the line sensor 16 reads a white band of a predetermined brightness that is set in advance as a reading reference prior to main scanning of the document 12, and the output signal is sent to the A/
Data obtained by A/D conversion by the D converter 20 may be used.

The line sensor 16 that read the original image as described above
The analog signal Sa for one line is sent to the A/D converter 20.
When the read reference data RD is supplied to the input terminal VIN of the D/A, the read reference data RD is read out from the line memory 22 in synchronization with the output operation of the line sensor 16.
The converter 24 performs D/A conversion, and the analog signal S[RD
as a conversion reference voltage input terminal VR of the A/D converter 20.
Supplied to EF. As a result, an A/D conversion standard that reflects the unique characteristics of the reading optical system is set for each pixel, and even if the sensitivity of each pixel of the line sensor 16 varies,
The variation is corrected by the conversion standard, and after A/D conversion, image data that accurately represents the intermediate gradation of the image is obtained.

Note that as a peripheral circuit of the line memory 22, an address circuit and a timing signal (
(none of which are shown), etc. are provided.

Now, the D/A converter 24 converts the read reference data RD from the line memory 22 into an analog signal S[RD], and the switch circuit is connected to the reference voltage input terminal V ref from the buffer 1 circuit 28. A variable bias voltage Cv1 selected by 26 is provided.

The D/A converter 24 is, for example, a voltage addition type as shown in FIG. In this circuit, each bit DBO- of the input digital signal (read reference data RD)
Depending on the logic state of DB- ("H" or "L"), each switch 5OS-S is switched to either the reference voltage V ref terminal or the ground potential terminal. When switched to the terminal of the reference voltage V ref, a voltage proportional to the weight of each digit and the reference voltage V ref is applied to the connection point N.
By superimposing these voltages, an output voltage of 1·V ref is obtained at the output terminal of the operational amplifier 24a. Here, the value of K1 is determined by the λ capacity. Note that the polarity of the reference voltage V ref may be positive or negative.

Therefore, in this embodiment, since the reference voltage V ref is given as a variable bias voltage CV1, the conversion reference voltage V REF supplied to the A/D converter 20 changes in proportion to the change in the bias voltage Cv1. , the contrast of the image changes depending on the amount of change.

FIG. 5 shows this situation. In the figure, a curve Sa indicates the output signal of the line sensor 16 when one line of image is read, and a solid line S [RD] indicates the output signal from the D/A converter 24 in synchronization with the output of the line sensor 18.

The voltage applied to the conversion reference voltage terminal of the A/D converter 20 is shown. According to this embodiment, when the bias voltage Cvt is increased, the conversion reference voltage V REF becomes the dotted line S [RD]
', the contrast is shifted upward (to a higher level) at the same rate throughout a line, thereby lowering the contrast. On the other hand, when the bias voltage CVi is lowered, the conversion reference voltage V REF shifts downward (to a lower level) at the same rate throughout one line as indicated by the dashed line S [RD]'', thereby increasing the contrast.

Thereby, by appropriately selecting the bias voltage CVI, it is possible to adjust the contrast to a desired level at any time.

FIG. 2 shows a specific example of the configuration of the switch circuit 26 and the buffer circuit 28. The switch circuit 26 includes a resistor 26R9.
... A voltage dividing resistor network consisting of 28R and an on/off switch 26a
, . . 2E3a, and an output voltage cvI can be obtained according to the combination of closed switches. In this example, since there are four switches, 15 values (types) can be selected for the output voltage cvi.

The buffer circuit 26 is a voltage follower consisting of an operational amplifier 28a.

It is composed of an operational amplifier 28b and a voltage amplification circuit consisting of resistors 28c to 28g, and works to amplify input voltage CVI to obtain bias voltage CVI, and at the same time works to prevent noise generated at the time of switching from appearing in bias voltage Cv1.

Therefore, the switch 2ea of the switch circuit 26,...
By selectively closing 28a by button operation, a desired bias voltage CVi is applied to the D/A converter 24 at any time to adjust the conversion reference voltage V of the A/D converter 20.
By changing REF, it is possible to change the contrast of the input image in real time.

As described above, according to this embodiment, real-time contrast adjustment is possible with a compact circuit configuration, and since the adjustment is made by changing the DC bias voltage CVI, it is immune to noise and environmental changes. It is strong and does not deteriorate gradation linearity.

Figure 6 shows the overall configuration of an image input device according to a second embodiment. This embodiment has a switch circuit 30 and a buffer circuit 32 added to the configuration of the first embodiment, and the brightness can be adjusted by the functions of both circuits.

That is, by adding the DC bias voltage BVI output from the buffer circuit 32 to the output signal Sa of the line sensor 16 and inputting it to the A/D converter 20, the seventh
As shown in the figure, the absolute value of the image signal increases or decreases, and as a result, the brightness of the image increases or decreases. In Figure 7, dotted line Sa
l is A/ when positive bias voltage BV1 is applied
The input signal of the D converter 20 is shown, and the brightness increases at this time. - Dotted chain line Sa'' indicates the input signal of the A/D converter 20 when a negative bias voltage BVI is applied,
At this time, brightness decreases.

FIG. 8 shows a specific configuration example of the switch circuit 30 and the buffer circuit 32. The switch circuit 30 includes a resistor 30R9.
... Consists of a voltage dividing resistor network of 30R and three open/close switches 30 al 30 b + 30 c,
An output voltage bvl can be obtained depending on the combination of closed switches. In this example, since there are three switches, eight values (types) can be selected for the switch output voltage bvi. The buffer circuit 32 is composed of a voltage follower made up of an operational amplifier 32a and a voltage amplification circuit made up of an operational amplifier 32b and resistors 32c to 32g. To prevent noise that sometimes occurs from appearing in the bias voltage BVI. The operational amplifier 32f and the resistors 32g to 32j form an adder circuit.

FIG. 9 is a circuit diagram of an embodiment showing a specific configuration example of a DC bias circuit provided with a black level detection circuit.

In this circuit, by inputting the output Sa of the line sensor 16 to the black level detection circuit 40, the black level DC voltage b
kvl is obtained, and a resistor 32d that defines a constant voltage is connected to the inverting input terminal of the operational amplifier 32b in the bias circuit.
Apply as input voltage to In this configuration example, the black level DC voltage bkv1 is further branched to the operational amplifier 32.
It is also applied as an input voltage to the inverting input terminal of f. The black level detection circuit 40 here constitutes a sample and hold circuit, and is constituted by a circuit capable of obtaining a DC voltage value obtained by holding the black level value in the line sensor over a period of one line.

As described above, according to this embodiment, in addition to the features of the first embodiment, real-time brightness adjustment is possible with a simple circuit configuration, and - rich gradation expression can be obtained. Can be done.

[Effects of the Invention] The invention has the following effects by having the above-described configuration.

When converting the output signal of the line sensor to A/D, the analog signal obtained by D/A converting the data that serves as the reading reference for each pixel of the line sensor is set as the A/D conversion reference voltage. It is possible to change the contrast of the image in real time by changing the reference voltage of the D/A converter to a desired value using a DC bias circuit while generating image data that accurately represents the gradation. Since the adjustment is made using a DC bias voltage, it is resistant to noise and environmental changes, does not deteriorate gradation linearity, and has an extremely compact circuit configuration. Furthermore, it is also possible to change the brightness of an image in real time using a DC bias circuit for brightness adjustment.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of an image input device according to an embodiment of the present invention, and FIG. 2 shows the switch circuit 26 and buffer circuit 2 of FIG.
8 is a circuit diagram showing a specific configuration example of the A/D converter 20 in FIG. 1, FIG. 4 is a circuit diagram showing a specific configuration example of the A/D converter 20 in FIG. FIG. 5 is a circuit diagram showing a specific example of the configuration of the converter 24; FIG. 5 is a diagram showing the operation of the contrast adjustment (change) function of the device shown in FIG. 1; FIG. 8 is a diagram showing another embodiment of the present invention. FIG. 7 is a block diagram showing the overall configuration of the image input device; FIG. 7 is a diagram showing the operation of the brightness adjustment (change) function of the device shown in FIG. 6; FIG. 8 is a block diagram showing the brightness adjustment switch circuit 30 of FIG. 7.
9 is a circuit diagram showing a specific example of the configuration of the buffer 1 circuit 32, FIG. 9 is a circuit diagram of an embodiment showing a specific example of the configuration of a DC bias circuit provided with a black level detection circuit, and FIG. 1 is a diagram showing a schematic configuration of a conventional image input device. In the drawings, 10...Fluorescent tube, 12...Original, 14...Condensing lens, 16...Line sensor, 20...A/D converter, 22...・Line memory, 24... D/A converter, 26... Contrast adjustment switch circuit, 2 B
...Contrast adjustment buffer 1 circuit, 30...
. . . Switch circuit for bright adjustment, 32 . . . Buffer circuit for bright adjustment, 40 . . . Black level detection circuit.

Claims (3)

[Claims] (1) In an image input device that reads and inputs an image with gradation one line at a time using a line sensor, an A/D converter converts the read output of the line sensor to digital.
a D converter; line memory means for storing reading reference data of each pixel of the line sensor and reading out the reading reference data in synchronization with the output operation of the line sensor; a D/A converter that converts the read reference data into an analog voltage and supplies the analog voltage to the A/D converter as a conversion reference voltage; and selecting a conversion reference voltage of the D/A converter to a desired value. An image input device comprising: a DC bias circuit for contrast adjustment; (2) A DC bias circuit for brightness adjustment is provided, which adds a desired value of DC voltage to the read output of the line sensor and provides an input signal to the A/D converter. 1. The image input device according to 1. (3) From the read output of the line sensor, A/D
A circuit for detecting a black level to define the lowest level of the input voltage range of the converter, and a DC voltage of the black level obtained from this circuit is added to the read output of the line sensor and sent to the A/D converter. Claim 1 characterized in that a direct current bias circuit for brightness adjustment is provided as an input signal.
The image input device described.