JPH0430671A - Picture input device - Google Patents

Abstract

PURPOSE:To realize picture reading without saturation in an A/D converter means even against the shading of a light means by devising a gain of an amplifier means giving a reference voltage to the A/D converter means to be controlled. CONSTITUTION:An image of a 1st white level reference plate 2 is subject to photoelectric conversion prior to reading of an original 1. A maximum gain is given to an amplifier 9 by a CPU 11. The CPU 11 reads a digital signal from a memory 16 to read a position Sa of the 1st white level reference plate 2 corresponding to a 2nd white level reference plate 3 and a nearly midposition Sb of the 1st white level reference plate 2, calculates G=Sb/Sa(b/a), decides a maximum gain not in excess of the G among gains selectable in the amplifier 9 and gives a gain designation signal to the amplifier 9. Through the operation above, the saturation of an A/D converter 10 due to a decreased reference voltage Vref of the A/D converter 10 caused by a baked edge of a fluorescent light 6 is avoided.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image input device that reads images using an image sensor, and is particularly resistant to fluctuations and deterioration of an illumination light source. This is a device that performs accurate image reading.

[Conventional technology]

An image input device generally includes an illumination light source that illuminates a document, an optical system that forms an image on the surface of the document, and an image sensor that serves as a photoelectric conversion means disposed on the surface of the document. Fluorescent lamps are often used as the illumination light source. However, when an illumination light source such as a fluorescent lamp is used, the brightness of the fluorescent lamp changes during the operation of reading a document, and the read image may deteriorate. FIG. 6 shows a method disclosed in Japanese Unexamined Patent Publication No. 316567/1983 as a method of preventing deterioration of a read image even with such fluctuations in luminance of the illumination light source.

In Fig. 6, 1 is the original set at the image reading position, 2 is the first white reference plate placed on the home position, and 3 is provided at the edge of the original l outside the reading range. a second white reference plate; 4 is a rod lens array as an imaging means; 5 is an image sensor comprising a plurality of photoelectric conversion elements arranged in a line shape, for example, and arranged at the imaging position of the rod lens array 4; It has a width that allows it to read the image of the document 1 illuminated by the fluorescent lamp 6 serving as the illumination means and at the same time read the white reference surface of the second white reference plate 3. The first white reference plate 2 has a width that is the sum of the widths of the original l and the second white reference Fi3, and is adjacent to them.

Rod lens array 4, image sensor 5 and fluorescent lamp 6
The optical system consisting of is arranged below the reading screen.

7 is an amplifier that amplifies the output signal from the image sensor 5; 8 is a sample-hold circuit that samples and holds the output signal of the amplifier 7 at the timing of the sample-and-hold signal S/H; and 20 is an amplifier that amplifies the output signal of the sample-and-hold circuit 8. The amplifying amplifier IO is an analog/digital converter (hereinafter referred to as an AD converter) that converts the output V from the amplifier 7 into a digital signal, and inputs the output signal of the amplifier 20 as a reference signal.

Next, the operation will be explained. First, the first white reference plate 2
Subsequently, an image of the original l and the second white reference plate 3 illuminated by the fluorescent lamp 6 is formed on the image sensor 5 by the rod lens array 4 . The serial analog signal output from the image sensor 5 is sent to the amplifier 7.
The signal is amplified by and guided to the AD converter 10.

On the other hand, among the signals amplified by the amplifier 7, the signal corresponding to the second white reference plate 3 is sampled and held by the sample and hold circuit 8, and guided to the amplifier 20. The output of the amplifier 20 is guided to a reference voltage input terminal of the AD converter 10.

FIG. 2 shows the output signal V of the amplifier 7 when scanning a blank document as the document 1 or when scanning the first white reference plate 2.
This shows the relationship between the waveform of and the reference voltage V rat of the AD converter lO.
A voltage corresponding to V rot is output, and converted by the amplifier 20 to the reference voltage V rot of the AD converter 10 . In AD conversion by the AD converter 1o, the relative value of the analog signal V output from the amplifier 7 with respect to the reference voltages V, , f is obtained as a digital output. Further, the first white reference plate 2 is used when correcting shading of the fluorescent lamp 6 and variations in sensitivity of the image sensor 5.

Note that when the optical system including the image sensor 5 is moving relative to the original 1 etc. in the sub-scanning direction (arrow As in the figure), for example, the image sensor 5! Main scanning is repeated in the main scanning direction (arrow Bi in the figure), and in the second M, signals for 1 main scanning 547 are representatively shown.

With such a configuration, the image input device shown in FIG.
If there is a change in the brightness of the fluorescent lamp 6 during the reading operation of the image of the original document 1, the reference voltage of the AD converter 101. ．． changes, but the reading operation can be performed without affecting the reading signal S, which is the output of the AD converter 10.

[Problem to be solved by the invention]

Since the conventional image input device is configured as described above, it is possible to obtain a good read image with respect to the overall luminance fluctuation of the fluorescent lamp, but there are problems as described below.

If a light source such as a fluorescent lamp is left on for a long time, the edges will turn black. In such a case, as shown by the broken line in FIG. 2, a phenomenon occurs in which the output at the end portions is extremely reduced compared to the output at the center portion. In the conventional image input device, in this case, the reference voltage of the AD converter 10 is
,. , both decrease, so in the center, amplifier 7
The output signal V is the reference voltage of the AD converter 10 ■7°,
However, there were problems such as saturation phenomenon in the digital converted value.

This invention was made to solve the above-mentioned problems, and an object of the present invention is to provide an image input device that does not deteriorate the read image even when the luminance distribution changes due to blackening of the edges of the illumination means. shall be.

[Means to solve the problem]

The image input device of the present invention includes amplification means for amplifying the output of a sample and hold means for sampling and holding a part of an output signal of an image sensor, and converts the output of the amplification means into an AD converter for digitizing the output of the image sensor. In this device, the gain of the amplifying means can be controlled from the outside.

The illumination means includes a first illumination means for reflective originals and a second illumination means for transparent originals, and the sample hold period setting means includes first illumination means for reflective originals and second illumination means for transparent originals. A sample hold period is set at an arbitrary position on the image sensor depending on how the second illumination means is used.

Another human-powered image device of the present invention includes selection means for selecting an output voltage and a constant voltage from an amplification means whose gain is externally controllable and using an external signal as a reference voltage for the AD conversion means. It was established.

[For production]

In the image input device according to the present invention, the reference voltage of the AD conversion means can be freely selected because the amplification means operates at any gain that can be variably set.

Furthermore, the gain of the amplification means can be arbitrarily set variably, and the sample hold period can be set at any position on the image sensor depending on the type of illumination means used by the sample hold period setting means.

In another image input device of the present invention, since the amplifying means operates with a controllable gain, the reference voltage of the A[) converting means can be freely set, and the selection means can adjust the reference voltage according to the external signal. The output voltage of the amplification means and a constant voltage can be selected and applied as a reference voltage to the AD conversion means.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, the parts 1 to 8.10 that are the same as those in FIG. 6 are the same as those in the conventional example, so a redundant explanation thereof will be avoided. Reference numeral 9 denotes an amplifier whose gain can be externally selected, and is connected between the output terminal of the sample hold circuit 8 and the reference signal input terminal of the AD converter 10. 11 is a central processing unit (hereinafter referred to as CPU) that performs predetermined signal processing of input data and controls the gain of the amplifier 9; 12 is a sample-and-hold signal generation circuit that provides a sample-and-hold signal 3/H to the sample-and-hold circuit 8; 13 is an interface circuit for interfacing with a host computer and the like. 14 is an image signal processing circuit that performs data processing such as enlargement/reduction, and 15 is a signal S sent from the AD converter IO.
This is an unevenness correction circuit that calculates the product of the signal and the signal stored in the memory 16 as a storage means, and transfers the obtained signal to the image signal processing circuit 14 at the next stage. CPUI 1,
The sample hold signal generation circuit 12, the interface circuit 13, the image signal processing circuit 14, the non-uniformity correction circuit 15, and the memory 16 are connected to each other via a lot line so that they can be controlled by the CPU II. Disclosure arrow A is in the sub-scanning direction, arrow B is in the sub-scanning direction,
indicates the main scanning direction.

Next, the operation of the first embodiment will be explained with reference to FIG. First, as in the conventional example, images of the original 1 and the second white reference plate 3 illuminated by the fluorescent lamp 6 are formed on the image sensor 5 by the rod lens array 4. The analog signal output from the image sensor 5 is amplified by the amplifier 7 and guided to the AD converter IO.

On the other hand, among the signals amplified by the amplifier 7, the signal corresponding to the second white reference plate 3 is the sample-and-hold signal S/H (
The signal is sampled and held by a sample and hold circuit 8 in synchronization with the timing (see FIG. 2), and then guided to an amplifier 9. The output of this amplifier 9 is guided to a reference voltage input terminal of an AD converter 10.

FIG. 2 shows the waveform of the output signal V of the amplifier 7 and the reference voltage V ref of the AD converter 10, which are similar to those described in the related art.
This shows the relationship between the sample and hold circuit 8 above.
A voltage corresponding to a is output from , and is converted by the amplifier 9 into reference voltages v and f for the AD converter 10 . Also,
The first white reference plate 2 is used when correcting shading of the fluorescent lamp 6 and variations in sensitivity of the image sensor 5, as in the conventional case.

Next, the gain setting operation of the amplifier 9, which is the main part of this embodiment, will be described. The image input device in this embodiment photoelectrically converts the image of the first white reference plate 2 before reading the original 1.

At this time, the amplifier 9 is given its maximum gain by the CPU 11. In the same manner as reading the images of the second white reference plate 3 and the original 1, the image of the first white reference plate 2 is photoelectrically converted by the image sensor 5, and then transferred to the A/D conversion converter l.
The signal is converted into an upstream digital signal and stored in the memory 16 via the non-uniformity correction circuit 15.

The CPU II reads the value of this digital signal from the memory 16, and determines the position (is, (corresponding to a in FIG. 2) of the first white reference plate 2 corresponding to the second white reference plate 3 and the first
The value S (corresponding to b in FIG. 2) at approximately the center of the white reference plate 2 is read. The CPU 11 is G = S b/5-
(=b/a), the maximum gain that does not exceed G is determined from among the selectable gains of the amplifier 9, and a signal specifying the gain is sent to the amplifier 9.

With this operation, the reference voltage v1 of the AD converter IO
゜ can always be set larger than the output V of the amplifier 7, thereby avoiding saturation in the AD converter 10 due to a decrease in the reference voltage Vrsf of the AD converter 10 due to blackening of the ends of the fluorescent lamp 6, etc. be able to. This is because the G value increases as the edge blackening of the fluorescent lamp 6 increases, so by setting the gain of the amplifier 9 larger than before, the reference voltage V ref of the AD converter 10 can be set higher than before. This is achieved by Furthermore, since the reference voltage V ref of the AD converter 10 can be selected to be the minimum value among the values larger than the maximum value of the output (2) of the amplifier 7, the dynamic range can always be kept at the maximum.

After this operation, the CPU II again selects the first white reference plate 2.
The non-uniformity correction circuit 15 writes a value corresponding to the reciprocal of the read value into the memory 16.

Next, the fluorescent lamp 6, the rod lens array 4, and the image sensor 5 move together in the sub-scanning direction A relative to the original 1, and read the image on the surface of the original 1.

The signal output from the image sensor 5 is sent to the amplifier 7, A.
The signal is guided to the non-uniformity correction circuit 15 via the D converter 10. The non-uniformity correction circuit 15 calculates the product of the signal S sent from the AD converter IO and the reciprocal equivalent signal stored in the memory 16, and sends the obtained signal to the next stage image signal processing circuit. Transfer to 14. In this image signal processing circuit 14,
The image signal is subjected to signal processing such as enlargement, reduction, and pseudo halftone, and is further transferred to the interface circuit 13.

This interface circuit 13 transfers the transferred image signal to the host convenience store.

In the human-powered image device like the above embodiment, film and OH
When reading a transparent original, such as a P-note, in which the image is read by illuminating the back of the original, it is no longer possible to apply the above-mentioned reference voltage to the AD converter. Therefore, in the next embodiment, an image input device that can also read transparent originals is constructed.

FIG. 3 shows the configuration of an image input device according to a second embodiment of the present invention, and the same or corresponding parts as in FIG.
6 to avoid redundant explanation.

Reference numeral 18a denotes a transparent plate provided between the first white reference plate 2 and the marked original 1 and having a longitudinal direction in the main scanning direction B. Reference numeral 18b indicates the second white reference plate 3 and the marked original 1. It is a transparent plate provided between the transparent plate 18a and having a longitudinal direction in the sub-scanning direction A, and is integrated with the transparent plate 18a. 1st. Second
The white reference plates 2, 3 form an L-shape, and the transparent plates 18a, 18b form an L-shape between the L-shaped white reference plate 2.3 and the set document 1. The transparent plates 18a and 18b are provided using transparent plates for placing an original on which the original l is placed.

The first fluorescent lamp 6 as an illumination means is provided on the image sensor 5 side with respect to the original 1, while the second fluorescent lamp 26 as an illumination means is provided on the image sensor 5 side with respect to the original l. is provided so as to transmit and illuminate the original 1 from the opposite position.

Of course, this second fluorescent lamp 26 is also provided so as to be integrated with the optical system and relatively move in the sub-scanning direction As during scanning.

Next, the operation of this second embodiment will be explained with reference to FIG. Using a reflective original as the original 1, the operation of illuminating the original 1 with the first fluorescent lamp 6 and reading the image is the same as that described in the first embodiment, and is self-explanatory, so a description thereof will be omitted.

FIG. 4A is a similar diagram under the same conditions as FIG. 2. (B) in FIG. 4 shows the output timing of the sample-and-hold signal, and the sample-and-hold signal corresponding to (A) in FIG. 4 is S/H1. In the fourth circle (C), when the original l is a transparent original without an image, the transparent plate 1 is illuminated by the second fluorescent lamp 26.
8a or the waveform of the output signal ■ of the amplifier 7 when reading the original 1 and the transparent plate 18b and the reference voltage V r of the A/D converter 10
The relationship with @f is representatively shown for one main scanning line. In FIG. 4(B), the sample and hold signal corresponding to FIG. 4(C) is S/H2. (C
) is the curve when the end of the second fluorescent lamp 26 is blackened. Also, the value a in (C) in FIG.
This is the value at the position corresponding to b.

Further, if the original 1 is a transparent original such as a film or an OHP sheet, the transparent plate 18a is read instead of the first white reference plate 2 prior to reading the original 1. lighting the second fluorescent lamp 26 instead of the first fluorescent lamp 60;
Except for reading the transparent plate 18b instead of the second white reference plate 3, the operation is almost the same as that of reading the reflective original described in the first embodiment, and since the operation is self-explanatory, detailed explanation thereof will be omitted. .

When reading the transparent plate 18a, the sample-and-hold signal generating circuit 12 generates the S/H2 signal shown in FIG. 4(B). Through such an operation, the reference voltage Vr1 of the AD converter 10 is adjusted to the fourth (A) (in the case of a reflective original) or (C) (i
3), it is possible to obtain a good read image regardless of variations in the shading characteristics of the first fluorescent lamp 6 and the second fluorescent lamp 26 as illumination means. I can do it.

FIG. 5 shows the configuration of an image input device according to a third embodiment of the present invention, and the same or corresponding parts as in FIG.
6 to avoid redundant explanation.

Reference numeral 17 denotes a selection circuit that selects either the constant voltage R or the output Rv of the amplifier 9 in accordance with the selection signal from the CPL III and outputs the selected one to the reference voltage input terminal of the AD converter 10.

Next, the operation of this third embodiment will be explained with reference to FIG. Original l and second white group 1! When scanning the image of the plate 3, the selection circuit 17 selects either the constant voltage R or the output Rv of the amplifier 9 according to the selection signal from the CPU II, and selects the base 1! of the AD converter IO. Output to voltage input terminal.

Other operations during document scanning are self-evident from the description of the first embodiment, so their description will be omitted.

Next, the gain setting operation of the amplifier 9 and the control operation of the selection circuit 17, which are the main parts of the second embodiment, will be described. The image input device photoelectrically converts the image of the first white reference plate 2 before reading the original 1 . At this time, the CPU
l outputs to the selection circuit 17 a selection signal for selecting the constant voltage RF. The image of the first white reference plate 2 is photoelectrically converted by the image sensor 5, and further converted into a digital signal by the AD converter 10, which is supplied with the constant voltage R as the reference voltage Vrsf, via the amplifier 7. It is stored in the memory 16 via the non-uniformity correction circuit 15.

The CPU t reads the value of the digital signal from the memory 16 and first examines the value S' at the center (corresponding to b in FIG. 2). Since the AD converter 10 is supplied with a constant voltage R as the reference voltage V ref, the value can be evaluated as a value equivalent to the absolute value of the output of the image sensor 5. If this value is less than a certain value b□a, that is, S', and if this value is less than a certain value S'baia, the CPU 1 determines that the light amount has decreased due to the life of the fluorescent lamp 6.

Next, the value S′1(
(corresponds to a in Fig. 2) and the value S' at the center.

Read. CPtJll is G = S'b/S'-(
= b / a), and this value G becomes a certain value G
If it is II m X or more, it is determined that the life of the fluorescent lamp 6 is due to blackening at the end. The above value is the above value b @i1
greater than 1, and the above value G is the above value G + a m +
If it is smaller than 1, it is determined that cpUll is in a normal state, the maximum gain that does not exceed the value G is determined from among the selectable gains of the amplifier 9, and a designation signal is sent to the amplifier 9. If the gain can be determined as above, then
CPUII is the output RvfJ of amplifier 9<AD converter 10
A selection signal is output to the selection circuit 17 so that the reference voltage V7° is reached.

After this operation, cptzt reads the image of the first white reference plate 2 and writes the reciprocal of the value into the memory 16, but the subsequent operation is the same as in the first embodiment, so the explanation thereof will be omitted. do.

As described above, saturation in the AD converter 10 can be avoided and the dynamic range can always be kept at the maximum, as in the case of the first embodiment.

Note that in each of the above embodiments, the gain of the amplifier 9 is selected from among a plurality of options, but the amplifier 9 may be one that can adjust the gain by applying an analog signal, and the same as in each of the above embodiments may be used. It has the effect of

〔Effect of the invention〕

As described above, according to the present invention, the gain of the amplifying means that provides the reference voltage of the AD converting means is configured to be controllable, so that saturation phenomenon does not occur in the AD converting means even with variations in shading of the illumination means. Image reading can be achieved without any problems.

In addition, since the illumination means is used for transparent originals and for reflective originals, and the sample hold period can be selected by the sample hold period setting means, it is possible to obtain a good read image for both reflection reading and transmission reading. can.

Furthermore, since a selection means is provided for selecting the output voltage of the amplification means whose gain is controllable and a constant voltage, saturation phenomenon does not occur in the AD conversion means even with fluctuations in shading of the illumination means, and The lifespan of the lighting means can also be determined.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an image input device according to a first embodiment of the present invention, and FIG. 2 shows the relationship between the reference voltage V of the AD converter and the input signal V together with the sample and hold signal S/H during one main scan. FIG. 3 is a timing diagram showing lines, FIG. 3 is a configuration diagram showing an image input device according to a second embodiment of the present invention, and FIG. 4 is an A
D converter reference voltage v7. ．． A timing diagram showing the relationship between input signal V and sample hold signal S/H for one main scanning line each in the case of reflection reading and transmission reading, Fig. 5i
A block diagram showing a human-powered image device according to a third embodiment of the present invention, and a sixth circle is a block diagram showing a conventional image input device. In the mouth, 4... Rod lens array, 5... Image sensor, 6... (First) fluorescent lamp, 8... Sample hold circuit, 9... Amplifier, 10... A'D Converter, 12... Sample and hold signal generation circuit, 17
. . . selection circuit, 26 . . . second fluorescent lamp. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent: Masuo Oiwa, Figure 14, Indication of the Case, Plain Patent Application No. 2-136651, 2, Name of the Invention, Image Input Device, 3, Person Making the Amendment, Representative: Moriya Shiki, 4, Agent: 5. "Target maximum" is corrected to "G or more and minimum". (2) "Maximum not exceeding G" in lines 5 to 6 of page 20 is corrected to "minimum not exceeding G". that's all

Claims (3)

[Claims] (1) An illumination device for illuminating the document, an image sensor including a plurality of photoelectric conversion elements, an imaging device for forming an image of the document surface onto the surface of the image sensor, and the image sensor an analog/digital conversion means for converting the output signal from the image sensor into a digital signal, a sample hold means for sampling and holding a part of the output signal from the image sensor, and a sample hold period for setting the sample hold period by the sample hold means. In an image input device comprising a setting means and an amplification means for amplifying the signal obtained by the sample and hold means, the output voltage of the amplification means is used as a reference voltage of the analog/digital conversion means, wherein the gain of the amplification means is An image input device characterized in that the image input device can be controlled from the outside. (2) The illumination means includes a first illumination means for illuminating the reflective original from the image sensor side, and a second illumination means for illuminating the transmissive original from the side opposite to the image sensor. 2. The image input device according to claim 1, further comprising a sample and hold period setting means capable of setting a sample and hold period at any position of said image sensor depending on the type of said illumination means used. (3) an illumination device for illuminating the document; an image sensor including a plurality of photoelectric conversion elements; an imaging device for forming an image of the document surface on the surface of the image sensor; and the image sensor. an analog/digital conversion means for converting an output signal from the image sensor into a digital signal, a sample hold means for sampling and holding a part of the output signal from the image sensor, and an amplification means for amplifying the signal obtained by the sample hold means. In the image input device, selecting means selects an output voltage from the amplifying means and a constant voltage, the gain of which is externally controllable, by an external signal and supplies the selected voltage to the analog/digital converting means as a reference voltage. An image input device comprising: